A computational study of hydrogen-bonded X3CH center dot center dot center dot YZ (X = Cl, F, NC; YZ = FLi, BF, CO, N-2) complexes

An MP2/6-311++G(3df, 3pd) computational study of a series of hydrogen-bonded complexes X3CH center dot center dot center dot YZ (X = Cl, F, NC; YZ = FLi, BF, CO, N-2) was undertaken to assess the trends in the relative stability and other molecular properties with variation of both the X group and the chemical hardness of the Y atom of YZ. The red-and blue-shifting propensities of the proton donor X3CH were investigated by considering the C-H bond length change and its associated vibrational frequency shift. The proton donor Cl3CH, which has a positive dipole moment derivative with respect to C-H bond extension, tends to form red-shifted complexes, this tendency being modified by the hardness (and dipole moment) associated with the proton acceptor. On the other hand, F3CH has a negative dipole moment derivative and tends to form blue-shifted complexes, suggesting that as X becomes more electron-withdrawing, the proton donor should have a negative dipole moment derivative and form blue-shifted complexes. Surprisingly, the most polar proton donor (NC)(3)CH was found to have a positive dipole moment derivative and produces red-shifted complexes. A perturbative model was found useful in rationalizing the trends for the C-H bond length change and associated frequency shift. (C) 2018 Elsevier B.V. All rights reserved.