The first authenticated example of geometrical isomers in organotin(IV) co-ordination chemistry. The crystal and molecular structures of octahedral cis- and trans-SnR2isomeric adducts of dichlorobis(4-chlorophenyl)tin(IV) with 4,4′-dimethyl-2,2′-bipyridyl

Abstract

The crystal structures of the cis- and trans-SnR2 skeletal isomers of the octahedral complex, Sn(C6H4Cl-4)2Cl2·(4,4′- Me2bipy)(4,4′- Me2bipy = 4,4′-dimethyl-2,2′-bipyridyl), solved by X-ray analysis, are reported together with some preliminary observations on their solution structures as studied by 1H and 119Sn Fourier-transform n.m.r. The complex is isolated exclusively as the cis isomer (2) upon mixing the Lewis-acid and -base components in ethanol medium. Recrystallization from hot methanol or dimethylformamide generates the trans isomer (1), which is readily reconverted to the cis form in toluene. Two crystalline modifications of the cis form, containing toluene molecules included in different host lattices, have been characterized as (2a)[C24H20Cl4N2Sn·C7H8, space group Pccn, a= 12.221(8), b= 28.10(2), c= 20.548(6)ÅZ= 8] and (2b)[C24H20Cl4N2Sn·C7H8, space group P21/n, a= 15.231(7), b= 12.422(6), c= 16.844(5)Å, β= 96.22(3)°, Z= 4]. Compound (2) exists as a discrete octahedral molecule in both (2a) and (2b) with the following respective molecular dimension: C(1)–Sn–C(7) 106.2(6), 106.3(3); Cl(1)–Sn–Cl(2) 163.5(1), 163.0(1); N(1)–Sn–N(2) 69.8(4), 69.4(2)°; Sn–C(1) 2.139(18), 2.158(7); Sn–C(7) 2.170(13), 2.183(8)Å; Sn–N(1) 2.311(12), 2.322(6); Sn–N(2) 2.327(12), 2.294(6); Sn–Cl(1) 2.459(4), 2.509(2); Sn–Cl(2) 2.491(4), 2.475(2)Å. Compound (1) crystallizes from dimethylformamide in space group P42 with a= 10.884(4), c= 10.204(2)Å, and Z= 2. The lattice of (1) contains discrete octahedral molecules [C(1)–Sn–C(1′) 177.4(7), N(1)–Sn–N(1′) 68.3(4), Cl(1)–Sn–Cl(1′) 104.2(2)°; Sn–C 2.156(9); Sn–Cl 2.482(5); Sn–N 2.402(8)Å], with a crystallographic C2 axis passing through Sn and the mid-point of the C–C bond joining the two halves of the bidentate ligand.