Solvate-Dependent Spin Crossover and Exchange in Cobalt(II) Oxazolidine Nitroxide Chelates
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- 作者：Ian A. Gass ; Subrata Tewary ; Gopalan Rajaraman ; Mousa Asadi ; David W. Lupton ; Boujemaa Moubaraki ; Guillaume Chastanet ; Jean-Francois L茅tard ; Keith S. Murray
- 刊名：Inorganic Chemistry
- 出版年：2014
- 出版时间：May 19, 2014
- 年：2014
- 卷：53
- 期：10
- 页码：5055-5066
- 全文大小：594K
- 年卷期：v.53,no.10(May 19, 2014)
- ISSN：1520-510X
文摘
Two oxazolidine nitroxide complexes of cobalt(II), [CoII(L鈥?/sup>)2](B(C6F5)4)2路CH2Cl2 (1) and [CoII(L鈥?/sup>)2](B(C6F5)4)2路2Et2O (2), where, L鈥?/sup> is the tridentate chelator 4,4-dimethyl-2,2-bis(2-pyridyl)oxazolidine N-oxide, have been investigated by crystallographic, magnetic, reflectivity, and theoretical (DFT) methods. This work follows on from a related study on [CoII(L鈥?/sup>)2](NO3)2 (3), a multifunctional complex that simultaneously displays magnetic exchange, spin crossover, and single molecule magnetic features. Changing the anion and the nature of solvation in the present crystalline species leads to significant differences, not only between 1 and 2 but also in comparison to 3. Structural data at 123 and 273 K, in combination with magnetic data, show that at lower temperatures 1 displays low-spin Co(II)-to-radical exchange with differences in fitted J values in comparison to DFT (broken symmetry) calculated J values ascribed to the sensitive influence of a tilt angle (胃) formed between the Co(dz2) and the trans-oriented O atoms of the NO radical moieties in L鈥?/sup>. Spin crossover in 1 is evident at higher temperatures, probably influenced by the solvate molecules and crystal packing arrangement. Complex 2 remains in the high-spin Co(II) state between 2 and 350 K and undergoes antiferromagnetic exchange between Co鈥搑adical and radical鈥搑adical centers, but it is difficult to quantify. Calculations of the magnetic orbitals, eigenvalue plots, and the spin densities at the Co and radical sites in 1 and 2 have yielded satisfying details on the mechanism of metal鈥搑adical and radical鈥搑adical exchange, the radical spins being in 蟺*NO orbitals.