A dimer of bis(N-heterocyclic carbene)rhodium(I) centres spanned by a dibenzo-18-crown-6 bridge from synchrotron radiation

Abstract

The compound (μ-3,3′,3′′,3′′′-{[2,5,8,15,18,21-hexaoxatricyclo[20.4.0.09,14]hexacosa-1(22),9,11,13,23,25-hexaene-11,12,24,25-tetrayl]tetrakis(methylene)}tetrakis(1-methyl-1H-imidazol-2-yl))bis[(η4-cycloocta-1,4-diene)rhodium(I)] bis(hexafluoridophosphate) acetonitrile sesquisolvate dihydrate, [Rh2(C8H12)2(C40H42N8O6)](PF6)2·1.5CH3CN·2H2O, crystallized from acetonitrile under an atmosphere of diethyl ether. In the crystal structure, the complex cation exhibits two square-planar RhI centres, each bound by a cyclooctadiene (COD) ligand and by two adjacent imidazolylidene N-heterocyclic carbene (NHC) donors from the same phenoxy ring of the {[dibenzo-18-crown-6-11,12,24,25-tetrayl]tetrakis(methylene)}tetrakis(1-methyl-1H-imidazol-2-yl) (L) ligand. The dibenzo-crown ether bridge of L spans the Rh centres and forms hydrogen bonds with water molecules. One water molecule with half occupancy bridges adjacent macrocycles in the lattice. Another water with full occupancy forms weak hydrogen bonds to the crown ether O atoms and is, in turn, part hydrogen bonded by a lattice water with half occupancy. The latter water is within hydrogen-bonding distance of a fourth water also with partial occupancy. The result of these interactions is the formation of a layer in the ab plane. Two PF6− ions, one of which is twofold disordered, and one ordered and one twofold disordered (with 0.5 occupancy) lattice acetonitrile molecules complete the crystal structure.