Mn(III) Chain Coordination Polymers Assembled by Salicylidene-2-ethanolamine Schiff Base Ligands: Synthesis, Crystal Structures, and HFEPR Study

Abstract

A family of eight polymeric manganese(III) complexes with the general formula Mn(HL 1,2 ) 2 X (H 2 L 1 = 2[(2-hydroxyethyl)iminomethyl]phenol, H 2 L 2 = 2[(2-hydroxyethyl)iminomethyl]-6-methoxy-phenol), while X = Cl (1, 5), Br (2, 6), I (3, 7), NCS (4, 8) for H 2 L 1 and H 2 L 2 , respectively were obtained using "the direct synthesis" approach, i.e., the oxidative dissolution of the manganese powder in the presence of a Schiff base (SB), an ammonium salt, and oxygen in the air. Single crystal X-ray diffraction studies for the new complexes 2, 3, 4, and 8 were compared with the previously reported crystallographic data for 1 and 7, showing that all complexes possess a one-dimensional polymeric structure. The main structural units in 1−7 are cationic chains [Mn(HL 1,2 ) 2 ] n n+ and anions X − linked together via electrostatic interactions and hydrogen bonds, while the complex 8 consists of polymeric chains of neutral [Mn(HL 2 ) 2 (NCS)] n units. The SB ligands are monodeprotonated as HL − , and coordinated by the metal atoms in a tridentate chelate-bridging fashion generating chains with Mn centers connected by double or single {−N−C−C−O−} bridges for 1−7 and 8, respectively. In 8, bridging and pure chelate modes of HL 2− occur. The intrachain Mn III •••Mn III distances vary from 5.700(2) Å for 1 to 6.6950(4) Å for 8. A high-field electron paramagnetic resonance study reveals narrow ranges of the zero-field splitting parameters of the spin Hamiltonian, D and E (−3.22 cm −1 to −3.44 cm −1 and −0.16 cm −1 to −0.21 cm cm −1 , respectively) and demonstrates a clear correlation between the degree of the structural distortion and the E parameter. The ab-initio CASSCF method was employed to calculate the zero-field splitting parameters. "Broken symmetry" density functional theory calculations were performed to estimate the magnitude of the Mn−Mn exchange interactions.

Quercetin as a Precursor for the Synthesis of Novel Nanoscale Cu (II) Complex as a Catalyst for Alcohol Oxidation with High Antibacterial Activity

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One-Dimensional CoII and NiII Helical Coordination Polymers Exhibiting Zero-Field Splitting

“…The synthesis of coordination compounds based on 3d cations has been of great interest for their various structures and topologies and their possible applications as functional materials in gas storage/adsorption, catalysis, magnetism, and luminescence, among others. − The formation of these compounds depends strongly on the metal ion properties and the nature of the ligands, , while the chemical characteristics of the ligand, rigidity, and the coordination modes can affect the structures and chemical properties of the coordination compounds. Besides, the electronic distribution of the transition metal cations is essential for physical properties. − Research efforts are focused on understanding and controlling the molecular organization in the solid state for the rational design and preparation of new materials with novel structures and promising properties. − In this sense, coordination polymers, which correspond to self-assembled metal ions and organic linkers into infinite arrays, have shown rapid development over recent past years. − Many ligands have been used to assemble coordination polymers, especially those containing carboxylate groups. As stated in many works, carboxylate-based ligands are attractive due to the plasticity of the coordination modes and the ability to link two or more metal cations simultaneously.…”