Density functional theory (DFT) calculations on the structures and stabilities of [C^sub n^O^sub 2^n+1]^sup 2^- and [C^sub n^O^sub 2n+1^]X^sub 2^ polycarbonates containing chainlike (CO^sub 2^)^sub n^ units (n = 2-6; X=H or Li)

The structures and stabilities of chainlike (CO2)n (n = 2-6) polycarbonates, where adjacent C atoms are linked by C-O-C bonds, were investigated at the density functional theory (DFT) level (B3PW91/6-311G(2d,p)), including dicarboxylic dianions, [...]..., and the corresponding acids, [...]H2, and Li salts, [...]Li2. At equilibrium, the most stable systems have Cs, C2, or C2v symmetries. In the gas phase, these dianions are generally metastable with respect to spontaneous ejection of one electron, yet in the presence of counterions they become stabilized, for example, as [...]...(Li+)2 ion pairs. [...]... linkages are also stabilized as dicarboxylic acids, [...]H2; we find the latter to have equilibrium conformations of higher symmetry than previously reported in the literature. To the best of our knowledge, none of the [...]X2 (X = Li or H) compounds with n ≥ 2 have been reported in the experimental literature (albeit, the alkyl esters ... and ... are commercially available). All CO bonds in ... to ... have single- to double-bond character (...140-118 pm), indicating that the [...] moieties are held together by strong chemical forces (in contrast to the weakly bound complexes (CO2)n and (CO2)..., n > 1). Vibrational frequencies were calculated to ensure all conformations were true minima. The IR and Raman intensities show that the high intensity C=O stretching modes (1750 ± 100 cm-1) will help in the spectral characterization of these compounds. Solvation calculations using the polarizable continuum model (PCM) find that ... can be formed via ... + CO2 as well as CO... + CO..., each reaction having ... < 0 in practically all solvents. This result confirms the experimentally observed large solubility of CO2(g) in molten carbonates, ... (M = Li, Na, or K). In contrast, starting with n = 2, the reactions [...]... + CO2 do not proceed spontaneously in any solvent (... > 0). (ProQuest: ... denotes formulae/symbols omitted.)