Hexahalorhenate (iv) salts of metal oxazolidine nitroxides

Eight coordination compounds of formulae [FeII(L•)2][ReIVCl6] (1a), [FeII(L•)2][ReIVBr6] (1b), [CoII(L•)2][ReIVCl6]·CH3CN (2a), [CoII(L•)2][ReIVBr6] (2b), [NiII(L•)(CH3CN)3][ReIVCl6]·CH3CN (3a), [NiII(L•)(CH3CN)3][ReIVBr6]·3CH3CN (3b), [CuII(L•)2][ReIVCl6] (4a)and [CuII(L•)2][ReIVBr6] (4b), where L• is the aminoxyl radical chelating ligand, 4,4-dimethyl-2,2-di(2-pyridyl)oxazolidine-N- oxide, have been synthesised. Structural and magnetic studies reveal metal-radical intramolecular antiferromagnetic interactions in the [MII(L•)2]2+ cations in the iron, cobalt and copper based compounds (1a, 1b, 2a, 2b, 4a and 4b) with the central metal ion low-spin in the case of Fe (1a and 1b) and a gradual, cobalt based, spin-crossover transition present in 2a and 2b. The nickel based compounds, 3a and 3b, were analysed in the dried form (3a(dried) and 3b(dried)) and directly in acetonitrile (3a(solvated) and 3b(solvated)). Microanalysis and IR spectroscopy on 3a(dried) and 3b(dried) suggests the dried samples are best formulated as [NiII(L•)(H2O)3][ReIVX6], where X = Cl (3a(dried)) and Br (3b(dried)). All forms for 3a and 3b exhibit cationic metal-radical ferromagnetic interactions resulting in S = 3/2 ground states. In addition, 3a(dried) exhibits spin-canting behaviour with an ordering temperature of 2.7 K, an open hysteresis loop with a coercive field Hc, = 580 Oe, and a remanent magnetisation Mr = 0.21 μB, resulting in a canting angle of ~1.8°. In contrast 3b(dried) shows no spin-canting behaviour; a maximum in χM vs. T at T = 3 K suggesting long-range antiferromagnetic order. 3a(solvated) and 3b(solvated) show no indication of long-range magnetic ordering, unlike 4a and 4b where anomalies are evident in the low-temperature magnetic susceptibility measurements

The use of the TCNQF₄^2-dianion in the spontaneous redox formation of [Fe^III(L^-)₂][TCNQF₄•-]

The reaction of [FeII(L •)2](BF4)2 with Li2TCNQF4 results in the formation of [FeIII(L-)2][TCNQF4•-] (1) where L• is the radical ligand, 4,4-dimethyl-2,2-di(2-pyridyl)oxazolidine-N-oxide and TCNQF4 is 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyano-quinodimethane. This has been characterised by x-ray diffraction, Raman and Fourier-transform infra-red (FTIR) spectroscopy, variable temperature magnetic susceptibility, Mössbauer spectroscopy and electrochemistry. X-ray diffraction studies, magnetic susceptibility measurements and Raman and FTIR spectroscopy suggest the presence of low-spin FeIII ion, the anionic form (L-­) of the ligand and the anionic radical form of TCNQF4; TCNQF4•-. Li2TCNQF4 reduces the [FeII(L•)2]2+ dication which undergoes a reductively induced oxidation to form the [FeIII(L-)2]+ monocation resulting in the formation of [FeIII(L-)2][TCNQF4•-] (1), the electrochemistry of which revealed four well-separated, diffusion controlled, one-electron, reversible processes. Mössbauer spectroscopy and electrochemical measurements suggest the presence of a minor second species, likely to be [FeII(L•)2][TCNQF42-]