4-Phenyl­pyridinium betaine of squaric acid.

The title compound, 4-phenyl­pyridinium-3-squarate, C15H9NO3, exhibits an inter­planar angle between the pyridinium and squarate rings of 0.6 (1)°. It displays a dipolar electronic ground-state structure, with a positively charged pyridinium fragment and a negatively charged squarate moiety. In the mol­ecule, the two aromatic rings are twisted by 31.6 (1)°. The bond lengths within the squarate system represent average values for the two possible resonance structures, with a central typical carbon­yl bond [1.203 (2) Å] flanked by two longer `semicarbon­yl' bonds of lengths 1.228 (2) and 1.221 (2) Å. [ABSTRACT FROM AUTHOR]