Resonance-Raman and infrared studies of cyanide-bridged dimetal complexes

Abstract

Raman and i.r. spectra have been determined in the ν(CN) region of the CN-bridged dimetal complex anions [(NC)₅Fe^II(CN)Co^III(CN)₅]^6– and [(NC)₅Fe^III(CN)Co^III(CN)₅]^5–. The spectra show bands at 2 130 and 2 185 cm^–1, respectively, which are assigned to the stretching modes of the bridging CN groups. Similar modes are assigned at 2 134 and 2 182 cm^–1 in the spectra of the two short-lived reaction intermediates [(NC)₅Fe^II(CN)Co^III(edta)]^5– and [(NC)₅Fe^III(CN)Co^III(edta)]^4–, respectively (edta =NNN′N′-ethylenediaminetetra-acetate). The terminal CN stretching modes all occur at much lower wavenumbers. ν(CN) Raman bands of the bridging group in both [(NC)₅Fe^II(CN)Co^III(CN)₅]^6– and [(NC)₅Fe^II(CN)Co^III(edta)]^5– show resonance enhancement associated with the absorption bands at 395 and 565 nm, respectively, indicating that these bands may be assigned to a charge-transfer transition of the type Fe^II→Co^III through the CN bridge.