The molecular and electronic structure of hexakisμ-(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, C12H36As6Cl1.5S13Zn4; 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.
The electronic structure of a series of thiophenolate-capped ionic/neutral clusters (Zn(SPh)42- (1); Zn4(μ2-SPh)6(SPh)42- (2); Zn10(μ3-S)4(μ2-SPh)12 (3); and Zn10(μ3-S)4(μ2-SPh)12(SPh)44- (4), Ph = ...phenyl), indicated as supertetrahedral fragments and possible molecular models of cubic ZnS, has been investigated by coupling density functional calculations to UV electronic and X-ray photoelectron (XP) spectroscopy. Theoretical outcomes indicate that, on passing from the tetrametallic to the decametallic clusters, there is a modification in the nature of the outermost occupied and lowermost unoccupied molecular orbitals. Actually, both in 1 and in 2 the frontier orbitals are delocalized and mainly composed of the S 3p pairs strongly mixed with the Ph π levels (the HOMOs) and of the linear combinations of Ph π* orbitals, the LUMOs. At variance to that, in 3 and 4 both the HOMO and LUMO are highly localized, the former on μ3-S atoms occupying C 3 v coordinatively unsaturated tetrahedral positions and the latter on peripheral Zn atoms. The nature of the electronic levels involved in the UV absorption bands is discussed, and the agreement between theory and experiment is satisfactory. Neither experimental nor theoretical electronic excitation energies are influenced by the cluster size. Moreover, XPS data match quite well variations of the Zn and S gross atomic charges along the series. The different Zn−S bonding scheme characterizing terminal, μ2-bridging, and μ3-pyramidal S atoms allows a rationalization of the cluster behavior in solution. Along the investigated series, the only species reasonably mimicking both the structural arrangement and the electronic structure of the solid ZnS is Zn10(μ3-S)4(μ2-SPh)12, which can be considered a molecular model of ZnS nonpolar surfaces.
Using high-resolution transmission electron microscopy and image simulation techniques in combination with ab initio calculations, we show the existence of two different superlattices of ...crystallographic shear planes, analogous to the Magneli phases of rutile, in oxygen-deficient films of anatase TiO sub(2) epitaxially grown on LaAlO sub(3) substrates. (103)- and (101)-oriented shear plane structures are detected in the outer film region and in proximity of the film/substrate interface, respectively. We show that these shear planes are characterized by TiO-like cubic local structures, which can deviate from the Ti sub(n) O sub(2n-1) stoichiometry of the classical rutile-derived Magneli phases, particularly in the outer part of the film. Computed formation energies provide insights into the thermodynamic stability of the observed structures and their relations to the growth dynamics.
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