Copper(I) and silver(I) complexes of 9,9-dimethyl-4,5-bis(di-tert-butylphosphino) xanthene: photophysical properties and structural rigidity under pressure

The heteroleptic complexes [Cu(tBu-xantphos)(bpy)][PF6] and [Ag(tBu-xantphos)(bpy)][PF6], where tBu-xantphos = 9,9-dimethyl-4,5-bis(di-tert-butylphosphino) xanthene and bpy = 2,2'-bipyridine have been synthesized and their photophysical properties investigated. Single crystal X-ray diffraction studies of the compounds under ambient and increased pressure are presented; increase in pressure results in little structural perturbation. For the copper(I) complexes, the effects of changing the (NN)-N-Lambda ligand from bpy to 6-methyl-2,2'-bipyridine (6-Mebpy), 6-bromo-2,2'-bipyridine (6-Brbpy), and 4,4'-di(tert-butyl)-2,2'-bipyridine (4,4'-tBu(2)bpy) were also investigated. Emissions from the copper(I) complexes are weak, both in solution and the solid state and this is attributed to vibrational quenching effects of the tert-butyl sub-stituents of the tBu-xantphos ligands.