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Please use this identifier to cite or link to this item: http://repository.iitr.ac.in/handle/123456789/12163
Title: Phosphonate-assisted tetranuclear lanthanide assemblies: Observation of the toroidic ground state in the TbIII analogue
Authors: Biswas S.
Kumar P.
Swain, Abinash Kumar
Gupta T.
Kalita P.
Kundu S.
Rajaraman G.
Chandrasekhar V.
Published in: Dalton Transactions
Abstract: The reaction of LnCl3·6H2O with a multidentate flexible Schiff base ligand (LH4), H2O3PtBu and trifluoroacetic acid (tfaH) afforded a series of homometallic tetranuclear complexes, [Ln4(LH2)2(O3PtBu)2(μ2-η1η1tfa)2][2Cl] (Ln = DyIII (1), TbIII (2) and GdIII (3)). The tetranuclear lanthanide core contains two structurally different lanthanide centres, one being in a distorted trigonal dodecahedron geometry and the other in a distorted trigonal prism. Complexes 1-3 were investigated via direct and alternating current (DC and AC) magnetic susceptibility measurements. Only 1 revealed a weak single-molecule magnet (SMM) behaviour. Alternating current (ac) magnetic susceptibility measurements on 1 reveal a frequency-dependent out-of-phase signal. However, the absence of distinct maxima in the χ′′ peak (within the temperature/frequency range of our experiments) prevented deduction of the experimental energy barrier for magnetization reversal (Ueff) and the relaxation time. We have carried out extensive ab initio (CASSCF + RASSI-SO + SINGLE-ANISO + POLY-ANISO) calculations on complexes 1-2 to gain deeper insights into the nature of magnetic anisotropy. Our calculations yielded only one exchange coupling parameter between the two LnIII centres bridged by the ligand (neglecting the exchange between the LnIII centres that are not proximal wrt each other). All the extracted J values indicate a weakly antiferromagnetic coupling between the metal centres (J = -0.025 cm-1 for 1 and J = -0.015 cm-1 for 2). Calculated exchange coupled Ucal values of ∼5 and ∼1 cm-1 in 1 and 2 respectively nicely corroborated the experimental observations regarding weak and no SMM characteristics. Our calculations indicated the presence of a net single-molecule toroidal (SMT) behaviour in complex 2. On the other hand, fitting the magnetic data (susceptibility and magnetization) in the isotropic cluster 3 revealed weak AFM exchange couplings of J1 = 0.025 cm-1 and J2 = -0.020 cm-1 which are consistent with those for GdIII ions. © 2019 The Royal Society of Chemistry.
Citation: Dalton Transactions (2019), 48(19): 6421-6434
URI: https://doi.org/10.1039/c9dt00592g
http://repository.iitr.ac.in/handle/123456789/12163
Issue Date: 2019
Publisher: Royal Society of Chemistry
ISSN: 14779226
Author Scopus IDs: 57202213070
57212043583
57193695689
7103271054
57192302207
56478153200
6602194731
7006003609
Author Affiliations: Biswas, S., Department of Geo-Chemistry, Keshav Deva Malaviya Institute of Petroleum Exploration, Dehradun, 248915, India
Kumar, P., Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
Swain, A., Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India
Gupta, T., Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India
Kalita, P., School of Chemical Sciences, National Institute of Science Education and Research Bhubaneswar, HBNI, Jatni, Khurda, 752050, India
Kundu, S., Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India
Rajaraman, G., Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, 400076, India
Chandrasekhar, V., Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, 208016, India, Tata Institute of Fundamental Research, Gopanpally, Hyderabad, 500 107, India
Funding Details: We thank the Department of Science and Technology (DST), India, for financial support, including support for a Single Crystal CCD X-ray Diffractometer facility at IIT-Kanpur. V. C. is grateful to the DST for a J. C. Bose fellowship. GR thanks the SERB (EMR/2014/000247) for the financial support. TG and AS thank the UGC for a fellowship.
Corresponding Author: Rajaraman, G.; Department of Chemistry, Indian Institute of Technology BombayIndia; email: rajaraman@chem.iitb.ac.in
Appears in Collections:Journal Publications [ME]

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