Overcoming Statistical Complexity: Selective Coordination of Three Different Metal Ions to a Ligand with Three Different Coordination Sites

In general, it is difficult to selectively introduce different metal ions at specific positions of a cluster-like structure. This is mainly due to statistical problems as well as the reversibility of the formation of coordination bonds. To overcome this statistical problem, we used a carefully designed ligand, H6L, which can accommodate three different kinds of metal ions in three types of coordination sites. The complex [LNiZn2La]3+, which contains three different metals, was quantitatively obtained by a stepwise procedure, but different products were obtained when the metal ions were added in a different order. However, equilibration studies indicated that this complex was almost solely formed among 54 (=3×3×3H2) possible products upon heating; the formation efficiency (ca. 100 %) was significantly higher than the statistical probability (2.47 %). Such carefully designed ligands should be useful for the synthesis multimetallic systems, which are of interest because of the interplay between the different metals.