Anisotropic Templating Effect in the Formation of Two-Dimensional Anionic Cadmium-Thiocyanate Coordination Solids [(12C4)(2)Cd][Cd(2)(SCN)(6)] and [(12C4)(2)Cd][Cd(3)(SCN)(8)] with Checkerboard and Herringbone Patterns, Respectively

This paper reports the syntheses, characterization, and structures of two new two-dimensional cadmium-thiocyanate coordination solids [(12C4)(2)Cd][Cd(2)(SCN)(6)] (1) and [(12C4)(2)Cd][Cd(3)(SCN)(8)] (2), where 12C4 denotes 12-crown-4, C(8)H(16)O(4). 1 crystallizes in a monoclinic unit cell, space group C2/c with lattice parameters a = 16.297(3) Å, b = 26.267(3) Å, c = 16.296(2) Å, beta = 90.20(1) degrees, and Z = 8. 2 crystallizes in a monoclinic unit cell, space group P2(1)/n with lattice parameters a = 11.604(7) Å, b = 11.366(7) Å, c = 15.736(4) Å, beta = 92.84(3) degrees, and Z = 2. The structure of 1 exhibits a two-dimensional tetragonal motif consisting of Cd(2) units arranged in a checkerboard pattern with the dimeric [Cd(2)(SCN)(6)](2)(-) complex as the building block. The crystal structure of 2 can be described as a two-dimensional hexagonal array of linear trimeric Cd(3) units arranged in a herringbone pattern with the [Cd(3)(SCN)(8)](2)(-) complex as the building block. In both 1 and 2, the [(12C4)(2)Cd](2+) dications are housed in cavities within and between the anionic cadmium-thiocyanate layers but with different orientations ("upright" in 1 and "sideways" in 2) with respect to the cadmium-thiocyanate layers, giving rise to an anisotropic templating effect.

Chemisorption on Thiol-Silicas: Divalent Cations as a Function of pH and Primary Amines on Thiol-Mercury Adsorbed

The silylating agent 3-trimethoxysilyl-1-propanethiol was immobilized on silica gel. Sulphur analysis showed 0.98 mmol of thiol groups per gram of support. These groups chemisorbed divalent cations: nickel, cobalt, copper, and mercury in the pH range from 1 to 6. The adsorption is more significant for mercury in relation to the other cations in the pH range studied. The primary amines, methylamine, ethylamine, n-butylamine, and benzylamine, were adsorbed on silica-thiol surface and on silica-thiol surface with mercury adsorbed. The values of adsorption constants were calculated using Langmuir isotherms data. Using these values, equilibrium constants and DeltaG values for each adsorption system were also obtained. When mercury is present on the silica surface, the adsorption of n-butylamine and benzylamine is significatively enhanced in relation to the other amines. This behavior suggests that the degree of adsorption of the studied amines is intimately related to their dissociation constants. Copyright 1997 Academic Press. Copyright 1997Academic Press