Structural investigations of the organoantimony(V) halides Ph4SbX and Ph3SbX2(X = Cl, Br or I) in the solid state and in solution

Abstract

X-Ray crystallography revealed a distorted trigonal-bipyramidal structure for Ph₄Sbl, with Sb–C_ax 2.141(3), Sb–C_eq 2.103(3)–2.117(3)Å and a long Sb–I distance of 3.341(1)Å in monoclinic crystals of P2₁/n symmetry. Consideration of the weak Sb–X bonds in Ph₄SbX (X = Cl, Br or I) leads to reassignment of their Raman spectra; Ph₄Sbl ionises forming [Ph₄Sb]⁺ in acetonitrile, as shown by ¹³C and ¹²¹Sb NMR spectra. The halide Ph₃Sbl₂ is reported in two phases, yellow, orthorhombic (Fdd2) crystals isomorphous with Ph₃SbBr₂ and off-white, cubic (P4₃32) crystals. In each the molecule is trigonal-bipyramidal, with axial Sb–l bonds of 2.865(1)Å in the former and 2.885(1)Å in the latter, and small differences in their respective bond angles. The phenyl groups of the cubic form are in the regular propeller arrangement whereas one group of the orthorhombic form has a reversed orientation. The vibrational spectra of the two forms differ slightly.