C−H···X Hydrogen Bonds of Acetylene, Ethylene, and Ethane with First- and Second-Row Hydrides

Abstract

The structures and binding energies of a series of C−H···X hydrogen-bonded complexes involving acetylene, ethylene, and ethane as proton donors and the first- and second-row hydrides CH4, NH3, OH2, FH, PH3, SH2, and ClH as proton acceptors have been determined. Geometries were optimized with both the MP2 and the B3-LYP methods in conjuction with the 6-311+G(3df,2p) basis set. In general, we note good agreement between MP2 and B3-LYP hydrogen-bonded structures. However, for some very weakly bound complexes larger differences exist, particularly in the r(H···X) distance, and in these instances the MP2 results are determined (from comparative CCSD(T) calculations) to be more reliable. The CCSD(T)/6-311+G(3df,2p) binding energies (De), which include corrections for basis set superposition errors, are very similar for the MP2 and B3-LYP geometries, reflecting the relative insensitivity of De to geometry for weakly bound complexes. The C−H···X hydrogen-bond strength (D0) shows a considerable dependence on the a...