Twisted [C₂O₅]²⁻-groups in Ba[C₂O₅] pyrocarbonate

Abstract

Ba[C2O5] was synthesized by reacting Ba[CO3] with CO2 and contains twisted [C2O5]2−-groups, an atomic arrangement previously not observed in carbonates.

High-pressure synthesis of acentric sodium pyrocarbonate, Na2[C2O5]

“…We found that the inorganic pyrocarbonate salt Na 2 [C 2 O 5 ] can be synthesized in analogy to the previously obtained pyrocarbonates, in a LH-DAC using Na 2 [CO 3 ] powder and CO 2 -I (dry ice) as starting materials. 1–3 In comparison to the previous experiments, the synthesis was successful at lower pressure (≈20 GPa) and significantly lower temperatures (≈800(200) K). For the synthesis, Na 2 [CO 3 ] powder was compacted between a diamond and a glass plate.…”

“…1,2 Subsequently, this family was enlarged by the synthesis of Ba[C 2 O 5 ], another pyrocarbonate containing a divalent alkali earth metal cation. 3 Very recently, the synthesis of the mixed carbonate–pyrocarbonate Al 2 [C 2 O 5 ][CO 3 ] 2 showed that pyrocarbonates containing trivalent cations may also be obtained. 4…”

“…It was found that the geometry of the pyrocarbonate group can vary significantly by a tilt of the two planar [CO 3 ] 2− -groups of the [C 2 O 5 ] 2− -complex anion around the common central bridging oxygen atom. 1–4…”

“…Raman modes occurring at these wavenumbers are characteristic for vibrations of a [C 2 O 5 ] 2− -group. 1–4 Hence, we mapped the phase distribution across the gasket hole in order to locate the new pyrocarbonate for the subsequent single crystal X-ray diffraction experiments (Fig. 1c, e and f).…”

“…However, the relative orientation of the two constituent [CO 3 ] 2− -groups differs from those in the other carbonates, showing again that the [C 2 O 5 ] 2− -group is very flexible. 1–4,10,11 In Na 2 [C 2 O 5 ] both Na atoms are irregularly coordinated by 8 oxygen atoms. It is worthwhile to note here, that in the chemically related pyroborate Na 4 [B 2 O 5 ] the two planar [BO 3 ] 4− -groups of the [B 2 O 5 ] 4− -group are also tilted with respect to each other at ambient conditions.…”