Coordination polymers with cyanoaurate building blocks: Potential new industrial applications for gold

This report illustrates the concept that aurophilic interactions of gold-containing building blocks, particularly cyanoaurates, could be used as a tool to increase structural dimensionality in systems containingother metals in addition to gold(I). Such high-dimensionality systems may have useful optical, magnetic, conducting or porous materials properties. Recent successes from our group and others in using the neglected, luminescent Au(CN)₂]⁻ building block to synthesize supramolecular coordination polymers with interesting and potentially commercially applicable physical properties will be surveyed. In most heterometallic Au(CN)₂]-based polymers, aurophilic interactions increase the structural dimensionality of the system and can impart increased thermal stability. The gold(I) ion can mediate significant magnetic interactions between transition-metal centres or influence iron(II) spin-transition behaviour in the polymers. The CuAu(CN)₂]₂(solvent)_x polymer system is dynamically vapochromic, i.e., it shows large, reversible colour changes upon exposure to solvent vapours, thereby illustrating a sensor-type application. The related d⁸, square-planer Au(CN)₄]⁻ building block, which has only recently been incorporated into coordination polymers, does not form any aurophilic interactions; weak Au-N(cyano) interactions control the intermolecular packing. Several structural examples of cyanoaurate-based coordination polymers are presented, including 2-D and 3-D arrays. The incorporation of cyanoaurates as components of advanced materials would provide a new utility and market for these key compounds of the gold mining and refining industry.