Formation and structure of [Co{Ph2PN(Bu)PPh2-P,P′}2(CO)][Co)(CO)4] - a cage molecule-pair or an ion-pair complex?

The strong π-acid ligand Ph₂PN(ⁱBu)PPh₂ reacts with Co₂(CO)_S (1:1) to give Co₂μ-Ph₂PN(ⁱBu)PPh₂] (μ-CO)₂(CO)₄ (1); however, when the ratio is 2:1 a novel species Co{Ph₂PN(ⁱBu)PPh₂-P,P′}₂(CO)]Co(CO)₄] (2) has been obtained. Crystal data for 2: M_r = 1140.83; triclinic, space group P , a = 12.330(2), b = 13.340(2), c = 18.122(3) Å, = 86.63(1), β = 80.75(1), γ = 84.24(1)°, V = 2924 ų, Z = 2; R = 0.060 for 3711 reflections having I 3σ(I). The results of X-ray diffraction, ESR, variable-temperature magnetic susceptibility, conductivity, and XPS analysis support that the species 2 is a d⁹-d⁹ cage molecule-pair. The mechanism for the formation of the species 2 has been investigated initially by ³¹P NMR.