Syntheses, Structures and Magnetic Properties of Novel Tetrameric Ln2Mn2 and Ring-like Ln4Mn4 Clusters
Three tetrameric Ln-Mn clusters with formulae as [Ln2Mn2(hmp)6(NO3)4(H2O)4](ClO4)2·xH2O (Ln = Y, x = 1 (1); Ln = Gd, x = 3 (2); Ln = Dy, x = 4 (3)) and three ring-like Ln-Mn clusters [Ln4Mn4(hmp)4(L)4(H2L)4(CH3CN)(H2O)7](NO3)4·H2O (Ln = Y (4), Gd (5), Dy (6), hmpH = 2-(Hydroxymethyl)pyridine, H3L = 2,2-Bis(hydroxymethyl)butyric acid) have been synthesized in the presence of alcohol ligands. Single X-ray analysis revealed that compounds 1–3 exhibited a zigzag metal core unit of [Y2Mn2(hmp)6]6+ ([Y-Mn-Mn-Y]), which can form a three-dimensional (3D) metal framework via - stacking. Compounds 4–6 formed the ring-shaped metal skeleton of Ln4Mn4 and displayed an ideal metal arrangement with the alternating Ln and Mn ions, which was consistent with the predicted metal arrangement of [-Ln-M-Ln-M-] with weak magnetic interaction. Magnetic investigation showed that 1 displayed significant ferromagnetic interaction and 2–6 displayed dominant antiferromagnetic interaction. Magnetic calculation showed that in 2 the Gd···Mn and Mn···Mn presented an antiferromagnetic interaction and a weak ferromagnetic interaction, respectively. For 5, the Gd···Mn showed a weak antiferromagnetic interaction and the Gd···Gd showed a much weaker ferromagnetic interaction due to the spacing of Gd(III) ions by Mn(III) ions which effectively weaken the antiferromagnetic coupling between Gd3+ ions, in addition, magnetothermal studies showed that 5 displayed magnetic entropy changes of 15.5 J kg–1 K–1 at 3.5 K for ΔH = 7 T.