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 Bu4N{[M(3NO(2),5Br-H3L1,1,4)](2)(mu-F)} (M = Dy, 1; M = Ho, 2; M = Gd, 3) and Bu4N{[Dy(3Br,5Cl-H3L1,2,4)](2)(mu-F)}center dot 2H(2)O, 4 center dot 2H(2)O. The crystal structures of 1 center dot 5CH(3)C(6)H(5),center dot 2 center dot 2H(2)O center dot 0.75THF, 3, and 4 center dot 2H(2)O center dot 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. Variabletemperature magnetization demonstrates a poor magnetocaloric effect for 3. Alternating current magnetic measurements for 1, 2, and 4 center dot 2H(2)O bring to light that 4 center dot 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 center dot 2H(2)O introduce important changes in the dipolar interactions, from antiferromagnetic in 1 to ferromagnetic in 4 center dot 2H(2)O.