| 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). Thecluster can exist in three different solid-state phases: a red crystalline phase, a blue solid phase obtainedby exposure of the red crystals to moisture, and a red solid phase obtained by desolvation of the blue solidphase in vacuo. The properties of cluster 1 are extremely sensitive to both temperature and solvent contentin each of these phases. Variable-temperature X-ray crystallography; 57Fe Mössbauer, vibrational, andoptical spectroscopies; and magnetochemical studies were used to study the three phases of 1 and relatedcompounds, 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 theunambiguous 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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