ABSTRACT
Dihydrogen bonds (DHBs) play a role in, among others, crystal packing, organometallic reaction mechanisms, and potential hydrogen-storage materials. In this work we have analyzed the central H-H bond in linear H(4), LiH...HX, BH(4)(-)...HX, and AlH(4)(-)...HX complexes with various X by using the quantitative molecular orbital model contained in Kohn-Sham density functional theory at the BP86/TZ2P level of theory. First, we address the questions of if and how one can distinguish, in principle, between a H...H donor-acceptor DHB and the formation of an H(2) molecule by using the simple H(4) model system. The results of these analyses have been used to gain an understanding of the bonding in more realistic model systems (some of which have been studied experimentally), and how this differs from the bonding in H(4).
Subject(s)
Algorithms , Hydrogen/chemistry , Models, Molecular , Hydrogen Bonding , Thermodynamics , Water/chemistryABSTRACT
B3LYP/6-31++G(d,p) and MP2/6-31++G(d,p) calculations for a series of hydrogen- and dihydrogen-bonded systems have been carried out in order to analyze the topology of the electron density and the energy densities at the respective energy-optimized bond critical points. Even though there are no significant differences when these properties are represented as a function of the dimerization energy, they can be separated into two well-defined sets if those properties are correlated with intermolecular distances. When analyzing the dependence of various properties with equilibrium bond lengths, the specific trends of dihydrogen bond systems consist of (a) lower electron density at the bond critical point, and (b) lower concentration/depletion of that density which can be translated in a different behavior for the Laplacian components. Furthermore, the sets of molecules form two different plots which allow for a valuable classification between hydrogen- and dihydrogen-bonded systems.
