PURPOSE: To obtain the subject compound, suitable as a raw material for thin film-forming materials in the electronic industry and having superior preservation stability, etc., when dissolved together with a metal resonate, etc., in a solvent by reacting a platinate with a specific compound, followed by specific treatment of the reaction mixture.

CONSTITUTION: Terpineol sulfide is initially added to an aqueous solution of a platinate [example; tetrachloroplatinic acid (II)] and sufficiently agitated and the reaction mixture is extracted with chloroform. The chloroform layer is then separated and washed with water and the water is separated. The chloroform is evaporated away, with an evaporator under heating. Finally, thus obtained oily substance is added to an alcohol to afford a crystal of the objective compound. 2-4mol terpineol in an amount of 1-2 times of a stoichiometric amount are preferably added to 1mol platinate.