Abstract
A series of five neutral mononuclear lanthanide complexes [Ln(HL)(L)] (Ln = Dy3+, Ho3+ Er3+ and Tb3+) with rigid pentadentate N3O2-type Schiff base ligands, H2LH (1-Dy, 3-Ho, 4-Er and 6-Tb complexes) or H2LOCH3, (2-Dy complex) has been synthesized by reaction of two equivalents of 1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))dibenzohydrazine (H2LH, [H2DAPBH]) or 1,1′-(pyridine-2,6-diyl)bis(ethan-1-yl-1-ylidene))di-4-methoxybenzohydrazine (H2LOCH3, [H2DAPMBH]) with common lanthanide salts. The terbium complex [Tb(LH)(NO3)(H2O)2](DME)2 (5-Tb) with one ligand H2LH was also obtained and characterized. Single crystal X-ray analysis shows that complexes 1–4 have the composition {[Ln3+(HL)−(L)2−] solv} and similar molecular structures. In all the compounds, the central Ln3+ ion is chelated by two interlocked pentadentate ligands resulting in the coordination number of ten. Each lanthanide ion is coordinated by six nitrogen atoms and four oxygen atoms of the two N3O2 chelating groups forming together a distorted bicapped square antiprismatic polyhedron N6O4 with two capping pyridyl N atoms in the apical positions. The ac magnetic measurements reveal field-induced single-molecule magnet (SMM) behavior of the two dysprosium complexes (with barriers of Ueff = 29 K at 800 Oe in 1-Dy and Ueff = 70 K at 300 Oe in 2-Dy) and erbium complex (Ueff = 87 K at 1500 Oe in 4-Er); complex 3-Ho with a non-Kramers Ho3+ ion is SMM-silent. Although 2-Dy differs from 1-Dy only by a distant methoxy-group in the phenyl ring of the ligand, their dynamic magnetic properties are markedly different. This feature can be due to the difference in long-range contributions (beyond the first coordination sphere) to the crystal-field (CF) potential of 4f electrons of Dy3+ ion that affects magnetic characteristics of the ground and excited CF states. Magnetic behavior and the electronic structure of Ln3+ ions of 1–4 complexes are analyzed in terms of CF calculations.
Highlights
Over the past decades, single-molecule magnets (SMMs) [1,2,3,4] have been attracting extensive research interest due to their huge forward-looking applications in the fields of quantum computing, high-density information storage and molecule spintronics [5,6,7]
There has been a report of true PBP (D5h) lanthanide complexes [LnIII(H2L)Cl2]− (Ln = Dy, Tb) with the pentadentate ligand (H2L = 2,6-diacetylpyridine bis-(salicylhydrazone)) in the equatorial plane and two apical Cl atoms; the Dy complex is an SMM with Ueff/kB = 70 K [50]. These results indicate that lanthanide complexes with a rigid five-membered chelate ring in the equatorial plane are a promising avenue for designing SMMs
We report syntheses, structural characterization and magnetic properties of novel neutral mononuclear lanthanide complexes with the general formula [Ln(HL)(L)](solv) (Ln = Dy, Ho, Er, Tb; solv = CH3OH, C2H5OH, H2O, CHCl3), in which the lanthanide ions are doubly chelated by five-membered rings (N3O2) of two pentadentate ligands, H2DAPBH = 2,6-bis(phenylhydrazone)pyridine or H2DAPMBH = 2,6-bis(4-methoxy-benzoylhydrazide)pyridine) resulting in a rather symmetric N6O4 ten-fold coordination
Summary
Single-molecule magnets (SMMs) [1,2,3,4] have been attracting extensive research interest due to their huge forward-looking applications in the fields of quantum computing, high-density information storage and molecule spintronics [5,6,7]. Coordination environment with a high-order symmetry axis can provide axial magnetic anisotropy, which minimize the quantum tunneling of magnetization leading to a high energy barrier Ueff and blocking temperature TB [9,10,11,12,17,18] In this regard, pseudo-linear complexes of heavy lanthanides with strongly donating axial ligands are of particular interest as high-performance SIMs, since they ensure the most advantageous Ising-type CF splitting pattern required for high energy barrier Ueff featuring a well isolated doubly degenerate ground energy level with pure MJ = ±J states and large total CF splitting energy [37]. We present results of static and dynamic magnetic measurements of complexes 1–4, which are analyzed in terms of detailed crystal-field (CF) calculations with the aim to relate magnetic relaxation properties of these complexes to the specific electronic structure of Ln3+ ions and to assess their SMM performance
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
