[Fe(µ2-OH)6]3- Linked Fe3O Triads: Mössbauer Evidence for Trigonal µ3-O2- or µ3-OH- Groups in Bridged versus Unbridged Complexes.

The syntheses, coordination chemistry, and Mössbauer spectroscopy of hepta-iron(III) complexes using derivatised salicylaldoxime ligands from two categories; namely, 'single-headed' (H2L) and 'double-headed' (H4L) salicylaldoximes are described. All compounds presented here share a [Fe3-µ3-O] core in which the iron(III) ions are µ3-hydroxo-bridged in the complex C1 and µ3-oxo-bridged in C2 and C3. Each compound consists of 2 × [Fe3-µ3-O] triads that are linked via a central [Fe(µ2-OH)6]3- ion. In addition to the charge balance and microanalytical evidence, Mössbauer measurements support the fact that the triads in C1 are µ3-OH bridged and are µ3-O bridged in C2 and C3.

Against the Norm: Non Irving-Williams Transmetalation in Transition Metal Dimers.

We report the synthesis and characterization of three dinuclear 3d3d' complexes, CuCu ([Cu2IIL(NO3)2]), MnMn ([Mn2IIL(MeOH)2(NO3)2]), and CuMn ([CuIIMnIIL(NO3)2]), that utilize the ligand, H2L (6,6'-dimethoxy-2,2'-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol). The relative stabilities of these complexes were investigated using experimental and computational techniques, revealing a non-Irving-Williams transmetalation, whereby a MnII ion can displace a CuII ion from its binding pocket in CuCu to yield the more stable CuMn complex. Magnetic characterization of the reported complexes revealed an unexpected ferromagnetic coupling between the two CuII ions of CuCu with J = +63.0 cm-1.

Lanthanide induced variability in localised CoII geometries of four triangular L3Co3 IILnIII complexes.

Four tetranuclear heterobimetallic triangle complexes [L3Co3Dy(NO3)2(H2O)(MeOH)5](NO3) (C1), [L3Co3Gd(NO3)3(MeOH)4] (C2), [L3Co3La(NO3)2(H2O)6](NO3)(H2O) (C3), and [L3Co3TbCl(NO3)2(H2O)0.5(MeOH)3.5] (C4), where H2L = 1,4-bisformylnaphthalene-2,3-diol, have been synthesised and structurally characterised. Each complex crystallises with a complete molecule in the asymmetric unit (Z' = 1) and displays near perfect octahedrality in two out of three CoII centres. The third CoII ion assumes a different coordination geometry in each complex: six-coordinate octahedral in C1, six-coordinate with a distortion towards trigonal prismatic in C2, five-coordinate trigonal bipyramidal in C3, and five-coordinate square pyramidal in C4; which has been attributed to increasing lanthanide cation size, coupled with a non-macrocyclic coordination environment. Continuous Shape Measurement (CShM) calculations and octahedral distortion parameter calculations were performed, using the SHAPE and OctaDist software packages, respectively, in order to aid in the assessment of each metal centre's local coordination geometry. The preliminary magnetic investigation of C3 found χ m T = 9.4 cm3 K mol-1 at 300 K and M = 7.1 µ B at 1.8 K, which are approximately two thirds the maximum theoretical values for three CoII ions and indicates the presence of a relatively large zero-field splitting parameter (D/k B = 65 K) operative in each CoII ion rather than exchange coupling between the CoII centres.

Computational studies of the magneto-structural correlations in a manganese dimer with Jahn-Teller distortions.

Inspired by the crystal structure of a MnIII dinuclear complex we obtained featuring both Jahn-Teller (JT) elongation and compression distortions, we have modelled a series of complex cations based on the disordered crystal formulation; [Mn2(L1)2(µ2-OH)2)4+ (1), [Mn2(L1)(L2)(µ2-OH)2)4+ (2), [Mn2(L2)(L1)(µ2-OH)2)4+ (3), and [Mn2(L2)2(µ2-OH)2)4+ (4) (where L1 = (1E,1'E)-5-tert-butyl-3-(((4-(((5-tert-butyl-2-hydroxy-3-((E)-(hydroxyimino)methyl)benzyl)(methyl)amino)methyl)benzyl)(methyl)amino)methyl)-2-hydroxybenzaldehyde and L2 = 3,3'-(1,4-phenylenebis(methylene))bis(methylazanediyl)bis(methylene)bis(5-tert-butyl-2-hydroxybenzaldehyde)) with different geometries to investigate the effects of the distortions on the magnetic coupling parameter. All computationally modelled dimers had a ferromagnetic interaction between the MnIII centres, with greater magnetic coupling calculated for complexes with both JT elongation and compression present. The ferromagnetic contribution to the J coupling was ascribed to the orthogonality of the singly occupied magnetic orbitals along with the cross-interaction between the unfilled Mn1(dx2-y2) and singly occupied Mn2(dx2-y2) orbitals. Constrained calculations showed that reducing the extent of the compression at Mn2 results in a concomitant increase in the dihedral angle between the JT axes, thereby reducing the relative magnitude of the magnetic coupling between MnIII centres.

Metallocyclic CuII-LnIII Single-Molecule Magnets from the Self-Assembly of 1,4-Diformylnaphthalene-2,3-diol.

We report the synthesis and characterization of seven new tetranuclear 3d-4f complexes derived from the 3:3:1 reaction of 1,4-diformylnaphthalene-2,3-diol (H2 L) with copper(II) nitrate and a lanthanide salt, Ln = Tb [L 3Cu3TbCl2(NO3)2(H2O)2] (C1), Ho [L 3Cu3HoCl3(H2O)3(MeOH)](H2O) (C2), Er [L 3Cu3ErCl3(H2O)3.5(MeOH)0.5](H2O) (C3), Gd [L 3Cu3Gd(NO3)2(H2O)2(MeOH)](NO3) (C4), Dy [L 3Cu3Dy(NO3)2(H2O)2(MeOH)](NO3) (C5), Yb [L 3Cu3Yb(NO3)2(H2O)2(MeOH)](NO3) (C6), and La [L 3Cu3La(NO3)2(H2O)2(MeOH)](NO3) (C7). Structural elucidation showed that the self-assembly using the acyclic ligand system was successful for all seven complexes, which exhibit the same near-planar Cu3LnO12 core. Five complexes (C1, C2, and C4-C6) were magnetically characterized at 300 K and 1.8 K. Complexes C1, C4, and C5 were observed to have ferromagnetic ground states and showed appreciable frequency dependence in their AC magnetic measurements, which yielded effective barriers between 7.82(4) and 13.2(3) K, confirming the presence of single-molecule magnet properties.

Self-assembly of non-macrocyclic triangular Ni3Ln clusters.

The synthesis and structural characterisation of four new heterometallic tetranuclear complexes is reported. Three L3Ni3Ln type complexes, where Ln = La (C1), Eu (C2), and Gd (C3), have been fully characterised including DC and AC magnetic measurements. A fourth complex featuring a diamagnetic BaII ion at its centre is also reported with structural characterisation. Structural elucidation showed that all four complexes successfully self-assembled from a stoichiometric mixture of the acyclic ligand, 1,4-diformylnaphthalene-2,3-diol, with nickel(II) nitrate and the appropriate heavy metal salt to produce the same near planar Ni3MO12 core. Ferromagnetic interactions were found to dominate the ground state of C3, exhibiting a maximal spin ground state of 13/2. The exchange coupling is quantitatively discussed along with the nickel(II) zero-field splitting effect. AC magnetic susceptibility experiments were carried out, but no frequency dependent signals were observed and thus no observable slow relaxation of magnetisation.

Structural trends in a series of bulky dialkylbiarylphosphane complexes of CuI.

CuI complexes containing the bulky dialkylbiarylphosphane 2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl (tBuXPhos, L) and an ancillary ligand (Cl-, Br-, I-, MeCN, ClO4- or SCN-) have been structurally characterized, namely, chlorido[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I), [CuCl(C29H45P)], 1, bromido[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I), [CuBr(C29H45P)], 2, [2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]iodidocopper(I), [CuI(C29H45P)], 3, (acetonitrile-κN)[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I) hexafluoridophosphate, [Cu(CH3CN)(C29H45P)]PF6, 4, [2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP](perchlorato-κO)copper(I), [Cu(ClO4)(C29H45P)], 5, and di-µ-thiocyanato-κ2S:N;κ2N:S-bis{[2-(di-tert-butylphosphanyl)-2',4',6'-triisopropylbiphenyl-κP]copper(I)}, [Cu2(NCS)2(C29H45P)2], 6. Iodide complex 3 shows significant CuI-arene interactions, in contrast to its chloride 1 and bromide 2 counterparts, which is attributed to the weaker interaction between the iodide ion and the CuI centre. When replacing iodide with an acetonitrile (in 4) or perchlorate (in 5) ligand, the reduced interaction between the CuI atom and the ancillary ligand results in stronger CuI-arene interactions. No CuI-arene interactions are observed in dimer 6, due to the tricoordinated CuI centre having sufficient electron density from the coordinated ligands.

Synthesis and Characterization of Symmetrically versus Unsymmetrically Proton-Bridged Hexa-Iron Clusters.

Syntheses and magnetic and structural characterization of hexa-iron complexes of derivatized salicylaldoximes are discussed. Complexation of Fe(BF4)2·6H2O with each ligand (H2 L1 and H4 L2) in a methanolic-pyridine solution resulted in hexa-iron compounds (C1 and C2, respectively), which each contain two near-parallel metal triangles of [Fe3-µ3-O], linked by six fluoride bridges and stabilized by a hydrogen-bonded proton between the µ3-O groups. Within each metal triangle of C2, Fe(III) ions are connected via the amine "straps" of (H4 L2-2H). Variable-temperature magnetic susceptibility and Mössbauer data of C1 and C2 indicate the presence of dominant antiferromagnetic interactions between the high-spin (S = 5/2) Fe(III) centers. For C1, two quadrupole doublets are observed at room temperature and 5 K, consistent with structural data from which discrete but disordered [Fe3-µ3-O] and [Fe3-µ3-OH] species were inferred. For C2, a single sharp quadrupole doublet with splitting intermediate between those determined for C1 was observed, consistent with the symmetric [Fe3-µ3-O···H···µ3-O-Fe3] species inferred crystallographically from the very short µ3-O···µ3-O separation. The differences in the physical properties of the complexes, as seen in the Mössbauer, X-ray, and magnetic data, are attributed to the conformational flexibility imparted by the nature of the linkages between the closely related ligands.

Breaking paracyclophane: the unexpected formation of non-symmetric disubstituted nitro[2.2]metaparacyclophanes.

Substituted [2.2]metaparacyclophanes are amongst the least studied of the simple cyclophanes. This is undoubtedly the result of the lengthy syntheses of these compounds. We report the simple synthesis of a rare example of a non-symmetric [2.2]metaparacyclophane. Treatment of [2.2]paracyclophane under standard nitration conditions gives a mixture of 4-nitro[2.2]paracyclophane, 4-hydroxy-5-nitro[2.2]metaparacyclophane and a cyclohexadienone cyclophane.

The structural manipulation of a series of Ni4 defective dicubanes: Synthesis, X-ray Structures, Magnetic and Computational analyses.

We report the synthesis and characterization of four new tetranuclear Ni(ii) complexes, C1-C4, all of which exhibit defective dicubane cores. C1-C4 are derived from the same salicylaldoxime derived ligand, H2L1. Complexes C1 and C4 have isostructural cores, differing in structure only by solvate molecules. Magnetic and computational analyses have revealed that complexes C1, C2, and C4 exhibit competing ferro- and antiferromagnetic interactions, however the different solvated species in C1 and C4 leads to notably different magnitudes in their magnetic coupling constants. Theoretical magneto-structural studies show that the pairwise magnetic exchange interaction is highly dependent on the Ni-X-Ni angle, as revealed by orbital overlap calculations.

Towards more effective beryllium chelation: an investigation of second-sphere hydrogen bonding.

A comparative study between three experimentally known beryllium chelators (EDTA, NTP, and 10-HBQS) and two tetradentate tripodal di-pyridine-based receptors (HL and HL-NH2), specifically designed to bind Be2+ cations, has been undertaken in the aqueous phase at the B3LYP/6-311++G(d,p) computational level. The relative binding energies of these five ligand systems to a variety of first row and pre-transition metal cations have been calculated, specifically to investigate their binding strength to Be2+ and the binding enhancement that a second sphere hydrogen bonding interaction could afford to the pyridyl based systems. The complexes of EDTA were calculated to have the highest average binding energy; followed by those of NTP, HL-NH2, HL, and finally 10-HBQS. The calculated binding energy of the HL-NH2Be complex, which includes second sphere interactions, was found to be almost 9% greater than the HL Be complex, with an average binding energy increase of 13.5% observed across all metals upon inclusion of second sphere hydrogen bonding.

Tuning receptors for the encapsulation of beryllium2.

Two series of tetradentate tripodal di-pyridine-based receptors designed to bind Be2+ cations have been studied in the aqueous phase at the B3LYP/6-311++G(d,p) computational level. The first series comprise simple tetrahedral receptors; the second series incorporates additional scaffolding groups capable of second sphere hydrogen-bonding in order to more finely tune the binding strength towards the Be2+ cation. Out of the five ligand candidates, one containing a tri-pyridyl N-donor along with a phenolato O-donor (L1) exhibited a significant improvement in binding energy stabilisation (47.8 kJ mol-1) towards the Be2+ cation in the presence of second-sphere H-bonding interactions.