HYDROPHOBIC HYDRATION STRUCTURES OF TRIS(1,10-PHENANTHROLINE)METAL AND TRIS(2,2'-BIPYRIDINE)METAL COMPLEX-IONS AND EFFECT OF THE IONIC CHARGE - X-RAY-DIFFRACTION STUDY WITH ISOMORPHOUS SUBSTITUTION

X-Ray diffraction measurements have been made for aqueous solutions of sulfates or chlorides of [Ru(phen)(3)](2+), [Ni-(phen)(3)](2+), [Ru(b py)(3)](2+), [Ni(bpy)(3)](2+), [Rh(bpy)(3)](3+), and [Cr(bpy)(3)](3+) (phen = 1,10-phenanthroline, bpy = 2,2'-bipyridine), Radial distributi on functions for the metal interactions were obtained by the isomorpho us substitution between ruthenium(II) and nickel(II) complexes or betw een rhodium(III) and chromium(III) complexes. Metal-nitrogen and metal -carbon distances within the complex ions in solution were essentially in agreement with those in the crystals. Regarding the divalent metal complexes, about two water molecules seemed to exist at a distance of 3.5-3.6 Angstrom (1 Angstrom = 10(-10) m) from the central metal atom and 10-11 water molecules existed in the region of 5.3 to 6.3 Angstro m, probably in the vicinity of peripheral hollows along the C-3 axis o f the complex. Further, large broad peaks with high electron density w ere observed around 7.7 and 11.2 Angstrom for the [Ru(bpy)(3)](2+) ion and around 8.0 and 11.5 Angstrom for the [Ru(phen)(3)](2+) ion, almos t independent of salt concentration and kinds of counter ions. These w ere attributed to the hydrophobic hydration shells having the hydrogen -bonded network structure. The hydration structure of the trivalent me tal complexes was significantly different from that observed for the d ivalent ones: 14-15 water molecules existed in the range of 4.7 to 6.0 Angstrom, a part of them presumably in the hollows along the C-2 axes of the complex, and only a single broad peak was observed around 7.7 Angstrom as the hydrophobic hydration shell. These results indicated t hat the hydrophobic hydration structure was reduced by the increase of the ionic charge, as predicted from a comparison of temperature coeff icients of the Walden product obtained by the conductivity measurement s of dilute solutions.