Syntheses and magnetic properties of a bis-bidentate nitronyl nitroxide radical based on triazolopyrimidine and its metal complexes

A novel bis-bidentate nitronyl nitroxide radical based on triazolopyrimidine, NIT-2-TrzPm (NIT-2-TrzPm = (2(2'-triazolopyrimidine)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide)) and six new transition metal complexes of this ligand, namely [M(hfac)2(NIT-2-TrzPm)]center dot CH2Cl2 (M = Mn (1Mn) and Co (2Co)), [M (hfac)2]2(NIT-2-TrzPm) (M = Mn (3Mn) and Co (4Co)), [Mn(NIT-2-TrzPm)2(MeOH)(2)](ClO4) 2 center dot MeOH (5Mn), and [Co (NIT-2-TrzPm)2(MeOH)2]2(ClO4) 4 center dot 4MeOH (6(Co)) were prepared and characterized structurally and magnetically. These complexes can be selectively synthesized by controlling the reaction ratio of M(hfac) 2 center dot 2H(2)O to the radical ligand ( for 1Mn to 4(Co)) or using metal perchlorates as the starting materials ( for 5Mn and 6Co). Single crystal X-ray crystallographic analyses confirmed that 1Mn and 2Co are isostructural 3d-2p MII-radical complexes, in which the NIT-2-TrzPm radical acts as a terminal bidentate ligand chelating to one 3d ion, while 3Mn and 4(Co) are isostructural 3d-2p-3d MII-radical-MII complexes with the NIT-2-TrzPm radical acting as a bridging ligand between two 3d ions. For complexes 5Mn and 6Co, two NIT-2-TrzPm ligands from the equatorial positions coordinate with the metal center to form the 2p-3d-2p structures with the axial positions occupied by two methanol molecules. Magnetic analysis on the Mn-II complexes revealed the existence of a strong antiferromagnetic interaction between the Mn-II and the NIT radical spin, while weak ferromagnetic coupling for Mn.Mn and Rad.Rad in the Mn-NIT-Mn and Rad-Mn-Rad spins was confirmed. Interestingly, although the NIT-bridged complexes 3(Mn) and 4Co possess significantly different magnetic anisotropy, field-induced slow magnetic relaxation can be observed in both complexes, whichwas assigned to the phonon bottleneck effect for 3(Mn) and field-induced SMM behavior for 4(Co). To the best of our knowledge, 3(Mn) is the first example of the NIT-bridged binuclear MnII complex undergoing slow magnetic relaxation.

Automated summary

A novel bis-bidentate nitronyl nitroxide radical and its six transition metal complexes were synthesized and characterized for their magnetic and structural properties.