Mondal Amit Kumar, Jena Himanshu Sekhar, Malviya Amita, Konar Sanjit
Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal-bypass road, Bahuri, Bhopal-462066, Madhya Pradesh, India.
Inorg Chem. 2016 Jun 6;55(11):5237-44. doi: 10.1021/acs.inorgchem.6b00177. Epub 2016 May 19.
A rare class of four tetranuclear lanthanide based quadruple stranded helicates namely, Ln4L4(OH)22·xH2O (Ln = Gd(III)(1), Dy(III)(2) and x = 4, 5 respectively), Er4L4(OH)22·9H2O (3), and Dy4L4(NO3)2·2CH3OH·H2O (4) were synthesized by employing succinohydrazone derived bis-tridentate ligand (H2L) and characterized. Structures of 1-3 are similar to each other except the nature of counterions and number of lattice water molecules. In 4, a distorted nitrate ion was arranged in a hexagonal manner holding four dysprosium centers in a slightly twisted manner. Because of the symmetrical nature of each complex, the C4 axis crosses the center of helicate resulting a pseudo-D4 coordination environment. Each ligand coordinates to lanthanide centers in helical manner forming mixture of left (Λ) and right (Δ) handed discrete units. Complex 1 exhibits antiferromagnetic exchange interaction between nearby Gd(III) centers and shows magnetic refrigeration (-ΔSm = 24.4 J kg(-1) K(-1) for ΔH = 7 T at 3 K). AC magnetic susceptibility measurements of 2 and 4 demonstrate slow relaxation behavior, with Ueff (effective energy barrier) of 20.5 and 4.6 K, respectively. As per our knowledge, complexes 1, 2, and 4 represent the first examples of aesthetically pleasing quadruple stranded helicates showing potential magnetocaloric effect and single-molecule-magnet-like behavior.
合成并表征了一类罕见的四核镧系四重螺旋配合物，即Ln₄L₄(OH)₂₂·xH₂O（Ln = Gd(III)(1)，Dy(III)(2)，x分别为4、5），Er₄L₄(OH)₂₂·9H₂O(3)，以及Dy₄L₄(NO₃)₂·2CH₃OH·H₂O(4)，该配合物采用琥珀酰腙衍生的双三齿配体(H₂L)合成。除抗衡离子的性质和晶格水分子的数量外，1-3的结构彼此相似。在4中，一个扭曲的硝酸根离子以六边形方式排列，以略微扭曲的方式容纳四个镝中心。由于每个配合物的对称性质，C₄轴穿过螺旋配合物的中心，形成伪D₄配位环境。每个配体以螺旋方式与镧系中心配位，形成左手(Λ)和右手(Δ)离散单元的混合物。配合物1在相邻的Gd(III)中心之间表现出反铁磁交换相互作用，并显示出磁制冷（在3K时，对于ΔH = 7T，-ΔSm = 24.4J kg⁻¹ K⁻¹）。对2和4的交流磁化率测量表明存在慢弛豫行为，有效能垒Ueff分别为20.5K和4.6K。据我们所知，配合物1、2和4代表了美观的四重螺旋配合物的首个实例，显示出潜在的磁热效应和类单分子磁体行为。
