Natural and synthetic compounds with kröhnkite-type chains: review and classification

Abstract

The crystal structure of kröhnkite [Na

Vibrational behavior of ions included in K2Zn(CrO4)2·2H2O and crystal structure of K2Zn(CrO4)2·2H2O: A new structure type containing kröhnkite-type chains

“…The atomic arrangement of K 2 Zn(CrO 4 ) 2 Á2H 2 O represents a new structure type among the large group of compounds [6,8,12] with the general formula Table 1 Crystal data and details of the data collection and structure refinement for [6,8,12,13]), or to the closely related triclinic collinsite structure type P 1,'type A'). Type A comprises, for example, the A-Me-X representatives Na-Co-Se, Na-Zn-Se, K-Co-Se [11], K-Mg-Cr [6], and K-Cd-Cr [7], type D the Na-Cd-S and Na-Cd-Se [11] compounds, whereas K-Cd-Se [14] belongs to the rare triclinic 'type C' ðP 1Þ [8]. Surprisingly, the title compound K 2 Zn(CrO 4 ) 2 Á2H 2 O adopts a further, new monoclinic structure with space group C2/c -designated 'type H' -with closest relationship to type A structures.…”

“…Guillem et al reported that the above compounds crystallize in the triclinic space group P 1 and have similar lattice parameters [5]. Indeed, recent single-crystal X-ray diffraction data of K 2 Mg(CrO 4 ) 2 Á2H 2 O [6] and K 2 Cd(CrO 4 ) 2 Á2H 2 O [7] confirm the statement that both compounds are isostructural and can be assigned to the structural type A (see classification in [8]) of compounds containing kröhnkite-type chains. In our previous paper vibrational spectra (infrared and Raman) of K 2 Me(CrO 4 ) 2 Á2H 2 O (Me = Mg, Cd) as well as infrared spectra of SO 4 2À guest ions included in the chromate matrices are presented and discussed with respect to the Cr-O and S-O stretching modes, respectively [7].…”

Dimensional reduction in zirconium phosphate; from layers to ribbons to chains

“…This type of chain structure can be related to that of krö hnkite-like materials, 34 even though in these compounds the terminal groups are water molecules instead of the fluorine atoms in our compounds. A very similar chain structure was previously described for zirconium phosphate 14 in which the positions of the fluorine atoms are occupied by OH groups [Fig.…”

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

“…Indeed, the ammonium ions are reported to exhibit a wide range of coordination numbers, going from four up to nine; in the latter case they show a strong pseudo-alkali character [16]. According to the structural data the ammonium groups in (NH 4 ) 2 Co(SeO 4 ) 2 ·6H 2 O and (NH 4 ) 2 Zn(SeO 4 ) 2 ·6H 2 O are [4+3] coordinated by oxygen [17]. Our spectroscopic experiments show that both compounds display four bands for ν 4 of the ammonium ions (the spectra will be published in forthcoming papers).…”

“…In our opinion, the difference in the vibrational behavior of the ammonium ions included in both Tutton compounds -sulfate and selenate is due probably to the different proton acceptor strengths of the SO 4 2-and SeO 4 2-ions. The latter are know to form stronger hydrogen bonds than the former [17][18][19]. Infrared spectra of the neat nickel compounds as well as those of the potassium salts containing about 10 mol% ammonium ions in the region of water librations are shown in figure 6.…”