Crystal structure and vibrational and luminescence spectra of a new erbium potassium pyrophosphate dihydrate, ErKP2O7⋅2H2O

A new erbium potassium pyrophosphate dihydrate salt, ErKP2O7⋅2H2O, has been synthesized and characterized by single-crystal X-ray diffraction [monoclinic space group P21/c, with unit cell parameters of a=7.6785(10)a=7.6785(10), b=10.4984(14)b=10.4984(14), c=10.0098(13) Åc=10.0098(13) Å, β=93.237(2)°β=93.237(2)°; Z=4Z=4]. One-dimensional heptagonal channels are formed along the slightly inclined a  -axis with the following dimensions: 5.6×6.7 Å5.6×6.7 Å. Perpendicularly, along the c-axis, the erbium and pyrophosphate ions form flattened hexagons channels in which the K+ ions are located together with water molecules. The diameters of the channels are between 4.95 and 5.95 Å. The three-dimensional, open-architecture framework of the new material is built up from connections of the erbium, potassium and pyrophosphates units resulting in the formation of cavities and channels in which the guest water molecules are located. The coincidences observed for the majority of the IR and Raman bands are attributed to site-group splitting. The vibrational spectra have been interpreted in part on the basis of site and factor group effects. In addition, UV-visible and fluorescence spectra of ErKP2O7⋅2H2O have been measured and interpreted.

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