文摘
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 paramagneticvanadyl species, these investigations were done at Q-band frequencies. It was possible to resolveinteractions of the paramagnetic vanadyl ions (VO2+) with all relevant nuclei, 1H, 31P, 51V, and 133Cs. Thelocation of the vanadyl species was studied by determination of the complete 31P hyperfine tensor. Thisapproach was done for both the fresh and the calcined Cs4PVMo11O40 materials, and no differences in thestructures of the VO2+ complexes were found. The ENDOR results give experimental evidence for thelocation of the V(IV) ions. For both samples, it was possible to exclude the incorporation of V(IV) at the Mosites. The VO2+ species are directly attached to the outer surface of the heteropolyanion and coordinatedto four of the outer oxygen atoms with a V-P distance of 3.96 Å.
