Synthesis and Structural Investigation of a Complete Series of Brightly Colored Alkali Metal 1,3‐Dimethylviolurates

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.