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

A family of eight polymeric manganese­(III) complexes with the general formula Mn­(HL1,2)2X (H2L1 = 2­[(2-hydroxyethyl)­iminomethyl]­phenol, H2L2 = 2­[(2-hydroxyethyl)­iminomethyl]-6-methoxy-phenol), while X = Cl (1, 5), Br (2, 6), I (3, 7), NCS (4, 8) for H2L1 and H2L2, 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(HL1,2)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(HL2)2(NCS)] n units. The SB ligands are mono-deprotonated 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 HL2– occur. The intrachain MnIII···MnIII 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.