Synthesis and crystal structure of two novel polymorphs of (NaCl)[Cu(HSeO₃)₂]: a further contribution to the family of layered copper hydrogen selenites

Abstract

Crystals of two new polymorphic forms of the known compound (NaCl)[Cu(HSeO3)2], which we term polymorphs II and III, were formed after a ca. one-year dwelling of a crystalline precipitate under mother liquor and upon crystallization in the presence of K+, respectively. Both structures belong to the “layered copper hydroselenite” family. The polymorph II is a structural analog of (KCl)[Cu(HSeO3)2] with a fully ordered Na+ site; the main difference concerns the environment of Cu2+ which is more regular in (NaCl)[Cu(HSeO3)2]-II. In contrast to some expectations, crystallization from solutions containing KCl. NaCl, CuCl2, and H2SeO3 upon evaporation does not result in formation of mixed (Na1−x K x Cl)[Cu(HSeO3)2] crystals, but rather in a separate crystallization of (KCl)[Cu(HSeO3)2] and (NaCl)[Cu(HSeO3)2]-III which exhibits a complex structure with four ordered and one disordered Na+ sites. It is possible that longer crystallization times enhance formation of ordered structures.

Protonated Organic Diamines as Templates for Layered and Microporous Structures: Synthesis, Crystal Chemistry, and Structural Trends among the Compounds Formed in Aqueous Systems Transition Metal Halide or Nitrate–Diamine–Selenious Acid

“…A numerous yet sparsely addressed family of mostly inorganic compounds is formed by the "layered hydroselenites", first described by Trombe et al [9][10][11] and further extended in our studies [12][13][14][15] among compounds of copper. Later, some zinc [16], cobalt [17][18][19][20], and cadmium [21] containing species were reported.…”

“…Until clearance, several drops of water were added to keep the solution volume constant. With M = Cu or Cd, which form less soluble selenites, the flaky green and white (respectively) precipitates were dissolved after heating and adding 0.1 to 0.7 mL of trifluoroacetic acid in the case of halides and 0.1–0.5 mL of 50% nitric acid for nitrates, according to the protocols developed earlier [ 13 , 15 ]. (In one or two cases, traces of CdSeO 3 ·aq persisted but dissolved over time when crystals of the targeted compounds started to form.)…”

“…The mean Cd-O separations in the [CdO 4 Br 2 ] (2.335(3) Å) and [CdO 4 Cl 2 ] (2.293(4) Å) in (enH 2 )[M(HSeO 3 ) 2 X 2 ] and (pipH 2 )[Cd(HSeO 3 ) 2 X 2 ] are rather close, yet Cd-X (<Cd-Br> = 2.653 Å, <Cd-Cl> = 2.587 Å). (14), (pipH 2 )[Mn(HSeO 3 )(Se 2 O 5 )] 2 (15), (enH 2 )(H 2 SeO 3 )Br 2 (16) (20), (pipH 2 )(NO 3 ) 2 respectively [21]). Each of the protonated nitrogen atoms of the enH2 2+ cation forms hydrogen bonds: two to the bromide anion and one to the oxygen atoms of two HSeO3 − species (Figure 3c).…”

“…The structures of these compounds contain quasi-planar [ M II (HSeO 3 ) 2 ] 0 layers formed by Cu 2+ cations and hydrogen-bonded dimers of HSeO 3 − anions forming a distorted quasi-square grid. The interlayer space can be either empty, as in Cu(HSeO 3 ) 2 [ 22 ], filled with water molecules, as in Cu(HSeO 3 ) 2 ·2H 2 O [ 9 ], various metal-halide [ 11 , 12 , 13 , 15 , 16 , 17 , 20 ] and metal-nitrate [ 14 ] slabs, or more complex species such as [ M II (H 2 O) 4 ][Cu(HSeO 3 ) 2 Cl 2 ] series ( M II = Mn–Zn, Fe excepted) [ 10 , 18 ] and [Co(H 2 O) 4 ][Co(HSeO 3 ) 2 Cl 2 ] [ 20 ]. It is noteworthy that the bromide analogs of the two latter compounds, as well as alkali–cobalt selenite chlorides [ 17 ], have not been reported, while within the ( A I X )[Cu(HSeO 3 ) 2 ] series ( A I = Na, K, Rb, Cs, NH 4 ) [ 13 ], as well as (Rb X )[Zn(HSeO 3 ) 2 ] [ 16 ], bromides are full structural analogs of the corresponding chlorides.…”