STRUCTURAL AND FAR-INFRARED STUDIES OF COMPOUNDS CONTAINING THE NOVEL TRINUCLEAR IODOCUPRATE(I) COMPLEX [CU3(ASPH3)3I4]-

Single-crystal X-ray diffraction and far-i.r. spectroscopy have been used to characterize a new type of ionic copper(1) complex. The anion in two crystalline forms (alpha and beta) 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) angstrom. The alpha-form is monoclinic, space group P2(1)/n, a = 18.098(5), b = 32.76(2), c = 26.95(2) angstrom, beta = 110.21(3)-degrees, Z = 8, R = 0.072 for 10 331 'observed' [I > 3-sigma (I)] reflections. The beta-form is monoclinic, space group P2(1)/c, a = 17.685(4), b = 12.028(5), c = 35.156(6) angstrom, beta = 94.29(2)-degrees, Z = 4, R = 0.051 for 5 584 'observed' [I > 3-sigma (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.