CHARGE-TRANSFER CRYSTALS OF OCTACARBONYLDIFERRATE - SOLID-STATE STRUCTURE AND OXIDATION-REDUCTION OF AN IRON-IRON-BONDED ELECTRON-DONOR

The dinuclear carbonylmetalate [Fe-2(CO)(8)](2-) forms deeply colored crystals A(2)[Fe-2(CO)(8)] with various phosphonium and pyridinium cat ions (A(+)) by metathesis in aqueous solution. Diffuse reflectance abs orption spectroscopy and X-ray crystallography establish the colors to derive from anion-to-cation charge-transfer (CT) within the triple io n [A(+), Fe-2(CO)(8)(2-), A(+)] extant in the solid state. Partial ele ctron transfer in the charge-transfer salts is established by the sign ificant shortening of the iron-iron bond in the [Fe-2(CO)(8)](2-) moie ty when it is ion paired with the N-methyllutidinium acceptor. In solu tion, the charge-transfer salts can undergo interionic electron transf er, and they lead to the dimeric A(2) and a series of iron carbonyl pr oducts that are uniquely dependent on the solvent (water, ether, and a cetonitrile).