Studies of dioxamide and dithio-oxamide metal complexes. Part 3. Confirmation of NN′-disubstituted dithio-oxamides as SS′-bidentate chelating ligands. Crystal and molecular structures of the six-co-ordinate tin(IV) complex SnBr4L1(L1=NN′-di-n-butyldithio-oxamide) and the seven-co-ordinate bismuth(III) complex BiCl3(L2)2(L2=NN′-diethyldithio-oxamide)

Abstract

Crystal structures of two metal complexes with NN′-disubstituted dithio-oxamides as bidentate chelating ligands have been determined. SnBr₄L₁·0.33C₆H₆(1; L¹=NN′-di-n-butyldithio-oxamide) is monoclinic, space group C2/c, with a= 20.766(15), b= 21.245(15), c= 14.835(9)Å, β= 91.4(1)°, and Z= 12. BiCl³(L²)₂·Me₂CO (2; L²=NN′-diethyldithio-oxamide) is monoclinic, space group P2₁/c, with a= 10.568(9), b= 8.780(9), c= 30.086(15)Å, β= 101.2(1)°, and Z= 4. 1 247 [For (1)] and 2 341 [for (2)] independent reflections above background were collected and the structures refined to R 0.10 and 0.08, respectively. Complex (1) has two equivalent molecules in the asymmetric unit, one with imposed C₂ symmetry. The tin atoms are six-co-ordinate octahedral, being bonded to four bromine atoms [2.527(11)–2.625(13)Å] and to a bidentate dithio-oxamide ligand through sulphur [Sn–S 2.551 (25)–2.609(25)Å]. In (2), the bismuth atom is seven-co-ordinate with a pentagonal bipyramidal geometry. Chlorine atoms occupy the axial sites [2.635(10) and 2.717(10)Å] while the equatorial girdle is occupied by two bidentate ligands [Bi–S′ 2.818(13)–3.042(12)Å] and another chlorine atom [2.651(12)Å]. In both structures all the ligand –NH groups are hydrogen bonded for the most part to halogen atoms but also in (2) to the acetone solvent molecule. This intermolecular hydrogen bonding is a direct cause of ring puckering in the chelates.