Synthesis, crystal structure and DFT study of carbonyl[3-(dibenzo[ <i>b</i> , <i>d</i> ]thiophen-4-yl)-6-(pyridin-2-yl-κ <i>N</i> )pyridazine-κ <i>N</i> ¹ ]bis(trimethylphosphane)iron(0)

The title compound, [Fe(C₂₁H₁₃N₃S)(CO)(PMe₃)₂] (<b>2</b>), bearing a 3-(dibenzo[<i>b</i>,<i>d</i>]thio-phen-4-yl)-6-(pyridin-2-yl)pyridazine ligand was obtained by the reaction of [Fe(C₂₁H₁₃N₃S)(CO)₃] (<b>1</b>) with [Fe(PMe₃)₄]. Crystal structure analysis of <b>2</b> revealed that the <i>N</i>,<i>N</i>-bidentate and three monodentate ligands form a five-coordinate square-pyramidal geometry around Fe, which differs from the trigonal-bipyramidal geometry observed in <b>1</b>. The steric and electronic factors were investigated by combining crystal structure and density functional theory (DFT) calculations. Compared with CO, the better σ donor properties of PMe₃ induce the square-pyramidal geometry of <b>2</b>, and a significant π-back-bonding inter-action was confirmed between Fe and the pyridazine moiety.