Synthesis and Study of Complexation Properties of a New Phenanthrenequinone Monohydrazone Derivative Containing an α-Pyridyl Fragment with Iron Triad Cations in Solutions and in the Solid Phase

Abstract A new heterocyclic hydrazocompound - 10-(2-(5-bromopyridine-2-yl)hydrazinelidene)phenanthrene-9(10H)-one (HL) - is prepared by the interaction of 5-bromo-2-hydrazinopyridine and 9,10-phenanthrenequinone. According to physicochemical data and quantum chemical simulations, the HL molecule in the crystal and in solutions exists in the form of a quinohydrazone tautomer stabilized by the N25H⋯O23 intramolecular H-bond. The “mobile” H atom is localized at the N25 atom of the azo group. The acidity constant of HL (pKa = 12.30±0.12) and formation and composition constants of Fe2+, Co2+, Ni2+ complexes with HL in solutions are determined. ML2 complexes (M = Fe2+, Co2+, Ni2+) are isolated in the crystal state. The mode the L ligand is coordinated by metal atoms is hypothesized. The crystal structure of the [FeL2] iron complex is determined by XRD. It is established that the HL molecule is attached to the iron atom in the form of an anion and performs the structural function of an O,N,N-tridentate chelate ligand. The configuration of the iron atom is a distorted octahedron.