Crystal structures and magnetic properties of two series of phenoxo-<i>O</i> bridged dinuclear Ln₂ (Ln = Gd, Tb, Dy) complexes

Six dinuclear lanthanide compounds of the formulae [Ln₂(3m-L4)₂(L2)₂(MeOH)₂]·6MeOH (Ln = Gd - 1a, Tb - 1b, and Dy - 1c) and [Ln₂(3m-L4)₂(L2)₂(DMF)₂] (Ln = Gd - 2a, Tb - 2b, and Dy - 2c; DMF = N,N-dimethylformamide, H₂3m-L4 = (2-[(E)-(3-metoxysalicylidene)amino]phenol), and HL2 = 1,3-diphenyl-1,3-diketopropane) were prepared and characterized by elemental analysis, FTIR spectroscopy, thermogravimetric measurements, single-crystal X-ray structural analysis, and magnetometry, and Gd₂ and Dy₂ compounds by ab initio methods as well. The structural analysis revealed the isostructurallity of the compounds within the series of 1a-c and 2a-c. The analysis of the variable temperature magnetic data showed the presence of a weak antiferromagnetic coupling in the Gd₂ compounds (J/cm^-1 = -0.13 for 1a and J/cm^-1 = -0.17 for 2a). The magnetocaloric effect was studied on compound 2a with the maximum value of -ΔS_M = 22.9 J kg^-1 K^-1 at T = 2.0 K and B = 9 T, which is the highest value among the Gd₂ double phenoxo-bridged compounds observed up to now. Both the Dy₂ compounds (1c and 2c) exhibit slow-relaxation of magnetization in zero external static magnetic field. Magnetic anisotropy, intradimer magnetic coupling and magnetization blocking barriers were also studied by ab initio methods for 1c and 2c.