Elsevier

Journal of Molecular Structure

Volume 1137, 5 June 2017, Pages 179-185
Journal of Molecular Structure

Syntheses, crystal structure and magnetocaloric effect of [Gd(PDOA)(NO3)(H2O)2]n

https://doi.org/10.1016/j.molstruc.2017.02.028Get rights and content

Highlights

  • Novel complex based on Gd(III) and o-phenylenedioxydiacetato ligand was prepared and characterized.

  • The crystal structure is formed of a ribbon-like arrangement of Gd(III) atoms linked by bridging carboxylate groups.

  • Enhanced magnetocaloric effect was observed suggesting appropriateness of the studied complex for magnetic cooling.

Abstract

The coordination polymer [Gd(PDOA)(NO3)(H2O)2]n (1) (PDOA = o-phenylenedioxydiacetato) has been prepared and spectroscopically and structurally characterized. Its crystal structure is formed of a ribbon-like arrangement of Gd(III) atoms linked by bridging carboxylate groups and placed at the cusps of fused triangles with Gd⋯Gd distances of about 6.1 Å. The Gd(III) central atoms exhibit decacoordination by oxygen atoms from hexadentate PDOA ligands with chelating and bridging functions, a chelating nitrato ligand and two aqua ligands. Intra- and intermolecular hydrogen bonds of the Osingle bondH⋯O and Csingle bondH⋯O types contribute to the stability of the structure. The temperature dependence of the magnetic susceptibility revealed weak magnetic interactions among Gd(III) ions which may be attributed to dipolar coupling. Investigation of the magnetocaloric effect gives an estimate of the maximum value of isothermal change of magnetic entropy –ΔSm ≈ 35 J kg−1 K−1 which suggests that 1 can be a good material for magnetic cooling at low temperatures.

Introduction

The technological limits of current cooling methods, along with environmental considerations, are driving forces for studying the magnetocaloric effect (MCE) [1]. For enhancing the MCE, a high value of the ground state spin, S and high magnetic density are favorable [2]; as a consequence compounds with a Gd(III) (S = 7/2) central atom are good candidates for observation of the MCE [3], [4], [5], [6]. It is generally accepted that Gd(III), like other lanthanoids, prefers coordination by O-donor ligands; this criterion is well fulfilled by the PDOA ligand (PDOA = o-phenylenedioxydiacetato, Scheme 1) with six oxygen atoms, all potential donors. Previously, the PDOA complex {[Gd2(PDOA)3(H2O)6]·2H2O}n with a ladder-like structure was synthesized and chemically and structurally characterized [7], [8]. As a continuation of our previous study on the Ce(III) complex [Ce(PDOA)(NO3)(H2O)2]n [9] we have successfully undertaken the preparation and isolation of the Gd(III) analog [Gd(PDOA)(NO3)(H2O)2]n, and here we report its syntheses and spectral and structural characterization along with the results of its magnetic properties with emphasis on its MCE.

Section snippets

Materials

Gadolinium(III) nitrate hexahydrate Gd(NO3)3·6H2O, o-phenylenedioxydiacetic acid (H2PDOA, C10H10O6), and sodium hydroxide were purchased from commercial sources and used as received.

Syntheses of [Gd(PDOA)(NO3)(H2O)2]n (1)

The syntheses of the title compound was done by two different procedures. First the microcrystalline material was prepared under reflux conditions as follows: a mixture of 0.226 g of Gd(NO3)3·6H2O (0.5 mmol), 0.113 g of H2PDOA (0.5 mmol), 20 ml of ethanol and 1 ml of 1 M water solution of NaOH were heated during 4 h

Preparation and identification of [Gd(PDOA)(NO3)(H2O)2]n (1)

Complex 1 was prepared by two different methods. While the bulk microcrystalline sample was formed under reflux conditions with ethanol as solvent, single crystals suitable for X-ray study were formed under solvothermal conditions. The phase purity and identity of the bulk sample of 1 was checked by comparison of the experimental X-ray powder diffraction pattern with the one calculated on the basis of the known crystal structure (see Fig. 1).

The IR spectrum of 1 is very similar to that of the

Conclusions

In conclusion, we have successfully prepared and chemically and spectroscopically characterized the novel coordination polymer [Gd(PDOA)(NO3)(H2O)2]n (1) (PDOA = o-phenylenedioxydiacetato). The polymeric crystal structure of 1 is built-up of a ribbon-like arrangement of Gd(III) atoms linked by bridging carboxylate groups from PDOA ligands. The chromophore GdO6O2O2 is composed of hexadentate PDOA ligands, a chelating nitrato ligand and two aqua ligands. The investigation of magnetic properties

Supplementary data

CCDC 1519503 (complex 1) contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected].

Acknowledgements

This work was supported by the Slovak grants VEGA (grant No. 1/0063/17) and APVV-14-0073. We thank also the European Union Regional Development Fund (Slovakia) (ITMS: 26220120005) for financial support. Funding from the Spanish Ministry of Science and Innovation under grant MAT2015-68200-C2-1-P, from the European Regional Development Fund, and from the Diputación General de Aragón (E16) is gratefully acknowledged.

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