Dinuclear Fluoride Single-Bridged Lanthanoid Complexes as Molecule Magnets: Unprecedented Coupling Constant in a Fluoride-Bridged Gadolinium Compound

Abstract

A new synthetic method allows isolating fluoride-bridged complexes Bu 4 N{[M(3NO 2 ,5Br-H 3 L 1,1,4 )] 2 (μ-F)} (M = Dy, 1 ; M = Ho, 2 ; M = Gd, 3 ) and Bu 4 N{[Dy(3Br,5Cl-H 3 L 1,2,4 )] 2 (μ-F)}·2H 2 O, 4 ·2H 2 O. The crystal structures of 1 ·5CH 3 C 6 H 5 ,· 2 ·2H 2 O·0.75THF, 3 , and 4 ·2H 2 O·2THF show that all of them are dinuclear compounds with linear single fluoride bridges and octacoordinated metal centers. Magnetic susceptibility measurements in the temperature range of 2–300 K reveal that the Gd III ions in 3 are weakly antiferromagnetically coupled, and this constitutes the first crystallographically and magnetically analyzed gadolinium complex with a fluoride bridge. Variable-temperature magnetization demonstrates a poor magnetocaloric effect for 3 . Alternating current magnetic measurements for 1 , 2 , and 4 ·2H 2 O bring to light that 4 ·2H 2 O is an SMM, 1 shows an SMM-like behavior under a magnetic field of 600 Oe, while 2 does not show relaxation of the magnetization even under an applied magnetic field. In spite of this, 2 is the first fluoride-bridged holmium complex magnetically analyzed. DFT and ab initio calculations support the experimental magnetic results and show that apparently small structural differences between 1 and 4 ·2H 2 O introduce important changes in the dipolar interactions, from antiferromagnetic in 1 to ferromagnetic in 4 ·2H 2 O.

Lanthanide Metal–Organic Frameworks Exhibiting Fluoro-Bridged Extended Chains: Synthesis, Crystal Structures, and Magnetic Properties

“…The interaction between the chains is expected to be substantially weaker, essentially negligible, given that the nearest interchain Gd•••Gd distance is 13.414 Å. We note that the antiferromagnetic exchange constants of the same order of magnitude were reported for interactions between fluoride-bridged Gd 3+ ions in a molecular Gd 2 dimer (J ex = 0.062 cm −1 ) 55 and in a pentanuclear Gd 3 Ga 2 complex (J ex = 0.028 cm −1 ). 56 The slightly stronger antiferromagnetic interaction in the former might be explained by a nearly linear Gd−F−Gd angle, which should allow for a better delocalization of spin density across the fluoride bridge.…”

Fluoride-bridged dinuclear dysprosium complex showing single-molecule magnetic behavior: supramolecular approach to isolate magnetic molecules

“…In a complex of dinuclear Dy bridged by a single fluoride ion, Dy–F bond lengths of 2.137–2.315 Å and Dy–F–Dy angles of 169.8–180° have been reported. 44,45 The Dy–F bond lengths (2.184 Å) and Dy–F–Dy angles (180°) found in Dy 2 POM are reasonable values. (Na)(B18C6) and H 2 O molecules coordinated to Na form 1D supramolecular arrays.…”

Zero-Field Single-Molecule Magnet Behavior in a Series of Dinuclear Dysprosium(III) Complexes Based on Benzothiazolyl-Based Ligands and β-Diketonates

“…In this sense, the orientation of the local anisotropic axis, parallel to the vector connecting the two magnetic centers, explains the significant ferromagnetic dipolar coupling, potentially serving as the driving force for the observed ferromagnetic interactions . To confirm this, the POLY_ANISO package was employed to simulate the dc magnetic properties, treating the Dy 3+ ions as pseudo spin S = 1/2.…”

“…In this sense, the orientation of the local anisotropic axis, parallel to the vector connecting the two magnetic centers, explains the significant ferromagnetic dipolar coupling, potentially serving as the driving force for the observed ferromagnetic interactions. 66 To confirm this, the POLY_-ANISO 67 package was employed to simulate the dc magnetic properties, treating the Dy 3+ ions as pseudo spin S = 1/2. Since the total magnetic interaction consists of two components, namely, dipole−dipole interaction (see full matrix Table S15) and exchange interaction, the dipolar term was calculated directly using the orientations of the anisotropic axis and gtensor values previously obtained from the fragments.…”