Structural studies of diorganotin(IV) bischelates. Crystallographic evidence of seven-coordinate tin in bis(2-carbomethoxyethyl)bis ( N,N-dimethyldithiocarbamato)tin(IV), [MeOC(O)(CH 2) 2] 2Sn[SC(S)NMe 2] 2

Abstract

The crystal structure of bis(2-carbomethoxyethyl)bis( N,N-dimethyldithiocarbamato)tin(IV) was determined from 2495 observed Mo- K α reflections and refined to an R factor of 0.053 (space group P2 1/ c; a 15.629(4), b 10.574(3), c 16.118(4) Å; β 117.00(2)°; V 2373(1) Å 3; Z = 4). The compound is monomeric and the tin is seven-coordinate in a distorted pentagonal bipyramid with the organic groups in apical positions (CSnC 154.3(3)°; the pentagonal girdle is made up of the four sulfur atoms of the anisobidentate dithiocarbamato ligands and the carbonyl oxygen atom of a bent apical organic group (SnS (short) 2.571(2), 2.598(2); SnS (long) 2.848(2), 2.913(2); SnO 2.751(5) Å). The oxygen atom and one sulfur atom are displaced equally but oppositely by 0.24(3) Å from the pentagonal least-squares plane, and the tin atom by 0.054(1) Å. The compound is six-coordinate in CDCl 3 solution, as shown by ambient 13C NMR data; the one-bond coupling constant, 1 J( 119Sn 13C), has the value 794.2 Hz, consistent with the lower coordination state. There is some evidence, however, of retention of the seven-fold coordination in pyridine solution.