Syntheses, structures, and magnetic properties of the lanthanide complexes of imidazole-substituted nitronyl nitroxide biradicals

Two new bis-bidentate imidazole-substituted nitronyl nitroxide biradicals, BNITIm-C2 (BNITIm-C2 = 1,1 '-(1,2-ethanediyl)bis(1H-imidazole-2-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide)) and BNITIm-C4 (BNITIm-C4 = 1,1 '-(1,4-butanediyl)bis(1H-imidazole-2-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxy-3-oxide)), and two series of lanthanide complexes, namely [(BNITIm-C2)Ln(NO3)(3)](MeOH) (Ln = Gd (1(Gd)) and Tb (2(Tb))), (BNITIm-C2)Dy(NO3)(3) (3(Dy)) and (BNITIm-C4)[Ln(hfac)(3)](2)(C7H8)(2) (Ln = Gd (4(Gd)), Tb (5(Tb)) and Dy (6(Dy)), hfac = hexafluoroacetylacetonate), have been prepared and characterized structurally and magnetically. Single crystal X-ray crystallographic analyses revealed that complexes 1(Gd)-3(Dy) exhibit 1D chain structures where the Ln(NO3)(3) units are bridged by the BNITIm-C2 bis-bidentate biradical, while complexes 4(Gd)-6(Dy) exhibit binuclear structures with two Ln(hfac)(3) units bridged by the BNITIm-C4 biradical. The bulky hfac anions prohibit the further coordination of Ln(III) to another NIT ligand and the formation of a similar 1D chain structure. Due to the very long intra- and intermolecular distances of the spin centers, complexes 1(Gd)-3(Dy) can be magnetically regarded as an isolated 2p-4f-2p tri-spin system while complex 4(Gd)-6(Dy) can be regarded as an isolated 2p-4f bi-spin system. Magnetic analyses on the two Gd-III compounds revealed the ferromagnetic Gd-III-NIT interactions and antiferromagnetic NIT-NIT interactions through the Gd-III ion in 1(Gd). Alternating-current (ac) magnetic susceptibility investigations revealed that complex 5(Tb) exhibits the typical SMM behavior under a zero dc field while complex 6(Dy) was proved to be a field-induced SMM. Ab initio calculations were performed on complexes 2(Tb) and 5(Tb) to understand their magnetic anisotropy together with their different magnetic dynamics.

Automated summary

In this study, two new bis-bidentate imidazole-substituted nitronyl nitroxide biradicals and their lanthanide complexes were synthesized and characterized. The structural and magnetic properties of these compounds were studied, and ab initio calculations were performed to understand their magnetic dynamics.