Anderson, Peter A., Astley, Timothy, Hitchman, Michael A., Keene, F. Richard, Moubaraki, Boujemaa, Murray , Keith S., Skelton, Brian W., Tiekink, Edward R.T., Toftlund, Hans, and White, Allan H. (2000) Structures and spectra of bis-tripodal iron(II) chelates, [FeL2]2 , where L = tris(pyrazol-1-yl)methane, tris(pyridin-2-yl)methane, bis(pyrazol-1-yl)(pyridin-2-yl)methane and tris(pyridin-2-yl)- phosphine oxide. Magnetism and spin crossover in the (pz)3CH case. Dalton Transactions, 2000. pp. 3505-3512.

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Abstract

A range of six-co-ordinate bis-tripodal iron(II) chelates, [FeL2]2+, has been synthesized from iron-(II) or -(III) precursors where L = tris(pyrazol-1-yl)methane (pz)3CH, tris(pyridyl-2-yl)methane (py)3CH, bis(pyrazol-1-yl)(pyridin-2-yl)methane (pz)2(py)CH and tris(pyridin-2-yl)phosphine oxide (py)3PO. Crystal structures have been determined for three compounds and in the (pz)3CH case for two polymorphs ( and ) which were obtained in two different laboratories from iron(III) salts using different crystallisation solvents. The electronic properties of the [FeL2]2+ series have been investigated by optical spectroscopic measurements. Low-spin d6 behaviour is indicated. Magnetic and Mössbauer effect measurements on [Fe{(pz)3CH}2]2+ show that a gradual spin crossover to the high-spin state occurs above 270 K, though this is far from developed at 350 K. Comparisons are made with the well studied boron ligand analogue [Fe{(pz)3BH}2], which displays similar crossover behaviour, and with bis(tridentate) ligand complexes containing the ligand 1,4,7-triazacyclononane.

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