Main Group Metal Halide Complexes with Sterically Hindered Thioureas. IX. New Complexes of Selected Post-Transition Metals and 1,3-dimethyl-2(3H)-imidazolethione and a Structural Investigation of Infrared Peak Shifts Associated with Coordination


Chemistry and Biochemistry

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MCl2(dmit)2 (M = Zn, Cd, Hg, Sn; dmit = 1,3-dimethyl-2(3H)imidazolethione), TeCl2(dmit)4, and SbCl5(dmit) were prepd. and characterized. The chem. of SbCl5(dmit) is more complex than that of the others, giving rise to unique redox products upon heating in soln. Solid-state spectra of these complexes as well as for other dmit complexes are reported and discussed with regard to the coordination sensitive NCN asym. stretch and the C:S stretch obsd. not only for dmit complexes but for tetramethylthiourea (tmtu) complexes reported in the literature as well. Greatest shifts on coordination are obsd. with the NCN asym. stretch for tmtu, causing shifts to higher wave nos. of 55-95 cm-1 relative to free tmtu. Shifts are explained on the basis of obsd. crystal structures of tmtu adducts showing a greater CN double bond character. Dmit adducts show much smaller shifts both to higher and lower frequencies for this mode relative to free ligand, and the C:S stretch shows little change also. Comparison to known crystal structures show little change in the bond distances of the dmit ligand upon coordination. Inductive effects based on correlations of shift magnitude to the Sanderson group electronegativity of the acceptor seem to be unrelated, with the exception of a small pos. correlation obsd. for the NCN asym. stretch of tmtu.