Abstracts 2005

Abstract of Publication No. 512

Curtis P. Berlinguette, Alina Dragulescu-Andrasi, Andreas Sieber, Hans-Ulrich Güdel, Catalina Achim and Kim R. Dunbar
A Charge-Transfer-Induced Spin Transition in a Discrete Complex: The Role of Extrinsic Factors in Stabilizing Three Electronic Isomeric Forms of a Cyanide-Bridged Co/Fe Cluster
J. Am. Chem. Soc. 127, 6766-6779 (2005)      Full Text (PDF)      DOI-Link      Supplementary Data (PDF)      Crystal Structure Data (CIF format)     

Abstract: A series of bimetallic, trigonal bipyramidal clusters of type {[Co(N-N)2]3[Fe(CN)6]2} are reported. The reaction of {Co(tmphen)2}2+ with [Fe(CN)6]3– in MeCN affords {[Co(tmphen)2]3[Fe(CN)6]2} (1). The cluster can exist in three different solid-state phases: a red crystalline phase, a blue solid phase obtained by exposure of the red crystals to moisture, and a red solid phase obtained by desolvation of the blue solid phase in vacuo. The properties of cluster 1 are extremely sensitive to both temperature and solvent content in each of these phases. Variable-temperature X-ray crystallography; 57Fe Mössbauer, vibrational, and optical spectroscopies; and magnetochemical studies were used to study the three phases of 1 and related compounds, Na{[Co(tmphen)2]3[Fe(CN)6]2}(ClO4)2 (2), {[Co(bpy)2]3[Fe(CN)6]2}[Fe(CN)6]1/3 (3), and {[Ni(tmphen)2]3[Fe(CN)6]2} (4). The combined structural and spectroscopic investigation of 1-4 leads to the unambiguous conclusion that 1 can exist in different electronic isomeric forms, {CoIII2CoIIFeII2} (1A), {CoIIICoII2FeIIIFeII} (1B), and {CoII3FeIII2} (1C), and that it can undergo a charge-transfer-induced spin transition (CTIST). This is the first time that such a phenomenon has been observed for a Co/Fe molecule.

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