Review: the multicolored coordination chemistry of violurate anions

Abstract

This review provides a comprehensive overview on the coordination chemistry of violuric acid, C₄H₃N₃O₄ (= H₃Vio), and its derivatives (e.g. 1,3-diorganovioluric acids and thiovioluric acid). The most remarkable property of these colorless compounds is the formation of brightly colored (pantochromic/polychromic) salts with colorless cations such as alkali metal and alkaline earth metal ions and organoammonium ions. These magnificent colors have fascinated chemists for more than a century. Only in recent years it has been fully recognized that the structural chemistry of violurates is rather interesting and diverse. Violurate anions are excellent building blocks for new supramolecular assemblies in the crystalline state. Various organoammonium violurates and transition metal violurate complexes have been structurally characterized through single-crystal X-ray diffraction. Highly characteristic for these structures is the formation of 1D, 2D, or 3D hydrogen-bonded assemblies in the crystalline state. This review provides a comprehensive overview on the multicolored coordination chemistry of violurate anions, with the focus being on structurally characterized species.

Graphical Abstract

Keywords:

• violuric acid
• organoammonium violurates
• transition metal violurates
• crystal structure
• hydrogen bond

Acknowledgments

Special thanks are due to Ms. Desirée Schneider and Mr. Marcel Kühling for preparing the ChemDraw schemes for this review article.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

General support of the authors’ own work by the Otto-von-Guericke-Universität Magdeburg is gratefully acknowledged.