High-Pressure Selective Topotactic Synthesis of Ordered Trans-Polymeric CS₂ in a Zeolite

High-pressure polymerization of CS₂ leads to structurally and stoichiometrically disordered solids, making characterization of the products and of reaction mechanisms challenging. This is due to the multiplicity of chemical pathways that CS₂ is subject to in the free space. We reduced this multiplicity by constraining polymerization in a confined space. We inserted liquid CS₂ in the one-dimensional pores of the all-siliceous zeolite Theta-One, subjected the mixture to maximum temperatures and pressures of 250 °C and 14 GPa, and recovered a darkened sample at ambient conditions. Synchrotron X-ray diffraction was performed on the materials. Full structural refinements, using ab initio calculated structures as starting models, show that CS₂ in the zeolite undergoes selective topotactic polymerization, resulting in the ordered trans-isomer of the long-sought-after Bridgman's black polymer (-(C═S)-S-)_<i>n</i>. We provide physical insight into the reaction mechanism by proposing that it consists of a molecular bending followed by addition. The trans-polymer forms spontaneously from the unstable, confined monomer upon relaxation in ab initio calculations.