Two dinuclear complexes of palladium(I) and platinum(II) have been prepared by using a tridentate ligand containing three kinds of coordination sites, i.e. oxygen, nitrogen, and phosphorus atoms. Treatment of palladium(II) acetate with a mixture of 6-(diphenylphosphino)-2-pyridone (abbreviated as PyphosH) and sodium methoxide in diglyme produced a dimeric palladium(I) complex containing a metal-metal bond, Pd-2(pyphos)(2)(pyphosH)(2) (1), in 43% yield. The dinuclear complex 1 has a Pd-Pd single bond [2.623(1) Angstrom] surrounded by two pyphos ligands and two pyphosH ligands, where the pyphos ligand connected to pyphosH through an intramolecular hydrogen bond [1 : monoclinic, space group C2/c with a=19.794(7) Angstrom, b=14.753(7) Angstrom, c=25.626(5) Angstrom, beta=107.65(2)degrees, V=7131(4) Angstrom(3), Z=4, and R=0.058 for 4760 reflections with I >3 sigma(I) and 451 parameters]. In the case of platinum, a dinuclear platinum(II) complex, Pt-2(pyphos)(4) (3), was prepared in 84% yield by treatment of PtCl2-(pyphosH)(2) (2) with 2 equiv of sodium methoxide in ethanol. The dimeric structure of 3 was confirmed by X-ray analysis. The interatomic distance between the two platinum atoms of 3 is 4.3615(6) Angstrom. Thus, complex 3 does not contain any metal-metal bond [3 : monoclinic, space group C2/c with a=19.646(2) Angstrom, b=11.411(4) Angstrom, c=30.368(3) Angstrom, beta=109.782(8)degrees, V=6406(1) Angstrom(3), Z=4, R=0.045 for 5844 reflections with I >3 sigma(I) and 425 parameters].