Synthesis, Crystal Structures, Magnetic Properties and HF–EPR Studies of Four Manganese(III) Compounds Derived From Schiff Base Ligands

ABSTRACT Three penta‐coordinate and one hexa‐coordinate mononuclear Mn III complexes were obtained by the combination of two types of tridentate ligands and divalent manganese salts in organic solvents. Single crystal x‐ray diffraction data indicate that the four complexes with formulas [Mn III (L 1 )(L 4 )]·CH 3 CH 2 OH·0.5H 2 O ( 1 ), [Mn III (L 2 )(L 4 )]·2CH 3 OH ( 2 ), [Mn III (L 3 )(L 4 )]·2CH 3 OH ( 3 ) and [Mn III (L 1 )(L 5 )]·CH 3 OH ( 4 ), where HL 1 = 2‐(5‐fluorobenzo[d]oxazol‐2‐yl)quinolin‐8‐ol, HL 2 = 2‐(5‐(trifluoromethyl)benzo[d]oxazol‐2‐yl)quinolin‐8‐ol, HL 3 = 2‐(5‐(tert‐butyl)benzo[d]oxazol‐2‐yl)quinolin‐8‐ol, H 2 L 4 = (E)‐2,4‐di‐tert‐butyl‐6‐((2‐hydroxybenzylidene)amino)phenol and H 2 L 5 = (E)‐2,4‐di‐tert‐butyl‐6‐((2‐hydroxy‐3‐methoxybenzylidene)amino)phenol. Except for complex 4 , which is hexa‐coordinate with octahedral coordination geometry of N 3 O 3 donor atoms, the remaining complexes 1–3 are penta‐coordinate with different coordination topology configurations of the identical donor atoms. Moreover, the coordination polyhedron of Mn III metal centers in 1 and 2 belongs to a spherical square pyramid ( C 4v ) of N 2 O 3 , while 3 belongs to trigonal bipyramidal ( D 3h ). The discrepancy in coordination polyhedron between complexes 1 , 2 and 3 is mainly due to the substitution group modifications of benzoxazole derivatives. Static magnetic susceptibility measurements revealed that complexes 1–4 maintain a high spin state and remain paramagnetic at the entire temperature range. Spin Hamiltonian parameters for each complex were derived from the analysis and simulation of electron paramagnetic resonance spectra. The negative value of D confirms the easy‐axis anisotropy for 1 – 3 with large rhombicity character.