X-ray crystallographic, morphological and thermal decomposition studies of 2:1 adducts of diisopropyl methylphosphonate with stannous and stannic halides

Abstract

X-ray and morphological studies of monomeric, trans-square planar Sn(dimp) 2X 2 ( X  Cl, Br; dimp = diisopropyl methylphosphonate) and trans-octahedral Sn(dimp) 2X 4 ( X = Cl, Br, I) adducts revealed that the crystals of these compounds are triclinic, space group P1. The Sn(II) and Sn(IV) chloride and bromide adducts have four molecules per unit cell, while the SnI 4 adduct has two molecules per unit cell. The two stannous halide adducts are almost isostructural. The X-ray powder patterns of the SnCl 4 and SnBr 4 complexes exhibit some similarities, but that of the SnI 4 adduct is significantly different. Studies of the thermal behavior of the Sn(IV) adducts at 140–210°C, indicated that Sn(dimp) 2 X 4 decomposes in two steps, i.e. (i) Formation of a linear oligomeric species of the type {[( i-C 3H 7O)CH 3POO] 2Sn X 2} n ( n = 4 for X  Cl), involvin Sn(OPO) 2Sn bridges, with simultaneous elimination of propylene and HX. (ii) Decomposition of the preceding oligomeric intermediate to yield highly cross-linked polymeric [(CH 3PO 3) 2Sn] n and isopropyl halide. Poor reproducibility in the amounts of volatile materials evolved from experiment to experiment did not allow the collection of consistent kinetic data for the thermal decomposition of Sn(dimp) 2 X 4. The Sn(dimp) 2 X 2 adducts also decompose at elevated temperatures, yielding a linear, high polymer of the [(CH 3(OH)POO) 2Sn] n type, via formation of the {[( i-C 3H 7O)CH 3POO] 2Sn} n intermediate, which is subsequently attacked by the hydrogen halide present in the system.