Unconventional hydrogen bond

Beyond these classical or conventional hydrogen bonds, unconventional or non-conventional interactions are also possible [32] (some examples are shown in Fig. 3). 

Hydrogen bonds [3] can be classified as nonconventional (or nonclassical), when they are formed with the participation of nonconventional proton donors and/or unconventional proton acceptors ... 

R.H. Crabtree et al., A new intermolecular interaction Unconventional hydrogen bonds with element-hydride bonds as proton acceptor. Acc. Chem. Res. 29, 348-354 (1996)... 

The H H interactions (1.75-1.9 A) here and related systems are referred to as proton-hydride bonding by Morris (60-62) and dihydrogen bonding by Crabtree (63-65), who along with others (66-68) have studied or reviewed such unconventional hydrogen bonds that include M-H H-M, M-H H-X, and X-H a interactions in general (X = C, N, P, 0, etc). These complexes represent intermediates in the heterolytic splitting of H2 and illustrate both the basicity of the M-H... 

Kar T, Scheiner S (2006) Cooperativity of conventional and unconventional hydrogen bonds involving imidazole. Int J Quantum Chem 106 843-851... 

Dihydrogen complexes (5) such as [Cr(H2)(CO)5] are covered in a separate article. Dihydrogen bonding, the tendency of an MH bond to act as proton acceptor in an unconventional hydrogen bond with an OH or NH group, is also covered in a separate article, see Hydrogen Bonding). ... 

An extensive discussion of weaker or unconventional hydrogen bonds is provided by Steiner, T. Desiraju, G. R. in The Weak Hydrogen Bond in Structural Chemistry and Biology 1999, Oxford University Press, New York. 

ACp could be made arbitrarily steep so as to very closely simulate the experimental glass transition. In the above expression, AHi refers to the maximum value of this enthalpy (at 0 K) Tr and D are adjustable temperatures. The idea of cooperativity used here is unconventional. It is understandable, however, that as temperature increases, a few secondary bonds get broken (such as hydrogen bonds in glassy water), the strains in... 

A. Fujii, G. N. Patwari, T. Ebata, and N. Mikami, Vibrational spectroscopic evidence of unconventional hydrogen bonds, Int. J. Mass Spectrom. 220, 289 (2002). 

S. J. Grabowski, Ab initio calculations on conventional and unconventional hydrogen bonds—Study of the hydrogen bond strength, J. Phys. Chem. A 105, 10739-10746 (2001). 

Epstein, L.M., Belkova, N.V., Gutsul, E.I., and Shubina, E.S., Spectral features of unconventional hydrogen bonds and proton transfer to transition metal hydrides, Polish. J. Chem., 11, 1371-1383 (2003). 

In this work, the unconventional and weak hydrogen bonds that involve transition elements, namely the dihydrogen bond (symmetric and asymmetric) and the X-H- - -M interactions, will be described and interpreted. More attention will be given to recent results, following an earlier publication [14]. The structures described were taken from the Cambridge Crystallographic Database [15]. 

In recent years, more examples of the unconventional X-H- M or X-H- H-M hydrogen bonds were found and computational studies were carried out more systematically and using better methods, including in most cases the BSSE correction. The application of the AIM theory to detect BCPs and therefore the presence and nature of bonds also increased significantly. The role of the unconventional hydrogen bonds in several reactions, namely proton transfer, has been emphasized. 

In Chapters 1, 2, and 3 unconventional liquid crystalline molecules with complex structures based on covalent bonding are described. In Chapter 4, Rowan and Mather demonstrate that non-covalent bonding such as hydrogen bonds may be used for the design and construction of liquid crystalline materials. 

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