An unusual electron-rich carbido platinum-ruthenium cluster from the reaction of diphenylacetylene with PtRu5(CO)16(.mu.6-C). Synthesis and crystallographic characterizations of PtRu5(CO)13(.mu.-PhC2Ph)(.mu.3-PhC2Ph)(.mu.5-C) and Ru6(CO)13(.mu.3-PhC2Ph)2(.mu.6-C)