Synthesis, crystal structure and DFT study of carbon-yl[3-(dibenzo[b,d]thio-phen-4-yl)-6-(pyridin-2-yl-κN)pyridazine-κN 1]bis-(tri-methyl-phosphane)iron(0).

The title compound, [Fe(C21H13N3S)(CO)(PMe3)2] (2), bearing a 3-(dibenzo[b,d]thio-phen-4-yl)-6-(pyridin-2-yl)pyridazine ligand was obtained by the reaction of [Fe(C21H13N3S)(CO)3] (1) with [Fe(PMe3)4]. Crystal structure analysis of 2 revealed that the N,N-bidentate and three monodentate ligands form a five-coordinate square-pyramidal geometry around Fe, which differs from the trigonal-bipyramidal geometry observed in 1. 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 2, and a significant π-back-bonding inter-action was confirmed between Fe and the pyridazine moiety.