Crystal structures of Pd(I) and Pt(I) dinuclear complexes, [MM′Cl₂(μ-Me₂Ppy)₂] (MM′ = Pd₂ (1), PdPt (2), and Pt₂ (3)) and [Pd₂Cl₂(μ-Ph₂Ppy)₂] (4), were determined by the single crystal X-ray diffraction method. Crystal data and final R values are: 1, triclinic, , a = 10.019(2), b = 10.902(2), c = 9.062(1) Å, α = 97.75(2), β = 102.45(2), γ = 82.64(2)°, V = 952.7(3) ų, Z = 2, and R = 0.047; 2, monoclinic, P2₁/n, a = 16.532(2), b = 19.205(3), c = 13.260(2) Å, β = 93.86(2)°, V = 4200(1) ų, Z = 8, and R = 0.043; 3, monoclinic, P2₁/n, a = 16.515(5), b = 19.095(10), c = 13.233(4) Å, β = 93.15(3)°, V = 4167(3) ų, Z = 8, and R = 0.047; 4, monoclinic, C2/c, a = 30.505(4), b = 17.896(2), c = 12.983(1) Å, β = 98.52(1)°, V = 7009(1) ų, Z = 8, and R = 0.041. All of the complexes were found to be the head-to-tail isomer of a side-by-side type dinuclear structure. The metal–metal bond distances of 2.584(1) Å in 1, 2.561(1) Å in 2, 2.573(1) Å in 3, and 2.594(1) Å in 4 are relatively short compared with those in the analogous dinuclear complexes bridged by diphosphine ligands. All of the M–P, M–N, and M–Cl distances in Me₂Ppy complexes become shortened in the order of the Pd₂ > PdPt > Pt₂ complexes.