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(1 H -imidazole-2-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazol-1-oxy-3-oxide)) and BNITIm-C4 (BNITIm-C4 = 1,1'-(1,4-butanediyl)bis(1 H -imidazole-2-4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazol-1-oxy-3-oxide)), and two series of lanthanide complexes, namely [(BNITIm-C2)Ln(NO 3 ) 3 ](MeOH) (Ln = Gd (1Gd) and Tb (2Tb)), (BNITIm-C2)Dy(NO 3 ) 3 (3Dy) and (BNITIm-C4)[Ln(hfac) 3 ] 2 (C 7 H 8 ) 2 (Ln = Gd (4Gd), Tb (5Tb) and Dy (6Dy), hfac = hexafluoroacetylacetonate), have been prepared and characterized structurally and magnetically. Single crystal X-ray crystallographic analyses revealed that complexes 1Gd-3Dy exhibit 1D chain structures where the Ln(NO 3 ) 3 units are bridged by the BNITIm-C2 bis-bidentate biradical, while complexes 4Gd-6Dy 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 1Gd-3Dy can be magnetically regarded as an isolated 2p-4f-2p tri-spin system while complex 4Gd-6Dy 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 1Gd. Alternating-current (ac) magnetic susceptibility investigations revealed that complex 5Tb exhibits the typical SMM behavior under a zero dc field while complex 6Dy was proved to be a field-induced SMM. Ab initio calculations were performed on complexes 2Tb and 5Tb to understand their magnetic anisotropy together with their different magnetic dynamics.