Stereochemistry of tetrahedral complexes of group VIII metals : Crystal and molecular structures of Co(CO) 2(NO)(PPh 3) and of Co(CO)(NO)(PPh 3) 2

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The crystal structures of Co(CO) 2(NO)(PPh 3)(I) and of Co(CO)(NO)(PPh 3) 2 (II) have been determined, by counter data, in order to provide further information on the stereochemistry of tetrahedral complexes of Group VIII metals. Compound (I) crystallizes in the triclinic space group P 1 with cell dimensions: a = 11.057(15), b = 10.251(15), c = 10.495(15) Å, α = 115.77(7)°, β = 117.60(7)°, γ = 79.04(7)° and Z = 2. Compound (II) crystallizes in the monoclinic space group P2/ c. The unit cell has dimensions: a = 11.734(15), b = 8.235(12), c = 17.236(18) Å, β = 106.33(7)°, Z = 2. The structures were refined by full matrix less squares using 2516 reflections for compound (I) and 1352 reflections for compound (II). The final values of the reliability index R were 0.060 and 0.059, respectively. The crystals consist of packings of discrete monomeric molecules. In both species the cobalt atoms display distorted tetrahedral geometries and the carbonyl and nitrosyl groups are indistinguishable because of disorder. The CoP and CoC/N distances are 2.224(3) and 1.738(5), 1.762(7), 1.720(7) Å in Co(CO) 2(NO)(PPh 3) and 2.230(3) and 1.718(8) Å in Co(CO)(NO)(PPh 3) 2. The angles at the metals deviate from the ideal tetrahedral value, the larger deviation being that of the (C/N)Co(C/N) angle, which has a value of 120.0(4)° in Co(CO)(NO)(PPh 3) 2. The enlargment of the (C/N)Co(C/N) angles is explained in terms of π repulsions between ligand orbitals, whereas the co-ordination geometry of the phosphine ligands is shown to be dominated by interactions with phenyl hydrogens.