CONTROL OF AXIAL LIGAND SUBSTITUTION IN TRANS-BIS(2,2'-BIPYRIDINE)RUTHENIUM(II) COMPLEXES - CRYSTAL AND MOLECULAR-STRUCTURE OF TRANS-(4-ETHYLPYRIDINE)(DIMETHYL SULFOXIDE)-BIS(2,2'-BIPYRIDINE)RUTHENIUM(II) HEXAFLUOROPHOSPHATE, TRANS-[RU(BPY)2(4-ETPY)(DMSO)](PF6)2

The ruthenium(II) complex in the salt trans-[Ru(bpy)2(H2O)2](CF3SO3)2 (bpy = 2,2'-bipyridine) is converted quantitatively into the correspon ding bis-DMSO complex by reaction at ambient temperature in DMSO and i s isolated as the salt trans-[Ru(bpy)2(DMSO)2](CF3SO3)2.0.5H2O (1). 1 reacts with a pyridyl ligand in DMSO at ambient temperature to give tr ans-[Ru(bpy)2(py)(DMSO)](PF6)2.nH2O (py = 4-ethylpyridine (4-Etpy), n = 0 (2); py = 4-(dimethylamino)pyridine (DMAP), n = 1.5 (3); py = ethy l isonicotinate (ISNE), n = 1 (4)). The single-crystal X-ray structure of trans-[Ru(bpy)2(4-Etpy)(DMSO)](PF6)2.0.5DMF (2.0.5DMF) has been de termined. This salt crystallizes in the monoclinic system, space group P2(1)/c with a = 15.0301 (9) angstrom, b = 18.1948 (12) angstrom, c = 14.6323(7) angstrom, beta = 97.769(5)-degrees, and Z = 4. The DMSO mo lecule is S-bound. 2 is converted into trans[Ru(bpy)2(4-Etpy)Cl]PF6.H2 O (5) by reaction with LiCl in DMF/water at elevated temperature. Remo val of the chloride ligand in 5 by AgCF3CO2 in acetone/water at room t emperature in the presence of a second pyridyl ligand (ISNE) affords a mixed-pyridine complex which is isolated in nearly quantitative yield as the salt trans-[Ru(bpy)2(4-Etpy)(ISNE)](PF6)2 (6).