Luminescent Au(I)/Cu(I) Alkynyl Clusters with an Ethynyl Steroid and Related Aliphatic Ligands: An Octanuclear Au4Cu4 Cluster and Luminescence Polymorphism in Au3Cu2 Clusters

Gold(I) bis(acetylide) complexes [PPN][AuR2] (1-3) where PPN = bis(triphenylphosphine)iminium) and R = ethisterone (1); 1-ethynylcyclopentanol (2); 1-ethynylcyclohexanol (3) have been prepared. The reaction of 1 with [Cu(MeCN)(4)][PF6] in a 1:1 or 3:2 ratio provides the octanuclear complex [Au4Cu4(ethisterone)(8)] (4) or pentanuclear complex [PPN][Au3Cu2(ethisterone)(6)] (5). Complexes 2 and 3 react with [Cu(MeCN)(4)][PF6] to form only pentanuclear Au(I)/Cu(I) complexes [PPN][Au3Cu2(1-ethynylcyclopentanol)(6)] (6) and [PPN][Au3Cu2(1-ethynylcyclohexanol)(6)] (7). X-ray crystallographic studies of 1-3 reveal nontraditional hydrogen bonding between hydroxyl groups and the acetylide units of adjacent molecules. Complexes 6 and 7 each form polymorphs in which the structures (6 a,b and 7 a,b,c) differ by Au center dot center dot center dot Au, Au center dot center dot center dot Cu, and Cu C distances. The polymorphs exhibit different emission energies with colors ranging from blue to yellow in the solid state. In solution, pentanuclear clusters 5-7 emit with lambda(max) = 570-580 nm and Phi = 0.05-0.19. Complex 4 emits at 496 nm in CH2Cl2 with a quantum yield of 0.65. Complex 5 exists in equilibrium with 1 and 4 in the presence of methanol, ethanol, ethyl acetate, or water. This equilibrium has been probed by X-ray crystallography, NMR spectroscopy, and luminescence experiments. DFT calculations have been performed to analyze the orbitals involved in the electronic transitions of 4, 6, and 7.