A series of water-bridged dinickel complexes of the general formula [Ni2(μ2-OH2)(μ2-O2CtBu)2(O2CtBu)2(L)(L′)] (L = HO2CtBu, L′ = HO2CtBu (1), pyridine (2), 3-methylpyridine (4); L = L′ = pyridine (3), 3-methylpyridine (5)) has been synthesized and structurally characterized by X-ray crystallography. The magnetic properties have been probed by magnetometry and EPR spectroscopy, and detailed measurements show that the axial zero-field splitting, D, of the nickel(II) ions is on the same order as the isotropic exchange interaction, J, between the nickel sites. The isotropic exchange interaction can be related to the angle between the nickel centers and the bridging water molecule, while the magnitude of D can be related to the coordination sphere at the nickel sites.

The synthesis, structure and magnetic properties of two isostructural heptametallic lanthanide discs are reported, showing single molecule magnet (SMM) behaviour with a large energy barrier for the dysprosium analogue and a large magnetocaloric effect (MCE) for the gadolinium analogue.

The design and study of organometallic mixed-valence complexes is complicated by the mixing of metal d and bridging ligand π orbitals, which often makes the assignment of metal oxidation states ambiguous. However, in the case of complexes based on the cycloheptatrienyl-ligated molybdenum fragment, Mo(dppe)(η-C7H7), the strong ring to metal π bonding and metal to ring δ back-bonding interactions stabilize four of the metal d orbitals, while the dz2 orbital is destabilized by filled−filled interactions with the a-type MO of the C7H7 ring. When the Mo(dppe)(η-C7H7) auxiliary is used in conjunction with a 1,12-bis(ethynyl)-1,12-carbaborane-based bridging ligand, a weakly coupled (Robin and Day class II) mixed-valence system, [{Mo(dppe)(η-C7H7)}2{μ-1,12-(C≡C)2-1,12-C2B10H10}]+ ([2]+), with well-defined molybdenum oxidation states can be prepared. The near-IR region of [2]+ exhibits three intervalence charge transfer (IVCT) transitions and two lower intensity interconfigurational (or dd) transitions, which have been resolved through spectral deconvolution. The band shape of the lowest energy IVCT transition associated with [2]+, which arises from electron exchange between the dz2-type orbitals at the two Mo centers, is in excellent agreement with the predictions of the Hush two-state model for weakly coupled mixed-valence complexes. The half-height bandwidths of the higher energy IVCT transitions, which arise from transitions between lower lying metal orbitals that have symmetry properties that permit more significant mixing with the bridging ligand, are in less good agreement with the Hush model, due to the breakdown of the two-state approximation through the greater involvement of the bridge-based orbitals in those transitions.

The synthesis and magnetic properties of enneametallic and octametallic Fe(III) cage complexes from tetraazamacrocycle ligands (1,7-H2DO2A) and (H3DO3A) respectively, are reported.

Syntheses, structural and magnetic and EPR data are reported for two octametallic VIII clusters with anisotropic S = 4 ground states arising from strong ferromagnetic exchange interactions.

The reaction between [UO2(ReO4)2·H2O] and two equivalents of either tri-n-butyl phosphine oxide (TBPO) or tri-iso-butyl phosphate (TiBP) results in the formation of [UO2(µ2-ReO4)(ReO4)(TBPO)2]2 (1) and [UO2(µ2-ReO4)(ReO4)(TiBP)2]2 (2) respectively. Both complexes crystallise as two structurally similar centrosymmetric dimers, the cores containing two uranyl moieties linked by bridging perrhenates. Two PO donor ligands and one monodenatate perrhenate complete the pentagonal bipyramidal coordination sphere at each metal centre. Both complexes have also been characterised in the solid state by vibrational and absorption spectroscopy. Solution spectroscopic characterisation indicates that both perrhenate and phosphine oxide (1) or phosphate (2) remain coordinated, although it is not possible to state conclusively that the dimeric species remain intact. A low resolution structural study of a minor product from the reaction that yielded 2 revealed a monomeric complex with only monodentate perrhenate coordination, [UO2(ReO4)2(H2O)(TiBP)2] (2′). These results represent the first structural evidence for the bridging coordination mode of perrhenate on coordination to an actinide and yields further insight into the possible solvent phase pertechnetate complexes that may exist in PUREX process phosphate rich solvent.

Reactions of [MoO2(acetylacetonate)2] with the proligands (N-hydroxyimino)diacetic acid (H3hidpa), R,R-2,2′-(N-hydroxyimino)dipropionic acid (R,R-H3hidpa) or R,S-2,2′-(N-hydroxyimino)dibutyric acid (R,S-H3hidba) yielded the compounds [PPh4][Δ,Λ-Mo(hida)2]·CH2Cl21, [H5O2][Δ-Mo(R,R-hidpa)2] 2, [PPh4][Mo(R,S-hidba)2]·2H2O 3a and Na[Δ,Λ-Mo(R,S-hidba)2]·¼iPr2O 3b, respectively. Reactions of H3hida with a methanolic solution of [PPh4][MoOCl4(H2O)] in the presence of NaOH (ca. pH 8) provided an alternative synthesis for 1. The complex of 1 when transferred into CH2Cl2 using [PPh4]Br yielded brown block-like crystals from a CH2Cl2–EtOH solution, however, 2 and 3b were crystallised from H2O and MeCN solutions with [H5O2]+ and [Na]+ counter cations, respectively. X-Ray crystallography confirmed the same distinctive eight-co-ordinate geometry of the complex anions of 1, 2 and 3b as identified for Amavadin, the form in which vanadium(IV) is bound in Amanita muscaria mushrooms. EPR and UV/vis spectra recorded for 1, 2 and 3a are consistent with the presence of molybdenum(V). Cyclic voltammetric studies using a glassy carbon working electrode in CH2Cl2 for 1 exhibited a reversible MoVI/MoV and a quasi-reversible MoV/MoIV redox couple at E1/2 = +0.96 and −0.99 V (vs. a saturated calomel electrode), respectively. Complex 3a also displayed a reversible MoVI/MoV redox couple at E1/2 = +0.77 V, whereas the MoV/MoIV couple was irreversible (Epc = −1.28 V). Additional electrochemical studies with 2 recorded a reversible MoVI/MoV redox couple in Me2SO (E1/2 = +0.77 V), however in H2O this one-electron oxidation process is irreversible.

A novel fluoride-centered triangular-bridged carboxylate complex, [Ni2Cr(μ3-F)(O2CtBu)6(HO2CtBu)3] (1), is reported. Simple postsynthetic substitution of the terminal pivalic acids in 1 with pyridine and 4-methylpyridine led to the isolation of [Ni2Cr(μ3-F)(O2CtBu)6(C5H5N)3] (2) and [Ni2Cr(μ3-F)(O2CtBu)6((4-CH3)C5H4N)3] (3). Structural and magnetic characterizations carried out on the series reveal a dominating antiferromagnetic interaction between the nickel and chromium centers leading to an S = 1/2 ground state with a very unusual value of geff = 2.48.

The synthesis, structure and magnetic properties of two isostructural heptametallic lanthanide discs are reported, showing single molecule magnet (SMM) behaviour with a large energy barrier for the dysprosium analogue and a large magnetocaloric effect (MCE) for the gadolinium analogue.

Syntheses, structural and magnetic and EPR data are reported for two octametallic VIII clusters with anisotropic S = 4 ground states arising from strong ferromagnetic exchange interactions.

The synthesis and magnetic properties of enneametallic and octametallic Fe(III) cage complexes from tetraazamacrocycle ligands (1,7-H2DO2A) and (H3DO3A) respectively, are reported.

The reaction between [UO2(ReO4)2·H2O] and two equivalents of either tri-n-butyl phosphine oxide (TBPO) or tri-iso-butyl phosphate (TiBP) results in the formation of [UO2(µ2-ReO4)(ReO4)(TBPO)2]2 (1) and [UO2(µ2-ReO4)(ReO4)(TiBP)2]2 (2) respectively. Both complexes crystallise as two structurally similar centrosymmetric dimers, the cores containing two uranyl moieties linked by bridging perrhenates. Two PO donor ligands and one monodenatate perrhenate complete the pentagonal bipyramidal coordination sphere at each metal centre. Both complexes have also been characterised in the solid state by vibrational and absorption spectroscopy. Solution spectroscopic characterisation indicates that both perrhenate and phosphine oxide (1) or phosphate (2) remain coordinated, although it is not possible to state conclusively that the dimeric species remain intact. A low resolution structural study of a minor product from the reaction that yielded 2 revealed a monomeric complex with only monodentate perrhenate coordination, [UO2(ReO4)2(H2O)(TiBP)2] (2′). These results represent the first structural evidence for the bridging coordination mode of perrhenate on coordination to an actinide and yields further insight into the possible solvent phase pertechnetate complexes that may exist in PUREX process phosphate rich solvent.