The crystal structures of the acid salts of some dibasic acids. Part II. Potassium hydrogen malonate: two X-ray studies

Potassium hydrogen malonate crystallises in the monoclinic space group C2/m with a= 9·473, b= 11·559, c= 4·726 A, β= 91·6°, Z= 4. Two independent X-ray analyses are reported, each based on three-dimensional, diffractometer data. They lead to closely similar sets of co-ordinates and vibrational parameters.The hydrogen-malonate residues have two-fold crystallographic symmetry, and are linked into infinite chains by ‘very short’ hydrogen bonds lying across centres of inversion. The atoms of each carboxy-group [C–C 1·516(4), C–O(H) 1·293(4), and CO 1·223(4)A] are coplanar with the methylenic carbon atom. The angle between the carboxy-planes, in each half of the residue, is ca. 10°.