A Q- and X-Band Pulsed Electron Nuclear Double Resonance Study of the Structure and Location of the Vanadyl Ions in the Cs Salt of Heteropolyacid PVMo11O40

• Published in: Journal of the American Chemical Society Vol. 126; no. 9; pp. 2905 - 2911
• Main Authors: Gutjahr, Marlen, Hoentsch, Joachim, Böttcher, Rolf, Storcheva, Oksana, Köhler, Klaus, Pöppl, Andreas
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 10.03.2004
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron-nuclear double resonance (endor), electron double resonance (eldor); Exact sciences and technology; Magnetic double resonances and cross effects; Magnetic resonances and relaxations in condensed matter, mössbauer effect; Physics; Hyperfine structure; Heteropoly acids; Electronic structure; Hyperfine coupling constant; Cesium compounds; ENDOR spectrometry; Experimental study; Electron localization; Alkali metals Compounds
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja030576z

The location and coordination geometry of vanadium(IV) ions in the cesium salt of molybdovanadophosphoric heteropolyacid Cs4PVMo11O40 were studied using orientation-selective pulsed ENDOR (electron nuclear double resonance) experiments. To enhance the orientation selectivity for the paramagnetic vanadyl species, these investigations were done at Q-band frequencies. It was possible to resolve interactions of the paramagnetic vanadyl ions (VO2+) with all relevant nuclei, 1H, 31P, 51V, and 133Cs. The location of the vanadyl species was studied by determination of the complete 31P hyperfine tensor. This approach was done for both the fresh and the calcined Cs4PVMo11O40 materials, and no differences in the structures of the VO2+ complexes were found. The ENDOR results give experimental evidence for the location of the V(IV) ions. For both samples, it was possible to exclude the incorporation of V(IV) at the Mo sites. The VO2+ species are directly attached to the outer surface of the heteropolyanion and coordinated to four of the outer oxygen atoms with a V−P distance of 3.96 Å.