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.

Modulating the Slow Relaxation Dynamics of Binuclear Dysprosium(III) Complexes through Coordination Geometry

“…From comparative point of view, even though 1 and 2 contain two Dy III centers, their relaxation dynamic behaviors are considerably different. The difference was attributed to the slight changes in the coordination environments around the Dy III centers [19,27,[40][41][42]. This is due to the nature and symmetry of crystal field which controls anisotropy and effects on overall effective energy barrier [43][44][45][46][47].…”

Zero Field SMM Behavior and Magnetic Refrigeration in Rare Heterometallic Double Stranded Helicates of Cu2Ln2 (Ln = Dy, Tb, Gd)

“…The chain can twist during molecular self‐assembly and offers different binding modes to metal centers. Recently, it has been found that H 4 L 1 can coordinate with Ln III ions and gives rise to helical complexes . Besides, the fact that H 4 L 1 has four labile protons [two –OH and two –C(O)–NH– protons] may also lead to versatile deprotonated states depending on the reaction conditions.…”

“…The total length of the helical strand is 13.71 (9) Å with an average pitch of 11.8 Å. [22b] Hydrazine N of [–C(O)NH–] group forms intramolecular H‐bonding (Table S7) with phenolate oxygen from L 2 (N–H ··· O, 2.76 Å). Apart from H‐bonding, C–H ··· π and C–H ··· O interactions support crystal packing arrangements (Figure S2–S3).…”

“…Nevertheless, out of phase signal ( χ M ′′) for complex 4 did not show any peak maxima at the mentioned temperature range. Thus Debye model equation[22a] was used to evaluate the energy barrier and relaxation time (eqn. 2) ln ( χ ′′/ χ ′) = ln ( ωτ 0 ) + U eff / KT (Figure S20).…”

Pseudohalide-directed Assembly of Two Zinc(II) Coordination Polymers with a 3,4-Bis(3-pyridyl)-5-(4-pyridyl)-1,2,4-triazole Tecton

“…Recently, investigations on the synthesis and explorations of novel coordination compounds with well‐defined properties are a major field of chemical research . A rational design of these arrays implies that the combination of organic components and metal ions has allowed us to access a variety of new material with intriguing architectures and promising applications such as catalysis, luminescence, magnetism, optics, and molecular storage .…”