A Tug of War between the Self‐ and Cross‐associating Hydrogen Bonds in Neutral Ammonia‐Water Clusters: Energetic Insights by Molecular Tailoring Approach

Abstract

In the present work, the energies of various types of individual HBs observed in neutral (NH3)m(H2O)n, (m+n=2 to 7) clusters were estimated using the molecular tailoring approach (MTA)‐based method. The calculated individual HB energies suggest that the O−H…N HBs are the strongest (1.21 to 12.49 kcal mol−1). The next ones are the O−H…O (3.97 to 9.30 kcal mol−1) HBs. The strengths of N−H…N (1.09 to 5.29 kcal mol−1) and N−H…O (2.85 to 5.56 kcal mol−1) HBs are the weakest. The HB energies in dimers also follow this rank ordering. However, the HB energies in dimers are much smaller than those obtained by the MTA‐based method due to the loss in cooperativity contribution in the dimers. Thus, the calculated cooperativity contributions, for different types of HBs, fall in the range 0.64 to 5.73 kcal mol−1. We wish to emphasize based on the energetic rank ordering obtained by the MTA‐based method that the O−H of water is a better HB donor than the N−H of ammonia. The reasons for the observed energetic rank ordering are two folds: (i) intrinsically stronger O−H…N HBs than the O−H…O ones as revealed by dimer energies and (ii) the higher cooperativity contribution in the former than the later ones. Indeed, the MTA‐based method is useful in providing the missing energetic rank ordering of various type of HBs in neutral (NH3)m(H2O)n clusters, in the literature.

Two-Step ONIOM Method for the Accurate Estimation of Individual Hydrogen Bond Energy in Large Molecular Clusters

“…In this regard, a method based on the molecular tailoring approach (MTA) was developed by Deshmukh and Gadre for the estimation of individual intramolecular HB energies in a wide variety of molecules and complexes. − Ahirwar et al extended this fragmentation methodology (hereafter mentioned as the MTA-based method) for estimating the individual HB energies and cooperativity in various molecular clusters. These include clusters of water (W n , n = 3 to 20), , benzene (Bz) n , ammonia (NH 3 ) n , hydrogen fluoride (HF) n , (HF) m (W) n , methanol–water (MeOH) m (W) n , and (NH 3 ) m (W) n . Furthermore, invoking the bond additivity principle, these estimated HB energies by the MTA-based method were shown to be reliable.…”

“…These include clusters of water (W n , n = 3 to 20), 31,32 benzene (Bz) n , 33 ammonia (NH 3 ) n , 34 hydrogen fluoride (HF) n , 35 (HF) m (W) n , 36 methanol−water (MeOH) m (W) n , 37 and (NH 3 ) m (W) n . 38 Furthermore, invoking the bond additivity principle, these estimated HB energies by the MTA-based method were shown to be reliable. For this purpose, the molecular energy of a given cluster was approximately obtained as a numerical addition of the sum of monomer energies and the sum of HB energies in a given cluster.…”

Interplay of Hydrogen, Pnicogen, and Chalcogen Bonding in X(H2O)n=1–5 (X = NO, NO+, and NO–) Complexes: Energetics Insights via a Molecular Tailoring Approach

“…The schematic fragmentation procedure for the estimation of energy of a hydrogen bond HB5 in a representative neutral NO­(H 2 O) 4 complex (denoted as M) by using the MTA-based method − is demonstrated in Scheme . Herein, four water molecules are indicated as W1, W2, W3, and W4.…”

“…Nonetheless, no direct information is available in the literature about the energetics of individual noncovalent interactions. By using the cardinality principle, Deshmukh and Gadre developed a fragmentation-based method, the molecular tailoring approach (MTA), for estimating individual intramolecular hydrogen bond energy (IHBE) in various systems. − Deshmukh and co-workers extended this methodology to assess the individual interaction energy and cooperativity in different molecular clusters. − They investigated the interactions in the molecular complexes formed by small molecules, such as HF, NH 3 , CH 3 OH, etc., with water clusters using the MTA-based method. The solute molecule binds water through the HBs in all of these clusters, and these individual HB energies were directly estimated.…”

On the Short-Range Nature of Cooperativity in Hydrogen-Bonded Large Molecular Clusters

“…To understand the nature of cooperativity in a given three-dimensional (3D) molecular cluster, the quantitative estimates of the individual HB strength and the cooperativity contribution of other HBs toward them are essential. With this understanding, Deshmukh and Gadre developed a method, based on the molecular tailoring approach (MTA), for estimating individual intramolecular HB energy in various molecular systems. − Ahirwar and Deshmukh extended this methodology (hereafter called as MTA-based method) for estimating the individual HB energies and cooperativity in a variety of molecular clusters. − This MTA-based methodology was tested for the energetics of individual HBs in the following clusters: [(H 2 O) n , n = 3 to 20], − benzene (Bz) n , ammonia (NH 3 ) n , hydrogen fluoride (HF) n , (HF) m (H 2 O) n , methanol–water (MeOH) m (H 2 O) n , and (NH 3 ) m (H 2 O) n clusters. Furthermore, the reliability of HB energies estimated by using the MTA-based method was examined by invoking the bond additivity principle.…”