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

Abstract

Four isostructural trinuclear 3d–4f–4(5)d heterotrimetallic complexes, with the general formula [L²CuLn(H₂O)₅(μ-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^IILn^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_CuMS_Cu·S_M). These results were used to simulate the magnetic properties of compound 3, using the isotropic spin Hamiltonian H = −2J_CuMoS_Cu·S_Mo − 2J_CuGdS_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.