The structures of 1:1 and 1:2 adducts of phosphane-tricarbo-nitrile with 1,4-di-aza-bicyclo[2.2.2]octa-ne

In the structures of 1:1 and 1:2 adducts of phosphanetricarbo-nitrile (C₃N₃P) with 1,4-di-aza-bicyclo-[2.2.2]octane (C₆H₁₂N₂), the 1:1 adduct crystallizes in the ortho-rhom-bic space group, Pbcm, with four formula units in the unit cell (Z' = 0.5). The P(CN)₃ unit lies on a crystallographic mirror plane while the C₆H₁₂N₂ unit lies on a crystallographic twofold axis passing through one of the C-C bonds. The P(CN)₃ moiety has close to C ₃ symmetry and is stabilized by forming adducts with two symmetry-related C₆H₁₂N₂ units. The phospho-rus atom is in a five-coordinate environment. As a result of the symmetry, the two trans angles are equal so τ₅ = 0.00 and thus the geometrical description could be considered to be square pyramidal. However, the electronic geometry is distorted octa-hedral with the lone pair on the phospho-rous occupying the sixth position. As would be expected from VSEPR considerations, the repulsion of the lone-pair electrons with the equatorial bonding electrons means that the trans angles for the latter are considerably reduced from 180° to 162.01 (4)°, so the best description of the overall geometry for phospho-rus is distorted square pyramidal. The 1:2 adduct crystallizes in the monoclinic space group, P2₁/m with two formula units in the asymmetric unit (i.e. Z' = 1/2). The P(CN)₃ moiety lies on a mirror plane and one of the two C₆H₁₂N₂ (dabco) mol-ecules also lies on a mirror plane. The symmetry of the P(CN)₃ unit is close to C ₃ There are three P⋯N inter-actions and consequently the mol-ecular geometry of the phospho-rus atom is distorted octa-hedral. This must mean that the lone pair of electrons on the phospho-rus atom is not sterically active. For the 1:1 adduct, there are weak associations between the phospho-rus atom and one of the terminal nitro-gen atoms from the C≡ N moiety, forming chains in the a-axis direction. In addition there are weak C-H⋯N inter-actions between a terminal nitro-gen atoms from the C≡N moiety and the C₆H₁₂N₂ mol-ecules, which form sheets perpendicular to the a axis.