Complex coordinate studies, quantum

The structure of the adsorbate systems formed by mercaptobenzothiazole and analogue molecules on CdS (1010) surface was studied quantum chemically using density functional theory [57]. Preliminary calculations of the free adsorptive molecules indicate an energetic preference of their thione form compared to the thiol form. For the anions of the adsorptive molecules, the role of the endocyclic nitrogen and the exocychc sulfur as possible donor atoms was examined by means of known chelate complexes. Geometry optimizations showed that the structure of the adsorbate systems is dominated by the formation of two coordinative bonds from the donor atoms of the adsorptive anions to two adjacent Cd atoms of the surface. It showed that the molecular plane of the adsorptives is tilted with respect to the normal of the crystal face. They have shown that the tilt angle is mainly determined by the tendency of the surface Cd atoms to continue the tetrahedral coordination from the bulk [57]. 

Van der Waals molecules containing a chemically bonded diatomic molecule weakly held to an atom have also been studied. The coordinates and quantum numbers needed to specify such a complex are shown in Fig. 2. We mean A-H B to represent all complexes of this type. The chemically bonded molecule is given by A-H and may be H2, HCl, or a molecule not containing hydrogen such as NO, N2, O2, and so on. 

The photochemically active bands of methylcobalamin have been identified as the intense hands due to -n—n transitions within the conjugated corrin ring, and the following quantum yields (< ) were obtained A = 490 nm, Similar quantum yields ( = 0.3-0.5) were also obtained for the photolysis of methylcobalamin in acid, where the base has been displaced and protonated, and the complex is present as a mixture of the methylaquo and five coordinate methyl complexes (/40). The effect of varying the second axial ligand on the rate of photolysis by white light has also been studied (134). 

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