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.

Small compound – big colors: synthesis and structural investigation of brightly colored alkaline earth metal 1,3-dimethylviolurates

“…Thus in the course of the present study we set out to isolate the entire series and fully characterize the compounds through analytical and spectroscopic methods as well as single-crystal X-ray diffraction studies. As in the case of the recently investigated alkali metal 1,3-dimethylviolurates M(Me 2 Vio) (M = Li-Cs) 40…”

“…red, purple, blue) are primarily a solid-state phenomenon. 9,[12][13][14]40 Even the bright blue rubidium and cesium violurates and dimethylviolurates dissolve in water or DMSO with the same pink-violet color of the free violurate anions. Thus it did not come as a surprise that the UV-vis spectra of the title compounds revealed the same effect.…”

“…The η 2 -mode is rare for metal violurates and has previously only been seen with cesium 1,3dimethylviolurate to the best of our knowledge. 40 Similarly to the calcium salt 4, barium 1,3-dimethylviolurate crystallizes as a tetrahydrate (6) with one formula moiety in the asymmetric unit (Fig. 9).…”

“…Recently we reported the X-ray structural characterization of the full series of alkali metal 1,3-dimethylviolurates M(Me 2 Vio) (M = Li–Cs). 40 It was found that these salts exist as one- (Li, Na), two- (K, Cs), or three-dimensional (Rb) coordination polymers in the crystalline state. In view of this rather diverse structural chemistry of the alkali metal 1,3-dimethylviolurate salts we now investigated the similar series of alkaline earth metal salts AE(Me 2 Vio) 2 (AE = Mg–Ba).…”

“…1,3-dimethylviolurates AE(Me 2 Vio) 2 (H 2 O) n (AE = Mg, n = 6 (3); AE = Ca, n = 8 (4), AE = Sr, n = 6 (5); AE = Ba, n = 4 (6)) as well as Sr (Me 2 Vio) 2 (18-crown-6) (5a) and Ba(Me 2 Vio)(Me 2 NO 2 Barb)•2H 2 O (8) have been fully characterized by their IR, Raman and NMR ( 1 H,13 C{ 1 H}) spectra, elemental analyses, and single-crystal X-ray diffraction. The colors of the crystalline salts range from red to purple and show less diversity than the corresponding alkali metal 1,3-dimethylviolurates where the salts of the heavier elements K, Rb, and Cs are bright blue 40. In contrast, the colors of the crystalline title compounds are mainly red to red-violet.…”