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−

•We correct the kq and k1 of [Ru(phen)3]2+–[Cr(mal)3]3− in LiCl in previous paper.•Cr(mal)33− exists near 4dmb of [Ru(phen)2(4dmb)]2+, which is anisotropic.•Ligand-mal of [Cr(mal)3]3− is better congeniality with ligand-4dmb than ligand-phen.•Cr(ox)33− exists equivalently around [Ru(phen)3−n(4dmb)n]2+, which is isotropic.•[Cr(CN)6]3− can enter the space of [Ru(phen)3−n(4dmb)n]2+ because of the small size.

Energy-transfer rate-constants, k1, 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–O2− = ox2− ((COO−)2), mal2− (CH2(COO−)2)) and [Cr(CN)6]3− in encounter complexes were evaluated in aqueous solutions. The dependence of the evaluated k1 values on the number of 4dmb, n, is divided into the following three types; the k1 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 k1 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 kq and k1 value of [Ru(phen)3]2+–[Cr(mal)3]3− in LiCl aqueous solution in our previous paper.

Graphical abstract[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.Figure optionsDownload full-size imageDownload as PowerPoint slide