Dielectric property of hydrogen-bonded squaric acid derivatives

The crystal of squaric acid (SQ) shows dielectric property caused by tautomerization coupled with intermolecular proton transfer. We prepared a squaric acid derivative, 1,4-phenylenebis(squaric acid) (PBSQ), and determined its crystal structure. In the unit cell one PBSQ molecule and two water molecules are incorporated. There are one dimensional hydrogen-bonded chains PBSQ molecules. The distance between hydrogen-bonded O···O is very short (2.48A). The result suggests that PBSA exists as mono deprotonated species accompanied by a counter cation of protonated 2H2O molecules (O···O distance of 2.45A).