Infrared spectroscopic study of ions included in K2Me(CrO4)2·2H2O (Me=Mg, Cd) and crystal structure of K2Cd(CrO4)2·2H2O

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

“…Note that this is in contrast to our recent description of the structure of K 2 Cd(CrO 4 ) 2 Á2H 2 O [7], where labels were used analogous to K 2 Mg(CrO 4 ) 2 Á2H 2 O [6] to allow easier comparison and discussion of the IR-spectroscopic features of both compounds (hence, the labels O1, O2, O3, O4, H1, H2 in K 2 Cd(CrO 4 ) 2 Á2H 2 O [7] are related to the present and earlier ones [11] in the following way: O3, O4, O2, O1, H2, H1, respectively). Table 1 compiles crystal data of K 2 Zn(CrO 4 ) 2 Á2H 2 O and details of the data collection and structure refinement.…”

“…The average Cr-O distance of 1.652 Å in K 2 Zn(CrO 4 ) 2 Á2H 2 O complies with crystal chemical expectation and is identical with the type A chromates of Mg [6] and Cd [7]. The sequence of the respective Cr-O bond lengths is identical too, but with a slightly weaker bond-length distortion in the title compound.…”

“…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.…”

“…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]. The spectroscopic experiments reveal that the SO 4 2À guest ions undergo a slightly stronger energetic distortion in the cadmium compound as deduced from the values of Dm 3 and Dm max due to the stronger lattice potential at the respective site in the cadmium matrix owing to the more covalent character of the Cd-O bonds.…”

“…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].…”