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···Au, Au···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 λmax = 570−580 nm and Φ = 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.