Gold（I）Complexes of Hydantoin Derivatives and Their Properties

Abstract

Among hydantoin derivatives, a monovalent gold complex was obtained when 1-methylhydantoin（MH）and hydantoin（HY）were used as ligands. These are more beneficial for use in gold plating solutions than trivalent gold complex of 5,5-dimethylhydantoin（DMH）. Moreover, these complexes can be extracted as crystals. Therefore, the chlorine concentration, constituting a major impurity in gold plating for the electronics industry, can be kept low. Each crystal coordinated two hydantoin derivatives to gold and had water of crystallization. The gold-HY complex solution is stable at pH 5-9. Moreover, no change in pH or decomposition occurs even when hydrogen peroxide is added. Higher stability can be expected in the gold plating solution than for gold sulfite.

A neutral（pH 6-7）gold plating solution using the gold-HY complex was investigated. When a large amount of DMH as the complexing agent is added in anticipation of an increase in the plating bath stability, the deposited film appeared to be dark brown. When DMH in the composition of the plating solution was set to a molar equivalent ratio with gold of 0.6-1, the deposited film appearance was bright yellow.