Polyhedral Cluster Expansion in Co3(CO)6[.mu.2-.eta.2:.eta.1-C(Ph)C:C(PPh2)C(O)OC(O)](.mu.2-PPh2). Characterization of the Hypho Cluster Co3(CO)5(.mu.-CO)(PMe3)[.mu.2-.eta.2:.eta.1-C(Ph)C:C(PPh2)C(O)OC(O)](.mu.2-PPh2) and the Phosphine-Substituted Arachno Cluster Co3(CO)5(PMe3)[.mu.2-.eta.2:.eta.1-C(Ph)C:C(PPh2)C(O)OC(O)](.mu.2-PPh2) - Simon Bott (Organometallics, 1995)