Syntheses, X-ray Structures, Solid State High-Field Electron Paramagnetic Resonance, and Density-Functional Theory Investigations on Chloro and Aqua Mn^II Mononuclear Complexes with Amino-Pyridine Pentadentate Ligands

The two pentadentate amino-pyridine ligands L52 and L53 (L52 and L53 stand for the N-methyl-N,N′,N′-tris(2-pyridylmethyl)ethane-1,2-diamine and the N-methyl-N,N′,N′-tris(2-pyridylmethyl)propane-1,3-diamine, respectively) were used to synthesize four mononuclear MnII complexes, namely [(L52)MnCl](PF6) (1(PF6)), [(L53)MnCl](PF6) (2(PF6)), [(L52)Mn(OH2)](BPh4)2 (3(BPh4)2), and [(L53)Mn(OH2)](BPh4)2 (4(BPh4)2). The X-ray diffraction studies revealed different configurations for the ligand L5n (n = 2, 3) depending on the sixth exogenous ligand and/or the counterion. Solid state high-field electron paramagnetic resonance spectra were recorded on complexes 1−4 as on previously described mononuclear MnII systems with tetra- or hexadentate amino-pyridine ligands. Positive and negative axial zero-field splitting (ZFS) parameters D were determined whose absolute values ranged from 0.090 to 0.180 cm−1. Density-functional theory calculations were performed unraveling that, in contrast with chloro systems, the spin−spin and spin−orbit coupling contributions to the D-parameter are comparable for mixed N,O-coordination sphere complexes.