Further studies of [x-(haloalkylstannyl)alkyl]phosphine oxides. Structures of bis[2-(bromodimethylstannyl)ethyl]phenylphosphine oxide and t-butyl[3-(iododimethylstannyl)propyl]phenylphosphine oxide William T.A. Harrison a , R. Alan Howie a, * , Marcel Jaspars a , Solange M.S.V. Wardell b , James L. Wardell c a Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, UK b Departamento de Qu  ımica Inorg^ anica, Instituto de Qu  ımica, Universidade Federal Fluminense, 24020-150 Niter oi, RJ, Brazil c Departamento de Qu  ımica Inorg^ anica, Instituto de Qu  ımica, Universidade Federal do Rio de Janeiro, 21945-970 Rio de Janeiro, RJ, Brazil Received 11 June 2003; accepted 21 July 2003 Abstract The crystal structures of bis[2-(bromodimethylstannyl)ethyl]phenylphosphine oxide 3 (X ¼ Br), and t-butyl[3-(iododimethyl- stannyl)propyl]phenylphosphine oxide 7 (X ¼ I), have been determined. Compound 7 (X ¼ I), grown from EtOH solution, is a chelated complex as a consequence of an intramolecular Sn–O interaction and hence contrasts with the previously reported [3- (iododimethylstannyl)propyl]diphenylphosphine oxide, grown from alcohol media solution, which has an intermolecular Sn–O linked chain structure. Molecules of 7 (X ¼ I) are linked into double chains via C–H–I and C–H–p interactions. Compound 3 (X ¼ Br), isostructural with previously reported 3 (X ¼ Cl) obtained from CH 2 Cl 2 solution, contains two distinct trigonal bipyra- midal tin centres. One Sn centre is intramolecularly bound to the O, i.e., one PhP(O)CH 2 CH 2 fragment is acting as a C,O-chelating unit, while the other Sn centre is weakly bonded to a Br ligand from another molecule to set up zig zag chains of molecules. In- termolecular interactions, C–H–Br and C–H–p, create a double layer of molecules. Detailed 1 H NMR spectra of 3 are reported. Ó 2003 Elsevier Ltd. All rights reserved. Keywords: Organotin; Phosphine oxide; Crystal structures; Chelation 1. Introduction Structures of x-(stannylalkyl)phosphine oxides, e.g., X n R 3  n Sn(CH 2 ) m P(O)R 0 R 00 , (R and R 0 ¼ alkyl or aryl; R 00 ¼ alkyl, aryl or alkoxy; m ¼ 2 [1–6] or 3 [3,7]) and [X n R 3  n Sn(CH 2 ) 2 ] 2 P(O)R 0 (X ¼ halide; R, R 0 and R 00 ¼ alkyl or aryl; n ¼ 0 or 1 [8]), have been variously studied. While in non-halogenated compounds, such as R 3 Sn(CH 2 ) m P(O)R 0 R 00 and [R 3 Sn(CH 2 ) 2 ] 2 P(O)R 0 (R and R 0 ¼ alkyl or aryl; R 00 ¼ alkyl, aryl or alkoxy; m ¼ 2 or 3) tin is invariably four coordinate both in solution and in the solid state at least five coordination occurs in the halide derivatives in both phases. As shown recently [6], XMe 2 SnCH 2 CH 2 P(O)Ph 2 1 (X ¼ Cl, Br or I), crystallises in two distinct unsolvated forms, a polymeric, zig zag chain form, with intermo- lecular Sn–O bonds, polymer-1, in which CH 2 CH 2 P(O)Ph 2 acts as a bridging ligand, and a molecular form, chelate-1 [6], with intramolecular Sn–O bonds and the CH 2 CH 2 P(O)Ph 2 moiety chelating with the formation of a five-membered ring. The tin centres in both forms have trigonal bipyramidal geometries with O and the X group in axial positions, see Figs. 1a and b. The poly- meric forms were isolated on recrystallisation from al- cohols, e.g., MeOH and EtOH, and the chelate forms from non-hydroxylic solvents, such as Me 2 CO and chlorocarbons. In contrast to 1 (X ¼ Cl, Br or I) 1 * Corresponding author. Tel.: +44-1224-272907; fax: +44-1224- 272921. E-mail address: r.a.howie@abdn.ac.uk (R.A. Howie). Polyhedron 22 (2003) 3277–3288 www.elsevier.com/locate/poly 0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0277-5387(03)00470-4