Novel 'main-part' isostructuralism in metal complexes with 1-methylimidazole: crystal structures, energy calculations and magnetic properties

Two new transition metal complexes with 1-methylimidazole (1-MeIm) and azide as ligands, namely, [Co(1-MeIm)₄(N₃)₂] (1) and [Ni(1-MeIm)₄(N₃)₂] (2), have been synthesized and characterized by IR, Raman, UV-Vis and XPS spectroscopy. Their crystal structures were solved by single-crystal X-ray diffraction. The supramolecular self-assembly of the two complexes is governed by non-classical C-H⋯N hydrogen bonds and C-H⋯π interactions. Lattice energies and intermolecular interaction energies for various molecular pairs are quantified using the PIXEL method. DFT computational studies to assess the binding energy through modern tools like non-covalent interaction (NCI plots) analysis and reduced density gradient (RDG) analysis have also been carried out. A detailed analysis of geometric descriptors revealed the existence of quasi-isostructural pairs or 'main-part' isostructuralism in a series formed by 1, 2, and a related cadmium complex, being more evident in the 1/2 pair. DFT studies using theoretical models have been used to disclose the relative importance of the H-bond and C-H⋯π noncovalent interactions. Magnetic measurements for compound 1 show weak ferrimagnetic coupling between adjacent M(II) centers, mediated by H-bonding and C-H⋯π non-covalent interactions.

Hydrogen bond mediated intermolecular magnetic coupling in mononuclear high spin iron(iii) Schiff base complexes: synthesis, structure and magnetic study with theoretical insight

The crystal structure and magnetic properties of two mononuclear iron(iii) Schiff base complexes, [FeL¹(NCS)₂] (1), HL¹ = 2-[1-[[2-[(2-aminoethyl)amino]ethyl]imino]ethyl]phenol and [FeL²(N₃)Cl] (2), HL² = 2-(-1-(2-(2-aminoethylamino)ethylimino)ethyl)-4-methylphenol are reported. Each complex contains a Fe(iii) ion surrounded by a N₃O Schiff base ligand and two NCS⁻ ligands (in 1) or one N₃⁻ and one Cl⁻ ligands (in 2). The magnetic properties can be well reproduced with zero field splittings in the high spin S = 5/2 Fe(iii) ions and weak intermolecular Fe–Fe interactions mediated by hydrogen bonds. This intermolecular antiferromagnetic interaction has been validated by using DFT calculations in complex 2. Moreover, the interaction energies of the H-bonded dimers in both complexes have been estimated using DFT calculations and characterized using a combination of QTAIM and NCI plot computational tools. Complexes 1 and 2 constitute two rare examples of Fe(iii) complexes with magnetic interactions through H-bonds.

H-Bond mediated magnetic interactions in mononuclear iron(iii) Schiff base complexes were studied experimentally and validated by using DFT calculations.