Temperature-controlled polymorphism of chiral CuII–LnIII dinuclear complexes exhibiting slow magnetic relaxation
He-Rui Wen, Jun Bao, Sui-Jun Liu, Cai-Ming Liu, Cai-Wei Zhang, Yun-Zhi Tang
A new family of 3d–4f dinuclear complexes derived from a chiral Schiff-base ligand, (R,R)-N,N′-bis(3-methoxysalicylidene)cyclohexane-1,2-diamine (H2L), has been synthesized and structurally characterized, namely, [Cu(L)Ln(NO3)3(H2O)] (Ln = Ce (1) and Nd (2)), [Cu(L)Sm(NO3)3]·2CH3CN (3) and [Cu(L)Ln(NO3)3] (Ln = Eu (4), Gd (5 and 5′), Tb (6 and 6′), Dy (7 and 7′), Ho (8), Er (9) and Yb (10)). Structural determination revealed that these complexes are composed of two diphenoxo-bridged CuII–LnIII dinuclear clusters with slight structural differences. Complexes 1, 2 and 4–7crystallize in the chiral space group P1, and the space group of 3 is P21, while the other six complexes (5′–7′ and 8–10) are isomorphous and each of them contains two slightly different CuII–LnIII dinuclear clusters in the asymmetric unit with the chiral space group P21. Magnetic investigations showed that ferromagnetic couplings between the CuII and LnIII ions exist in 5–7and 5′–7′. Moreover, the alternating current (ac) magnetic susceptibilities of 6, 6′, 7 and 7′ showed that both the in-phase (χ′) and out-of-phase (χ′′) are frequency- and temperature-dependent with a series of frequency-dependent peaks for the χ′′, which being typical features of field-induced slow magnetic relaxation phenomena. For 8, a frequency dependent χ′ with peaks but χ′′ without peaks appeared; however, the compound displays field-induced slow magnetic relaxation behavior. Furthermore, no obvious frequency-dependent ac signal was observed in 9 owing to the absence of the easy-axis anisotropy. More significantly, we observed the temperature-controlled reversible conversion from one chiral single-crystal (5–7) to another chiral single-crystal (5′–7′) exhibiting slow magnetic relaxation.
Circular dichroism, Coordination chemistry