Vibrational behavior of matrix-isolated ions in Tutton compounds IV. Infrared spectroscopic study of NH₄+ and SO₄2- ions included in nickel sulfates and selenates

摘要

Infrared spectra of K₂Ni(SeO₄)₂·6H₂O and (NH₄)₂Ni(SeO₄)₂·6H₂O containing SO₄2- ions and those of K₂Ni(SO₄)₂·6H₂O and K₂Ni(SeO₄)₂·6H₂O containing NH₄+ ions are presented and discussed in the region of ν₃ and ν₁ of the sulfate ions and in the region of ν₄ of the NH₄+ ions, respectively. The SO₄2- ions matrix-isolated in the selenate matrices (approximately 1 mol%) exhibit three bands for ν₃ and one band for ν₁ in agreement with the low site symmetry C₁ of the host selenate ions. The NH₄+ guest ions included in the potassium sulfate matrix are characterized also with three bands for ν₄. However, the ammonium ions in (NH₄)₂Ni(SeO₄)₂·6H₂O as well as those included in K₂Ni(SeO₄)₂·6H₂O display four infrared bands corresponding to ν₄ due probably to some kind of disorder of the ammonium ions. The extent of energetic distortion of the isomorphously included sulfate ions as deduced from the values of Δν₃ and Δν_max is commented. The spectroscopic experiments reveal that the SO₄2- guest ions are weaker distorted in the selenate matrices as compared to the same ions in the neat sulfates due to the larger unit-cell volumes of the selenate compounds. The band positions of the water librations in the host potassium compounds are affected by the included ammonium cations. The formation of hydrogen bonds between the NH₄+ guest ions and the XO₄2- host ions leads to a decrease in the proton acceptor capabilities of the anions and as a result the hydrogen bonds weaken on going from the neat potassium compounds to the mixed crystals. (? 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)