TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Precursor: The polymetallic precursor is a non-cluster. First metal(s):second metal(s) at least 1. Preferred Metal: At least one of the first and the second metal is a noble metal.Preferred Support: The support is electrically conductive. It comprises particulate carbon with a mean particle diameter less than about 30 nanometers and a specific surface area of at least about 250 m2/g. Preferred Ratio: The selected atomic ratio is approximately equal to a stoichiometric ratio of the first metal to the second metal in the polymetallic precursor. Preferred Nanoparticles: The nanoparticles have a mean diameter less than or equal to about 20 nanometers, more preferably less than or equal to 5 nanometers.    TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Method: The metallic precursor is preferably the novel polymetallic precursor.Step (i) further comprises contacting the support with a suspension or a solution of the precursor. Prior to step (ii), the liquid from the suspension or solution is removed. Step (ii) further comprises heating the support in the presence of a hydrogen-containing gas reducing agent, heating the support to a temperature greater than the degradation temperature of X, thermally annealing the polymetallic nanoparticles by holding the support at that temperature for a period of time sufficient to form a crystalline structure, heating the support using microwave radiation and/or controlling the rate of heating the support to about 10 - 20 degreesC/min.After step (i), the method further comprises (a) heating the contacted support in the presence or absence of an oxidizing agent; (b) contacting the heated support with the polymeric precursor; (c) heating the support in the presence or absence of an oxidizing agent; and (d) repeating steps (a) - (b) at least once. Preferred Definitions:    X = an atom of chlorine, mercury, phosphorus, sulfur or selenium; or at least one (un)substituted group of (alkyl)sulfide, arylsulfide, (alkyl)selenide, arylselenide, (alkyl)phosphide, arylphosphide, (alkyl)mercuric, arylmercuric, alkyl, alkenyl, alkynyl, aryl, aralkyl, carbon monoxide, amines, ammonia, heteroatomic aromatic molecules or arsenes    When the precursor comprises a trigonal-bipyramidal Pt3Hg2 moiety,    M = platinum;    X = mercury.    SPECIFIC COMPOUNDS - There are 9 claimed specific precursors. One of them is platinum(dihaptoethylene)(chlorine)(mu-chlorine)2-ruthenium(chlorine)( trihapto:trihapto-2, 7-dimethyloctadienediyl).    EXAMPLE - A dinuclear non-cluster precursor complex Pt(dihaptoethylene)(Cl)(mu-Cl)2Ru(Cl)(trihapto:trihapto-2,7- dimethyl octadienediyl) was prepared according to the synthesis of analogous complexes in Severin et al, Inorg. Chim. Acta., 240, 339 (1995) 0.640 g Pt2Cl2(mu2-Cl)2(C2H4)2 and 0.637 g Ru2Cl2(mu2-Cl)2(trihapto:trihapto-2, 7-dimethyloctadienediyl)2 were placed in a round bottom flask and dissolved in approximately 75 ml dichloromethane. The solution was stirred for several hours under a nitrogen atmosphere. The solvent was removed from the solution to produce a brown powder. Recrystallization from methylene/hexane solution produced a yield of 1.187 g of a 95% Pt(dihaptoethylene)(Cl)(mu-Cl)2Ru(Cl)-(trihapto:trihapto-2,7-dimethyl octadienediyl).