Synthesis, Characterization, and Reactions of the Cluster Complexes Containing the Tetrahedral Cluster Core MFeCoS (M = Mo, W) and a Functionally Substituted Cyclopentadienyl Ligand. The Single Crystal X-ray Structures of Two Double Clusters, [.eta.5-C5H4C(O)CH2CH2C(O)C5H4-.eta.5][M(CO)2Fe(CO)3Co(CO)3(.mu.3-S)]2 (M = Mo, W)