Synthesis and Mössbauer spectra of six-co-ordinate tin–metal compounds: quotient of the partial quadrupole splittings of the six- and four-co-ordinate species

Abstract

Nine new six-co-ordinate tin(IV) compounds have been prepared of the type [M(SnCl₃L)][M = Mn(CO)₅, Mn(CO)₄(PPh₃), Fe(cp)(CO)₂; L = phen or bipy], [M(SnXL′₂)](X = Cl or Ph; L′= quin or pd), and [M{SnPhCl₂(phen)}]. Structures for these and other similar compounds have been assigned using carbonyl i.r. stretching frequencies and ¹¹⁹Sn Mössbauer quadrupole splittings. Partial quadrupole splittings for six-co-ordinate species, (p.q.s.)_L^oct, have been calculated from these quadrupole splittings. There is an excellent linear corrleation (R 0.991) between the (p.q.s.)_L^oct values and previously calculated (p.q.s.)_L^tet values: (p.q.s.)_L^oct= 0.73(p.q.s)_L^tet–0.01. The gradient of 0.73 is compared with that (0.67) calculated previously from molecular-orbital arguments. The relative bonding characteristics for the M groups in six-co-ordination are the same as those evaluated for M groups in four-co-ordinate compounds. Thus, the order of p-donor strength in six-co-ordination is Mo(cp)(CO)₃ < Mn(CO)₅ < Mn(CO)₄(PPh₃)≈ Fe(cp)(CO)₂ < Ph < Me, while the M–Sn bonds have substantially higher Sn 5s character than Me or Ph–Sn bonds.