Further studies on dialkyltin 1,3-dithiole-2-thione-4,5-dithiolates, R₂Sn(dmit). Crystal structures of orthorhombic- and monoclinic-Et₂Sn(dmit), and Me₂Sn(dmit)

The crystal structures of orthorhombic and monoclinic diethyltin bis(1,3-dithiole-2-thione-4,5-dithiolate), [Et2Sn(dmit)], ortho-3 and mono-3, and dimethyltin bis(1,3-dithiole-2-thione-4,5-dithiolate) (4) have been determined. Transformation of solid ortho-3 to mono-3 occurs at 139-140 degreesC. Molecules of ortho-3, obtained by recrystallisation from aqueous acetone, and 4, are linked into chains as a result of intermolecular Sn-thione S(5) interactions: the tin centres are penta-coordinate with distorted trigonal bipyramidal geometries. The intermolecular, Sn-S(S) thione bonds {3.0083(15) Angstrom in ortho-3 at 150 K} [3.037(4) at 298 K], and 3.001(2) and 2.960(2) Angstrom in the two independent molecules of 4 at 150 KJ, are considerably longer than the primary intramolecular Sn bonds to the dithiolato S atoms [between 2.440(3) and 2.5235(15) Angstrom]. The two independent molecules of mono-3, obtained from aqueous methanol, have quite different arrangements: tin atoms in molecule A form two relatively weak intermolecular Sn-thione S bonds, 3.567(2) and 3.620(3) Angstrom, with the formation of sheets, while those in molecule B form one similar bond, Sn-S = 3.555(2) Angstrom to give chains, with a much longer contact, Sn . . .S = 3.927(2) Angstrom to another chain. The latter is only ca. 0.12 Angstrom less than the van der Waals radii sum for Sn and S. Sulfur-sulfur contacts, within the sum of the van der Waals radii of two S atoms, 3.60 Angstrom, in 3 and 4, not only reinforce the chains but also help to establish 3D networks. (C) 2001 Elsevier Science B.V. All rights reserved.