From molecular to polymeric CO2: bonding transformations under pressure

Abstract

The chain of bonding changes induced by pressure in molecular phases of CO2 is analyzed in order to shed light into the controversial process of polymerization of simple molecular crystals under pressure. The evolution of the bonding network in the pseudo-molecular CO2-II phase is found to point towards an incipient stabilization of six-fold coordinated carbon at high pressure (stishovite-like) as proposed by Iota et al. [V. Iota, C.-S. Yoo, J.-H. Klepeis, Z. Jenei, W. Evans, and H. Cynn, Nat. Mater. 6 (2007), pp. 34–38]. The relevance of secondary interactions in the polymerization is identified as a polarization of the oxygen lone pairs that gives rise to a synchronic birth of a new intermolecular C− O bond along with the weakening of the intramolecular (C= O) double bond. These results have been derived thanks to a new computational code developed in our laboratory that allows us to perform general topological analysis of the electron localization function in crystalline solids.