The reactions of SbX 3 (X = Cl, Br, I) with N-methylbenzothiazole-2-thione (mbtt) and N-methylbenzothiazole-2-selone (mbts). Formation of the mixed mer/ fac-complex [ mer-SbBr 3(mbts) 2( μ-mbts) fac-SbBr 3(mbts) 2]·CH 2Cl 2

Abstract

The reactions of the antimony(III) halides, SbX 3 (X = Cl, Br, I) with the heterocyclic thione, N-methylbenzothiazole-2-thione (mbtt) and the analogous selone, N-methylbenzothiazole-2-selone (mbts) are reported. The products formed are highly dependent upon the identity of the halide, and in one case on the identity of the chalcogen donor atom. The reaction of SbCl 3 with both mbtt and mbts (and the reaction of SbBr 3 with mbtt), forms complexes in CH 2Cl 2 with a 2:1 ligand to metal ratio, [SbX 3(L)( μ-L) 2SbX 3(L)]·CH 2Cl 2, [X = Cl, L = mbtt ( 1), L = mbts ( 2); X = Br, L = mbtt ( 3)]. These complexes are weakly held together, and feature a primary pyramidal SbX 3 coordination sphere with weak secondary donor-acceptor bonding to the chalcone donor ligands, giving an overall [3+3] octahedral geometry around each antimony atom. In contrast, the reaction of SbBr 3 with mbts in CH 2Cl 2 produces a highly unusual 5:2 ligand:SbBr 3 complex, [ mer-SbBr 3(mbts) 2(-mbts) fac-SbBr 3(mbts) 2]·CH 2Cl 2 ( 4). The fac-substituted antimony center has a [4+2] bonding arrangement, consisting of a primary [SbBr 3(mbts)] coordination sphere and weaker secondary bonds to two further mbts ligands. In contrast, the bonding at the mer-substituted antimony atom is better described as [5+1], with a primary [SbBr 3(mbts) 2] coordination sphere and only one secondary bond to another mbts ligand. The complex is highly unusual in featuring two antimony atoms with different primary/secondary coordination spheres in the same complex. The reactions of mbtt and mbts with SbI 3 result in the formation of 1:1 complexes [SbI 3L], which display chain polymeric structures, {[SbI 2(mbtt)( μ-I)]} n ( 5) and {[SbI 2(mbts)( μ-I)]} n ( 6). The complexes consist of see–saw [SbI 3L] units linked into polymeric chains by bridging iodine atoms, the antimony atoms thus exhibits a square pyramidal geometry. The iodide complexes feature a stereochemically active lone pair trans to the apical iodine atom, and feature much shorter antimony–chalcogen bonds than observed for 1– 4.