Heterometallic Zn3Ln3 Ensembles Containing (μ6‐CO3) Ligand and Triangular Disposition of Ln3+ ions: Analysis of Single‐Molecule Toroic (SMT) and Single‐Molecule Magnet (SMM) Behavior. Issue 65 (25th October 2017)

• Record Type: Journal Article
• Authors: Goura, Joydeb; Colacio, Enrique; Herrera, Juan Manuel; Suturina, Elizaveta A.; Kuprov, Ilya; Lan, Yanhua; Wernsdorfer, Wolfgang; Chandrasekhar, Vadapalli
• Is Part Of: Chemistry. Volume 23:Issue 65(2017)
• Page Start: 16621
• Page End: 16636
• Publication Date: 2017-10-25
• Subjects: heterometallic 3d/4f complexes -- Mannich base ligand -- single-molecule toroic (SMT) -- zero-field SMMs -- Zn2+/Ln3+ complexes; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201703842
• Languages: English
• ISSNs: 0947-6539

Abstract

Abstract: Two new heterometallic Zn3 Ln3 (Ln 3+ =Dy, Tb) complexes, with a double triangular topology of the metal ions, have been assembled from the polytopic Mannich base ligand 6, 6′‐{[2‐(dimethylamino)ethylazanediyl]bis(methylene)}bis(2‐methoxy‐4‐methylphenol) (H2 L) with the aid of an in situ generated carbonate ligand from atmospheric CO2 fixation. Theoretical calculations indicate axial ground states for the Ln 3+ ions in these complexes, with their local magnetic moments being almost coplanar and tangential to the Ln 3+ atoms that define the equilateral triangle. Therefore, they can be considered as single‐molecule toroics (SMTs) with almost zero total magnetic moment. Micro‐SQUID measurements on the Dy 3+ counterpart show hysteresis loops below 3 K that have an S‐shape, with large coercive fields opening upon cooling. This behavior is typical of a single molecule magnet (SMM) with very slow zero‐field relaxation. At around ±0.35 T, the loops have a broad step, which is due to a direct relaxation process and corresponds to an acceleration of the relaxation of the magnetization, also observed at this magnetic field from ac susceptibility measurements. Simulations suggest that the broad step corresponds to two level avoidance of crossing points where the spin chiral Kramers doublet meets excited states of the coupled manifold, whose position is defined by exchange and dipole interactions. The Tb 3+ counterpart does not exhibit SMM behavior, which is due to the fact that the degeneracy of the ground state of the exchange coupled system is lifted at zero field, thus favoring quantum tunneling of magnetization (QTM). Abstract : Eternal triangle : Two new heterometallic Zn3 Ln3 (Ln 3+ =Dy, Tb) complexes, with a double triangular topology of the metal ions held together by an in situ generated carbonate ligand from atmospheric CO2 fixation, have been assembled. Zn3 Dy3 shows single‐molecule toroics (SMTs) and hysteresis loops below 3 K, which have S‐shape with large coercive fields opening upon cooling.