Polynuclear Metal Complexes with Bridging Carbene or Carbyne Ligands. Part 63. Synthesis of Eight-Membered-Ring Metallacycles: X-Ray Crystal Structures of (Pt4W4(μ-CR)(μ3-CR)3(μ-CO)(CO)7(η-C5H5)4)·CH2Cl2, (Ni2Pt2W4(μ-CR)(μ3-CR)3(μ-CO)