The first authenticated example of geometrical isomers in organotin(IV) co-ordination chemistry. The crystal and molecular structures of octahedral cis- and trans-SnR2 isomeric 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.