Abstract
The title carbonate hydrate, Cs2Mg4(CO3)5·10H2O, was crystallized at room temperature out of aqueous solutions containing caesium bicarbonate and magnesium nitrate. Its monoclinic crystal structure (P21/n) consists of double chains of composition 1 ∞[Mg(H2O)2/1(CO3)3/3], isolated [Mg(H2O)(CO3)2]2- units, two crystallographically distinct Cs+ ions and a free water mol-ecule. The crystal under investigation was twinned by reticular pseudomerohedry.
Highlights
Up to now, only two magnesium salts containing hydrogenbiscarbonate anions [H(CO3)23–] were known, viz. KMgH(CO3)2Á4H2O and RbMgH(CO3)2Á4H2O
Each of the magnesium cations Mg1, Mg3 and Mg4 forms [Mg(H2O)2(CO3)3]4– units that are linked by bridging carbonate anions of the carbon atoms C1, C2 and C3 (Fig. 2)
The symmetry of the carbonate anions deviates significantly from ideal D3h; the sum of all O—C—O angles remains 360 and planarity is kept, which is typical for all carbonate structures (Zemann, 1981; Cirpus, 1997)
Summary
Only two magnesium salts containing hydrogenbiscarbonate anions [H(CO3)23–] were known, viz. KMgH(CO3)2Á4H2O and RbMgH(CO3)2Á4H2O. Each of the magnesium cations Mg1, Mg3 and Mg4 forms [Mg(H2O)2(CO3)3]4– units that are linked by bridging carbonate anions of the carbon atoms C1, C2 and C3 (Fig. 2). The water molecules are located in the trans-positions and have no bridging character In this way, double chains of composition 11[Mg(H2O)2/1(CO3)3/3] are formed, extending parallel to the [101] direction (Fig. 3). In comparison with other crystal structures containing carbonate units and deposited in the Inorganic Structure Database (ICSD; Zagorac et al, 2019), these deviations of the bond lengths and angles from ideal values of a equilateral triangle are not unusual (Cirpus, 1997). The coordination numbers of the caesium cations are [6 + 12] for Cs1 and [7 + 6] for Cs2, whereby the first numeral indicates the number of the coordinating O atoms
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