Experimental and Theoretical Investigation of the Molecular and Electronic Structure of [Zn₄(μ₄-S){μ-S₂As(CH₃)₂}₆] and [Cd₄(μ₄-S){μ-S₂As(CH₃)₂}₆]:  Two Possible Molecular Models of Extended Metal Chalcogenide Semiconductors^†

The molecular and electronic structure of hexakis[μ-(dimethylarsinodithioate-S:S‘)]-μ₄-thioxotetrazinc has been investigated by combining X-ray diffraction measurements, electrospray mass spectrometry (ESI), UV absorption spectroscopy, and density functional calculations. The polynuclear zinc complex consists of discrete “tetrazinc sulfide” moieties held together by van der Waals interactions. The unit cell contains four independent molecules and four solvent molecules. Each independent unit is characterized by a central μ₄-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 synthesis of the analogous Cd derivative was successful. Crystal data are as follows:  chemical formula, C₁₂H₃₆As₆Cl_1.5S₁₃Zn₄; monoclinic space group P2₁/n (no. 14); a = 30.4228(7) Å, b = 18.3720(5) Å, c = 32.3758(8) Å, β = 95.857(1)°; Z = 16. Theoretical calculations indicate that, despite their structural arrangement, neither the Zn nor the Cd complex can be considered molecular models of the extended ZnS and CdS. Nevertheless, the electronic transitions localized in the Zn₄(μ₄-S) and Cd₄(μ₄-S) inner cores of the title compounds have the same nature as those 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.; Weller, M. T. Chem. Phys. Lett. 1995, 234, 177].