A new family of [Cu(II)Ln(III)M(V)] heterotrimetallic complexes (Ln = La, Gd, Tb; M = Mo, W): model systems to probe exchange interactions and single-molecule magnet properties

Four isostructural trinuclear 3d-4f-4(5)d heterotrimetallic complexes, with the general formula [L(2)CuLn(H2O)(5)(mu-NC)M(CN)(7)], were obtained from the association of binuclear 3d-4f complexes and {M-V(CN)(8)}(3-) metalloligands (M = Mo, Ln = La 1; M = W, Ln = La 2; M = Mo, Ln = Gd 3; M = Mo; Ln = Tb 4, where H2L2 = 1,2-ethanediylbis(2-iminomethylene-6-methoxy-phenol)). The metalloligand coordinates through a single-cyanido group at the apical position of the copper(II) ion belonging to the {Cu(II)Ln(III)} binuclear complex. The analysis of the magnetic data for the La(III) derivatives (compounds 1 and 2), in the 1.85-300 K temperature range, shows a weak ferromagnetic exchange interaction between Cu-II and Mo-V/W-V ions across the cyanido bridge (J(CuM)/k(B) = 3.6(6) K; g = 2.23(5) for 1 and J(CuM)/k(B) = 3.8(6) K, g = 2.21(5) for 2, with H = -2J(CuM) S-Cu.S-M). These results were used to simulate the magnetic properties of compound 3, using the isotropic spin Hamiltonian H = -2J(CuMo) S-Cu.S-Mo -2J(CuGd) S-Cu.S-Gd. The resulting magnetic interaction between Cu-II and Gd-III ions via the phenoxo-bridge was found to be weakly ferromagnetic (J(CuGd)/k(B) = +4.5(2) K with J(CuMo)/k(B) = +3.6(2) K, g(Gd) = g(Cu) = 2.00 and g(Mo) = 1.98). The dc magnetic properties for compound 4 also show a predominant ferromagnetic interaction, while the ac magnetic measurements indicate the presence of the slow relaxation of the magnetization below 3.5 K.