Synthesis and characterization of triangulo copper(I) complexes containing mono- and bicapping systems of asymmetric .mu.3-.eta.1-acetylide ligands: molecular structures of [Cu3(.mu.3-.eta.1-C.tplbond.CPh)(.mu.-dppm)3][BF4]2, [Cu3(.mu.3-.eta.1-C.tplbond.CPh)2(.mu.-dppm)3][BF4], and [Cu3(.mu.3-.eta.1-C.tplbond.CPh)(.mu.3-Cl)(.mu.-dppm)3][BF4] [dppm = bis(diphenylphosphino)methane]