Exploring supramolecular architectures in Mn(iii) two-compartment o-vanhd Schiff base complexes: insights from apical aqua ligands and bond valence sum analysis

Abstract

Three novel Mn(III) vanhd complexes, namely [Mn(o-vanhd)(N₃⁻)(H₂O)]·CH₃OH (1), [Mn(o-vanhd)(NCS⁻)(H₂O)]·2CH₃CN (2), and [Mn(o-vanhd)(H₂O)]·ClO4·H₂O (3), have been successfully synthesized using compartmental ligands paired with ancillary ligands including azide (N₃), perchlorate (ClO₄), and thiocyanate (NCS). The investigation of these complexes involves a comprehensive analysis encompassing single-crystal analysis, paramagnetic ¹H NMR, IR, CD, and UV spectroscopy. The findings highlight the formation of supramolecular architectures through robust hydrogen bonding and π–π stacking interactions among neighboring units. Complexes 1 and 3 crystallize in the monoclinic P2₁ space group, while complex 2 adopts the triclinic P1 space group; all three complexes exhibit an octahedral geometry. Notably, the behavior of the azomethine functional groups within the complexes significantly varies based on the nature of the ancillary ligands. Temperature-dependent CD spectra demonstrate the structural stability of these complexes. The congruence between solution and solid-state UV-Vis spectra is evident. Variable NMR spectra exhibit noteworthy chemical shifts at temperatures of 233 K, 333 K, and 398 K. The results from various physicochemical techniques collectively affirm the formation of complexes 1 and 3. Consequently, the bond valence sum (BVS) values for complexes 1, 2, and 3 exhibit a minor elevation due to ligand constraints and hydrogen interactions.