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Dimerization of Paramagnetic Trinuclear Complexes by Coordination Geometry Changes Showing Mixed Valency and
Atsushi Takamori1, Kazuhiro Uemura1
1Department of Chemistry and Biomolecular Science, Faculty of Engineering, Gifu University, Yanagido 1-1, Gifu 501-1193, Japan.
Abstract:
Paramagnetic trinuclear complexes, trans-[Pt2M(piam)4(NH3)4](ClO4) (; piam = pivalamidate, M = Mn, Fe, Co, Ni, and Cu, x = 2 or 3), aligned as Pt-M-Pt were successfully synthesized and characterized. The dihedral angles between the Pt and M coordination planes in are approximately parallel, showing straight metal-metal bonds with distances of approximately 2.6 Å. Except for , the trinuclear complexes are dimerized with close contact (approximately 3.9 Å) between the end Pt atoms to form Pt-M-Pt···Pt-M-Pt alignments with high-spin M(+2) containing five (), three (), two (), and one () unpaired electrons localized on M atoms. Several physical measurements and calculations revealed that the dimerized structures were maintained in MeCN, where cyclic voltammograms for exhibited two-step oxidation and reduction attributed to Pt-M(+2)-Pt···Pt-M(+2)-Pt ↔ Pt-M(+3)-Pt···Pt-M(+2)-Pt ↔ Pt-M(+3)-Pt···Pt-M(+3)-Pt via mixed-valent states. Magnetic susceptibility measurements for showed antiferromagnetic interaction, : J = -0.9 cm-1, : J = -3.5 cm-1, : J = -7.3 cm-1, and : J = 0.0 cm-1, between the two M centers with distances of 9.0 Å through Pt···Pt bonds.
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