Notes. The crystal structure of diaquadichlorodimethyltin(IV)–purine (1/4)

Abstract

The structure of the compound Sn(CH₃)₂Cl₂(H₂O)₂·4C₅H₄N₄ has been determined by single-crystal X-ray diffraction methods. The compound crystallizes in the monoclinic system, space group P2₁/a, with unit-cell dimensions a= 11.218(4), b= 18.374(5), c= 7.193(3)Å, β= 101.9(4)°, and Z= 2. The structure is centrosymmetric at the all-trans Sn(CH₃)₂Cl₂(H₂O)₂ octahedral units, which are surrounded by four purine molecules hydrogen bonded to the H₂O ligands. Each purine also makes hydrogen bonds with purines adjacent to different Sn(CH₃)₂Cl₂(H₂O)₂ units to form a three-dimensional network. The purine molecules are present in tautomeric pairs: in one isomer a hydrogen atom is attached to the atom N(7) of the imidazole ring, as found in crystals of free purine, and in the other one to the atom N(9). Proton n.m.r. measurements on the system Sn(CH₃)₂Cl₂–purine in acetone show that also in solution direct co-ordination of the base to tin does not occur.