Molecular and Electronic Structures of Bis(pyridine-2,6-diimine)metal Complexes [ML2](PF6)n (n = 0, 1, 2, 3; M = Mn, Fe, Co, Ni, Cu, Zn)

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Abstract
A series of mononuclear, octahedral first-row transition metal ion complexes mer-[MIIL02](PF6)2 containing the tridentate neutral ligand 2,6-bis[1-(4-methoxyphenylimino)ethyl]pyridine (L0) and a MnII, FeII, CoII, NiII, CuII, or ZnII ion have been synthesized and characterized by X-ray crystallography. Cyclic voltammetry and controlled potential coulometry show that each dication (except those of CuII and ZnII) can be reversibly one-electron-oxidized, yielding the respective trications [MIIIL02]3+, and in addition, they can be reversibly reduced to the corresponding monocations [ML2]+ and the neutral species [ML2]0 by two successive one-electron processes. [MnL2]PF6 and [CoL2]PF6 have been isolated and characterized by X-ray crystallography; their electronic structures are described as [MnIIIL12]PF6 and [CoIL02]PF6 where (L1)1- represents the one-electron-reduced radical form of L0. The electronic structures of the tri-, di-, and monocations and of the neutral species have been elucidated in detail by a combination of spectroscopies: UV−vis, NMR, X-band EPR, Mössbauer, temperature-dependent magnetochemistry. It is shown that pyridine-2,6-diimine ligands are noninnocent ligands that can be coordinated to transition metal ions as neutral L0 or, alternatively, as monoanionic radical (L1)1-. All trications are of the type [MIIIL02]3+, and the dications are [MIIL02]2+. The monocations are described as [MnIIIL12]+ (S = 0), [FeIIL0L1]+ (S = 1/2), [CoIL02]+ (S = 1), [NiIL02]+ (S = 1/2), [CuIL02]+ (S = 0), [ZnIIL1L0]+ (S = 1/2) where the MnIII and FeII ions are low-spin-configurated. The neutral species are described as [MnIIL12]0, [FeIIL12]0, [CoIL0L1]0, [NiIL0L1]0, and [ZnIIL12]0; their electronic ground states have not been determined.

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