121Sb, 57Fe and 127I Mössbauer spectroscopic study on antimony-transition metal bond in metal carbonyl derivatives of tertiary stibines

Abstract

Antimony-transition metal bonds in five- or six-coordinate [M(CO) n (SbR 3)] (M=Fe, Ru; n=4, M=Cr, Mo, W; n=5, R=Me, Ph), seven-coordinate [MI 2(CO) 3(SbPh 3)L] − (M=Mo, W, L=PPh 3, AsPh 3) and [MI 3(CO) 3(SbPh 3)] − (M=Mo, W) have been investigated using the 121Sb, 57Fe and 127I Mössbauer spectroscopy. Coordination of SbR 3 to the transition metal atom results in the increase in the values of isomer shift and the decrease in the values of quadrupole coupling constant of the 121Sb Mössbauer spectra. This indicates that the lone pair electron of the stibine is transferred to the transition metal atom. The degree of the transfer increases in the order of Mo<W<Ru, and Cr≪Fe, being the order of the Allred–Rochow's electronegativity for the transition metal atom. The same trend holds for [MI 2(CO) 3(SbPh 3)L] (M=Mo, W). 57Fe Mössbauer spectra of [Fe(CO) 4(SbR 3)] at 80 K are not so different from that of Fe(CO) 5, suggesting that some redistribution of electron density around Fe atom occurs. The 127I Mössbauer spectra for [MI 2(CO) 3(SbPh 3)L] and [MI 3(CO) 3(SbPh 3)] show a typical σ interaction in MI bonds.