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

Abstract

4 + guest ions are presented and discussed in the region of the stretching modes m 3 and m 1 of the sulfate ions and in the region of the asymmetric bending modes m 4 of the NH 4 + ions. The SO 4 2À ions matrix-isolated in the selenate matrices (approximately 5 mol%) exhibit three bands for m 3 and one band for m 1 in agreement with the low site symmetry C 1 of the SeO 4 2À host anions. The NH 4 + guest ions included in the potassium matrices are characterized also with three site symmetry components of m 4 (C 1 site symmetry of the K + cations). The spectral regions of m 4 and m 2 of the SO 4 2À guest ions as well as those of m 1 , m 3 and m 2 of the NH 4 + guest ions could not be analyzed precisely due to the overlapping of these motions with motions of other entities in the structures (for example, the normal modes of water molecules and water librations).The extent of energetic distortion of the isomorphously included ions as deduced from the values of Dm 3 and Dm 4 (site-group splitting for the SO 4 2À and NH 4 + guest ions, respectively) and Dm max (the difference between the highest and the lowest components of the stretching modes for the sulfate ions) are commented. The spectroscopic experiments show that the degree of energetic distortion of the guest ions is not affected by the guest ion concentration up to 20 mol%. It has been established that the SO 4 2À guest ions are stronger distorted in (NH 4 ) 2 Mg(SeO 4 ) 2 Á6H 2 O than in K 2 Mg(SeO 4 ) 2 Á6H 2 O (Dm 3 have values of 34 cm À1 in the potassium matrix and 45 cm À1 in the ammonium one; samples containing about 5 mol% sulfate ions, respectively). The formation of hydrogen bonds between the SO 4 2À guest ions and NH 4 + host ions increases the electrostatic field strength at the lattice sites where the guest ions are located, thus leading to a larger extent of energetic distortion of the sulfate ions included in (NH 4 ) 2 Mg(SeO 4 ) 2 Á6H 2 O. The NH 4 + guest ions are stronger distorted in K 2 Mg(SO 4 ) 2 Á6H 2 O than in K 2 Mg(SeO 4 ) 2 Á6H 2 O (Dm 4 have values of 73 cm À1 in the former compound and 66 cm À1 in the latter one) owing to the smaller unit-cell volume of the sulfate than that of the selenate (repulsion potential of the lattice). The analysis of the spectra reveals that the band positions of the water librations in the host compounds are affected by the included NH 4 + guest ions. The formation of hydrogen bonds between the NH 4 + guest ions and the XO 4 2À host ions leads to a decrease in the proton acceptor capabilities of the anions (anti-cooperative or proton acceptor competitive effect) and as a result the hydrogen bonds weaken on going from the neat potassium compounds to mixed crystals K 1.8 (NH 4 ) 0.2 Mg(SO 4 ) 2 Á6H 2 O and K 1.8 (NH 4 ) 0.2 Mg(SeO 4 ) 2 Á6H 2 O (the bands corresponding to water librations broaden and shift to lower frequencies).

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

“…The inclusion of NH 4 + leads to the formation of new hydrogen bonds between the guest cations and the XO 4 2-host ions additionally to those with water molecules, thus resulting in the decrease of the proton acceptor capabilities of the anions (anticooperative or proton acceptor competitive effect). The same phenomenon was observed when ammonium ions are incorporated in the crystals of the respective magnesium and copper Tutton compounds [1,2]. It is worthy of note that the shifts of water librations in the mixed crystals K 2-x (NH 4 ) x Ni(XO 4 ) 2 ·6H 2 O are smaller than those in the respective magnesium compounds K 2-x (NH 4 ) x Mg(XO 4 ) 2 ·6H 2 O and larger than those in the respective copper ones K 2-x (NH 4 ) x Cu(SeO 4 ) 2 ·6H 2 O.…”

“…Recently, we have published infrared spectra of SO 4 2-and NH 4 + ions included in the magnesium and copper Tutton salts [1,2]. The spectroscopic experiments allowed us to draw several main conclusions: (i) The matrixisolated SO 4 2-ions in the structures of the selenate compounds (concentration of the guest ions up to 5-7 mol%) exhibit three infrared bands for ν 3 and one band for ν 1 in good agreement with the low site symmetry C 1 of the host selenate ions.…”

Salt efflorescence in historic wooden buildings

“…However, in the crystal state, the normal modes may shift or split due to various interactions. The above modes can be identified in efflorescence spectra as follows; 1090 and 1170 (ν 3 [27][28][29]. Given the content in metal elements determined by XRF, the occurrence of double sulfate salts in the efflorescence appears as very likely.…”

Template-free preparation and characterization of nanoporous g-C3N4 with enhanced visible photocatalytic activity

“…Clearly, the FTIR spectra of BM-CN and BMP-CN are similar to that of pristine g-C 3 N 4 , which further confirms that the graphitic stacking structure is well-kept after the ball milling and protonation process. Additionally, a new peak at 619 cm À1 is observed which can be ascribed to the SO 4 2À introduced by sulfuric acid [32]. It is worth mentioning that the surface zeta-potential of g-C 3 N 4 is changed from À16.9 to +26 mV although the SO 4 2À absorbed on the surface, further proving a successful protonation (Table S1).…”