Dinuclear and tetranuclear cages of oxodiphenylantimony phosphinates: synthesis and structures

The novel dimeric compounds [Ph2Sb(O2PR2)O]2.2CH2Cl2 [R = cycl-C6H11 (2) and cycl-C8H15 (3)] have been synthesized by reacting diphenylantimony trichloride (1) with 3 mol equiv of silver acetate followed by 1 mol equiv of the phosphinic acid. By the same route under more stringent conditions to exclude moisture, the mixed phosphinate-acetate [Ph2Sb(O2P(C6H11)2)(O2CMe)]2O (4) was isolated and characterized. Treatment of 2 with acetic acid/water affords the tetranuclear cage Ph8Sb4O4(OH)2(O2P(C6H11)2)2.CH3COOH.CH2Cl2 (5); it is possible to convert 5 to 2 by heating it with an excess of the phosphinic acid. Compounds 2, 3, and 5 have been characterized by X-ray structural analysis. All of them possess four membered Sb2O2 rings with hexacoordinated antimony. In 5 the antimony atoms in the two Sb2O2 rings are connected by oxo bridges on two sides to give an Sb4O6 cage. These structures are correlated with those of known tin cages