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

We have synthesized the orthocarbonate Sr 2 CO 4, in which carbon is tetrahedrally coordinated by four oxygen atoms, at moderately high pressures [20(1) GPa] and high temperatures (≈3500 K) in a diamond anvil cell by reacting a SrCO 3 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 CO 4 4– group, can be recovered at ambient conditions. The C–O bond distances are all of similar lengths [≈1.41(1) Å], and the O–C–O angles deviate from the ideal tetrahedral angle by a few degrees only.