title: Lanthanide-Directed Fabrication of Four Tetranuclear Quadruple Stranded Helicates Showing Magnetic Refrigeration and Slow Magnetic Relaxation.
abstract: A rare class of four tetranuclear lanthanide based quadruple stranded helicates namely, [Ln4L4(OH)2](OAc)2·xH2O (Ln = Gd(III)(1), Dy(III)(2) and x = 4, 5 respectively), [Er4L4(OH)2](NO3)2·9H2O (3), and [Dy4L4(NO3)](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.
authors.affiliation: Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal-bypass road, Bahuri, Bhopal-462066, Madhya Pradesh, India.
authors.forename: Amit Kumar
authors.initials: AK
authors.lastname: Mondal
authors.affiliation: Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal-bypass road, Bahuri, Bhopal-462066, Madhya Pradesh, India.
authors.forename: Himanshu Sekhar
authors.initials: HS
authors.lastname: Jena
authors.affiliation: Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal-bypass road, Bahuri, Bhopal-462066, Madhya Pradesh, India.
authors.forename: Amita
authors.initials: A
authors.lastname: Malviya
authors.affiliation: Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal-bypass road, Bahuri, Bhopal-462066, Madhya Pradesh, India.
authors.forename: Sanjit
authors.initials: S
authors.lastname: Konar