Design, Characterization, and Reactivity of Copper (I)-Zirconium (IV) Halide Analogs of Metal Chalcogenides

Abstract

In this work, new metal-halide materials are designed by using a novel charge matching methodology whereby structural analogs of metal chalcogenides are prepared using a halide-for-chalcogenide substitution strategy. In particular, the metal-halide materials prepared herein are analogous to known phosphate, phosphonate, and silicate-based clay-type materials. Following this charge matching strategy, dimethyl ammonium cations were shown to organize copper(I) and zirconium(IV) primary building blocks into (CuZrCl6)- chains, which are analogous to the thiophosphate chains in (MPS4)-. Hydrogen bond formation to the dimethylammonium cations results in significant distortions to the metal chloride building blocks, which can be understood as second order Jahn-Teller-type distortions. In the absence of an extra-framework cation, the primary tetrahedral and octahedral building blocks were assembled into a condensed three-dimensional network Cu2ZrCl6, which is constructed from adamantane-type building blocks. Cu2ZrCl6 is shown to undergo reversible thermochromic phase changes because of a structural distortion of the cuprous chloride tetrahedra due to second-order mixing. This material also exhibits an approximately temperature independent (TIP), or Van Vleck, paramagnetism that increases at the low temperature phase transition. The change at the phase transition appears to be related to the band gap differences in the low- and high-temperature phases of Cu2ZrCl6. The reactivity of Cu+ in the presence of the Lewis acidic Zr4+ is then demonstrated by the solvothermal reaction of Cu2ZrCl6 in benzene, which breaks up the three-dimensional framework into a one-dimensional [((bz)CuCl3)2Zr]∞ chain that is described as a metal-halide phosphonate analog. Chains of ((bz)CuCl3)2Zr are linked along the crystallographic c direction via an edge-to-face p-stacking of the coordinated benzene molecules. The crystal packing forces are shown to influence dramatic second-order Jahn-Teller distortions making each of the two ((bz)CuCl3)2- units distinct. The distortions of the distinct ((bz)CuCl3)2- units emphasize the unique donor and acceptor properties of the Cu(I) ion. Addition of ZrCl4 to the solvothermal reaction of Cu2ZrCl6 in benzene yields the molecular species (bz)2Cu2Zr2Cl10obz, which loses solvent in a stepwise fashion. These desolvated materials exhibit reversible binding of ethylene reminiscent of the reversible sorption behavior typically observed for silicate-based clays.