Transition metal complexes with bridging PF3 groups are unknown analogous to metal carbonyls with bridging carbonyl groups. The possibility of bridging PF3 groups in binuclear Co2(PF3) n complexes (n = 9, 8, 7, 6, 5) and the tetranuclear Co4(PF3)12 has now been investigated by density functional theory (DFT). The lowest energy Co2(PF3)8, Co2(PF3)7, and Co4(PF3)12 structures are predicted to be unbridged structures with cobalt-cobalt bond distances of ∼2.8 Å, ∼2.5 Å, and ∼2.6 Å, respectively. The lowest energy Co2(PF3)6 structure is an unsymmetrical unbridged structure with a Co–Co distance of ∼2.5 Å. For the more highly unsaturated Co2(PF3)5 both triplet and singlet structures are found, consisting of two Co(PF3)2 units linked by two bridges, namely a PF2 group and a F atom. Such Co2(PF3)5 structures have square planar cobalt coordination and a Co…Co distance too long for direct bonding. In addition, a singlet Co2(PF3)5 structure is found, with two semi-bridging PF3 groups and a very short Co ··· Co distance of ∼2.1 Å indicative of the formal quadruple bond required to give both cobalt atoms the favoured 18-electron configuration. Bridging PF3 groups with no cobalt-cobalt bond are found in a high energy structure of Co2(PF3)7 and in a Co2(PF3)9 structure unstable with respect to PF3 loss to give Co2(PF3)8. The dissociation of Co2(PF3)8 into two Co(PF3)4 radicals is predicted to be only slightly endothermic at −14.3 kcal/mol (B3LYP) or 7.1 kcal/mol (BP86). However, in contrast to its carbonyl analogue Co4(CO)12, the dissociation of Co4(PF3)12 into 2 Co2(PF3)6 is highly exothermic. Optimization of the structure of the experimentally known but not structurally characterized bis(difluorophosphido) derivative Co2(PF3)6(µ-PF2)2 predicts the expected structure with a long Co ··· Co distance of ∼3.5 Å indicating the lack of a direct cobalt-cobalt bond. DFT predicts tetrahedral structures for Co(PF3)4 and HCo(PF3)3 as well as the experimentally known trigonal bipyramidal structure for HCo(PF3)4.