EPR Study on the Intercalation of Azoles into Transition Metal Oxides
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Applied Magnetic Resonance
ORIGINAL PAPER
EPR Study on the Intercalation of Azoles into Transition Metal Oxides E. A. Konstantinova1,2 · A. I. Kokorin3,4 · A. S. Logvinovich5 · T. V. Sviridova5 · E. N. Degtyarev3 · D. V. Sviridov5 Received: 2 April 2020 / Revised: 11 May 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract Four azoles of different chemical structure were intercalated into M oO3, V2O5, and WO3 oxides synthetized via polycondensation of corresponding oxo-acids under the solvothermal conditions. Structural and morphology peculiarities of these hybrid materials were characterized using X-ray and neutron diffraction, electron microscopy and EPR spectroscopy. The EPR measurements provided the evidence that azole molecules coordinate monomers and oligomers of molybdic, tungstic and vanadic acids during the course of solvothermal synthesis of azole-oxide hybrid structures. This coordination is accompanied with reorganization of growing oxide frame leading to the unprecedently high azole loading. As the result, the azole-intercalated layered oxides with high concentration of ordered paramagnetic centers are formed.
1 Introduction Non-compact structure inherent in the layered polymorphs of molybdenum, tungsten and vanadium oxides makes them effective hosts for intercalation of small organic molecules [1–4]. Moreover, the possibility of combining the synthesis of these transition-metal oxides via polycondensation of oxo-compounds [5] with intercalation of guest molecules facilitates formation of organic-oxide hybrid materials with high degree of intercalation which show much promise as the depot medias (analogues of * E. A. Konstantinova [email protected] 1
Physics Department, M.V. Lomonosov Moscow State University, Moscow, Russian Federation
2
National Research Center “Kurchatov Institute”, Moscow, Russian Federation
3
N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, Moscow, Russian Federation
4
Plekhanov Russian University of Economics, Moscow, Russian Federation
5
Chemistry Department, Belarusian State University, Minsk, Republic of Belarus
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the nanocontainer structures). In the case of transition-metal oxides, chemical intercalation is accompanied with coordination of guest molecules that generally leads to the pseudomorphous structural transformations of the oxide host [6, 7]. Intercalative polymerization of aniline, pyrrole or 2,2′-bithiophene in V 2O5 xerogels was shown to be useful method of synthesis of layered composites of metaloxide and conductive polymers as a novel electrically conductive material [8]. Since the driving force for such intercalation materials is redox chemistry, the conductivity type appears to be a function of the polymer/V2O5 xerogel ratio [8]. Polyaniline was inserted in V2O5·nH2O xerogel by oxidative polymerization/ intercalation of aniline or anilinium [9]. The interlayer separation (5.6 Å) was consistent with a monolayer of polyaniline ch
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