Coordination supramolecular chemistry provides a versatile entry into materials with functionalities of technological relevance at the nanoscale. Here, we describe how two different bis-pyrazolylpyridine ligands (L1 and L2) assemble with Co(II) ions into dinuclear triple-stranded helicates, in turn, encapsulating different anionic guests. These constructs are described as (Cl@[Co2(L1)3])3+, (SiF6@[Co2(L1)(L2)3])2+ and (ClO4@[Co2(L2)3])3+, as established by single-crystal X-ray diffraction. Extensive magnetic and calorimetric measurements, numerical treatments and theoretical calculations reveal that the individual Co(II) centers of these supramolecular entities exhibit field-induced slow relaxation of magnetization, dominated by direct and Raman mechanisms. While the small variations in the spin dynamics are not easily correlated with the evident structural differences among the three species, the specific heat measurements suggest two vibronic pathways of magnetic relaxation: one that would be associated with the host lattice and another linked with the guest.

L. A. Barrios, N. Capo, H. Boulehjour, D. Reta, I. Tejedor, O. Roubeau, C Bo, G. Aromí., Dalton Trans., 2024,53, 7611-7618

Single-molecule magnets are among the most promising platforms for achieving molecular-scale data storage and processing. Their magnetisation dynamics are determined by the interplay between electronic and vibrational degrees of freedom, which can couple coherently, leading to complex vibronic dynamics. Building on an ab initio description of the electronic and vibrational Hamiltonians, we formulate a non-perturbative vibronic model of the low-energy magnetic degrees of freedom in monometallic single-molecule magnets. Describing their low-temperature magnetism in terms of magnetic polarons, we are able to quantify the vibronic contribution to the quantum tunnelling of the magnetisation, a process that is commonly assumed to be independent of spin-phonon coupling. We find that the formation of magnetic polarons lowers the tunnelling probability in both amorphous and crystalline systems by stabilising the low-lying spin states. This work, thus, shows that spin-phonon coupling subtly influences magnetic relaxation in single-molecule magnets even at extremely low temperatures where no vibrational excitations are present.

A. Mattioni, J. J. Staab, W. J. A. Blackmore, D. Reta, J. Iles-Smith, A. Nazir, N. F. Chilton, Nat Commun 2024, 15, 485.

Electron–phonon coupling is important in many physical phenomena, e.g. photosynthesis, catalysis and quantum information processing, but its impacts are difficult to grasp on the microscopic level. One area attracting wide interest is that of single-molecule magnets, which is motivated by searching for the ultimate limit in the miniaturisation of binary data storage media. The utility of a molecule to store magnetic information is quantified by the timescale of its magnetic reversal processes, also known as magnetic relaxation, which is limited by spin–phonon coupling. Several recent accomplishments of synthetic organometallic chemistry have led to the observation of molecular magnetic memory effects at temperatures above that of liquid nitrogen. These discoveries have highlighted how far chemical design strategies for maximising magnetic anisotropy have come, but have also highlighted the need to characterise the complex interplay between phonons and molecular spin states. The crucial step is to make a link between magnetic relaxation and chemical motifs, and so be able to produce design criteria to extend molecular magnetic memory. The basic physics associated with spin–phonon coupling and magnetic relaxation was outlined in the early 20th century using perturbation theory, and has more recently been recast in the form of a general open quantum systems formalism and tackled with different levels of approximations. It is the purpose of this Tutorial Review to introduce the topics of phonons, molecular spin–phonon coupling, and magnetic relaxation, and to outline the relevant theories in connection with both the traditional perturbative texts and the more modern open quantum systems methods.

J. G. C. Kragskow, A. Mattioni, J. J. Staab, D. Reta, J. M. Skelton, N. F. Chilton, Chem. Soc. Rev., 2023, 52, 4567-4585.

Single-molecule magnets (SMMs) are of interest for storage and quantum processing of information. Herein, we report three new SMMs, ([K(DME)2][Er(COTTBS2)2] (1), [K(18-C-6)(THF)2][Er(COTTBS2)2] (2), and [K(2,2,2-cryptand)][Er(COTTBS2)2] (3)), each of which features an Er(III) ion sandwiched by two bis(mono-tert-butyldimethylsilyl) substituted cyclooctatetraenide (1,4-(tBuMe2Si)2C8H6 or COTTBS2) ligands, leading to uniaxial magnetic anisotropy. With the chemically identical complex anion of [Er(COTTBS2)2]─, these SMMs differ only in the specific complex form of the same counterion K+, namely, [K(DME)2]+ (DME = ethylene glycol dimethyl ether) in 1, [K(18-C-6)(THF)2]+ in 2, and [K(2,2,2-cryptand)]+ in 3. Magnetic studies reveal comparable blocking temperatures of around 10 K and similar energy barriers (193(10) K for 1, 171(10) K for 2, and 166(9) K for 3) for magnetization reversal. By using the vibrating sample magnetometry waveform method, the transformed AC frequency is down to 0.0004 Hz; this frequency is 4 orders of magnitude smaller than the usual instrumentation limit. Accurate measurement of the quantum tunnelling of magnetization (QTM) relaxation time (τQTM) made possible at such a low frequency allows for confident assessment and comparison between closely related SMMs. For 1, 2, and 3, the τQTM was found to be 17(1) s, 13(1) s, and 65(2) s, respectively. The multifold difference in τQTM between 3 and 1 or 2 indicates that magnetic relaxation by QTM can be profoundly influenced by the nonmagnetic component and crystal environment of an SMM, and specifically the form of the counterion in the present case. Our findings thus suggest a new and different approach to tuning the QTM behavior and the overall characteristics of SMMs.

T Xue, Y.-S. Ding, D. Reta, Q-W. Chen, X. Zhu, Z. Zheng, Cryst. Growth Des. 2023, 23, 1, 565–573.

Two-coordinate transition metal complexes are exciting candidates for single-molecule magnets (SMMs) because their highly axial coordination environments lead to sizeable magnetic anisotropy. We report a series of five structurally related two-coordinate Fe(II) m-terphenyl complexes (4-R-2,6-Xyl2C6H2)2Fe [R = tBu (1), SiMe3 (2), H (3), Cl (4), CF3 (5)] where, by changing the functionalisation of the para-substituent (R), we alter their magnetic function. All five complexes are field-induced single-molecule magnets, with relaxation rates that are well-described by a combination of direct and Raman mechanisms. By using more electron donating R groups we were able to slow the rate of magnetic relaxation. Our ab initio calculations predict a large crystal field splitting (>850 cm−1) and sizeable zero-field splitting parameters (ca. −60 cm−1, |E| < 0.2 cm−1) for 1–5. These favourable magnetic properties suggest that m-terphenyl ligands have untapped potential as chemically versatile ligands able to impose highly axial crystal fields.

A. J. Valentine, A. M. Geer, T. J. Blundell, W. Tovey, M. J. Cliffe, E. S. Davies, S. P. Argent, W. Lewis, J. McMaster, L. J. Taylor, D. Reta, D. L. Kays. Dalton Trans. 2022,51, 18118-18126.

Heterometallic lanthanide [LnLn′] coordination complexes that are accessible thermodynamically are very scarce because the metals of this series have very similar chemical behaviour. Trinuclear systems of this category have not been reported. A coordination chemistry scaffold has been shown to produce molecules of type [LnLn′Ln] of high purity, i.e. exhibiting high metal distribution ability, based on their differences in ionic radius. Through a detailed analysis of density functional theory (DFT) based calculations, we discern the energy contributions that lead to the unparalleled chemical selectivity of this molecular system. Some of the previously reported examples are compared here with the newly prepared member of this exotic list, [Er2Pr(LA)2(LB)2(py)(H2O)2](NO3) (1) (H2LA and H2LB are two β-diketone ligands). A magnetic analysis extracted from magnetization and calorimetry determinations identifies the necessary attributes for it to act as an addressable, conditional multiqubit spin-based quantum gate. Complementary ab initio calculations confirm the feasibility of these complexes as composite quantum gates, since they present well-isolated ground states with highly anisotropic and distinct g-tensors. The electronic structure of 1 has also been analyzed by EPR. Pulsed experiments have allowed the establishment of the quantum coherence of the transitions within the relevant spin states, as well as the feasibility of a coherent control of these states via nutation experiments.

D. Maniaki, D. Garay-Ruiz, L. A. Barrios, D. de O. Tavares, D. Aguilà, F. Tuna, D. Reta, O. Roubeau, C Bo, G. Aromí. Chem. Sci. 2022, 13, 5574-5581.

Metal-metal bonding interactions can engender outstanding magnetic properties in bulk materials and molecules, and examples abound for the transition metals. Extending this paradigm to the lanthanides, herein we report mixed-valence dilanthanide complexes (CpiPr5)2Ln2I3 (Ln is Gd, Tb, or Dy; CpiPr5, pentaisopropylcyclopentadienyl), which feature a singly occupied lanthanide-lanthanide σ-bonding orbital of 5dz2 parentage, as determined by structural, spectroscopic, and computational analyses. Valence delocalization, wherein the d electron is equally shared by the two lanthanide centers, imparts strong parallel alignment of the σ-bonding and f electrons on both lanthanides according to Hund’s rules. The combination of a well-isolated high-spin ground state and large magnetic anisotropy in (CpiPr5)2Dy2I3 gives rise to an enormous coercive magnetic field with a lower bound of 14 tesla at temperatures as high as 60 kelvin.

C. A. Gould, K. R. McClain, D. Reta, J. G. C. Kragskow, D. A. Marchiori, E. Lachman, J. G. Analytis, R. D. Britt, N. F. Chilton, B. G. Harvey, J. R. Long, Science, 2022. 375, 198-202

The hexagonal-bipyramidal lanthanide(III) complex [Dy(OtBu)Cl(18-C-6)][BPh4] (1; 18-C-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane ether) displays an energy barrier for magnetization reversal (Ueff) of ca. 1000 K in a zero direct-current field. Temperature-dependent X-ray diffraction studies of 1 down to 30 K reveal bending of the Cl–Ln–OtBu angle at low temperature. Using ab initio calculations, we show that significant bending of the O–Dy–Cl angle upon cooling from 273 to 100 K leads to a ca. 10% decrease in the energy of the excited electronic states. A thorough exploration of the temperature and field dependencies of the magnetic relaxation rate reveals that magnetic relaxation is dictated by five mechanisms in different regimes: Orbach, Raman-I, quantum tunnelling of magnetization, and Raman-II, in addition to the observation of a phonon bottleneck effect.

Y.-S. Ding, W. J. A. Blackmore, Y.-Q. Zhai, M. J. Giansiracusa, D. Reta, I. Vitorica-Yrezabal, R. E. P. Winpenny, N. F. Chilton, Y.-Z. Zheng, Inorg. Chem. 2022, 61, 1, 227–235.

The mononuclear complexes [Dy(3Br,5Cl-H3L1,1,4)(D)]·solvate (D = H2O, solvate = 0.25MeOH, 1W·0.25MeOH; D = Py without solvate, 1Py), and [Dy(3NO2,5Br-H3L1,1,4)(H2O)] (2W) were isolated. The crystal structures of 1W·0.25MeOH, 1Py and 2W·2CH3C6H5 show that the DyIII ion is octacoordinated, in N4O4 or N5O3 environments, with distorted geometries, between square antiprism, biaugmented trigonal prism and triangular dodecahedral. A similar environment for the metal ion is shown in the chiral crystals of the diamagnetic yttrium analogue [Y(3Br,5Cl-H3L1,1,4)(MeOH)] (3M), which were spontaneously resolved. Magnetic analyses of the three dysprosium complexes, and their diluted analogous 1W@Y, 1Py@Y and 2W@Y, reveal that none of them seem to relax through an Orbach mechanism at Hdc = 0. However, the three complexes show Orbach relaxation under Hdc = 1000 Oe, and 1Py is the in-field SIM with the highest energy barrier among these complexes, with a Ueff value of 358 K. Analysis of ac magnetic data shows that the electron-withdrawing substituents on the phenol rings of the aminophenol ligands, as well as the auxiliary oxygen donors from water ligands, reduce the energy barriers of the complexes, which is attributed to a charge reduction in the coordinating atoms of the aminophenol donor. Ab initio calculations support the experimental results.

M. Fondo, J. Corredoira-Vázquez, A. M. GarcíaDeibe, J. SanmartínMatalobos, D. Reta, E. Colacio, Dalton Trans., 2021, 50, 15878-15887

We discuss a cost-effective approach to understand magnetic relaxation in the new generation of rare-earth single-molecule magnets. It combines ab initio calculations of the crystal field parameters, of the magneto-elastic coupling with local modes, and of the phonon density of states with fitting of only three microscopic parameters. Although much less demanding than a fully ab initio approach, the method gives important physical insights into the origin of the observed relaxation. By applying it to high-anisotropy compounds with very different relaxation, we demonstrate the power of the approach and pinpoint ingredients for improving the performance of single-molecule magnets.Item description

E. Garlatti, A. Chiesa, P. Bonfà, E. Macaluso, I. J. Onuorah, V. S. Parmar, Y-S. Ding, Y-Z. Zheng, M. J. Giansiracusa, D. Reta, T. Guidi, D. P. Mills, N. F. Chilton, R. E. P. Winpenny, P. Santini, S. Carretta, J. Phys. Chem. Lett. 2021, 12, 36, 8826–8832

Organometallic molecules based on [Dy(CpR)2]+ cations (where CpR is a substituted cyclopentadienyl anion) have emerged as clear front-runners in the search for high-temperature single-molecule magnets. Within this family of structurally similar molecules, significant variations in their magnetic properties are seen, demonstrating the importance of understanding magneto-structural relationships to develop more efficient design strategies. Here we develop an ab initio spin dynamics methodology and show that it is capable of quantitative prediction of relative relaxation rates in the Orbach region. Applying it to all reported [Dy(CpR)2]+ cations allows us understand differences in their relaxation dynamics, highlighting that the main discriminant is the magnitude of the crystal field splitting, rather than differences in spin-vibrational coupling. We subsequently employ the method to predict relaxation rates for a series of hypothetical organometallic sandwich compounds, revealing an upper limit to the effective barrier to magnetic relaxation of around 2100–2200 K, which has been reached by existing compounds. Our conclusion is that further improvements to monometallic single-molecule magnets require moving vibrational modes off-resonance with electronic excitations.

D. Reta, J. Kragskow, N. F. Chilton, JACS. 2021, 143, 15, 5943–5950

The magnetic hysteresis of a metallacrown magnet opens after introducing axial ferromagnetic by linking two mono-decker Dy[15-MCCu-5] units with a single hydroxide bridge to give the double-decker {Dy[15-MCCu-5]}2 single-molecule magnet in which the anisotropy axes of the two DyIII ions are nearly collinear and the magnetic relaxation times are approximately 200 000 times slower than for the mono-decker unit.

J. Wang, Q.-W Li, S-G. Wu, Y-C. Chen, R.-C. Wan, G.-Z. Huang, Y. Liu, J.-L. Liu, D. Reta, M. J. Giansiracusa, Z.-X. Wang, N. F. Chilton, M.-L. Tong, Angew. Chem. Ed., 2021, 60, 5299 –5306.

Magnetic relaxation times are the central observable in defining the characteristics of single-molecule magnets. It is not uncommon to observe multiple distinct relaxation timescales for a pure material, and sometimes only one relaxation timescale is observed in samples containing multiple components. Herein we examine the conditions required for two distinct relaxation processes to be observable in alternating current susceptibility experiments. We find that there must be at least one order of magnitude difference in the two relaxation times I log10[taumu,1/taumu,2] I > 0.922, even when the intrinsic distributions of the two processes are infinitely sharp (alpha = 0 in the generalised Debye model). In the case where only one process is observable, we provide an expression to estimate the two underlying relaxation times, allowing extraction of “hidden” information from AC susceptibility data.

D. Reta, N. F. Chilton, Chem2, 2020, 4, 3.

A dinuclear dysprosocenium dication has been synthesised that is bound together by weak interactions between {Dy(Cp*)2}+ fragments and neutral NEt3AlMe3 molecules. The axiality of the Dy3+ crystal fields are perturbed by these equatorial interactions but a relatively large effective barrier to magnetisation reversal of 860(60) cm−1 and magnetic hysteresis up to 12 K are observed.

P. Evans, D. Reta, C. A. P. Goodwin, F. Ortu, N. F. Chilton, D. P. Mills, Chem. Comm., 2020, 56, 5677-5680

The fluid synergy between experimentalists and theoreticians has, for decades, led to a deeper understanding of the processes that govern single-molecule magnets. This approach has allowed for the establishment of proven design criteria for the control of magnetic properties through molecular architecture and the development of new magnetic measurement techniques and innovative computational methodologies. Here, we give an account of the experimental and theoretical joint endeavor carried out as part of the synthesis group led by David Mills and the computational/theoretical team led by Nicholas Chilton, together with colleagues in synthetic f-element chemistry and magnetism at the University of Manchester. In addition, we provide a personal perspective on collaborative work in molecular magnetism and how such collaborations are essential for advancing the field further.

C. A. P. Goodwin, F. Ortu, D. Reta, Int J Quantum Chem. 2020;120:e26248.

The recent discovery of single-ion magnets with magnetic hysteresis above liquid-nitrogen temperatures placed these compounds among the best candidates to realize high-density storage devices. Starting from a prototypical dysprosocenium molecule, showing hysteresis up to 60 K, we derive here a general recipe to design high-blocking-temperature rare-earth single-ion magnets. The complex magnetic relaxation is unraveled by combining magnetization and nuclear magnetic resonance measurements with inelastic neutron scattering experiments and ab initio calculations, thus disentangling the different mechanisms and identifying the key ingredients behind slow relaxation.

A. Chiesa, F. Cugini, R. Hussain, E. Macaluso, G. Allodi, E. Garlatti, M. Giansiracusa, C. A. P. Goodwin, F. Ortu, D. Reta, J. M. Skelton, T. Guidi, P. Santini, M.Solzi, R. De Renzi, D. P. Mills, N. F. Chilton, S. Carretta, Phys. Rev. B, 2020, 101, 174402.

Design criteria for dysprosium(III) single-molecule magnets (SMMs) with large thermal energy barriers to magnetic reversal have been established and proven, and the challenge to enhance performance is in understanding and controlling electron-vibration coupling that is the origin of magnetic reversal. We have prepared an SMM, [Dy(L)2(py)5][BPh4] 1 (HL = (S)-(-)-1-phenylethanol), based on the archetype [Dy(OtBu)2(py)5][BPh4] 2. Compounds 1 and 2 have similarly large energy barriers of Ueff = 1,130(20) cm−1 and Ueff = 1,250(10) cm−1, and yet 1 shows magnetic hysteresis at a far higher temperature of 22 K cf. TH = 4 K for 2. Ab initio calculation of the electron-vibration coupling and spin dynamics shows that substitution of the alkoxide ligand in fact enhances relaxation over the energy barrier for 1 compared with 2, in agreement with experiment, and that the higher temperature of magnetic hysteresis likely owes to reduced quantum tunneling at low temperatures.

K.-X. Yu, J. Kragskow, Y.-S. Ding, Y.-Q. Zhai, D. Reta, N. F. Chilton, Y.-Z. Zheng, Chem, 2020, 6, 7, 1777-1793.

An extended and systematic study of a family of lanthanide single-molecule magnets (SMMs) with pentagonal-bipyramidal geometry reveals the relaxation parameters and correlations. The energy barriers correlate with structure, mainly the electronegativity of donor atoms on the axial sites (the axial Dy−X bond lengths), and the energy barriers correlate with the blocking and hysteresis temperatures.

Y-S., Ding, T. Han, Y. Q. Zhai, D. Reta, N. F. Chilton, R. E. P. Winpenny, Y. Z. Zheng, Chem. Eur. J., 2020, 26, 26, 5893-5902.

The use of alternating current (AC) magnetometry to measure magnetic relaxation times is one of the most fundamental measurements for characterising single-molecule magnets (SMMs). These measurements, performed as a function of frequency, temperature and magnetic field, give vital information on the underlying magnetic relaxation process(es) occurring in the material. The magnetic relaxation times are usually fitted to model functions derived from spin–phonon coupling theories that allow characterisation of the mechanisms of magnetic relaxation. The parameters of these relaxation models are then often compared between different molecules in order to find trends with molecular structure that may guide the field to the next breakthrough. However, such meta-analyses of the model parameters are doomed to over-interpretation unless uncertainties in the model parameters can be quantified. Here we determine a method for obtaining uncertainty estimates in magnetic relaxation times from AC experiments, and provide a program called CC-FIT2 for fitting experimental AC data as well as the resulting relaxation times, to obtain relaxation parameters with accurate uncertainties. Applying our approach to three archetypal families of high-performance dysprosium(III) SMMs shows that accounting for uncertainties has a significant impact on the uncertainties of relaxation parameters, and that larger uncertainties appear to correlate with crystallographic disorder in the compounds studied. We suggest that this type of analysis should become routine in the community.

D. Reta, N. F. Chilton, Phys. Chem. Chem. Phys, 2019, 21, 23567-23575.

Single-molecule magnets (SMMs) have potential applications in high-density data storage, but magnetic relaxation times at elevated temperatures must be increased to make them practically useful. Bis-cyclopentadienyl lanthanide sandwich complexes have emerged as the leading candidates for SMMs that show magnetic memory at liquid nitrogen temperatures, but the relaxation mechanisms mediated by aromatic C5 rings have not been fully established. Here we synthesize a bis-monophospholyl dysprosium SMM [Dy(Dtp)2][Al{OC(CF3)3}4] (1, Dtp = {P(CtBuCMe)2}) by the treatment of in-situ-prepared “[Dy(Dtp)2(C3H5)]” with [HNEt3][Al{OC(CF3)3}4]. SQUID magnetometry reveals that 1 has an effective barrier to magnetization reversal of 1760 K (1223 cm–1) and magnetic hysteresis up to 48 K. Ab initio calculation of the spin dynamics reveals that transitions out of the ground state are slower in 1 than in the first reported dysprosocenium SMM, [Dy(Cpttt)2][B(C6F5)4] (Cpttt = C5H2tBu3-1,2,4); however, relaxation is faster in 1 overall due to the compression of electronic energies and to vibrational modes being brought on-resonance by the chemical and structural changes introduced by the bis-Dtp framework. With the preparation and analysis of 1, we are thus able to further refine our understanding of relaxation processes operating in bis-C5/C4P sandwich lanthanide SMMs, which is the necessary first step toward rationally achieving higher magnetic blocking temperatures in these systems in the future.

P. Evans, D. Reta, G. F. S. Whitehead, N. F. Chilton, D. P. Mills, JACS, 2019, 141, 50, 19935-19940.

The exposure of green crystals of the [CrF(O2CtBu)2]8Cr8 metallacrown to SO2 and H2S gases results in the binding of the gas molecules in the internal molecular cavity, despite the absence of any pores or channels in the structure. Single crystal X-ray diffraction studies show that the gas molecules bind weakly to the bridging fluoride ligands. The desorption process was followed by TGA, DSC and in situ variable temperature single crystal X-ray diffraction, obtaining the gas binding energies for the gas guest molecules. These results are supported by DFT calculations.

D. F. Sava, D. Reta, G. A. Timco, J. J.W. McDouall, R. E.P. Winpenny. Dalton Trans., 2019, 48, 13184-13189.

We report magnetic hysteresis studies of three Dy(III) single-molecule magnets (SMMs). The three compounds are [Dy(tBuO)Cl(THF)5][BPh4] (1), [K(18-crown-6-ether)(THF)2][Dy(BIPM)2] (2, BIPM = C{PPh2NSiMe3}2), and [Dy(Cpttt)2][B(C6F5)4] (3), chosen as they have large energy barriers to magnetisation reversal of 665, 565, and 1223 cm−1, respectively. There are zero-field steps in the hysteresis loops of all three compounds, that remain in magnetically dilute samples and in samples that are isotopically enriched with 164Dy, which has no nuclear spin. These results demonstrate that neither dipolar fields nor nuclear hyperfine coupling are solely responsible for the quantum tunnelling of magnetisation at zero field. Analysing their vibrational modes, we find that the modes that most impact the first coordination sphere occur at the lowest energies for 1, at intermediate energies for 2 and at higher energies for 3, in correlation with their coercive fields. Therefore, we suggest that the efficiency of quantum tunnelling of magnetisation is related to molecular flexibility.

F. Ortu, D. Reta, C. A. P. Goodwin, Y-D. Ding, M. P. Gregson, Y. Zheng, E. J. L. McInnes, S. T. Liddle, R. E. P. Winpenny, D. P. Mills, N. F. Chilton, Dalton Trans., 2019, 48, 8541 - 8545.

As the dysprosocenium complex [Dy(Cpttt)2][B(C6F5)4] (Cpttt=C5H2tBu3-1,2,4, 1-Dy) exhibits magnetic hysteresis at 60 K, similar lanthanide (Ln) complexes have been targeted to provide insights into this remarkable property. We recently reported homologous [Ln(Cpttt)2][B(C6F5)4] (1-Ln) for all the heavier Ln from Gd–Lu; herein, we extend this motif to the early Ln. We find, for the largest LnIII cations, that contact ion pairs [Ln(Cpttt)2{(C6F5-κ1-F)B(C6F5)3}] (1-Ln; La–Nd) are isolated from reactions of parent [Ln(Cpttt)2(Cl)] (2-Ln) with [H(SiEt3)2][B(C6F5)4], where the anion binds weakly to the equatorial sites of [Ln(Cpttt)2]+ through a single fluorine atom in the solid state. For smaller SmIII, [Sm(Cpttt)2][B(C6F5)4] (1-Sm) is isolated, which like heavier 1-Ln does not exhibit equatorial anion interactions, but the EuIII analogue 1-Eu could not be synthesised due to the facile reduction of EuIII precursors to EuII products. Thus with the exception of Eu and radioactive Pm this work constitutes a structurally similar family of Ln metallocenium complexes, over 50 years after the [M(Cp)2]+ series was isolated for the 3d metals.

J. Liu, D. Reta, J. A. Cleghorn, Y.X. Yeoh, F. Ortu, C. A. P. Goodwin, N. F. Chilton, D. P. Mills, Chem. Eur. J. 2019, 25, 7749 –7758.

A 3d–4f heterometallic metallacrown with formula of [EuCu5(quinha)5(sal)2(py)5]CF3SO3·py·3H2O (1) (H2quinha = quinaldichydroxamic acid; Hsal = salicylaldehyde) has been synthesized. This complex shows field-induced slow magnetic relaxation via a Raman-like process, where studies of the isostructural {LuCu5} (2) and {YCu5} (3) complexes show that the slow dynamics mainly arise from the {Cu5} S = 1/2 ground state rather than the EuIII ion. However, the EuIII ion enhances the relaxation rates of the {Cu5} unit which likely arises from second-order effects in the formally diamagnetic 7F0 ground state of EuIII.

J. Wang, Z-Y. Ruan, Q-W. Li, Y-C. Chen, G-Z Huang, J-L Liu, D. Reta, N. F. Chilton, Z. Wang, M-L. Tong, Dalton Trans., 2019, 48, 1686.

A series of heavy lanthanide metallocenium cations [Ln(Cpttt)2]+ (Ln = Y, Gd, Dy, Ho, Er, Tm, Yb, Lu; Cpttt = C5H2tBu3-1,2,4) were recently prepared by halide abstraction of [Ln(Cpttt)2(Cl)], but curiously the Tb analogues remained elusive. Here we report an alternative anion abstraction strategy to access [Tb(Cpttt)2]+, completing the heavy [Ln(Cpttt)2]+ family.

C. A. P. Goodwin, D. Reta, F. Ortu, J. Liu, N. F. Chilton, D. P. Mills, Chem. Comm., 2018, 54, 9182.

The accuracy of post-B3LYP functionals is analyzed using an open-shell database of Cu(II) dinuclear complexes with well-defined experimental values of the magnetic coupling constants. This database provides a sound open-shell training set to be used to improve the fitting schemes in defining new functionals or when reparametrizing the existing ones. For a large set of representative hybrid exchange-correlation functionals, it is shown that the overall description of moderate-to-strong antiferromagnetic interactions is significantly more accurate than the description of ferromagnetic or weakly antiferromagnetic interactions. In the case of global hybrids, the most reliable ones have 25–40% Fock exchange with SOGGA and PBE0 being the most reliable and M06 the exception. For range-corrected hybrids, the long-range corrected CAM-B3LYP and ωB97XD provide acceptable results, and M11 is comparable but more erratic. It is concluded that the reliability of the calculated values is system- and range-dependent, and this fact introduces a serious warning on the blind use of a single functional to predict magnetic coupling constants. Hence, to extract acceptable magnetostructural correlations, a “standardization” of the method to be used is advised to choose the optimal functional.

R. Costa, D. Reta, I. de P. R. Moreira, F. Illas, J. Phys. Chem. A, 2018, 122 (13), 3423.

Understanding quantum tunnelling of the magnetisation (QTM) in single-molecule magnets (SMMs) is crucial for improving performance and achieving molecule-based information storage above liquid nitrogen temperatures. Here, through a field- and temperature-dependent study of the magnetisation dynamics of [Dy(tBuO)Cl(THF)5][BPh4]·2THF, we elucidate the different relaxation processes: field-independent Orbach and Raman mechanisms dominate at high temperatures, a single-phonon direct process dominates at low temperatures and fields >1 kOe, and a field- and temperature-dependent QTM process operates near zero field. Accounting for the exponential temperature dependence of the phonon collision rate in the QTM process, we model the magnetisation dynamics over 11 orders of magnitude and find a QTM tunnelling gap on the order of 10−4 to 10−5 cm−1. We show that removal of Dy nuclear spins does not suppress QTM, and argue that while internal dipolar fields and hyperfine coupling support QTM, it is the dynamic crystal field that drives efficient QTM.

Ding, Y-S.; Yu, K-X; D. Reta, F. Ortu, R. E. P. Winpenny, Y. Zheng, N. F. Chilton, Nat. Comm., 2018, 9, 3134.

Molecular uranium complexes are the most widely studied in actinide chemistry, and make a significant and growing contribution to inorganic and organometallic chemistry. However, reliable computational procedures to accurately describe the properties of such systems are not yet available. In this contribution, 18 experimentally characterized molecular uranium compounds, in oxidation states ranging from III to VI and with a variety of ligand environments, are studied computationally using density functional theory. The computed geometries and vibrational frequencies are compared with X-ray crystallographic, and infra-red and Raman spectroscopic data to establish which computational approach yields the closest agreement with experiment. NMR parameters and UV–vis spectra are studied for three and five closed-shell U(VI) compounds respectively. Overall, the most robust methodology for obtaining accurate geometries is the PBE functional with Grimme's D3 dispersion corrections. For IR spectra, different approaches yield almost identical results, which makes the PBE functional with Grimme's D3 dispersion corrections the best choice. However, for Raman spectra the dependence on functional is more pronounced and no clear recommendation can be made. Similarly, for 1H and 13C NMR chemical shifts, no unequivocal recommendation emerges as to the best choice of density functional, although for spin-spin couplings, the LC-PBE functional with solvent corrections is the best approach. No form of time-dependent density functional theory can be recommended for the simulation of the electronic absorption spectra of uranyl (VI) compounds; the orbitals involved in the transitions are not calculated correctly, and the energies are also typically unreliable. Two main approaches are adopted for the description of relativistic effects on the uranium centres: either a relativistic pseudopotential and associated valence basis set, or an all-electron basis set with the ZORA Hamiltonian. The former provides equal, if not better, agreement with experiment vs all-electron basis set calculations, for all properties investigated.

D. Reta, F. Ortu, S. Randall, D. P. Mills, N. F. Chilton, R. E. P. Winpenny, L. Natrajan, B. Edwards and N. Kaltsoyannis. J. Organomet. Chem., 2018, 857, 58.

The origin of 60 K magnetic hysteresis in the dysprosocenium complex [Dy(Cpttt)2][B(C6F5)4] (Cpttt = C5H2tBu3-1,2,4, 1-Dy) remains mysterious, thus we envisaged that analysis of a series of [Ln(Cpttt)2]+ (Ln = lanthanide) cations could shed light on these properties. Herein we report the synthesis and physical characterization of a family of isolated [Ln(Cpttt)2]+ cations (1-Ln; Ln = Gd, Ho, Er, Tm, Yb, Lu), synthesized by halide abstraction of [Ln(Cpttt)2(Cl)] (2-Ln; Ln = Gd, Ho, Er, Tm, Yb, Lu). Complexes within the two families 1-Ln and 2-Ln are isostructural and display pseudo-linear and pseudo-trigonal crystal fields, respectively. This results in archetypal electronic structures, determined with CASSCF-SO calculations and confirmed with SQUID magnetometry and EPR spectroscopy, showing easy-axis or easy-plane magnetic anisotropy depending on the choice of Ln ion. Study of their magnetic relaxation dynamics reveals that 1-Ho also exhibits an anomalously low Raman exponent similar to 1-Dy, both being distinct from the larger and more regular Raman exponents for 2-Dy, 2-Er, and 2-Yb. This suggests that low Raman exponents arise from the unique spin-phonon coupling of isolated [Ln(Cpttt)2]+ cations. Crucially, this highlights a direct connection between ligand coordination modes and spin-phonon coupling, and therefore we propose that the exclusive presence of multihapto ligands in 1-Dy is the origin of its remarkable magnetic properties. Controlling the spin-phonon coupling through ligand design thus appears vital for realizing the next generation of high-temperature single-molecule magnets.

C. A. P. Goodwin, D. Reta, F. Ortu, N. F. Chilton, D. P. Mills, J. Am. Chem. Soc., 2017, 139 (51), 18714.

Lanthanides have been investigated extensively for potential applications in quantum information processing and high-density data storage at the molecular and atomic scale. Experimental achievements include reading and manipulating single nuclear spins1,2, exploiting atomic clock transitions for robust qubits3 and, most recently, magnetic data storage in single atoms4,5. Single-molecule magnets exhibit magnetic hysteresis of molecular origin6—a magnetic memory effect and a prerequisite of data storage—and so far lanthanide examples have exhibited this phenomenon at the highest temperatures. However, in the nearly 25 years since the discovery of single-molecule magnets7, hysteresis temperatures have increased from 4 kelvin to only about 14 kelvin8,9,10 using a consistent magnetic field sweep rate of about 20 oersted per second, although higher temperatures have been achieved by using very fast sweep rates11,12 (for example, 30 kelvin with 200 oersted per second)12. Here we report a hexa-tert-butyldysprosocenium complex—[Dy(Cpttt)2][B(C6F5)4], with Cpttt = {C5H2tBu3-1,2,4} and tBu = C(CH3)3—which exhibits magnetic hysteresis at temperatures of up to 60 kelvin at a sweep rate of 22 oersted per second. We observe a clear change in the relaxation dynamics at this temperature, which persists in magnetically diluted samples, suggesting that the origin of the hysteresis is the localized metal–ligand vibrational modes that are unique to dysprosocenium. Ab initio calculations of spin dynamics demonstrate that magnetic relaxation at high temperatures is due to local molecular vibrations. These results indicate that, with judicious molecular design, magnetic data storage in single molecules at temperatures above liquid nitrogen should be possible.

C. A. P. Goodwin, F. Ortu, D. Reta, N. F. Chilton, D. P. Mills, Nature, 2017, 548, 439.

Through-bond interacting organic polyradicals, rendered by customizable capacities of the state-of-the-art synthetic routes, are ideal systems to investigate spin topologies. Relying on Rajca and co-workers’ synthetic efforts, hereby we investigate the role of borders in the stability of the high-spin ground state in a series of realistic linear and ring-like arylmethyl polyradical derivatives. We show that, compared to their linear counterpart, the absence of borders in a ring-like arrangement of arylmethyl radicals imposes a larger number of spin-alternation rule violations, which strongly stabilizes the high-spin ground state. In addition, the structural flexibility of the investigated compounds translates into the existence of various structural energy minima for which the ferromagnetic ground state is always maintained. In view of the present results we propose these rings as possible candidates for the development of enhanced high spin single molecule toroics.

D. Reta, I. de P. R. Moreira, F. Illas, Phys. Chem. Chem. Phys., 2017, 19, 24264.

Embedding a magnetic electroactive molecule in a three-terminal junction allows for the fast and local electric field control of magnetic properties desirable in spintronic devices and quantum gates. Here, we provide an example of this control through the reversible and stable charging of a single all-organic neutral diradical molecule. By means of inelastic electron tunnel spectroscopy we show that the added electron occupies a molecular orbital distinct from those containing the two radical electrons, forming a spin system with three antiferromagnetically coupled spins. Changing the redox state of the molecule therefore switches on and off a parallel exchange path between the two radical spins through the added electron. This electrically controlled gating of the intramolecular magnetic interactions constitutes an essential ingredient of a single-molecule quantum gate.

R. Gaudenzi, J. de Bruijckere, D. Reta, I. de P. R. Moreira, C. Rovira, J. Veciana, H. S. J. van der Zant, E. Burzurí. ACS Nano 2017, 11, 5879.

Triarylmethyls (TAMs) are prominent highly attractive open shell organic molecular building blocks for materials science, having been used in breakthrough syntheses of organic magnetic polymers and metal organic frameworks. With their radical π-conjugated nature and a proven capacity to possess high stability via suitable chemical design, TAMs display a variety of desirable characteristics which can be exploited for a wide range of applications. Due to their particular molecular and electronic structure, the spin localization in TAMs almost entirely depends on the dihedral angles of their three aryl rings with respect to the central methyl carbon atom plane, which opens up the possibility of controlling their fundamental properties by twisting the three aryl rings. Aryl ring twist angles can be tuned to a single value by specific chemical functionalisation but controlling them by external means in organic materials or devices represents a challenging task which has not yet been experimentally achieved. Herein, through rational chemical design we propose two 2D covalent organic frameworks (2D-COFs) based on specific TAM building blocks. By employing ab initio computational modeling we demonstrate that it is possible to externally manipulate the aryl ring twist angles in these 2D-linked TAM frameworks by external mechanical means. Furthermore, we show this structural manipulation allows for finely tuning the most important characteristics of these materials such as spin localization, optical electronic transitions and magnetic interactions. Due to the enormous technological potential offered by this new class of material and the fact that our work is guided by real advances in organic materials synthesis, we believe that our predictions will inspire the experimental realization of radical-2D-COFs with externally controllable characteristics.

I. Alcón, D. Reta, I. de P. R. Moreira, S. T. Bromley, Chem. Sci., 2017, 8, 1027.

In the most general case of three electrons in three symmetry unrelated centers with Ŝ1 = Ŝ2 = Ŝ3 = 1/2 localized magnetic moments, the low energy spectrum consists of one quartet (Q) and two doublet (D1, D2) pure spin states. The energy splitting between these spin states can be described with the well-known Heisenberg–Dirac–Van Vleck (HDVV) model spin Hamiltonian, and their corresponding energy expressions are expressed in terms of the three different two-body magnetic coupling constants J12, J23, and J13. However, the values of all three magnetic coupling constants cannot be extracted using the calculated energy of the three spin-adapted states since only two linearly independent energy differences between pure spin states exist. This problem has been recently investigated by Reta et al. (J. Chem. Theory Comput. 2015, 11, 3650), resulting in an alternative proposal to the original Noodleman’s broken symmetry mapping approach. In the present work, this proposal is validated by means of ab initio effective Hamiltonian theory, which allows a direct extraction of all three J values from the one-to-one correspondence between the matrix elements of both effective and HDVV Hamiltonian. The effective Hamiltonian matrix representation has been constructed from configuration interaction wave functions for the three spin states obtained for two model systems showing a different degree of delocalization of the unpaired electrons. These encompass a trinuclear Cu(II) complex and a π-conjugated purely organic triradical.

D. Reta, I. de P. R. Moreira, F. Illas, J. Chem. Theory Comput., 2016, 12 (7), 3228.

Magnetic ordering in purely organic π-conjugated materials is a challenging, rare, and desirable event. The interest lies on the unique magnetic properties derived from high-spin carbon-based polymers/macromolecules tailored through appropriate synthetic routes. Ground-breaking achievements have been reported regarding magnetic ordering in an organic polymer using spin clusters as building blocks. This strategy leads to two-dimensional extended polyradicals with a concomitant loss of appealing macroscopic properties such as expected magnetic anisotropy in elongated shaped macromolecules containing carbon-bearing radicals. Here we provide compelling evidence of a secondary structure-induced stabilization of ferromagnetic polyradicals with robust magnetic properties and strongly suggest revisiting a discarded attempt to obtain polymeric linear-like radicals. An alternative synthetic approach is also proposed, based on polyradicals obtained from discrete molecular precursors (oligomers) long enough to ensure a secondary structure, rather than from polymerization processes.

D. Reta Mañeru, I. de P. R. Moreira, F. Illas, J. Am. Chem. Soc., 2016, 138 (16), 5271.

The magnetic properties of a nanoscale system are inextricably linked to its local environment. In adatoms on surfaces and inorganic layered structures, the exchange interactions result from the relative lattice positions, layer thicknesses, and other environmental parameters. Here, we report on a sample-dependent sign inversion of the magnetic exchange coupling between the three unpaired spins of an organic triradical molecule embedded in a three-terminal device. This ferro-to-antiferromagnetic transition is due to structural distortions and results in a high-to-low spin ground-state change in a molecule traditionally considered to be a robust high-spin quartet. Moreover, the flexibility of the molecule yields an in situ electric tunability of the exchange coupling via the gate electrode. These findings open a route to the controlled reversal of the magnetic states in organic molecule-based nanodevices by mechanical means, electrical gating, or chemical tailoring.

R. Gaudenzi, E. Burzuri, D. Reta, I. de P. R. Moreira, S. T. Bromley, C. Rovira, J. Veciana, H. S. J. van der Zant, Nano Lett., 2016, 16 (3), 2066.

The K4 structure was theoretically predicted for trivalent chemical species, such as sp2 carbon. However, since attempts to synthesize the K4 carbon have not succeeded, this allotrope has been regarded as a crystal form that might not exist in nature. In the present work, we carried out electrochemical crystallization of the radical anion salts of a triangular molecule, naphthalene diimide (NDI)-Δ, using various electrolytes. X-ray crystal analysis of the obtained crystals revealed the K4 structure, which was formed by the unique intermolecular π overlap directed toward three directions from the triangular-shape NDI-Δ radical anions. Electron paramagnetic resonance and static magnetic measurements confirmed the radical anion state of NDI-Δ and indicated an antiferromagnetic intermolecular interaction with the Weiss constant of θ = −10 K. The band structure calculation suggested characteristic features of the present material, such as a metallic ground state, Dirac cones, and flat bands.

A. Mizuno, Y. Shuku, R. Suizu, M. Matsushita, M. Tsuchiizu, D. Reta Mañeru, F. Illas, V. Robert, K. Awaga, J. Am. Chem. Soc. 2015, 137 (24), 7612.

The problem of deriving three different two-body magnetic couplings in three electrons/three centers in a general geometric arrangement is investigated using the trinuclear Cu(II) HAKKEJ complex as a real case example. In these systems, one quartet and two doublet low lying electronic states exist, which define the magnetic spectra. However, the two possible linearly independent energy differences do not provide enough information to extract the three magnetic coupling constants. Here, we show how to obtain these parameters without making any assumption on the symmetry of the system from a combination of density functional- and wave function-based calculations. The density functional calculations explore various broken symmetry solutions and relate the corresponding energy to the expectation value of the Heisenberg Hamiltonian. This allows one to obtain all magnetic couplings, although their magnitude strongly depends on the exchange–correlation functional. Interestingly, a constant ratio between the magnetic coupling constants along a series of investigated functionals is found. This provides an additional equation to be used when relying on energy differences between spin states, which in turn allow solving the Heisenberg spectrum. The magnetic couplings thus obtained are compared to the experiment. Implications for the appropriate interpretation of the experiment and for the study of more complex systems are discussed.

D. Reta Mañeru, R. Costa, M. G. Mañé, I. de P. R. Moreira, F. Illas, J. Chem. Theory Comput. 2015, 11 (8), 3650.

The performance of a series of wave function and density functional theory based methods in predicting the magnetic coupling constant of a family of heterodinuclear magnetic complexes has been studied. For the former, the accuracy is similar to other simple cases involving homodinuclear complexes, the main limitation being a sufficient inclusion of dynamical correlation effects. Nevertheless, these series of calculations provide an appropriate benchmark for density functional theory based methods. Here, the usual broken symmetry approach provides a convenient framework to predict the magnetic coupling constants but requires deriving the appropriate mapping. At variance with simple dinuclear complexes, spin projection based techniques cannot recover the corresponding (approximate) spin adapted solution. Present results also show that current implementation of spin flip techniques leads to unphysical results.

R. Costa, R. Valero, D. Reta Mañeru, I. de P. R. Moreira, F. Illas, J. Chem. Theory Comput., 2015, 11, 1006.

A key factor in the search of high-spin ground state purely organic molecules concerns the effect of the inherent non-rigid structures on the magnetic and optical properties. This structural feature has not been properly addressed in previous theoretical works. Here, based on the experimentally characterized high-spin ground state of dendritic and star-branched polyradicals, we study four alternant hydrocarbon biradicals that intend to model these effects and, at the same time, provide a fi rst step toward understanding more extended experimental structures. A series of density functional theory (DFT) and of wave function-based methods have been used to explore the richness of structural minima in the corresponding potential energy surfaces and to discuss its effect on the triplet–singlet gap of the proposed model systems. For a given model, the DFT-based B3LYP, M06-2X and MN-12SX methods provide a consistent description. Likewise, a multiconf i gurational quasi-degenerate perturbation theory approach with the minimal π space as CASSCF reference is found to provide unbiased results. Despite the conformational richness found for these systems, they all can be described by a reduced set of values referred to only two structural parameters, being those the dihedral angles between the phenyl rings. For a given model, there is no signifi cant change in the triplet–singlet gap depending on the chosen local minima.

D. Reta Mañeru, I. de P. R. Moreira, F. Illas, Theor. Chem. Acc. 2015 134:18.

Theoretical calculations have been carried out to predict N(1s) binding energy values in N-doped graphene which take into account initial and final state effects. A simple way to carry out ΔSCF Hartree–Fock calculations is proposed, validated against experiment for a series of N-containing organic molecules and applied to realistic N-doped nanosized pristine and defective graphene models. Final state effects appear to be important and strongly suggest that only two types of N are likely to be detected on N-doped pristine graphene by X-ray Photoelectron Spectroscopy with binding energy values of 398.6 and 400.5 eV, respectively and relative to C(1s) at 285 eV in agreement to recent experiments for quasi free standing N-doped graphene. Two cases of N-doping in defective graphene have also been considered and calculated results compared with recent experimental measurements. Calculated values for C(1s) including final state effects strongly suggests that values for core level binding energy of N and other dopants will be close to their absolute values if referred to C(1s) at 290.2 eV. The proposed approach is general enough to be successfully applied to other cases of interest.

N. P. Bellafont, D. Reta Mañeru, F. Illas, Carbon. 2014, 76, 155

The new diimine fluorescent ligand ACRI-1 based on a central acridine yellow core is reported along with its coordination complex [Co2(ACRI-1)2] (1), a fluorescent weak ferromagnet. Due to the strong fluorescence of the acridine yellow fluorophore, it is not completely quenched when the ligand is coordinated to CoII. The magnetic properties of bulk complex 1 and its stability in solution have been studied. Complex 1 has been deposited on highly ordered pyrolitic graphite (HOGP) from solution. The thin films prepared have been characterized by AFM, time-of-flight secondary ion mass spectrometry (TOF-SIMS), grazing incidence X-ray diffraction (GIXRD), X-ray absorption spectroscopy (XAS), X-ray magnetic circular dichroism (XMCD) and theoretical calculations. The data show that the complex is robust and remains intact on the surface of graphite.

M. J. Heras Ojea, D. Reta Mañeru, L. Rosado, J. A. Zuazo, G. R. Castro, S. Tewary, G. Rajamaran, G. Aromí, E. Jiménez, E. C. Sañudo, Chem. Eur. J. 2014, 20, 10439.

We predict the magnetic exchange coupling constant (J) for 27 m-phenylene-based nitronyl nitroxide (NN) diradicals with nine different substituents in three unique (common ortho, ortho–meta and common meta) positions on the coupler unit by using the broken-symmetry density functional methodology. For all investigated diradicals, J values are computed using B3LYP, B3LYP-D3 and M06-2X functionals with 6–311+G(d,p) basis set. The J M06-2X value is larger than J B3LYP and closer to the observed value for the unsubstituted species. Substitutions at common ortho position always produce a greater angle of twist between the spin source and the coupler units. When the twist angle is very large, the nature of intramolecular magnetic interaction changes from ferromagnetic to antiferromagnetic. In these cases, the coupler–NN bond order becomes small. Substitution at the common meta position of m-phenylene in the diradical has little steric and hydrogen-bonding effects. Electron-withdrawing groups reveal a specific trend for single-atom substitution. An ortho substitution generally decreases J and a meta substitution always increases J with a decreasing −I effect. Variation of J with planarity as well as Hammett constant is investigated. The nucleus-independent chemical shift value is found to decrease from the corresponding mono-substituted phenyl derivatives. The dependence of J on these factors is explored.

A. K. Pal, D. Reta Mañeru, I. A. Latif, I. de P. R. Moreira, F. Illas, S. N. Datta, Theor. Chem. Acc. 2014, 133, 4, 1472.

Meta-benzoquinodimethane (MBQDM) or m-xylylene provides a model for larger organic diradicals, the triplet–singlet gap being the key property. In the present work this energy difference has been the object of a systematic study by means of several density functional theory-based methods including B3LYP, M06, M06-2X, HSE and LC-ωPBE potentials and a variety of wave function-based methods such as complete active space self consistent field (CASSCF), Multireference second-order Møller–Plesset (MRMP), difference dedicated configuration interaction (DDCI), and Multireference configuration interaction (MRCI). In each case various basis sets of increasing quality have been explored, and the effect of the molecular geometry is also analyzed. The use of the triplet and broken symmetry (BS) solutions for the corresponding optimized geometries obtained from B3LYP and especially M06-2X functionals provide the value of the adiabatic triplet–singlet gap closer to experiment when compared to the reported value of Wenthold, Kim, and Lineberger, (J. Am. Chem. Soc. 1997, 119, 1354) and also for the electron affinity. The agreement further improves using the full π-valence CASSCF(8,8) optimized geometry as an attempt to correct for the spin contamination effects on the geometry of the BS state. The CASSCF, MRMP, and MRCI, even with the full π valence CAS(8,8) as reference and relatively large basis set, systematically overestimate the experimental value indicating either that an accurate description must go beyond this level of theory, including σ electrons and higher order polarization functions, or perhaps that the measured value is affected by the experimental conditions.

D. Reta Mañeru, A. K. Pal, I. de P. R. Moreira, S. N. Datta, F. Illas, J. Chem. Theory Comput., 2014, 10, 335.

Nanoparticles of a neutral fluorescent Co(II) ferromagnet and a high nuclearity coordination Ni(II) complex have been prepared. The stability in solution of the complexes has been studied by paramagnetic proton NMR. The formation of nanoparticles from 5 to 500 nm in size, depending on the synthetic conditions, has been checked by TEM, UV–Vis and fluorescence.

M. J. Heras Ojea, A. Pons-Balagué, D. Reta Mañeru, E. C. Sañudo, J. Nanopart. Res., 2014, 16:2209.

In this paper we report the synthesis and characterization of a new fluorescent ligand, ACRI-1 and its Co(II) coordination complex 1, [Co2(ACRI-1)2]. Complex 1 has been characterized by X-ray crystallography, magnetism and paramagnetic proton NMR. Nanostructuration of complex 1 has been achieved as monodisperse fluorescent nanoparticles and as thin layers on a HOPG surface. The thin layers have been characterized by AFM and GIXRD.

D. Reta Mañeru, M. J. Heras Ojea, L. Rosado, G. Aromí, J. Zuazo, G. Castro, E. C. Sañudo, Polyhedron, 2013, 66, 136.

Microwave assisted synthesis is presented as a very useful tool in coordination chemistry. The synthesis assisted by microwave radiation has proven to be an excellent tool for the achievement of new structural types of polynuclear transition metal complexes. Several reaction conditions are studied and the results reported here. New examples of complexes of Mn, Co and Ni are reported along with their characterization.

A. Pons-Balagué, M. J. Heras Ojea, M. L. Gairaud, D. Reta Mañeru, S. J. Teat, J. S. Costa, G. Aromí, E. C. Sañudo, Polyhedron, 2013, 52, 781.