Structural studies on polynuclear osmium carbonyl hydrides. Part 35. Coordination and scission of alkynes on a tungsten-triosmium framework. Crystal structures of (.eta.5-C5H5)WOs3(CO)10[.mu.3-.eta.2-C2(C6H4CH3)2]H and (.eta.5-C5H5)WOs3(CO)10[.mu.3-.eta.2-C2(CO2C2H5)2]H - species with an alkyne ligand bound to Os3 and WOs2 faces of tetrahedral WOs3 clusters