Tuning Nuclearity of Biradical-Ln Functional Compounds with Single-Molecule Magnet Behavior and Near-Infrared Luminescence

Abstract

Utilizing an hexadentate nitronyl nitroxide biradical bisNITbpym, two series of biradical-4f clusters, namely [Tb2(hfac)6(bisNITbpym)2]·CHCl3 (1), [Dy2(hfac)6(bisNITbpym)2] (2), and [Ln4(hfac)12(bisNITbpym)2] (LnIII = YIII3, TbIII4 and YbIII5) (bisNITbpym = 2,2′-dipyridyl-5,5′-bis(1′-oxyl-3′-oxido-4′,4′,5′,5′-tetramethyl-4,5-hydro-1H-imidazol-2-yl); hfac = hexafluoroacetylacetonate), have been smoothly obtained via regulating the ratio of LnIII metal to biradical bisNITbpym. In compounds 1 and 2, the bisNITbpym ligand links two TbIII ions to yield a dinuclear pattern. Meanwhile, 3–5 exhibit an annular tetranuclear structure with biradical bisNITbpym, enwrapping and bridging four LnIII ions. Single-molecule magnet behavior of the Dy derivate is confirmed through frequency-dependent ac signals. Furthermore, this comparative exploration of dinuclear and tetranuclear systems indicates that spatial symmetries around LnIII ions have an important impact on magnetic dynamics. Near-infrared luminescence and slow magnetic relaxation have been observed in the YbIII derivative, which can act as a promising multifunctional probe in the aspect of fluoroimmuno assays. Our present work not only successfully acquires a multifunctional YbIII-based compound but also achieves the regulation of nuclearity and magnetic property of the nitronyl nitroxide biradical-LnIII system.