THERMOCHROMISM IN COPPER(II) COMPLEXES - THERMAL, SPECTROSCOPIC, SOLID-STATE BROAD-LINE H-1-NMR AND ROOM-TEMPERATURE SINGLE-CRYSTAL X-RAY-ANALYSIS OF BIS(N,N'-DIMETHYL-1,2-ETHANEDIAMINE)COPPER(II) DINITRATE

The complex bis(N,N'-dimethyl-1,2-ethanediamine)copper(II) dinitrate, Cu (NN'-dMen)2(NO3)2, Undergoes a first-order thermochromic phase tran sition at ca 148-degrees-C, changing from blue-violet to blue. The low -temperature phase has been characterized by X-ray crystallography. Th e copper ion possesses distorted (4 + 2) octahedral geometry with two five-membered chelate rings, in the deltalambda conformation, forming the CuN4 plane [Cu-N = 2.000(6) and 2.033(7) angstrom] and oxygens fro m the two nitrate groups weakly coordinated in the two axial coordinat ion sites [Cu-O = 2.506(8) angstrom]. The broad-line H-1 NMR indicates the onset of a dynamic disorder of diamine chelate rings at the phase transition temperature region. The electronic spectrum broadens on ph ase transition.