Abstract
In the presented research, we address the original concept of resonance-assisted hydrogen bonding (RAHB) by means of the many-body interaction approach and electron density delocalization analysis. The investigated molecular patterns of RAHBs are open chains consisting of two to six molecules in which the intermolecular hydrogen bond stabilizes the complex. Non-RAHB counterparts are considered to be reference systems. The results show the influence of the neighbour monomers on the unsaturated chains in terms of the many-body interaction energy contribution. Exploring the relation between the energy parameters and the growing number of molecules in the chain, we give an explicit extrapolation of the interaction energy and its components in the infinite chain. Electron delocalization within chain motifs has been analysed from three different points of view: three-body delocalization between C=C-C, two-body hydrogen bond delocalization indices and also between fragments (monomers). A many-body contribution to the interaction energy as well as electron density helps to establish the assistance of resonance in the strength of hydrogen bonds upon the formation of the present molecular chains. The direct relation between interaction energy and delocalization supports the original concept, and refutes some of the criticisms of the RAHB idea.
Highlights
The hydrogen bond is one of the most important noncovalent interactions that occur in nature
We have investigated the strength of hydrogen bonding for selected systems taken part of the chain, as well as in the delocalization indices
The NPA charges for the atoms from crystal structures, which are the open-chain motifs of proton donating and accepting involved in hydrogen bond formation are represented, with the more polarized centres coupled through a sequence of formally double and single bonds, forming the bonds being the most central ones
Summary
The hydrogen bond is one of the most important noncovalent interactions that occur in nature. The so-called charge-assisted H-bonds (CAHBs) [9,10,11,12,13,14,15] may link molecular fragments, with their strength being sometimes close to that of covalent interactions, which, for instance, take place in the so-called salt bridges, CAHB(+/−) [16], mostly due to their dominant electrostatic contribution to the interaction energy [17]. Another type of H-bond assisted by additional effects is the polarisationassisted H-bond (PAHB), in which the additional strengthening of the H-bridging occurs due to the additional polarisation of interacting fragments (molecules) and the presence of adjacent molecular entities.
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