Triphenylphosphine oxide adducts of diphenylantimony(V) and diorganotin(IV) Lewis acids: structures of SnPh 2Cl 2·OPPh 3, SnPh 2Cl 2·2OPPh 3, SnPh 2Br 2·OPPh 3 and SbPh 2Cl 3·OPPh 3

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1:1 and 1:2 adducts of diphenyltin dichloride with triphenylphosphine oxide can be isolated in the solid state but the preparative conditions necessary to isolate an adduct of specific stoichiometry are difficult to define; none of acid: base ratio, choice of solvent or reaction temperature are significant factors. Adventitious crystal seeding probably has a dominant role. Both the 1:1 and 1:2 adducts of SnPh 2Cl 2, but only the 1:1 adduct of SnPh 2Br 2, were isolated. 1:1 and 1:2 adducts of both SnMe 2Cl 2 and SnBu n 2Cl 2 were readily isolated whereas only 1:2 adducts were obtained with SnPh 2(NCS) 2 and SnBu n 2(NCS) 2. SbPh 2Cl 3 readily forms a 1:1 adduct with triphenylphosphine oxide and the same adduct is obtained from the reaction of the phosphine oxide with SbPhCl 2. Crystallographic data are reported for SnPh 2Cl 2·OPPh 3, SnPh 2Cl 2·2OPPh 3, SnPh 2Br 2·OPPh 3 and SbPh 2Cl 3·OPPh 3. Both SnPh 2Cl 2·OPPh 3 and SnPh 2Br 2·OPPh 3 have tin in trigonal bipyramidal environments. 119Sn Mössbauer quadrupole splitting data are consistent with the same trigonal bipyramidal geometry for tin in SnMe 2Cl 2·OPPh 3 whereas the data for the butyl analogue suggest the presence of six-coordinated tin as a result of intermolecular Sn–Cl interactions. A notable feature of all of the adducts subjected to crystallographic studies is the presence of intramolecular π-interactions involving phenyl groups of the phosphine oxide and phenyl groups bonded to the metal.