The crystal structure of the title compound has been determined from single-crystal X-ray diffraction data by Patterson and Fourier methods. Crystals are monoclinic, space group C2/c with Z= 4 in a unit cell of dimensions a= 10"422 (8), b = 5.676 (4), c= 13.618 (7) A,, fl= 108"50 (5) °. The structure was refined by least-squares methods to R 0.071 for 1193 reflexions. The oxalates are equivalent and are chelated to Sn through one oxygen on each carbon atom to give one Sn-O bond of 2.25 and one of 2.36 A,. The tin atoms are in distorted pyramidal sites surrounded by two oxygen atoms at 2.25 and two at 2.36 A.