Geometry, Energy, and Vibrational Frequencies of the Bis(dicyanomethylene)squarilium Dianion

Similarly to its 1,2-isomer, the bis(dicianomethylene)squaraine (BCSQ) atom connectivity can be a dianion, a radical anion, and a neutral, electron-poor species. This makes it attractive as a constituent unit of new materials. In the present paper we investigate the stable dianion, using theoretical calculation results to connect the geometry determined by X-ray diffraction of the single crystal of Na2BCSQ·4H2O and the vibrational frequencies determined by solution- and solid-state infrared and Raman spectroscopy of various neutral salts.