A-H—B interaction

However, the question What makes hydrogen unique in forming such bonds remains to be answered. More specifically, what makes A—H bonds (and antibonds) so distinctively suitable for strong A—H- B interactions with general lone-pairbearing atoms B We now briefly address this question in the context of examples cited above. 

A—H B interaction Mainly covalent Mainly electrostatic Electrostatic... 

Like the classical A-H...B interaction, a predominantly electrostatic origin was proposed. In line with this idea, the presence of the following features was suggested for identification of an A-H...M hydrogen bond 1) protonic AH 2) basic M 3) a downfield proton NMR shift on bridging (the opposite situation from a-complexes) and 4) linear A-H...M. The metal could be electronically saturated (e.g., [Co(CO)4] ) or not [e.g., square planar Pt(II)]. 

Exopolyhedral Metallacarboranes. Many metaHacarboranes are known that exhibit exopolyhedral bonding to metals. Most commonly metals are bound via M—H—B interactions in which the B—H group can be regarded as a two-electron donor to the metal center. In other cases, M—B,... 

When the core-repulsion function involves either hydrogen-oxygen or hydrogen-nitrogen interactions, a modified form of this function is used (A = H, B = O, N Eq. 5-5). 

The strueture of the di-iron eomplex [Fe2(p, t, t -BH6)(PEt3)g] (127) contains a boron atom in the oetahedral environment of 6 equiv. hydrides capped on the opposite faeets by two iron atoms.Thus, neglecting the second iron center, the geometry is very reminiseent of the complex 125. DFT calculations supplemented by an AIM study eonfirmed the presence of six H-B interactions and direct Fe B bonds. The strueture was eonsidered as containing a boron trication B " sandwiched between two anions [Fe(H)3(PEt3)3] . 

In 1947 the present writer published a paper [1] in which he studied the interaction between the polar covalent diatomic molecule A—X and the atom B which has a complete electronic shell. The atom X, in particular, may be a hydrogen atom. To simplify the problem only four electrons were considered two electrons from the bond A—H, and the unshared pair of electrons from atom B, viz. A H B. The respective problem was solved approximately by the method of valence structures. The following structures were adopted ... 

Carvalho, E. R., Martin-Neto, L., Milori, D. M. B. P., Rocha, J. C., and Rosa, A. H. (2004). Interactions of clorine with tropical aquatic fulvic acids and formation of intermediates observed by fluorescence spectroscopy. J. Brazilian Chem. Soc. 15(3), 421-426. 

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