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

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.