Refinement of the crystal structure of malonic acid, C<SUB>3</SUB>H<SUB>4</SUB>O<SUB>4</SUB>

A reinvestigation of the X-ray crystal structure of malonic acid (CHO) has been made in the light of some observations arising from solid-stateC NMR studies on this compound. The unit cell parameters are:a = 5.156(1), b = 5.341(1), c = 8.407(1) Å, α = 71.48° (2), β = 76.12° (2) γ = 85.09° (2), space group P‾1, Z=2. The structure was solved by direct methods and refined by full-matrix least-squares refinement to a final R value of 0.038 for 711 unique reflections with l > 3σ. The packing of the molecules involves dimeric hydrogen bonded association of each carboxyl group with a centrosymmetrically related neighbor. The angles O - C - O (123.3° and 124.8°, respectively) for the two carboxyl groups agree qualitatively with the values predicted from a linear relationship relating the observed σ22 component of the Carbon-13 NMR chemical shielding tensor for the carboxyl carbon atom to the bond angle O - C - O at the carbon atom