Studies of biomineralization in marine sponges led to our identification of a critical role for the slow, catalytic hydrolysis of molecular precursors in the biogenesis of silica.  This motivated us to study the role of kinetically controlled hydrolysis of hydrated metal ions in aqueous solutions.  As a model system, we have developed a process for preparing inorganic materials involving the diffusion of a hydrolytic catalyst across an air-water interface to reproduce some aspects of the chemistry found in biomineralization, namely kinetic and vectorial control.  Variation of the catalyst concentration yields an entire family of materials related to the a-Co(OH)2 structure, each with a unique composition, despite being prepared from identical mother liquors.  We utilize synchrotron X-ray and time-of-flight neutron total scattering methods to locate the atomic positions, which are not aptly described by a traditional crystallographic unit cell because of inter-lamellar disorder.  Our tightly coupled control of synthesis and knowledge of local and average structures of these materials gives us insight into the unusual magnetic properties of these cobalt hydroxides.  The low-temperature magnetism is glassy as a result of short-range uncompensated clusters of spins which coexist within Ne�l-type ferrimagnetic order as determined from powder neutron diffraction.  We discuss the origin of this behavior in the context of the local arrangement of metal ions and demonstrate how this structure and its associated magnetic behavior are directly determined by the precursor hydrolysis rate.  By systematically varying the kinetic conditions of synthesis, we demonstrate interesting control of local structure and properties not attainable through traditional means.

Cobalt coordination and clustering in <i>α</i>-Co(OH)<sub>2</sub>: Tuning magnetic properties with kinetically controlled hydrolysis

240th National Meeting (2010)

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Cobalt coordination and clustering in α-Co(OH)2: Tuning magnetic properties with kinetically controlled hydrolysis

Cobalt coordination and clustering in α-Co(OH)₂: Tuning magnetic properties with kinetically controlled hydrolysis