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

Abstract

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 (≈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 sp3-hybridized carbon in a CO4 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.

Orthocarbonates of Ca, Sr, and Ba—The Appearance of sp3-Hybridized Carbon at a Low Pressure of 5 GPa and Dynamic Stability at Ambient Pressure

“…The experimental work performed by Spahr and co-authors, who appeared after this manuscript’s submission, provides unambiguous confirmation of the unexpected fact of dynamic stability of sp 3 orthocarboantes at ambient pressure.…”

Fe3+ -hosting carbon phases in the deep Earth

“…Calculations in which a low spin state was imposed gave too small lattice parameters, which differed markedly from the experimental values. Similar to recent results on other carbonates in which the carbon is fourfold coordinated by oxygen [24,25], the DFT calculations show that all C-O bonds are covalent, with bond populations ranging from 0.8-0.6 e − /Å 3 . The carbon atoms are therefore tetrahedrally coordinated by oxygen and thus sp 3 hybridized.…”

“…These investigations allowed us to derive an understanding of pressure-induced structural phase transitions and changes in the structure-property relations and the electronic state, depending on thermodynamic conditions and composition [7][8][9][10][11][12][13][14][15]. Only recently has it been shown that carbonates in which carbon is tetrahedrally coordinated by oxygen atoms, i.e., sp 3 -hybridized carbon, are stable at high pressures [16][17][18][19][20][21][22][23][24][25]. Specifically, at conditions prevalent in the deeper mantle with pressures >50 GPa, siderite (FeCO 3 ) transforms via self-oxidation-reduction reactions into new phases containing sp 3 carbon [19][20][21][22].…”

Sr3[CO4]O Antiperovskite with Tetrahedrally Coordinated sp3-Hybridized Carbon and OSr6 Octahedra

“…28 In addition to the established orthoanions, it was recently predicted and experimentally shown that carbonates with [CO 4 ] 4− groups may even be recovered at ambient conditions. 21,25 Further, stable structures with stoichiometries M 2 [CO 4 ] and M 3 [CO 4 ]O (M = Mg, Ca, Sr, and Ba) have been predicted by DFT-based calculations. 22−25 Here, we report the successful outcome of the synthesis of one of these structures using M = Sr.…”