NOVELTY - Manufacturing (M1) of a platinum complex involves mixing chloroplatinic acid and a chelating agent with a solvent, where the chloroplatinate ions of the chloroplatinic acid are reacted with the chelating agent to form the platinum complex.    USE - For manufacturing a platinum complex used for manufacturing a platinum catalyst and platinum catalyst on supports (all claimed), where the catalysts are useful in fuel cells, in the exhaust gas-cleaning facilities for vehicles, in petrochemical industry, petroleum refineries, and energy industry.    ADVANTAGE - The process provides the platinum complex having even dispersion of the platinum ions. The process also provides the platinum catalyst having narrow particle size distribution and increased uniformity of the particles of the catalyst, so that the catalyst having increased surface area and improved activity is formed.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) new platinum complex of formula of Pt(R)2+;    (2) manufacturing (M2) of a platinum catalyst obtained through a platinum complex involving: a chelating step of mixing chloroplatinic acid and a chelating agent with a solvent to form a platinum complex solution; a reduction step of adding a reductant into the platinum complex solution to form a suspension for reducing the platinum complex to form platinum (Pt) nanoparticles; and drying Pt-nanoparticles after the reduction step to obtain the platinum catalyst; and    (3) manufacturing (M3) a platinum catalyst on supports involving: a chelating step of mixing chloroplatinic acid, a chelating agent, and supports with a solvent to form a platinum complex solution with the supports to form a platinum complex which is incorporated on the supports; a reduction step of adding a reductant into the platinum complex solution with the supports to form a suspension so that the platinum complex which is incorporated on the supports can be reduced to form Pt-nanoparticles on the supports; and drying Pt-nanoparticles on the supports to obtain the platinum catalyst on the supports.    R=ethylenediamine, 1,10-phenanthroline, 2,2'-bipyridine, diethylenetriamine, triethylenetetraamine, phenanthroline, or bipyridine.