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

摘要

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)_e]~(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; ~(57)Fe Moessbauer, 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}(CIO_4)_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, {Co_2~(Ⅲ)Co~(Ⅱ)Fe_2~(Ⅱ)} (1 A), {Co~(Ⅲ)-Co_2~(Ⅱ)Fe~(Ⅲ)lFe~(Ⅱ)} (1B), and {Co_3~(Ⅱ)Fe_2~(Ⅲ)} (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.