Luminescence Spectra of Cobalt(III) Cyano Complexes

Abstract

Abstract Luminescence spectra of M3[Co(CN)6] (M=K, Rb, Cs), cis-K3Na2[Co(CN)4(SO3)2], and trans-Na5[Co(CN)4(SO3)2] were measured at 20 K. Single crystal luminescence spectra of the hexacyanocobaltates(III), centered at 14100–14200 cm−1, exhibited vibrational structure associated with three components, and the separation between the members of the progression was about 400 cm−1. Luminescence spectra of powdered cis-K3Na2[Co(CN)4(SO3)2] and trans-Na5[Co(CN)4(SO3)2] were structureless and broad centered at 13200 and 14400 cm−1, respectively. Comparison of these luminescence spectra with the corresponding spin-forbidden bands indicated that the 0-0 transition lies at 18300–18600 cm−1 for hexacyanocobaltates(III), at 16500–17000 cm−1 for cis-K3Na2[Co(CN)4(SO3)2], and at 17700–18200 cm−1 for trans-Na5[Co(CN)4(SO3)2]. The vibrational structure in luminescence spectra of hexacyanocobaltates(III) can be interpreted in terms of the ν8,ν9,ν12 and ν13 ungerade skeletal modes, a lattice mode, and the totally symmetric ν2 vibrational mode. Analysis of the relative intensity of the vibrational structure in the luminescence spectra gave information about the change in the Co–C internuclear equilibrium distance from the ground state to the excited luminescent state. The relationship between luminescence and photochemical behavior of cobalt(III) complexes was also considered.