We synthesized two C-S-H compounds from a mixture of carbon and sulfur in hydrogen—$\mathrm{C}:{\left({\mathrm{H}}_2\mathrm{S}\right)}_2{\mathrm{H}}_2$ and from sulfur in mixed methane-hydrogen fluids—${\left(\mathrm{C}{\mathrm{H}}_4\right)}_x{\left({\mathrm{H}}_2\mathrm{S}\right)}_{\left(2-x\right)}{\mathrm{H}}_2$ at 4 GPa. X-ray synchrotron single-crystal diffraction and Raman spectroscopy have been applied to these samples up to 58 and 143 GPa, respectively. Both samples show a similar ${\mathrm{Al}}_2\mathrm{Cu}$-type $I4/mcm$ basic symmetry, while the hydrogen subsystem evolves with pressure via variously ordered molecular and extended modifications. The methane-bearing sample lowers symmetry to an orthorhombic Pnma structure after laser heating to 1400 K at 143 GPa. The results suggest that C-S-H compounds are structurally different from a common $Im\text{−}3m$ ${\mathrm{H}}_3\mathrm{S}$.

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• Chemical bonding
• Composition
• Pressure effects
• Structural properties
• Superconductivity