Synthesis and structural investigation of a complete series of brightly colored alkali metal 1,3‐dimethylviolurates

Abstract

A complete series of alkali metal 1,3-dimethylviolurates M(Me2Vio) was synthesized and fully characterized. The title compounds M(Me2Vio)(H2O) [M = Li (3), Na (4)], K(Me2Vio)(H2O)0.5 (5) and M(Me2Vio) [M = Rb (6), Cs (7)] were prepared by neutralizing 1,3-dimethylvioluric acid (= HMe2Vio; 2) with 1 equiv. of the corresponding metal hydroxides MOH. The resulting salts exhibit striking colors ranging from orange-red (3) through purple (4, 5) to bright blue (6, 7). In contrast to the monohydrate 4, the classical synthesis of sodium 1,3-dimethylviolurate from 1,3-dimethylbarbituric acid and NaNO2 afforded the purple trihydrate Na(Me2Vio)(H2O)3 (4a). All new compounds have been fully characterized by their IR and NMR (1H, 13C) spectra as well as elemental analyses. X-ray crystal structure determination revealed that the title compounds exist as one- (Li, Na), two- (K, Cs), or three-dimensional (Rb) coordination polymers in the solid state.