Mechanisms of Reactivity and Lattice Reconstructions in Ternary Copper (I) Halides.

Abstract

The work in this thesis consists of a two-part study in which families of ternary copper (I) halides are use to explore mechanisms of phase transitions and reactions in solids. Lewis acid modified copper (I) chloride networks of the formula CuMCl4 (M = Al, Ga) bind up to 2 molar equivalents of either ethylene or CO at low gas pressures. These reactions proceed at room temperature to give crystalline adduct phases through a dramatic expansion and restructuring of the CuMCl4 lattice. The CO adducts of CuMCl4 are characterized by in situ powder X-ray diffraction, UV-vis diffuse reflectance spectroscopy, and FTIR spectroscopy. The structure of the β-(CO)CuAlCl4 adduct is determined by single crystal X-ray diffraction. A sorptive reconstruction mechanism is proposed for the formation of β-(CO)CuAlCl4 in which Sn2 attack on copper is directed along van der Waals channels in the α-CuAlCl4 lattice. To demonstrate the effect of Lewis acids on the bonding between Cu(I) and π-coordinating ligands, the reactivity of the series of solids CuCl, CuGaCl4 and CuAlCl4 with both ethylene and CO gas is considered. The bonding of copper (I) to CO in the Lewis acid-modified frameworks is shown to be non-classical, consisting predominantly of σ-bonding. The enhancement to the σ-bonding component of the Cu-L bond provided by the Lewis acid results in competitive bonding of CO and ethylene. The reactions of CuAlCl4 are studied at 35 degrees C by TGA⁄DSC and optical microscopy provide kinetic data for use in evaluating the proposed sorptive reconstruction mechanism of gas sorption and lattice rearrangement. The reactions to give (C2H4)CuAlCl4 and (C2H4)2CuAlCl4 are shown to follow 1-D phase boundary controlled growth kinetics. A dual reaction mechanism is proposed for the low pressure formation of (C2H4)CuAlCl4, which is shown to be a liquid at 35 degrees C. A linear rate dependence on the ethylene partial pressure for the crystallization of (C2H4)2CuAlCl4 is consistent with an associative reaction mechanism.

In the second study the phase transition of melting in copper halides is probed by the examination of the molten structure of ternary compounds of composition ACu2Cl3 (A = monovalent templating cation) are studied by synchrotron X-ray and neutron diffraction. The structure of these compounds consist of covalently bonded [Cu2Cl3]- chains which run parallel to one another. Neutron diffraction and PDF analysis shows that these chains persist into the molten state and can serve as a structural unit for designing order into the molten state. This order can be further manipulated by choice of the templating cation. This work is relevant to understanding and designing structure in the molten state.