We report isostructural heptametallic dysprosium and gadolinium complexes with high energy barrier single molecule magnet behaviour or large magnetocaloric effect, respectively.

The monometallic pseudo-octahedral complex, [Co(H₂O)₂(CH₃COO)₂(C₅H₅N)₂], is shown to exhibit slow magnetic relaxation under an applied field of 1500 Oe. The compound is examined by a combination of experimental and computational techniques in order to elucidate the nature of its electronic structure and slow magnetic relaxation. We demonstrate that any sensible model of the electronic structure must include a proper treatment of the first-order orbital angular momentum, and we find that the slow magnetic relaxation can be well described by a two-phonon Raman process dominating at high temperature, with a temperature independent quantum tunnelling pathway being most efficient at low temperature.

The unprecedented spectroscopic and structural characterisation of a series of 17-electron, monometallic diynyl radicals, [Mo(CC–CCR)L₂(η-C₇H₇)]˙⁺ (L₂ = bipy, R = SiMe₃ ; L₂ = dppe, R = SiMe₃ or H), are reported; the (L₂ = dppe, R = SiMe₃ ) derivative is reactive to chain-centred C_β –C_β′ dimerisation.

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.