Abstract A new modification of CuI · py was prepared by the reaction of a saturated solution of CuI in CH3CN with a solution of pyridine in ethanol at 60 °C. It crystallizes monoclinic with four formula units in the space group P21/c. (CuI · py)∞ forms a polymeric ribbon structure. Contrary to the cubane-like tetrameric modification, (CuI · py)∞ does not show luminescence thermochromism. The luminescence properties of both modifications of Cul · py are interpreted.

The luminescence spectra of AxCo(CN)6 and [(C6H5)4P]3Cr(CN)6 were investigated at T = 15 K with respect to their vibrational structure, the structure's equidistance and intensity distribution over the vibrational quantum number. As in almost all Cr(III) complexes, the π* → π* luminescence of [(C6H5)4P]3Cr(CN)6 is distinctly structured. The main features of the spectrum can be ascribed to a coupling with the νa1g (CrC) and νa1g (CN) normal modes. The broad σ* → π* luminescence of AxCo(CN)6 is structured, but much less as in the Cr(III) complex, if Ax = K3, Cs3, Cs2Li and not structured at all if Ax = Cd1.5 on In. The structure can be assigned to a progression of the νa1g (CoC) vibration over 17 vibrational quanta with an anharmonicity of 2–3 cm−1 per quantum. From the intensity distribution of the spectra it was calculated that the CoC distance is lengthened by about 0.11 Å and that the CrC distance is shortened by 0.02–0.03 Å in the first excited electronic state.