Experimental and theoretical investigation of the molecular and electronicstructure of [Zn-4(mu(4)-S){mu-S2As(CH3)(2)}(6)] and [Cd-4(mu(4)-S){mu-S2As(CH3)(2)}(6)]: Two possible molecular models of extended metal chalcogenide semiconductors

The molecular and electronic structure of hexakis[mu-(dimethylarsinodithioa te-S:S')]-mu(4)-thioxotetrazinc has been investigated by combining X-ray di ffraction measurements, electrospray mass spectrometry (ESI), UV absorption spectroscopy, and density functional calculations. The polynuclear zinc co mplex consists of discrete "tetrazinc sulfide" moieties held together by va n der Waals interactions. The unit cell contains four independent molecules and four solvent molecules. Each independent unit is characterized by a ce ntral mu(4)-S coordinated to four Zn ions, each of them at the center of an irregular tetrahedron of S atoms. ESI measurements point out that the synt hesis of the analogous Cd derivative was successful. Crystal data are as fo llows: chemical formula, C12H36As6Cl1.5S13Zn4; monoclinic space group P2(1) /n (no. 14); a = 30.4228(7) Angstrom, b = 18.3720(5) Angstrom, c = 32.3758( 8) Angstrom, beta = 95.857(1)degrees; Z = 16. Theoretical calculations indi cate that, despite their structural arrangement, neither the Zn nor the Cd complex can be considered molecular models of the extended ZnS and CdS. Nev ertheless, the electronic transitions localized in the Zn-4(mu(4)-S) and Cd -4(mu(4)-S) inner cores of the title compounds have the same nature as thos e giving rise to the maxima in the excitation spectra of the extended Zn4S( BO2)(6) and Cd4S(AlO2)(6) [Blasse, G.; Dirksen, G. J.; Brenchley, M. E.; We ller, M. T. Chem. Phys. Lett. 1995, 234, 177].