Monomer-polymer forms of solid, unsolvated, 5-coordinate halodimethyl(2-diphenylphosphinylethyl)stannanes, XMe₂SnCH₂CH₂P(O)Ph₂ (X = Cl, Br or I). Effects of different recrystallisation media

As determined by X-ray crystallography, unsolvated XMe2SnCH2CH2P(O)Ph2 (X = Cl, Br or I) crystallises in two forms: linear chain polymers, obtained by recrystallisation from EtOH or MeOH, and chelated monomers from non-hydroxylic solvents, such as chlorocarbons and acetone. The linear chains are formed by intermolecular Sn–O interactions [at 301 K, 2.339(2) (X = Cl): 2.309(3) (X = Br): 2.282(3) Å (X = I)]: the resulting 5-coordinate tin centres have trigonal bipyramidal geometries, with the halide and the oxygen atoms in axial sites. The chelated forms, with intramolecular Sn–O interactions [also at 301 K: 2.3989(15) (X = Cl): 2.381(2) (X = Br): 2.386(2) Å (X = I)], also contain 5-coordinate tin centres, with trigonal bipyramidal geometries and with the halide and the oxygen atoms in axial sites. As shown by X-ray powder patterns, cooling the melt of polymer-(2: X = I) gave chelate-(2: X = I). The isothiocyanato analogue, (SCN)Me2SnCH2CH2P(O)Ph2, crystallises in the monomeric chelated form from all solvents attempted for recrystallisation [Sn–O = 2.3865(19) and 2.3920(19) Å], in two independent molecules.