SYNTHESIS AND CHARACTERIZATION OF [(RHCL2)-CL-III(ETA(1)-C6H5)(PYR)(2)(SBPH3)], [(RHCL2)-CL-III(ETA(1)-C6H5)(PY)(2)(THZ)], [(RHCL2)-CL-III(ETA(1)-C6H5)(PY)(2)(PYR)], AND [(RHCL2)-CL-III(ETA(1)-C6H5)(CEP)(SBPH3)(2)] [PYR = PYRAZINE PY = PYRIDINE THZ = THIAZOLE CEP = N-(2-CYANOETHYLPYRROLE)] - CRYSTAL AND MOLECULAR-STRUCTURE OF [(RHCL2)-CL-III(ETA(1)-C6H5)(PYR)(2)(SBPH3)] AND [(RHCL2)-CL-III(ETA(1)-C6H5)(PY)(2)(THZ)]

The mononuclear compounds trans-dichloro(eta(1)-phenyl) cis-bis(pyrazi ne)(triphenylstibine) rhodium(III) (i), and -(2-cyanoethylpyrrole)}tra ns-bis(triphenylstibine) rhodium (III) (3) were prepared from chloro(e ta(1)-phenyl)tris(triphenylstibine)rhodium (III) in ethanol. The monon uclear compounds )-phenyl)trans-bis(pyridine)(thiazole)rhodium(III) (2 ) and trans-dichloro )-phenyl)trans-bis(pyridine)(pyrazine)rhodium(III ) (4) were obtained from-trans-dichloro(eta(1)-phenyl) tris(pyridine)r hodium(III) in methanol. Compounds 1 and 2 were analysed via X-ray dif fraction techniques from single crystals. The four compounds were char acterized by spectroscopy and elemental analysis. The coordination sph ere geometry for all the complexes is octahedral; the trans influence exerted by the phenyl ligand is responsible for a long Rh-N bond dista nce (2.263(3) Angstrom) and of large downfield shifts for H-1 NMR sign als. The pyrazine ligands are monodentate in both 1 and 4. In the soli d state the pyrazine ligands do not bridge the metal centres, Compound s 1 and 2 are barely stable in solution at room temperature. The thiaz ole molecule of 2 binds the metal through the nitrogen atom whereas su lfur does not show any donating ability. An extended-Huckel analysis s hows that the pyrazine ligands contribute significantly to the frontie r unoccupied molecular orbitals. The atomic charges on the non-metal b ound nitrogen atoms of pyrazine ligands is -0.175 e in agreement with a bridging ability between two metal centres for this-ligand. (C) 1997 Elsevier Science Ltd. All rights reserved.