Tin-119 Mössbauer study of complexes with chlorine-bridged tin–molybdenum and tin–tungsten bonds

Abstract

Tin-119 Mössbauer spectra have been recorded for a number of complexes of the type [L₂M(CO)₃(SnR_3–nCl_n)Cl](L₂=αα′-bipyridyl, o-phenanthroline, dithiahexane; M = Mo or W; R = Me or Ph; n= 1–3), in which the M–Sn bond is bridged by a Cl atom. Measurements in applied magnetic fields of 50 kG show that the quadrupole coupling constant e²qQ is positive and the asymmetry parameter η is small when n= 2 or 3. These facts, together with trends in isomer shift and quadrupole-splitting values, indicate that in these complexes W is a better σ-donor than Mo. For [(bipy)Mo(CO)₃(SnPh₂Cl)Cl], e²qQ < 0 and η≃ 0·8. It is concluded that the Mo atom and the two C atoms in this complex occupy approximately equatorial positions in the distorted trigonal bipyramidal Sn environment, and the large η is attributed to geometrical constraints imposed by the bridging Cl atom. The Mössbauer spectrum of [(bipy)Mo(CO)₃(Snl₃)l] suggests partial dissociation of the complex to [(bipy)Mo(CO)₃(l)l]and Snl₂.