Syntheses of iron(III) aroyl hydrazones containing pyridoxal and salicylaldehyde. The crystal and molecular structure of two iron(III)-pyridoxal isonicotinoyl hydrazone complexes

Abstract

Iron(III) complexes of three aroyl hydrazones, pyridoxal isonicotinoyl hydrazone (H 2pih), pyridoxal benzoyl hydrazone (H 2pbh), and salicylaldehyde benzoyl hydrazone (H 2sbh), were synthesized and characterized. In aqueous medium at pH 7, [Fe(pih)(Hpih)]·3H 2O is formed. In acidic methanol, a 1:1 ligand-to-metal complex is formed, [FeCl 2(H 2pih)]Cl ( 1), whereas in aqueous medium at low pH cis-[FeCl 2(H 2pih)(H 2O)]Cl·H 2O ( 2) is formed. Compounds 1 and 2 are high-spin d 5 with μ eff = 5.88 μ B and 5.93 μ B (298 K). The crystal structures of 1 and 2 show that H 2pih acts as a tridentate neutral ligand in which the phenolic and hydrazidic protons have shifted to the pyridine nitrogen atoms. The co- ordination polyhedron of 1 is ‘square’ pyramidal, whereas that of 2 is pseudo-octahedral. Compound 1 is triclinic, space group P l , with a = 12.704(2) Å, b = 8.655(2) Å, c = 8.820(2) Å, α = 105.42(1)°, β = 89.87(1)°, γ = 107.60(1)°, V = 888 Å 3, and Z = 2; 2 is monoclinic, space group P2 1/ c, with a = 15.358(4) Å, b = 7.304(3) Å, c = 17.442(4) Å, β = 101.00(2)°, V = 1921 Å 3, and Z = 4.