New hydride, alkyl, aryl, halide, alkene, alkyne, acetylide, and vinylidene members of the (.eta.5-C5Me5)Os(CO)(L)X family. Crystal and molecular structures of [(.eta.5-C5Me5)Os(CO)3][BF4] and [(.eta.5-C5Me5)Os(CO)(PPh3)(:C:C(tert-Bu)H)][BF4]