Anisotropic energy-transfer in encounter complex in aqueous solutions: Ligand congeniality between photo-excited mixed-ligand tris(α,α′-diimine)-ruthenium(II) [Ru(phen)3-n(4dmb)n]2+ and tris(malonato)chromate(III) [Cr(mal)3]3-

Energy-transfer rate-constants, k(1), from photo-excited mixed-ligand [Ru(phen)(3 n)(4dmb)(n)] (2+) (n = 0-3; phen = 1,10-phenanthroline, 4dmb = 4,4'-dimethyl-2,2'-bipyridine) to [Cr(O-O)(3)](3) (O-O-2 = ox(2) ((COO )(2)), mal(2) (CH2(COO )(2))) and [Cr(CN)(6)](3) in encounter complexes were evaluated in aqueous solutions. The dependence of the evaluated k(1) values on the number of 4dmb, n, is divided into the following three types; the k(1) values (i) are independent of n in [Cr(CN)(6)](3) system, (ii) decrease gradually as n increases in [Cr(ox)(3)](3) system, and (iii) drop suddenly from n = 0 to n = 1 in [Cr(mal)(3)](3) system. These results indicate that [Cr(ox)(3)](3) would exist equivalently around [Ru(phen)(3) (n)(4dmb)(n)](2+) in encounter-complex in [Ru(phen)(3) (n)(4dmb)(n)](2+)-[Cr(ox)(3)](3) system. However, in [Ru(phen)(3) (n)(4dmb)(n)](2+)-[Cr(mal)(3)](3) system, [Cr(mal)(3)](3) would exist selectively near ligand-4dmb of [Ru(phen)(2)(4dmb)](2+) in aqueous solution (anisotropic). Ligand congeniality between ligand-4dmb of [Ru(Phen)(3) (n)(4dmb)(n)](2+) and ligand-mal of [Cr(mal)(3)](3) would be better than that between ligand-phen and ligand-mal in the encounter complex. [Cr(CN)(6)](3) could penetrate between the ligand-phen and/or ligand-4dmb in [Ru(phen)(3) (n)(4dmb)(n)](2+) without being interrupted by methyl-base of ligand-4dmb because the k(1) values in [Ru(phen)(3) (n)(4dmb)(n)](2+)-[Cr(CN)(6)](3) system are very large and almost constant. In addition, we correct the mistake of the k(q) and k(1) value of [Ru(phen)(3)](2+)-[Cr(mal)(3)](3) in LiCl aqueous solution in our previous paper. (C) 2014 Elsevier B.V. All rights reserved.