The additive properties of the electron density at the bond critical points in hydrogen-bonded complexes (original) (raw)
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A density functional study of weakly bound hydrogen bonded complexes
Chemical physics, 1998
. Ž . Density functional theory DFT calculations with B3LYP exchange-correlation functional and using 6-31 qqG d,p Ž . basis functions have been performed on weakly bound hydrogen bonded complexes between HX X s F,Cl and alkenes and Ž . alkynes, such as C H , C HX X s H,F,Cl , C H and allene. Calculations have also been carried out at MP2 s full level 2 4 2 4 2 of theory and using the same basis set as mentioned above for comparison with the DFT results. It has been observed that the BSSE uncorrected binding energies obtained from the B3LYP calculations are always lower than the corresponding MP2 results whereas opposite trend has been observed after BSSE correction. Hydrogen bond lengths obtained from MP2 and B3LYP calculations differ insignificantly. The H-X frequency shift due to complex formation has been well reproduced by the B3LYP method. q 1998 Elsevier Science B.V. All rights reserved. 0301-0104r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 3 0 1 -0 1 0 4 9 8 0 0 1 1 1 -6
Journal of The American Chemical Society, 1975
Hydrogen-bonded dimers involving first-and second-row hydrides have been studied theoretically with ab initio molecular orbital methods, using a 431G basis set. Certain generalizations about H-bonded dimers found in a previous stu-dyZa of first-row dimers (those involving "3, H20, and HF) are supported by this study; others require modification. In addition to studying the dependence of H-bond energy and properties on the row of the periodic table, we examine the dependence of H-bond energies on the "hybridization" of the electron donor, including HCN, H2C0, H2CS, HNC, and HCP as electron donors. We have also studied ionic H bonds, ''P" H bonds, and H-bonded trimers in an attempt to relate their properties to those of the more conventional H-bonded dimers. Can a C-H bond be an effective H-bond proton donor? We attempt to answer this question by examining the proton donor ability of CH4 and CHF3. Electrostatic potentials turn out to facilitate our understanding of H-bond energies and structures, being more useful than Mulliken populations in rationalizing H-bond energies. Finally we address ourselves to the question of predicting dimer H-bond energies from the monomers involved. Using a very simple algebraic model, we are able to predict the H-bond energy of a total 144 H-bonded complexes, using as a basis our theorctical calculations on 25 complexes.
A Molecular Electrostatic Potential Analysis of Hydrogen, Halogen, and Dihydrogen Bonds
Hydrogen, halogen, and dihydrogen bonds in weak, medium and strong regimes (<1 to ∼60 kcal/mol) have been investigated for several intermolecular donor−acceptor (D-A) complexes at ab initio MP4//MP2 method coupled with atoms-in-molecules and molecular electrostatic potential (MESP) approaches. Electron density ρ at bond critical point correlates well with interaction energy (E nb ) for each homogeneous sample of complexes, but its applicability to the entire set of complexes is not satisfactory. Analysis of MESP minimum (V min ) and MESP at the nuclei (V n ) shows that in all D-A complexes, MESP of A becomes more negative and that of D becomes less negative suggesting donation of electrons from D to A leading to electron donor−acceptor (eDA) interaction between A and D. MESP based parameter ΔΔV n measures donor−acceptor strength of the eDA interactions as it shows a good linear correlation with E nb for all D-A complexes (R 2 = 0.976) except the strongly bound bridged structures. The bridged structures are classified as donor−acceptor−donor complexes. MESP provides a clear evidence for hydrogen, halogen, and dihydrogen bond formation and defines them as eDA interactions in which hydrogen acts as electron acceptor in hydrogen and dihydrogen bonds while halogen acts as electron acceptor in halogen bonds. − (electron donors) with different electron acceptors. Throughout this paper, E nb represents the interaction energy calculated at MP4//MP2 method and the standard notations ρ and ∇ 2 ρ are used to indicate the electron density at the bond critical point (bcp) of the electron donor−acceptor bond and the Laplacian of the electron density at the bcp. Figure 7. Change in V min upon bond formation in electron donor−acceptor−donor complexes (a) F − ...IF and (b) F − ...IBr. The black dots represent the location of the most negative MESP-valued point and the corresponding V min values in kcal/mol are also depicted.
Organometallics, 1996
+ , and OsH 4 (PR 3 ) 3 ) spanning a large range of H-H values is optimized at the B3LYP computational level, yielding satisfactory agreement with available neutron-diffraction data. The electron density resulting from these theoretical calculations is analyzed afterward within the "atoms in molecules" formalism, resulting in a positive assignment of the complexes W(H 2 )(CO) 3 (PR 3 ) 2 and IrH(H‚‚‚H)Cl 2 (PR 3 ) 2 as dihydrogen complexes and of the complexes [Os(H‚‚‚H)(NH 2 (CH 2 ) 2 NH 2 ) 2 (RCO 2 )] + and OsH 4 -(PR 3 ) 3 as dihydride complexes.
Characterization of C-H-0 Hydrogen Bonds on the Basis of the Charge Density
It is shown that the total charge density is a valid source to confirm hydrogen bonding without invoking a reference charge density. A set of criteria are proposed based on the theory of "atoms in molecules" to establish hydrogen bonding, even for multiple interactions involving C-H-O hydrogen bonds. These criteria are applied to several van der Waals complexes. Finally a bifurcated intramolecular C-H-O hydrogen bond is predicted in the anti-AIDS drug AZT, which may highlight a crucial feature of the biological activity of a whole class of anti-AIDS drugs.
On the electron-pair nature of the hydrogen bond in the framework of the atoms in molecules theory
2003
Delocalization indices, as defined in the atoms in molecules theory, have been calculated between hydrogen-bonded atoms in 20 molecular complexes that are formed between several H-donor and acceptor molecules. In general, the delocalization index associated to an intermolecular hydrogen bond depends on the interaction energy of the complex, but also on the nature of the H-donor and acceptor atoms.
Chemical Physics, 2009
Individual hydrogen bond (HB) energies have been estimated in several systems involving multiple HBs such as adenine-thymine and guanine-cytosine using electron charge densities calculated at XÁ Á ÁH hydrogen bond critical points (HBCPs) by atoms in molecules (AIM) method at B3LYP/6-311++G ** and MP2/6-311++G ** levels. A symmetrical system with two identical H bonds has been selected to search for simple relations between q HBCP and individual E HB . Correlation coefficient between E HB and q HBCP in the base of linear, quadratic, and exponential equations are acceptable and equal to 0.95. The estimated individual binding energies E HB are in good agreement with the results of atom-replacement approach and natural bond orbital analysis (NBO). The E HB values estimated from q values at HÁ Á ÁX BCP are in satisfactory agreement with the main geometrical parameter HÁ Á ÁX. With respect to the obtained individual binding energies, the strength of a HB depends on the substituent and the cooperative effects of other HBs.