Reaction of Co(CO)4- with a bridging carbyne complex, [Cp2Fe2(CO)2(.mu.-CO)(.mu.-CSMe)]PF6. Crystal and molecular structures of Cp2Fe2Co(CO)3(.mu.-CO)2(.mu.3-CSMe) and Cp2Fe2Co(CO)2(PPh3)(.mu.-CO)2(.mu.3-CSMe)