Chemicals for coating surfaces with metal, in particular for electroplating and for wet chemical, electroless plating; galvanizing baths; chemical baths for coating surfaces, namely, chemical baths for electroplating and for electroless plating; chemical baths for the pre-treatment of surfaces prior to the coating thereof, and for the post-treatment of surfaces after the coating thereof; metal salts, in particular precious metal salts; metal salt solutions for electroplating and chemical baths