A theoretical study on the importance of steric effects, electronic properties, interaction and solvation energies in the ‘host–guest’ chemistry of protonated azacryptands and halide anions

Significant geometry and charge difference between the E54− bare clusters of group 14 Zintl anions and their coordinated form in [E5{M(CO)3}2]4− (E = Si, Ge, Sn, Pb; M = Cr, Mo, W) complexes

It is shown that while none of the E₅ⁿ (E = Si, Ge, Sn, Pb; n = 0, 2−, 4−) bare clusters can be stabilized in planar pentagon (D_5h) geometry, E₅⁴⁻ ions as a five-membered planar ring form stable complexes with two {M(CO)₃} (M = Cr, Mo, W) metal carbonyls. Interestingly, the negative charge of all [E₅{M(CO)₃}₂]⁴⁻ complexes is distributed on two {M(CO)₃} fragments rather than the coordinated Zintl ion.

Where and How Does an Organic Molecule Having a C-X Bond Release X- Anion Like an Inorganic Compound? A Theoretical Study

In this research, at first, a comparative DFT study on hydride or fluoride release from a number of known orthoamides, their fluorine derivative having a central C-F bond and some simple organic compounds, is reported. The obtained data show that orthoamides release hydride or fluoride anions much easier than do other known organic compounds studied here. Interestingly, three simulated orthoamides having a central C-F bond, spontaneously and like an inorganic compound, release fluoride anion upon dissolving in polar solvents. The calculations confirmed that hyperconjugation interactions in the initial orthoamides facilitate the anion release from these compounds. However, the data clearly show that the proper overlap of an empty p orbital of the central carbon atom with adjacent lone-pair orbitals of nitrogen atoms ( lpN → lp*C or, in other words, the pπ-pπ interaction) in the resulting carbocations is a more important factor that must be taken into consideration when designing the hydride, fluoride, or other anion releasing agents. In addition, for the first time, a mechanism of hydride and fluoride removal from the orthoamides either through their reaction with BH₃ and BF₃ molecules, respectively, or upon their protonation is provided. To continue and for generalization of results to other groups attached to the central carbon atom of orthoamides, the reactions of H⁺ with orthoamides having the CH₃, OH, CN, NH₂, or C₅H₅ substituents were studied. The results showed that in all cases and in both gas and solution phases the above substituents easily leave the carbon atom as an anion and bond to H⁺. Thus, we have to conclude that upon the reaction of orthoamides with usual Lewis acids, many types of substituents on their central carbon atom can leave these compounds as anions.

Comparison of the selectivity of [M(12-Crown-4)]+ (M=Li+, Na+, K+) complexes for halide anions and some neutral molecules; a computational study

A theoretical study on the selectivity of a series of [M(12C4)][Formula: see text] (M = Li[Formula: see text], Na[Formula: see text], K[Formula: see text], 12C4 = 12-crown-4) complexes for F[Formula: see text], Cl[Formula: see text] and Br[Formula: see text] anions and a number of neutral molecules (CH3CN, CH3OH, NH3, H2O, py, and 12C4) is reported. At first, it was shown that in the gas phase among all studied halide anions and neutral molecules, halides have much more bonding interaction with all [M(12C4)][Formula: see text] cations. Calculated interaction energies of above anions and [M(12C4)][Formula: see text] cations decrease from F[Formula: see text] to Br[Formula: see text]. Also the interaction energy of halide anions with [M(12C4)][Formula: see text] complexes, decreases from [Li(12C4)][Formula: see text] to [K(12C4)][Formula: see text]. The electron decomposition analysis showed that the bond between [M(12C4)][Formula: see text] complexes and both the neutral and anion guests is mainly electrostatic in nature. Then the selectivity of [M(12C4)][Formula: see text] complexes for studied anions and neutral molecules are compared in methanol, acetone, acetonitrile, and nitromethane solutions. It was shown that both the desolvation process of reactants and the strength of host–guest interactions have significant effect on the selectivities. Thus the selectivity of [Li(12C4)][Formula: see text] cation for NH3and H2O neutral molecules in solution, in contrast to the gas phase, is higher than that for bromide anion. The results of calculations showed that all [M(12C4)][Formula: see text] complexes, specially [Li(12C4)][Formula: see text], have high selectivity for F[Formula: see text] over other halide anions and neutral molecules.

Theoretical study of adsorption of amino acids on graphene and BN sheet in gas and aqueous phase with empirical DFT dispersion correction

Suitability of BN nanosheet/graphene towards the adsorption of amino acids established by dispersion corrected DFT calculations.

What causes the weakest host to act as the strongest one? A theoretical study on the host-guest chemistry of five azacryptands and fluoride anions

In this work we have attempted to computationally analyze the important parameters affecting the selectivity in host-guest systems in order to show that the solvent effect in some host-guest systems is even more important than the hole-size fitting and/or host-guest interaction energy. For this purpose, the fluoride anion selectivities of the five most studied azacryptands with different affinities, moieties, cavity sizes and degrees of preorganization, in their fully protonated forms, were studied at PBE/TZVP and B3P86/TZVP levels of theory. The factors affecting the selectivity such as hole size fitting, steric effects, electronic properties, preorganization of hosts, as well as solvent effects were investigated. The results showed that among the five studied azacryptands, one of them, which ranks fifth for selectivity according to its weak interaction energy with fluoride anions, ranks fourth due to its good preorganization. However, a surprising improvement occurs when its selectivity for fluoride anions ranks first due to the existence of less solvent hindrance. The results of the calculations were further confirmed by a good correlation between the calculated and experimental formation constants.

MP2 and DFT studies on interaction of a halide anion with the fully protonated form of 1,4,7-triazacyclononane

Density functional theory (DFT) using PBE, PBE1PBE, B3P86, B97-1, and BHandHLYP functionals as well as MP2 calculations employing the TZVP basis set were used to study the formation of four host–guest complexes with formula [ H 3 L ⋯ X ]2+ ( X = F -, Cl -, Br -, and I -). The result of calculations on the structural parameters of [ H 3 L ⋯ Cl ]2+ shows that the calculated data with BHandHLYP functional have the best agreement with the experimental data and all five DFT methods give the better result than MP2. The largest amounts of interaction energies between the halide anions and protonated macrocycle were also calculated by PBE functional. The results show the following trend for the formation of complexes in the gas phase: [ H 3 L ⋯ F ]2+ > [ H 3 L ⋯ Cl ]2+ > [ H 3 L ⋯ Br ]2+ > [ H 3 L ⋯ I ]2+. Formation of the complexes in solution also shows the above trend where the [ H 3 L ⋯ Br ]2+ and [ H 3 L ⋯ I ]2+ complexes have positive [Formula: see text] values and probably cannot be formed.