Inelastic Neutron Scattering Measurement of the Ground State Tunneling Gap in Tb and Ho Analogues of a Dy Field-Induced Single-Molecule Magnet.

Recent advances in single-molecule magnet (SMM) research have placed great value on interpretation of inelastic neutron scattering (INS) data for rare earth (RE)-containing SMMs. Here, we present the synthesis of several rare earth complexes where combined magnetic and INS studies have been performed, supported by ab initio calculations. The reaction of rare earth nitrate salts with 2,2'-bipyridine (2,2'-bpy) and tetrahalocatecholate (X4Cat2-, X = Br, Cl) ligands in methanol (MeOH) afforded two new families of compounds [RE(2,2'-bpy)2(X4Cat)(X4CatH)(MeOH)] (X = Br and RE = Y, Eu, Gd, Tb, Dy, Ho, Yb for 1-RE; X = Cl and RE = Y, Tb, Dy, Ho, and Yb for 2-RE). Addition of triethylamine (Et3N) to the reaction mixture delivered Et3NH[RE(2,2'-bpy)2(Br4Cat)2] (3-RE, RE = Er and Yb). Interestingly, cerium behaves differently to the rest of the series, generating (2,2'-bpyH)2[Ce(Br4Cat)3(2,2'-bpy)] (4-Ce) with tetravalent Ce(IV) in contrast to the trivalent metal ions in 1-3. The static magnetic properties of 1-RE (RE = Gd, Tb, Dy and Ho) were investigated in conjunction with INS measurements on 1-Y, 1-Tb, and 1-Ho to probe their ground state properties and any crystal field excitations. To facilitate interpretation of the INS spectra and provide insight into the magnetic behavior, ab initio calculations were performed using the single-crystal X-ray diffraction structural data of 1-RE (RE = Tb, Dy and Ho). The ab initio calculations indicate ground doublets dominated by the maximal angular momentum projection states of Kramers type for 1-Dy and Ising type for 1-Tb and 1-Ho. Dynamic magnetic susceptibility measurements indicate that 1-Dy exhibits slow magnetic relaxation in the presence of a small applied magnetic field mainly through Raman pathways. Inelastic neutron scattering spectra exhibit distinct transitions corresponding to crystal field-induced tunneling gaps between the pseudo-doublet ground state components for 1-Tb and 1-Ho, which is one of the first direct experimental measurements with INS of such tunneling transitions in a molecular nanomagnet. The power of high-resolution INS is demonstrated with evidence of two distinct tunneling gaps measurable for the two crystallographically unique Tb coordination environments observed in the single crystal X-ray structure.

Efficient synthetic route to heterobimetallic trinuclear complexes [Ln-Mn-Ln] and their single molecule magnetic properties.

A series of mononuclear lanthanoidate complexes isolated as [Bu4N][Ln(QCl4)] 1Ln (QCl = 5-chloro-8-quinolinolate; Ln = Eu, Gd, Tb, Dy, Ho, and Er) have been prepared, characterised, and used as facile precursors to obtain a series of new heterobimetallic complexes as crystalline materials. Reaction of 1Ln with manganese nitrate forms [Ln2Mn(QCl)8] (2Ln, where Ln = Tb, Dy, Er and Yb) which have been structurally characterised in the cases of 2Tb and 2Yb. The heteroleptic trinuclear complex [Dy3(QCl)8Cl(OH2)], 3, has also been obtained. Compounds 1Dy, 1Tb, and 1Er display slow relaxation of magnetisation below 10K, particularly for the prolate Er3+ ion. These results also suggest that the positive effects of the change from mononuclear to trinuclear lanthanoid complexes enhance their single molecule magnetic (SMM) behaviour, as evidenced by the well resolved frequency dependent AC out-of-phase susceptibility maxima seen in the 2Ln systems, that have been analysed quantitatively. The synthesis used here provides a promising strategy in obtaining heterobimetallic complexes with quinolinolate ligands and also constructing efficient heterobimetallic SMMs.

A Convenient DFT-Based Strategy for Predicting Transition Temperatures of Valence Tautomeric Molecular Switches.

The ability to identify promising candidate switchable molecules computationally, prior to synthesis, represents a considerable advance in the development of switchable molecular materials. Even more useful would be the possibility of predicting the switching temperature. Cobalt-dioxolene complexes can exhibit thermally induced valence tautomeric switching between low-spin CoIII-catecholate and high-spin CoII-semiquinonate forms, where the half-temperature (T1/2) is the temperature at which there are equal amounts of the two tautomers. We report the first simple computational strategy for accurately predicting T1/2 values for valence tautomeric complexes. Dispersion-corrected density functional theory (DFT) methods have been applied to the [Co(dbdiox)(dbsq)(N2L)] (dbdiox/dbsq•- = 3,5-di-tert-butyldioxolene/semiquinonate; N2L = diimine) family of valence tautomeric complexes, including the newly reported [Co(dbdiox)(dbsq)(MeO-bpy)] (1) (MeO-bpy = 4,4'-dimethoxy-2,2'-bipyridine). The DFT strategy has been thoroughly benchmarked to experimental data, affording highly accurate spin-distributions and an excellent energy match between experimental and calculated spin-states. Detailed orbital analysis of the [Co(dbdiox)(dbsq)(N2L)] complexes has revealed that the diimine ligand tunes the T1/2 value primarily through π-acceptance. We have established an excellent correlation between experimental T1/2(toluene) values for [Co(dbdiox)(dbsq)(N2L)] complexes and the calculated lowest unoccupied molecular orbital energy of the corresponding diimine ligand. The model affords accurate T1/2(toluene) values for [Co(dbdiox)(dbsq)(N2L)] complexes, with an average error of only 3.7%. This quantitative and simple DFT strategy allows experimentalists to not only rapidly identify proposed VT complexes but also predict the transition temperature. This study lays the groundwork for future in silico screening of candidate switchable molecules prior to experimental investigation, with associated time, cost, and environmental benefits.

Enhancing the barrier height for magnetization reversal in 4d/4f RuIII2LnIII2 "butterfly" single molecule magnets (Ln = Gd, Dy) via targeted structural alterations.

A series of 4d-4f {RuIII2DyIII2} and {RuIII2GdIII2} 'butterfly' (rhombohedral) complexes have been synthesized and characterized and their magnetic properties investigated. Earlier, we have reported the first 4d/4f SMM - [RuIII2DyIII2(OMe)2(O2CPh)4(mdea)2(NO3)2] (1Dy) with a Ueff value of 10.7 cm-1. As the structural distortion around the DyIII centres and the RuIII⋯DyIII exchange interactions are key to enhancing the anisotropy, in this work we have synthesised three more {Ru2Dy2} butterfly complexes where structural alteration around the DyIII centres and alterations to the bridging groups are performed with an aim to improve the magnetic properties. The new complexes reported here are [Ru2Dy2(OMe)2(O2C(4-Me-Ph)4(mdea)2(MeOH)4], 2Dy, [Ru2Dy2(OMe)2(O2C(2-Cl,4,5-F-Ph)4(mdea)2(NO3)2], 3Dy, and an acac derivative [Ru2Dy2(OMe)2(acac)4(NO3)2(edea)2], 4Dy, where acac- = acetylacetonate, edea2- = N-ethyldiethanolamine dianion. Complex 2Dy describes alteration in the DyIII centers, while complexes 3Dy and 4Dy are aimed to alter the RuIII⋯DyIII exchange pathways. To ascertain the 4d-4f exchange, the Gd-analogues of 1Dy and 4Dy were synthesised [Ru2Gd2(OMe)2(O2CPh)4(mdea)2(NO3)2], 1Gd, [Ru2Gd2(OMe)2(acac)4(NO3)2(edea)2], 4Gd. Both ac and dc susceptibility studies were performed on all these complexes, and out-of-phase signals were observed for 3Dy in zero-field while 2Dy and 4Dy show out-of-phase signals in the presence of an applied field. Complex 3Dy reveals a barrier height Ueff of 45 K. To understand the difference in the magnetic dynamic behavior compared to our earlier reported {RuIII2DyIII2} analogue, detailed theoretical calculations based on ab initio CASSCF/RASSI-SO calculations have been performed. Calculations reveal that the JRu⋯Dy value varies from -1.8 cm-1 (4Dy) to -2.4 cm-1 (3Dy). These values are also affirmed by DFT calculations performed on the corresponding GdIII analogues. The origin of the largest barrier and observation of slow magnetic relaxation in 3Dy is routed back to the stronger single-ion anisotropy and stronger JRu⋯Dy exchange which quenches the QTM effects more efficiently. This study thus paves the way forward to tune local structure around the LnIII center and the exchange pathway to enhance the SMM characteristics in other {3d-4f}/{4d-4f} SMMs.

Lanthanoid pyridyl-ß-diketonate 'triangles'. New examples of single molecule toroics.

Trinuclear lanthanoid clusters have been synthesised and investigated as toroidal spin systems. A pyridyl functionalised ß-diketonate, 1,3-bis(pyridin-2-yl)propane-1,3-dione (o-dppdH) has been used to synthesise a family of clusters of the form [Dy3(OH)2(o-dppd)3Cl2(H2O)4]Cl2·7H2O (1), [Tb3(o-dppd)3(µ3-OH)2(CH3CH2OH)3Cl3][Tb3(o-dppd)3(µ3-OH)2(H2O)(CH3CH2OH)2Cl3]Cl2·H2O (2), [Ho3(OH)2(o-dppd)3Cl(H2O)5]Cl3·3H2O (3) and [Er3(OH)2(o-dppd)3Cl2(H2O)3(CH3OH)]Cl2·3H2O·CH3OH (4). Despite the previous occurrence of this structural motif in the literature, these systems have not been widely investigated in terms of torodic behaviour. Magnetic studies were used to further characterise the complexes. DC susceptibility studies support weak antiferromagnetic exchange in the complexes. Slow magnetic relaxation behaviour is observed in the dynamic AC magnetic studies for complex 1. Theoretical studies predict that complex 1 and 3 have a non-magnetic ground state based on a toroidal arrangement of spins. Changes to the coordination environment in 2 do not support a toroic spin state. The prolate nature of the ErIII centres in complex 4 and large transverse anisotropy do not support the toroidal arrangement of lanthanoid spins in the complex.

Spin Crossover in Iron(III) Quinolylsalicylaldiminates: The Curious Case of [Fe(qsal-F)2](Anion).

A family of iron(III) spin crossover complexes with different counteranions, [Fe(qsal-F)2]A (qsal-F = 4-fluoro-2-[(8-quinolylimino)methyl]phenolate; A = PF6- 1, OTf- 2, NO3- 3, ClO4- 4, BF4- 5, or NCS- 6) have been prepared. All compounds are isostructural and crystallize (triclinic P1̅ space group) with two independent iron(III) centers (Fe1 and Fe2) in the asymmetric unit. No solvent molecules are found in the crystal lattice, allowing us to directly probe the relative influence of anion variation on the spin crossover characteristics. The crystal packing is governed by three types of π-π interactions (type A, type B, and type C), which form undulating 1D chains. Additional interactions (π-F, C-H···O/F, and P4AE) connect the neighboring chains to form a complex supramolecular network. Hirshfeld surface analysis supports these findings. The anions are located between the cationic [Fe(qsal-F)2]+ chains; hence, similar interchain distances (dchain) are observed irrespective of the anion. However, the interplane distances (dplane) are influenced by the crystal packing and increase proportionally with the anion size. Magnetic studies reveal that smaller anions tend to stabilize the low-spin state (NO3- 3, ClO4- 4, and BF4- 5), while larger anions (PF6- 1 and OTf- 2) exhibit lower transition temperatures (Tonset for 1 = 200 K and T for 2 = 190 K) and gradual spin crossovers. The anomaly is 6, where, despite having the smallest anion, it exhibits the lowest transition temperature with magnetic hysteresis in the first step (T1/2↑ = 170 K and T1/2↓ = 157 K). This suggests the size, shape, and supramolecular connectivity of the anion all influence the magnetic properties.

Coordination polymers of a bis-isophthalate bridging ligand with single molecule magnet behaviour of the CoII analogue.

A linear diamine-bisisophthalate bridging linker N,N'-bis(1,3-dicarboxyphenyl-5-methylene)-1,3-dimethylpropanediamine, designed to incorporate amine/ammonium functionalities in the core of the ligand, has been isolated as the pentahydrate of its dihydrochloride salt (H6L)Cl2·5H2O. Using this compound, four new coordination polymers have been formed, namely poly-[M(H2L)]·4.5H2O (1M, where M = Co, Zn, Cd) and poly-[Cd(H2L)(OH2)]·DMF·7H2O (2). Compounds 1M are isostructural 2D coordination polymers that contain 1D channels occupied by water molecules. In the case of 1Co these form a well ordered hydrogen-bonding network as determined by single crystal X-ray studies. Compound 2, synthesised under similar conditions, is a 1D coordination polymer in which the metal is partially solvated. DC and AC magnetic studies of 1Co, which posseses a mononuclear cobalt(ii) node, revealed single molecule magnet behaviour (SMM) with an effective barrier height Ueff of 37.7 K and τ0 = 1.02 × 10-9 s, among the highest reported for CoII coordination polymers.

Effects of Mixed Valency in an Fe-Based Framework: Coexistence of Slow Magnetic Relaxation, Semiconductivity, and Redox Activity.

A 2-D coordination framework, (NEt4)2[Fe2(fan)3] (1·5(acetone); H2fan = 3,6-difluoro-2,5-dihydroxy-1,4-benzoquinone), was synthesized and structurally characterized. The compound is structurally analogous to a formerly elucidated framework, (NEt4)2[Fe2(can)3] (H2can = 3,6-dichloro-2,5-dihydroxy-1,4-benzoquinone), and adopts a 2-D (6,3) topology with the symmetrical stacking of [Fe2(fan)3]2- sheets that are held in position by the NEt4+ cations between the sheets. The investigation of the dc and ac magnetic properties of 1·5(acetone) revealed ferromagnetic ordering behavior and slow magnetization relaxation, as evinced from ac susceptibility measurements. Furthermore, the exposure of 1·5(acetone) to air led to the formation of a heptahydrate 1·7H2O which displayed distinct magnetic properties. The study of the redox state and extent of delocalization in 1·5(acetone) was undertaken via crystallography, in combination with Mössbauer and vis-NIR spectroscopy, to reveal the mixed-valence and delocalized nature of the as-synthesized material. As a result, the conductivity studies conducted on a pressed pellet showed a relatively high conductivity of 1.8 × 10-2 S cm-1 (300 K). In order to compare structurally related anilate-based structures, a relationship among the redox state, spectroscopic properties, and electronic properties was elucidated in this work. A preliminary investigation of 1·5(acetone) as a candidate anode material in lithium ion batteries revealed a high reversible capacity of 676.6 mAh g-1 and high capacity retention.

Single-ion anisotropy and exchange coupling in cobalt(ii)-radical complexes: insights from magnetic and ab initio studies.

The concurrent effects of single-ion anisotropy and exchange interactions on the electronic structure and magnetization dynamics have been analyzed for a cobalt(ii)-semiquinonate complex. Analogs containing diamagnetic catecholate and tropolonate ligands were employed for comparison of the magnetic behavior and zinc congeners assisted with the spectroscopic characterization and assessment of intermolecular interactions in the cobalt(ii) compounds. Low temperature X-band (ν ≈ 9.4 GHz) and W-Band (ν ≈ 94 GHz) electron paramagnetic resonance spectroscopy and static and dynamic magnetic measurements have been used to elucidate the electronic structure of the high spin cobalt(ii) ion in [Co(Me3tpa)(Br4cat)] (1; Me3tpa = tris[(6-methyl-2-pyridyl)methyl]amine, Br4cat2- = tetrabromocatecholate) and [Co(Me3tpa)(trop)](PF6) (2(PF6); trop- = tropolonate), which show slow relaxation of the magnetization in applied field. The cobalt(ii)-semiquinonate exchange interaction in [Co(Me3tpa)(dbsq)](PF6)·tol (3(PF6)·tol; dbsq- = 3,5-di-tert-butylsemiquinonate, tol = toluene) has been determined using an anisotropic exchange Hamiltonian in conjunction with multistate restricted active space self-consistent field ab initio modeling and wavefunction analysis, with comparison to magnetic and inelastic neutron scattering data. Our results demonstrate dominant ferromagnetic exchange for 3+ that is of similar magnitude to the anisotropy parameters of the cobalt(ii) ion and contains a significant contribution from spin-orbit coupling. The nature of the exchange coupling between octahedral high spin cobalt(ii) and semiquinonate ligands is a longstanding question; answering this question for the specific case of 3+ has confirmed the considerable sensitivity of the exchange to the molecular structure. The methodology employed will be generally applicable for elucidating exchange coupling between orbitally-degenerate metal ions and radical ligands and relevant to the development of bistable molecules and their integration into devices.

Hysteretic thermal spin-crossover in heteroleptic Fe(ii) complexes using alkyl chain substituted 2,2'-dipyridylamine ligands.

The alkyl chain carrying ligands N,N-di(pyridin-2-yl)butanamide (LC4) and N,N-di(pyridin-2-yl)decanamide (LC10) were combined with NCS- co-ligands to form the neutral heteroleptic Fe(ii) complexes trans-[FeII(LC4)2(NCS)2] (1C4) and trans-[FeII(LC10)2(NCS)2] (1C10). Variable temperature crystallographic studies revealed that 1C4 is in the orthorhombic space group Pna21 between 85-200 K whereas 1C10 is in the monoclinic space group P21/c between 85-140 K. The average Fe-N bond lengths suggest that at 85 K 1C4 contains LS Fe(ii) centres; however, the ca. 0.18 Å increase in the average Fe-N bond lengths between 85 and 120 K suggests a spin-transition to the HS state occurs within this temperature interval. 1C10 contains LS Fe(ii) centres between 85 and 105 K. Upon warming from 105 to 140 K the average Fe-N bond lengths increase by ca. 0.19 Å, which suggests a spin-transition to the HS state. Solid-state magnetic susceptibility measurements showed that 1C4 undergoes semi-abrupt spin-crossover with T1/2 = 127.5 K and a thermal hysteresis of ca. 13 K whereas, 1C10 undergoes an abrupt spin-crossover with T1/2 = 119.0 K, and is also accompanied by thermal hysteresis of ca. 4 K. The crystallographic and magnetic data show that the length of the complex's alkyl chain substituents can have a large impact on the structure of the crystal lattice as well as a subtle effect on the T1/2 value for thermal spin-crossover.

Double spin crossovers: a new double salt strategy to improve magnetic and memory properties.

The structural, magnetic and Mössbauer spectral properties of a double salt, mixed-valent material, [FeII(3,5-Me2TPM)(TPM)][FeIII(azp)2]ClO4·2MeCN, 1, reveal spin transitions occur at both the metal sites, with hysteresis, indicative of 1 being a double spin crossover material.

New examples of triangular terbium(iii) and holmium(iii) and hexagonal dysprosium(iii) single molecule toroics.

The structural, magnetic and theoretical aspects are described for three triangular lanthanide complexes, [Tb(OH)(teaH2)3(paa)3]Cl2 (1), [Dy(OH)(teaH2)3(paa)3]Cl2 (2) and [Ho(OH)(teaH2)3(paa)3]Cl2 (3), and a hexanuclear wheel of formula [Dy(pdeaH)6(NO3)6] (4) [teaH3 = triethanolamine, paaH = N-(2-pyridyl)-acetoacetamide and pdeaH3 = 3-[bis(2-hydroxyethyl)amino]propan-1-ol]. Each complex displays single molecule toroidal behaviour as rationalised using high-level ab initio calculations. Complexes 2 and 3 are the first examples of mixed moment single molecule toroidal complexes featuring non-Kramers ions.

Tetraoxolene-bridged rare-earth complexes: a radical-bridged dinuclear Dy single-molecule magnet.

Two families of neutral tetraoxolene-bridged dinuclear rare earth complexes of general formula [((HBpz3)2RE)2(µ-tetraoxolene)] (RE = Y and Dy; HBpz3- = hydrotris(pyrazolyl)borate; tetraoxolene = fluoranilate (fa2-; 1-RE) or bromanilate (ba2-; 2-RE)) have been synthesised and characterised. In each case, the bridging tetraoxolene ligand is in the diamagnetic dianionic form and each rare earth metal centre has two HBpz3- ligands completing the coordination. Electrochemical studies on the soluble 2-RE family reveal a tetraoxolene-based reversible one-electron reduction. Bulk chemical reduction with cobaltocene affords the cobaltocenium (CoCp+) salt of the 1e-reduced analogue: [CoCp][((HBpz3)2RE)2(µ-ba˙)] (3-RE) that incorporates a radical trianionic form of the bromanilate bridging ligand. Alternating current (ac) magnetic susceptibility studies of 2-Dy reveal slow magnetic relaxation only in the presence of an applied magnetic field, but reduction to radical-bridged 3-Dy affords frequency-dependent peaks in the out-of-phase ac susceptibility in zero applied field. Exchange coupling between the Dy(iii) ions and the radical bridging ligand thus reduces zero-field magnetisation quantum tunnelling and confers single-molecule magnet status on the complex. Comprehensive analysis of the magnetic relaxation data indicates that a combination of Orbach, Raman and direct relaxation processes are required to fit the data for both dysprosium bromanilate complexes.

Abrupt spin crossover in iron(iii) complexes with aromatic anions.

Two iron(iii) spin crossover complexes, [Fe(qsal-X)2]OTs·nH2O, (Br 1·H2O; I, 2·2H2O or non-solvated 1, 2) have been prepared and fully characterized. Structural studies of 1·H2O and 2·2H2O reveal the presence of 1D π-π chains linking the Fe(iii) centres and a strong XO halogen bond. In both complexes the 1D π-π chains are angled relative to each other, enforced by C-HX interactions. Magnetic studies reveal abrupt spin crossover in 1 (T1/2↓ = 258 K and T1/2↑ = 260 K) and 2 (T1/2 = 298 K) with T1/2 increasing on going from Br to I. The presence of abrupt spin crossover in both complexes shows that aromatic anions can be effective in the design of cooperative spin crossover systems.

The First Observation of Hidden Hysteresis in an Iron(III) Spin-Crossover Complex.

Molecular magnetic switches are expected to form the functional components of future nanodevices. Herein we combine detailed (photo-) crystallography and magnetic studies to reveal the unusual switching properties of an iron(III) complex, between low (LS) and high (HS) spin states. On cooling, it exhibits a partial thermal conversion associated with a reconstructive phase transition from a [HS-HS] to a [LS-HS] phase with a hysteresis of 25 K. Photoexcitation at low temperature allows access to a [LS-LS] phase, never observed at thermal equilibrium. As well as reporting the first iron(III) spin crossover complex to exhibit reverse-LIESST (light-induced excited spin state trapping), we also reveal a hidden hysteresis of 30 K between the hidden [LS-LS] and [HS-LS] phases. Moreover, we demonstrate that FeIII spin-crossover (SCO) complexes can be just as effective as FeII systems, and with the advantage of being air-stable, they are ideally suited for use in molecular electronics.

Square Grid Metal-Chloranilate Networks as Robust Host Systems for Guest Sorption.

Reaction of the chloranilate dianion with Y(NO3 )3 in the presence of Et4 N+ in the appropriate proportions results in the formation of (Et4 N)[Y(can)2 ], which consists of anionic square-grid coordination polymer sheets with interleaved layers of counter-cations. These counter-cations, which serve as squat pillars between [Y(can)2 ] sheets, lead to alignment of the square grid sheets and the subsequent generation of square channels running perpendicular to the sheets. The crystals are found to be porous and retain crystallinity following cycles of adsorption and desorption. This compound exhibits a high affinity for volatile guest molecules, which could be identified within the framework by crystallographic methods. In situ neutron powder diffraction indicates a size-shape complementarity leading to a strong interaction between host and guest for CO2 and CH4 . Single-crystal X-ray diffraction experiments indicate significant interactions between the host framework and discrete I2 or Br2 molecules. A series of isostructural compounds (cat)[MIII (X-an)2 ] with M=Sc, Gd, Tb, Dy, Ho, Er, Yb, Lu, Bi or In, cat=Et4 N, Me4 N and X-an=chloranilate, bromanilate or cyanochloranilate bridging ligands have been generated. The magnetic properties of representative examples (Et4 N)[Gd(can)2 ] and (Et4 N)[Dy(can)2 ] are reported with normal DC susceptibility but unusual AC susceptibility data noted for (Et4 N)[Gd(can)2 ].

Oblate versus Prolate Electron Density of Lanthanide Ions: A Design Criterion for Engineering Toroidal Moments? A Case Study on {LnIII 6 } (Ln=Tb, Dy, Ho and Er) Wheels.

We report four new complexes based on a {LnIII 6 } wheel structure, three of which possess a net toroidal magnetic moment. The four examples consist of {TbIII 6 } and {HoIII 6 } wheels, which are rare examples of non DyIII based complexes possessing a toroidal magnetic ground state, and a {DyIII 6 } complex which improves its toroidal structure upon lowering the crystallographic symmetry from trigonal (R 3 ‾ ) to triclinic (P 1 ‾ ). Notably the toroidal moment is lost for the trigonal {ErIII 6 } analogue. This suggests the possibility of utilizing the popular concept of oblate and prolate electron density of the ground state MJ levels of lanthanide ions to engineer toroidal moments.

Solvatomorphism and anion effects in predominantly low spin iron(iii) Schiff base complexes.

A series of iron(iii) complexes [Fe(naphEen)2]X·sol (naphEen = 1-{[2-(ethylamino)-ethylimino]methyl}-2-naphtholate; X = F, sol = 0.5CH2Cl2·H2O 1; sol = H2O, X = Cl, 2 and X = Br 3) and [Fe(naphEen)2]I 4 has been prepared. The UV-Vis spectra reveal clear differences for 1 which DFT/TDDFT calculations suggest are due to an equilibrium between [Fe(naphEen)2]F and [Fe(naphEen)2F], the latter having a coordinated F ligand. The X-ray crystal structures of 2-4 show LS Fe(iii) centres in all cases and extensive aryl interactions that link the Fe centres into supramolecular squares. In 3 at room temperature the compound loses half an equivalent of water resulting in a change in space group from Monoclinic P21/n to C2/c. Magnetic studies indicate that 1 is trapped in a mixed spin state being ca. 40% HS while 2-4 are effectively low spin up to 350 K. In contrast, Mössbauer spectroscopic studies of 1 indicate a gradual but incomplete spin crossover. The magnetic properties of 2-4 contrast with the related [Fe(salEen-X)2]anion derivatives which are often spin crossover active.

Rationalizing the sign and magnitude of the magnetic coupling and anisotropy in dinuclear manganese(iii) complexes.

We have synthesised twelve manganese(iii) dinuclear complexes, 1-12, in order to understand the origin of magnetic exchange (J) between the metal centres and the magnetic anisotropy (D) of each metal ion using a combined experimental and theoretical approach. All twelve complexes contain the same bridging ligand environment of one µ-oxo and two µ-carboxylato, that helped us to probe how the structural parameters, such as bond distance, bond angle and especially Jahn-Teller dihedral angle affect the magnetic behaviour. Among the twelve complexes, we found ferromagnetic coupling for five and antiferromagnetic coupling for seven. DFT computed the J and ab initio methods computed the D parameter, and are in general agreement with the experimentally determined values. The dihedral angle between the two Jahn-Teller axes of the constituent MnIII ions are found to play a key role in determining the sign of the magnetic coupling. Magneto-structural correlations are developed by varying the Mn-O distance and the Mn-O-Mn angle to understand how the magnetic coupling changes upon these structural changes. Among the developed correlations, the Mn-O distance is found to be the most sensitive parameter that switches the sign of the magnetic coupling from negative to positive. The single-ion zero-field splitting of the MnIII centres is found to be negative for complexes 1-11 and positive for complex 12. However, the zero-field splitting of the S = 4 state for the ferromagnetic coupled dimers is found to be positive, revealing a significant contribution from the exchange anisotropy - a parameter which has long been ignored as being too small to be effective.

Self-assembly of a mixed-valence FeII-FeIII tetranuclear star.

A unique self-assembled mixed-valence FeII-FeIII tetranuclear star has been comprehensively characterised showing a large magnetic anisotropy at the peripheral FeII centres, ferromagnetic coupling between the iron centres and field-induced SMM behaviour.