Tetrahedrally Coordinated sp3-Hybridized Carbon in Sr2CO4 Orthocarbonate at Ambient Conditions

We have synthesized the orthocarbonate Sr2CO4, in which carbon is tetrahedrally coordinated by four oxygen atoms, at moderately high pressures [20(1) GPa] and high temperatures (approximate to 3500 K) in a diamond anvil cell by reacting a SrCO3 single crystal with SrO powder. We show by synchrotron powder X-ray diffraction, Raman spectroscopy, and density functional thoery calculations that this phase, and hence sp(3)-hybridized carbon in a CO44- group, can be recovered at ambient conditions. The C-O bond distances are all of similar lengths [approximate to 1.41(1) angstrom], and the O-C-O angles deviate from the ideal tetrahedral angle by a few degrees only.