Sulfur coordination geometries

Comparison of the experimental data with the trends predicted from quantum chemistry ab initio simulations demonstrated that the multiple conductance values of Au-alkanedithiol-Au junctions could be attributed to different Au-sulfur coordination geometries and to different conformations of the alkyl chain. In particular, the medium conductance corresponds to an all-trans conformation of the alkyl chain, with each sulfur atom coordinated in atop position to a single... 

TiCRjtftc) was prepared starting from Ti(NR2)4 4,5) or TiCl4 (6). The structure of the ethyl compound was elucidated by X-ray studies (7, S). The titanium atom is eight-coordinated by the sulfur atoms of the four chelating ligands and the coordination geometry closely approximates to that of a dodecahedron. 

The molecular structure of the complex [Ni([9]aneN2S)2]2+ reveals a center of symmetry, i.e., the sulfurs are placed trans to each other, which leads to a coordination geometry that is... 

Reduction of both nickel porphyrins and thiaporphyrins to Ni1 species has been studied by EPR and 2H NMR spectroscopy.179, 2 58 The Ni1 complex of 5,10,15,20-tetraphenyl-21-thiaporphyrin has been isolated and characterized. Reaction of this complex with sulfur dioxide produced a paramagnetic five-coordinated Ni1 S02 adduct, while reaction with nitrogenous base ligands (amines, pyridines, imidazoles) yielded five- and six-coordinate complexes. In addition, the crystal structure of Ni1 diphenyldi-p-tolyl-21-thiaporphyrin has been determined. The coordination geometry about the nickel center is essentially square planar with extremely short Ni—N and Ni—S bonds (Ni—N = 2.015(2) A, 2.014(12) A, and 1.910(14) A and Ni—S = 2.143(6) A).2359... 

Au atom (see Fig. 15b). The high conductance values H represent an all-trans alkyl chain in combination with both sulfurs coordinated to two Au atoms in a bridge geometry (Fig. 15c). The theoretically predicted fourfold increase of the conductance, as compared to an atop-atop all-trans bridge, is close to the experimentally observed increase by a factor of 5. Other possible configurations with all-trans conformations (e.g., atop-bridge, multiple molecular junctions) are assumed to contribute as part of the distribution to the less-dominant peaks in the conductance histograms (e.g., M2, H2, and H3 in Fig. 13). 

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