Abstract
Six sets of tetracyanoaurate(III) salts were synthesized and structurally characterized using the metal-ligand complex cations [RE(bipyO(2))(4)](3+) (RE = Sc, Y, La; bipyO(2) = 2,2'-bipyridine-N,N'-dioxide), [Fe(bipyO(2))(3)](3+), [Ln(dmbipyO(2))(4)](3+) (Ln = Ce, Eu, Yb; dmbipyO(2) = 4,4'-dimethyl-2,2'-bipyridine-N,N'-dioxide), [Ca(tcmc)](2+) (tcmc = 1,4,7,10-tetrakis-(carbamoylmethyl)-1,4,7,10-tetraazacyclododecane), and [Ca(12-crown-4)(2)](2+). Noncovalent assembly of the [Au(CN)(4)](-) anions tended to occur via Au···N(cyano) interactions; however, rare Au(III)···Au(III) contacts between the [Au(CN)(4)](-) groups - suggesting aurophilicity - could be induced when certain cation shape requirements were met. Specifically, cations with shape, size, and symmetry that allowed for packing in a complementary fashion with Au(III)···Au(III) aligned [Au(CN)(4)](-) dimers or trimers - providing efficiently close-packed layers - were found to be sufficient for manifesting Au(III)···Au(III) contacts. Modifying the [RE(bipyO(2))(4)](3+) cation with peripheral methyl groups (the [Ln(dmbipyO(2))(4)](3+) cation) caused isoreticular replacement of a {[Au(CN)(4)](3)}(3-) trimer with a dumbbell-shaped {[Au(CN)(4)](2)Cl}(3-) tri-anion featuring an unusual Au···Cl···Au bridge - illustrating that the assembly of the anionic groups will adapt to conserve the same close packing. Au(III) aurophilicity between the [Au(CN)(4)](-) groups was studied using computational methods, crystal packing of the structures was probed using Hirshfeld surface analysis, and the emission properties of compounds containing the [Eu(dmbipyO(2))(4)](3+) luminophore were investigated, showing high quantum yields of ca. 50%.