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Kinetic Control of Intralayer Cobalt Coordination in Layered Hydroxides: Co1−0.5xoctCoxtet(OH)2(Cl)x(H2O)n

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posted on 07.12.2009, 00:00 by James R. Neilson, Birgit Schwenzer, Ram Seshadri, Daniel E. Morse
We report the synthesis and characterization of new structural variants of the isotypic compound with the generic chemical formula, Co1−0.5xoctCoxtet(OH)2(Cl)x(H2O)n, all modifications of an α-Co(OH)2 lattice. We show that the occupancy of tetrahedrally coordinated cobalt sites and associated chloride ligands, x, is modulated by the rate of formation of the respective layered hydroxide salts from kinetically controlled aqueous hydrolysis at an air−water interface. This new level of structural control is uniquely enabled by the slow diffusion of a hydrolytic catalyst, a simple technique. Independent structural characterizations of the compounds separately describe various attributes of the materials on different length scales, revealing details hidden by the disordered average structures. The precise control over the population of distinct octahedrally and tetrahedrally coordinated cobalt ions in the lattice provides a gentle, generic method for modulating the coordination geometry of cobalt in the material without disturbing the lattice or using additional reagents. A mechanism is proposed to reconcile the observation of the kinetic control of the structure with competing interactions during the initial stages of hydrolysis and condensation.