Double beryllium iodate dihydrates, M2Be(IO3)4·2H2O (M = K, NH4+, Rb): Preparation, X-ray powder diffraction and vibrational spectra

Infrared spectroscopic experiments show that comparatively strong hydrogen bonds are formed in the potassium and rubidium salts as deduced from the wavenumbers of νOD of matrix-isolated HDO molecules (isotopically dilute samples) owing to the strong Be-OH2 interactions (synergetic effect). However, the IO3− ions in the ammonium compound are involved in hydrogen bonds with NH4+ ions additionally to those with water molecules and as a result of these intermolecular interactions the proton acceptor strength of the iodate ions decreases (anti-cooperative effect), thus leading to the formation of weaker hydrogen bonds in this compound (bonds of moderate strength) as compared to those formed in the potassium and rubidium ones. The normal vibrations of other entities (IO3− ions and BeO4 tetrahedra (skeleton vibrations)) are also discussed.