Effect of ligand substituents and tuning the spin-state switching in manganese(iii) complexes

Three mononuclear manganese(iii) complexes based on flexible hexadentate ligands obtained from the condensation of N,N '-bis(3-aminopropyl)ethylenediamine and salicylaldehyde or salicylaldehyde with substitutions at the 5 or 3,5 positions, namely [Mn(X-sal(2)-323)](BPh4) (X = 5 H, 1; X = 5 Br, 2, and X = 3,5 Br, 3) have been synthesized. The impact of ligand substituents has been studied by variable temperature single-crystal X-ray diffraction analyses, and magnetic, spectroscopic and electrochemical investigations. The complexes have an analogous monocationic MnN4O2 surrounding offered by the flexible hexadentate ligand in a distorted octahedral geometry. Complex 1 remains in the high spin state over the entire temperature range, while complex 2 shows a reversible and complete two-step thermo-induced spin-state switching. An incomplete spin-state switching from a high spin to an intermediate high-spin low-spin (1 : 1) state was observed for complex 3. Single-crystal X-ray structural studies show the presence of three different spin states in 2 during the occurrence of the spin-state switching process. Electrochemical investigations showed that the reduced state of manganese(iii) centers in 3 is easily accessible in comparison to complexes 1 and 2.

Automated summary

Three mononuclear manganese(iii) complexes based on flexible hexadentate ligands were synthesized, and the impact of ligand substituents was studied through various analyses. The complexes exhibit different spin-state switching behaviors, with complex 2 showing reversible two-step spin-state switching and complex 3 demonstrating incomplete spin-state switching. Single-crystal X-ray structural studies revealed the presence of three different spin states in complex 2 during the spin-state switching process. Electrochemical investigations showed that the reduced state of manganese(iii) centers in complex 3 is more easily accessible compared to complexes 1 and 2.