Decanuclear Ln10 Wheels and Vertex-Shared Spirocyclic Ln5 Cores: Synthesis, Structure, SMM Behavior, and MCE Properties

• Published in: Chemistry : a European journal 2015-11, Vol.21 (47), p.16955-16967
• Main Authors: Das, Sourav, Dey, Atanu, Kundu, Subrata, Biswas, Sourav, Narayanan, Ramakirushnan Suriya, Titos-Padilla, Silvia, Lorusso, Giulia, Evangelisti, Marco, Colacio, Enrique, Chandrasekhar, Vadapalli
• Format: Article
• Language: English
• Subjects: Chemistry; lanthanide complexes; ligands; macrocycles; magnetic properties; X-ray diffraction
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201501992

The reaction of a Schiff base ligand (LH3) with lanthanide salts, pivalic acid and triethylamine in 1:1:1:3 and 4:5:8:20 stoichiometric ratios results in the formation of decanuclear Ln10 (Ln=Dy(1), Tb(2), and Gd (3)) and pentanuclear Ln5 complexes (Ln=Gd (4), Tb (5), and Dy (6)), respectively. The formation of Ln10 and Ln5 complexes are fully governed by the stoichiometry of the reagents used. Detailed magnetic studies on these complexes (1–6) have been carried out. Complex 1 shows a SMM behavior with an effective energy barrier for the reversal of the magnetization (Ueff)=16.12(8) K and relaxation time (τo)=3.3×10−5 s under 4000 Oe direct current (dc) field. Complex 6 shows the frequency dependent maxima in the out‐of‐phase signal under zero dc field, without achieving maxima above 2 K. Complexes 3 and 4 show a large magnetocaloric effect with the following characteristic values: −ΔSm=26.6 J kg−1 K−1 at T=2.2 K for 3 and −ΔSm=27.1 J kg−1 K−1 at T=2.4 K for 4, both for an applied field change of 7 T. Homometallic complexes: The reaction of a multidentate flexible Schiff base ligand (LH3; see figure) with [LnCl3]⋅6 H2O affords homometallic decanuclear complexes, [Ln10(LH)10(κ2‐Piv)10] (Ln=Dy, Tb, and Gd), and homometallic pentanuclear complexes, [Ln5(LH)4(μ2‐η1η1Piv)4(η1Piv)(S)] (Ln=Dy, Tb, and Gd). The Dy3+ analogues exhibit single‐molecule magnet (SMM) behavior, whereas the Gd3+ complexes show a significant magnetocaloric effect (MCE).