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−

[Cr(mal)3]3− exists selectively near ligand-4dmb of [Ru(phen)2(4dmb)]2+ in encounter complex even in aqueous solution when energy transfer occurs. This is because ligand-mal of [Cr(mal)3]3− is better congeniality with ligand-4dmb than ligand-phen in [Ru(phen)3−n(4dmb)n]2+. This results mean that the encounter-complex of [Ru(phen)2(4dmb)]2+ and [Cr(mal)3]3− is anisotropic.