Refinement of the crystal structure of malonic acid, C3H4O4

A reinvestigation of the X-ray crystal structure of malonic acid (C3H4O4) has been made in the light of some observations arising from solid-state13C NMR studies on this compound. The unit cell parameters are:a=5.156(1),b=5.341(1),c=8.407(1) A, α=71.48o (2), β=76.12o (2), γ=85.09o (2), space group\(P\bar 1\),Z=2. The structure was solved by direct methods and refined by full-matrix least-squares refinement to a finalR value of 0.038 for 711 unique reflections withl>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 (123.3o and 124.8o, 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.