An insight into the hydrogen bonding, halogen bonding and chalcogen bonding interactions in manganese(iii) complexes with N2O2donor salicylidine Schiff base ligands

Abstract

Four manganese(III) complexes, [MnL¹(H₂O)₂]ClO₄·H₂O (1), [MnL²(H₂O)₂]ClO₄ (2), [MnL³(DMSO)(H₂O)]ClO₄ (3) and [MnL⁴(DMSO)(H₂O)]ClO₄ (4), where H₂L¹ = N,N′-bis(5-bromosalicylidene)-1,3-diaminopropane, H₂L² = 2,2-dimethyl-N,N-bis(3-methyloxysalicylidene)-1,3-diaminopropane, H₂L³ = N,N′-bis(5-chlorosalicylidene)-2,2-dimethyl-1,3-diaminopropane and H₂L⁴ = 2-hydroxy-N,N′-bis(3-ethyloxysalicylidene)-1,3-diaminopropane are tetradentate N₂O₂-donor ligands and DMSO = dimethyl sulfoxide, have been synthesized and characterised by elemental analysis, IR and UV-vis spectroscopy and single-crystal X-ray diffraction studies. All are monomeric complexes. Complex 1 crystallises in orthorhombic space group P2₁2₁2₁, complex 3 crystallises in triclinic space group P-1, whereas complexes 2 and 4 crystallize in monoclinic space groups, C2/c and C2/m respectively. In all the complexes, manganese(III) has a six-coordinated pseudo-octahedral geometry in which imine nitrogen atoms and phenolate oxygen atoms of the deprotonated di-Schiff base constitute the equatorial plane. In complexes 1 and 2, water molecules are present in the fifth and sixth coordination sites in the axial positions while in complexes 3 and 4 they are occupied by one water and one DMSO. The coordinated water molecules initiate hydrogen-bonded networks in all complexes. DFT calculations have been carried out to analyze two aspects of these complexes viz. the formation of halogen (HaB) and chalcogen bonding (ChB) interactions in complexes 1 and 3 where the electron donor is the perchlorate anion and the acceptor either bromine or chlorine atoms for the HaBs and the sulfur atom of the coordinated DMSO for the ChB. In addition, other intermolecular effects are discussed in the solid state for complexes 1, 2 and 4, where the hydrogen atoms of the coordinated water molecules interact with the electron rich cavities formed by the phenolate and alkyloxy oxygen atoms of the Schiff-base ligand.