Structural, Spectroscopic, Electrochemical, and Magnetic Properties for Manganese(II) Triazamacrocyclic Complexes.

We report the synthesis of [Mn(tacud)](OTf) () (tacud = 1,4,8-triazacycloundecane), [Mn(tacd)](OTf) () (tacd = 1,4,7-triazacyclodecane), and [Mn(tacn)](OTf) () (tacn = 1,4,7-triazacyclononane). Electrochemical measurements on the Mn redox couple show that complex has the largest anodic potential of the set ( = 1.16 V vs NHE, Δ = 106 mV) compared to ( = 0.95 V, Δ = 108 mV) and ( = 0.93 V, Δ = 96 mV). This is due to the fact that has the fewest 5-membered chelate rings and thus is least stabilized. Magnetic studies of - revealed that all complexes remain high spin throughout the temperature range investigated (2 - 300 K). X-band EPR investigations in methanol glass indicated that the manganese(II) centers for and resided in a more distorted octahedral geometric configuration compared to . To ease spectral interpretation and extract ZFS parameters, we performed high-frequency high-field EPR (HFEPR) at frequencies above 200 GHz and a field of 7.5 T. Simulation of the spectral data yielded = 2.0013 and = -0.031 cm for , = 2.0008, = -0.0824 cm, |/| = 0.12 for , and = 2.00028, = -0.0884 cm for . These results are consistent with possessing the most distorted geometry. Calculations (PBE0/6-31G(d)) were performed on -. Results show that has the largest HOMO-LUMO gap energy (6.37 eV) compared to (6.12 eV) and (6.26 eV). Complex also has the lowest HOMO energies indicating higher stability.