Preparation and structural characterization of Re[subscript]2[superscript]n+ compounds containing sulfato, amidino, phosphine and methyl ligands

Abstract

Four new complexes containing the quadruply bonded Re₂ (superscript n+) unit have been synthesized and the structure of each has been determined by X-ray crystallographic methods. The first compound, Na₂Re₂(SO)₄)₄, was prepared by the reaction of [(n-C₄H₉)₄N]₂Re₂Cl₈ with excess sulfate ion in (CH₃ OCH₂CH₂)₂O. The structure of the blue octahydrate, obtained by recrystallization from acidified methanol contains Re₂(SO₄)₄(H₂O)₂²⁻ ions which lie on crystallographic centers of inversion and have virtual C₄(subscript h) symmetry. As in the structurally similar Mo₂(SO₄)₄⁴⁻, the four sulfato ligands, which are appreciably distorted, bridge the metal atoms. A coaxially coordinated water molecule completes each metal atom's distorted octahedral configuration. The compound Re₂Cl₄(Ph₃N₂C)₂ was prepared by fusing N,N'-diohenylbenzamidine (HN₂CPh₃) with (Bu₄N)₂Re₂Cl₈ under N₂. The burgundy-colored product was washed with THF and recrystallized from chloroform. Two different kinds of crystals were formed and their structures have been determined. The first type consists entirely of Re₂ Cl₄(Ph₃N₂C)₂ molecules, in which the Re-Re distance, 2.177(2)A, is the shortest yet observed, located on centers of inversion. The amidine ligands are trans to each other and the metal atoms, forming nearly planar Re-N-C-N-Re rings. The chlorine atoms, in essentially equatorial positions, have Re-Re-Cl angles of 106(2)°. The approximate symmetry of the molecule is D (subscript 2h). Crystals of the second type were dark purple and consisted of Re₂Cl₄(Ph₃N₂C)₂ (THF) molecules with no crystallographically imposed symmetry. The THF molecule is coordinated to one Re atom and the Re-Re distance, 2.209(1)A, is longer than that in the molecule lacking THF. Other dimensions are similar, though slight differences of significance exist..