Synthesis, structures and properties of Fe(III) complexes with dihydrazone ligand

Abstract

The pentadentate N3O2 Schiff base ligand, H2L = 2,6-diacetylpyridine bis(picolinoylhydrazone), has been used for the synthesis of two mononuclear iron(III) complexes: [Fe(H2L)(H2O)2](NO3)3∙2.5H2O (1) and [Fe(H2L)(H2O)2](ClO4)3∙2.5H2O (2), which were characterized by IR spectroscopy and X-ray

diffraction. The crystal structures of these complexes contain mononuclear cations - [Fe(H2L)(H2O)2]3+, NO3- /ClO4‒ anions, and water molecules. The Schiff base ligand in both compounds is coordinated in the form of a double zwitterions [1]. It was found that in cation complex

of 1 and 2 there are protons transfer from the N atoms of the amide groups to N atoms of the pyridine rings. This migration of protons was confirmed by IR spectroscopy. The band ν(NH), observed in the

free ligand at 3324 cm-1, is absent in the IR spectra of complexes 1 and 2. The broad absorption in the region of 3650-2600 cm-1 could be explained by the joining of hydrogen bonds due to their lengths into several groups and the broad bands of weak intensity might be PyH+ oscillations. The crystal structures of compounds 1 and 2 are stabilized by hydrogen bonding that give rise to a supramolecular 3D-networks via coordinated and crystallization water molecules, NO3- or ClO4-anions and NH+ (PyH+) (Figure 1).

The hydrogen bond mediated intermolecular magnetic couplings in mononuclear high spin iron(III) Schiff base complexes have been studied by TB2J python package used for calculating the magnetic interaction parameters in Heisenberg models from Density Functional Theory [2].

The photoluminescence study was performed on both samples and luminescence excitation was carried out by pulse nitrogen laser (337.1 nm) at a temperature of 300 К. The weak photoluminescence was observed in the 350 - 750 nm spectral range with maxima in the red (1.9 eV), yellow (2.1 eV) and blue (2.6 eV) spectral regions.