Syntheses, crystal structures and magnetic properties of a series of Zn II2Ln III2 compounds (Ln = Gd, Tb, Dy, Ho and Er): contrasting structural and magnetic features†
Abstract
This report describes the syntheses, crystal structures and magnetic properties of a series of ZnII2LnIII2 compounds of composition [ZnII2LnIII2L2Cl2(acetate)4(MeOH)2] (Ln = Gd (1), Tb (2), Dy (3) and Ho (4)) and [ZnII2ErIII2L2Cl2(acetate)4(MeOH)2]·2MeOH·2H2O, where H2L is 2-methoxy-6-[{2-(2-hydroxyethylamino)ethylimino}-methyl]phenol. Compounds 1–4 are isomorphous with similar composition. Although the space group of 5 is the same as that of 1–4, the values of unit cell parameters of the former are significantly different from those of 1–4. The composition (in terms of solvent of crystallization) of 5 is also different from those of 1–4. However, the tetranuclear ZnII2LnIII2 cores in all five compounds are similar. The tetranuclear cores in these compounds can be considered as a dimer of dinuclear subunits in which two μ-phenoxido-μ-alkoxido ZnIILnIII fragments are linked by two η1:η2:μ2-acetate moieties; in the dinuclear fragment, ZnII and LnIII occupy, respectively, the O(phenoxide)N(imine)N(amine)O(alkoxide) and O(methoxy)O(phenoxide) sites. Direct current (dc) magnetic susceptibilities (at 0.1 T in the temperature range 300–2 K) and magnetization (few fixed low temperatures, ≤10 K, and up to 5 T) of 1–5 have been measured, revealing the following: (i) ferromagnetic interaction in the GdIII and DyIII analogues; (ii) magnetic anisotropy in the TbIII, DyIII, HoIII and ErIII analogues, 2–5; (iii) the magneto-caloric effect (MCE) in the GdIII analogue (ΔSm = 26.97 J kg−1 K−1 at 2 K for ΔH = 5 T). Alternating current susceptibility measurements reveal that the DyIII and HoIII analogues don’t show slow relaxation of magnetization even under a bias field of 3000 Oe, while the TbIII and ErIII analogues show slow magnetization dynamics under a bias field of 1000, 3000 and 5000 Oe. The Ueff values determined from the data at 5000 Oe are as follows: 18.6 cm−1 (70 Hz) and 11.8 cm−1 (700 Hz) for 2 (TbIII) and 12.3 cm−1 (70 Hz) and 9.4 cm−1 (700 Hz) for 5 (ErIII).