Di- and tetra-nuclear mixed-valence complexes of rhodium(III,I) and rhodium(III)–iridium(I) with the 2,2′-bi-imidazolate(2–) anion (bim) as bridging ligand. Crystal structure of [{(η-C5Me5)[P(OEt)3]Rh(bim)Rh(nbd)}2][ClO4]2

Abstract

The reaction of the new mononuclear species [RhIII(η-C5Me5)Cl(Hbim)](H2bim = 2,2′-bi-imidazole) and [RhIII(η-C5Me5)(Hbim)L′][ClO4][L′= pyridine (py), NCBut, PPh3, or P(OEt)3] with the corresponding acetylacetonate (acac) complexes of formulae [MI(acac) L2][M = Rh; L = CO, L2= tetrafluorobenzobarrelene (tfb)(5,6,7,8- tetrafluoro-1,4-dihydro-1,4-ethenonaphthalene) or norborna-2,5-diene (nbd). M = Ir, L2= tfb] yields di- and tetra-nuclear mixed-valence compounds of the types [{(η-C5Me5)ClRhIII(bim)RhIL2}2][L = CO or L2= tfb], [{(η-C5Me5) L′RhIII(bim) RhI L2}n][ClO4]n[L′= py; L2= tfb (n= 1). L′= py; L = CO or L2= nbd (n= 2). L′= NCBut, PPh3, or P(OEt)3; L = CO, L2= tfb or nbd (n= 2)] and [{(η-C5Me5)L′RhIII(bim)IrI(tfb)}n][ClO4]n[L′= py (n= 1), L′= PPh3 or P(OEt)3(n= 2)]. The structure of [{(η-C5Me5)[P(OEt)3] RhIII(bim) RhI(nbd)}2][ClO4]2 has been determined by X- ray diffraction methods. Crystals are orthorhombic, space group Fddd with Z= 16 in a unit cell of dimensions a= 21.337(3), b= 41.943(5), and c= 31.815(7)Å. The structure was solved by direct and Fourier methods and refined by full- matrix least squares to R= 0.075 for 2 984 observed reflections. The complex cation [{(η-C5Me5)[P(OEt)3] RhIII(bim) RhI(nbd)}2]2+, having imposed C2symmetry, is tetranuclear with two bim2– ligands bridging the metal atoms. Each bim2– anion co- ordinates to the Rh metals in an unsymmetrical tetradentate manner through its four nitrogen atoms of the two imidazolate rings, being chelated to one formally six-co-ordinated Rh atom [Rh(1)] through two N atoms and being bonded in an unidentate manner to two four-co-ordinated Rh atoms [Rh(2)], through the other two N atoms. The co-ordination around Rh(1) is completed by an η-C5Me5 group and by a P(OEt)3ligand, that around Rh(2) by a nbd molecule interacting through the two double bonds. A short non-bonding Rh(2)–Rh(2′) distance [3.250(5)Å] is present in the cation.