Influence of configuration of carboxylic acid capping ligands on the salt-induced aggregation of gold clusters

Oxalic acid (Ox) and 1,2,3,4-cyclobutanetetracarboxylic acid (CBTCA) were employed as capping ligands in the preparation of gold colloids. FTIR indicated that Ox adopted a linear configuration through one oxygen atom and one gold atom, while CBTCA adopted a bridge configuration through two oxygen atoms and two gold atoms. Ox-gold colloids exhibited aggregation upon addition of NaClO₄, while they remained as isolated particles upon NaCl. For CBTCA-gold colloids, not NaClO₄ but NaCl resulted in aggregation. The reversed results were considered to have been influenced by the different configurations of Ox and CBTCA, which were combined results of the Lewis basicity and steric hindrance of the added ions.