Structural and far-infrared studies of compounds containing the novel trinuclear lodocuprate(I) complex [Cu3(AsPh3)3I4]–

Abstract

Single-crystal X-ray diffraction and far-i.r. spectroscopy have been used to characterize a new type of ionic copper(I) complex. The anion in two crystalline forms (α and β) of [AsPh₃Me][Cu₃(AsPh₃)₃I₄] contains three AsPh₃ ligands co-ordinated to the copper atoms of a Cu₃I₄ unit. This unit consists of an apical iodine atom which is bound in a triply bridging bonding mode to three equivalent copper atoms. Adjacent pairs of copper atoms are further connected by doubly bridging iodine atoms. The co-ordination environment of each copper atom is pseudo-tetrahedral, the fourth co-ordination site being occupied by a terminally bonded AsPh₃ ligand. The average bond lengths in the anion are Cu–I_t 2.73(1)(I_t= triply bridging iodine), Cu–I_d 2.63(2)(I_d= doubly bridging iodine), and Cu–As 2.38(1)Å. The α-form is monoclinic, space group P2₁/n, a= 18.098(5), b= 32.76(2), c= 26.95(2)Å, β= 110.21(3)°, Z= 8, R= 0.072 for 10 331 ‘observed’[I > 3σ(I)] reflections. The β-form is monoclinic, space group P2₁/c, a= 17.685(4), b= 12.028(5), c= 35.156(6)Å, β= 94.29(2)°, Z= 4, R= 0.051 for 5 584 ‘observed’[I > 3σ(I)] reflections. The two forms are solvated by 1.5 CH₂Cl₂ and 1 CHCl₃ respectively. The structure of the anion is closely related to that of the neutral tetranuclear ‘cubane’ complex [Cu₄(AsPh₃)₄I₄], from which it is derived by removal of a [Cu(AsPh₃)]⁺ unit. The far-i.r. spectrum of [AsPh₃Me][Cu₃(AsPh₃)₃I₄] shows a band at 138 cm^–1 which is assigned to the Cu–I stretching modes of the Cu₃I₄ unit. Attempts to prepare complexes of the same stoicheiometry with PPh₃ in the place of AsPh₃ were unsuccessful. However, changing the cation from [AsPh₃Me]⁺ to [PPh₃Me]⁺ resulted in the formation of the compound [PPh₃Me][Cu₃(AsPh₃)₃I₄] which gave a far-i.r. spectrum similar to that of the corresponding [AsPh₃Me]⁺ compound with a Cu–I stretching frequency of 134 cm^–1.