Massive dihydrogen uptake by anionic carbon chains

Abstract

Acetylene and polyyne carbon chains show a negligible ability to bind even a single dihydrogen molecule. M06L/6-311++G(d,p) DFT and CCSD(T)/aug-cc-pVTZ//CCSD/aug-cc-pVDZ calculations corroborate that these carbon chains in the first deprotonated anionic and second deprotonated dianionic forms display massive dihydrogen uptake capabilities (45.3 to 62.8 wt%). The coordinatively saturated complexes of these anions and dianions with chain lengths of up to six carbons hold 20–32 H₂ molecules. The interaction energy (E_int) values of the saturated state of the monoanions (44.5–50.0 kcal mol⁻¹) and dianions (79.8–87.4 kcal mol⁻¹) indicate substantial energetic stabilization per H₂ molecule adsorbed. The binding of H₂ to the carbon chain is established by the observation of bond critical points in the electron density analysis. The noncovalently bonded interconnections of the adsorbed H₂ molecules indicated by H₂⋯H₂ bond critical points, provide additional stability to the complex keeping the system a fully noncovalently allied entity. Further, molecular electrostatic potential analysis (MESP) is conducted to study the delocalization of the extra electron(s) over the entire complex.