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

The two pentadentate amino-pyridine ligands L-5(2) and L-5(3) (L-5(2) and L-5(3) stand for the N-methyl-N,N',N'-T-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 Mn-II complexes, namely [(L-5(2)) MnCl](PF6) (1(PF6)), [(L-5(3)) MnCl](PF6) (2(PF6)), [(L-5(2)) Mn(OH2)](BPh4)(2) (3(BPh4)(2)), and [(L-5(3))Mn(OH2)](BPh4)(2) (4(BPh4)(2)). The X-ray diffraction studies revealed different configurations for the ligand L-5(n) (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 Mn-II 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.