High-Pressure Synthesis and Structural Studies of La, Sm, Gd, and Dy Chlorides and Chloride Carbides

High-pressure synthesis provides unique pathways to materials with unprecedented structures and properties. Here we report the synthesis and structural characterization of novel rare-earth (La, Sm, Gd, Dy) chlorides, chloride carbides, and oxychloride phases obtained due to complex chemical reactions in diamond anvil cells after laser heating of rare-earth metals and NaCl at pressures of 39-127 GPa and temperatures of 2500-2800 K. Synchrotron single-crystal X-ray diffraction analysis allowed us to solve previously unknown crystal structures of binary (La₂Cl, LaCl, LaCl₃, DyCl) and ternary (DyNa₂Cl₅, Sm₂ClC₂, Gd₂ClC₂, Dy₂ClC₂, Sm₁₉ClC₁₈, Gd₁₉ClC₁₈, Dy₅Cl₃C, DyOCl) compounds. Significantly, we identified trans-polyacetylene-like carbon chains in lanthanide chloride carbides, a structural motif previously hypothesized but not observed experimentally. Our findings highlight the enhanced chemical reactivity of alkali halides under extreme conditions, uncovering novel chemical bonding and expanding the landscape of potential functional materials accessible through high-pressure synthesis.