Cu[Au(CN)2]2(DMSO)2:: Golden polymorphs that exhibit vapochromic behavior

Two polymorphs of an [Au(CN)(2)]-based coordination polymer, Cu[Au(CN)(2)](2)(DMSO)(2), one green (1) and one blue (2), have been identified. In polymorph 1, alternation of five-coordinate Cull and [Au(CN)(2)](-)units generates 1-D chains, while 2-D corrugated sheets are obtained in polymorph 2, which contains six-coordinate Cu-11 centers. Both polymorphs form 3-D networks by virtue of aurophilic interactions of 3.22007(5) Angstrom and 3.419(3) Angstrom, respectively, and show similar weak antiferromagnetic coupling, but have different thermal decomposition temperatures. They both show vapochromic properties and, importantly, despite their significantly different solid-state structures, the vapochromic behavior of the two polymorphs is essentially identical. Upon solvent exchange, both polymorphs convert to the same Cu[Au(CN)212(solvent), complex (solvent = H2O, CH3CN, dioxane, N,N-dimethylformamide, pyridine, NH3). The Cu[Au(CN)(2)](2)(DMF) and Cu[Au(CN)212(pyridine)2 complexes have very similar 2-D square grid structures, comparable to that of 2. The solvent molecules adsorbed by Cu[Au(CN)(2)](2) bind to the Cu-11 centers, thereby altering the visible spectrum associated with the Cu-11 chromophores and the number and frequency of the v(CN) as well. The network-stabilizing gold-gold interactions and the flexible coordination sphere of Cull probably facilitate reversible solvent exchange at room temperature.