Molecular geometry of M(NO)(CO) complexes. Crystal structure of acetonitrilecarbonylnitrosylbis(triphenylphosphine)iron tetrafluoroborate–dichloromethane

Fe(CO)2(NO)(CH3CN)(PPh3)2+BF4−CH2Cl2 5 crystallizes in the triclinic system, space group [Formula: see text], with a = 9.7782(7), b = 10.2832(7), c = 20.5752(14) Å, α = 92.903(6), β = 99.535(6), γ = 91.930(6)°, V = 2035.8(1) Å3, Z = 2. The coordination around Fe is trigonal bipyramidal, with CH3CN and disordered NO and CO in the equatorial plane and the PPh3 ligands displaced from true apical positions (P—Fe—P = 170.20 (4)°). Comparison of the structure of 5 with those of the two independent molecules 21 and 22 of Fe(CO)(NO)(H)(PPh3)22 shows that upon a formal H− for CH3CN substitution, the Fe—P bond lengths shorten by ca. 0.09 Å, the (O)C—Fe—N(O) angle opens up by ca 3° (5 → 21) and 8° (5 → 22), whereas the P—Fe—P angle decreases by ca. 30°. These variations are interpreted in terms of electron-pair repulsions, with those within the Fe (equatorial ligand) (axial ligand) molecular portions suggested to play a predominant role. Keywords: [Formula: see text] NO/CO complexes, bond repulsions, steric influences in phosphine complexes.