The molecular structure of the recently synthesized compound bisquaric acid was investigated by high-resolution solid state C-13 NMR spectroscopy and electronic structure calculations. Variable temperature 13C NMR spectra were found quite unusual compared with the solution phase spectra and not explainable on the basis of the literature data on squaric acid. In particular, the C-13-OH peaks were found to be coincident with the C-13=O peaks. An extensive electronic structure analysis using the density functional theory (B3LYP) was thus performed, including the calculation of the C-13 shifts by the GIAO method. Indeed, the calculations indicate that the linker C-C bond has a substantial double-bond character, thereby leading to a strong deshielding of the C-OH carbons. In addition, the theoretical study shows significant differences between bisquaric acid and squaric acid in several molecular properties, such as aromaticity, hydrogen-bonding, dipole moment, and acid-base behavior. Unlike squaric acid, no phase transition was detected for bisquaric acid by C-11 NMR. However, the theoretical results suggest the possibility of such a transition at temperatures lower than about 100 degreesC, but it should be probed by other methods such as specific heat measurements.