3d-4f magnetic exchange interactions and anisotropy in a series of heterobimetallic vanadium(IV)-lanthanide(III) Schiff base complexes.

A series of heterobimetallic LnIII-VIV compounds [Ln(VO)L(NO3)3(H2O)] (Ln = Gd(1), Tb(2), Dy(3), and Er(4)) assembled by a Schiff base ligand (H2L = N,N'-bis(1-hydroxy-2-benzylidene-6-methoxy)-1,7-diamino-4-azaheptane) were prepared and studied with experimental and theoretical methods. The single-crystal X-ray analysis revealed the change of the coordination number from 10 found in 1-3 to 9 confirmed in 4. The DC magnetic data were fit with several Hamiltonians to extract the exchange and anisotropy parameters of complexes 1-4. This investigation of magnetic properties was carried out using both DFT and CASSCF theoretical calculations. It was found out that exchange interactions in 1, 3 and 4 are antiferromagnetic, while 2 has ferromagnetic exchange interactions. Moreover, the AC susceptibility measurements revealed the field-induced slow relaxation of magnetization in complexes 2 and 3 which is complicated by the presence of three relaxation channels. Nevertheless, these compounds belong to the first TbIII-VIV and DyIII-VIV single-molecule magnets in this class of compounds.