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On the Significance of Lone Pair/Lone Pair and Lone Pair/Bond Pair Repulsions in the Cation Affinity and Lewis Acid/Lewis Base Interactions.

ABSTRACT: Interaction of H2O, H2S, H2Se, NH3, PH3, and AsH3 with cations H+, CH3 +, Cu+, Al+, Li+, Na+, and K+ was studied from the energetic and structural viewpoint using B3LYP/6-311++G(d,p) method. The charge transfer from the Lewis bases to the cations reduces lone pair/lone pair (LP/LP) repulsion in H2O, H2S, and H2Se and LP/bond pair (LP/BP) repulsion in NH3, PH3, and AsH3. In parallel, changes in the H-M-H angles (M = O, S, Se, N, P, and As) are observed. The change in the H-M-H angle during the interactions was proportional to the amount of charge transferred from the bases to the cations and electron density (?) at the molecule/cation bond critical point. Also, the opposite trend for proton affinities of these two families, that is, NH3 > PH3 > AsH3 and H2O < H2S < H2Se, was interpreted on the basis of LP/BP repulsion in their neutral and protonated forms. Interaction of the Lewis bases with neutral Lewis acids including BeH2, BeF2, and BH3 was studied energetically and structurally. The calculated energies for interactions of H2O and NH3 with BeH2, BeF2, and BH3 are larger than the corresponding values for H2S, H2Se, PH3, and AsH3. This difference was interpreted on the basis of the lower stability of H2O and NH3 because of large LP/LP and LP/BP repulsion in H2O and LP/BP repulsion in NH3.

SUBMITTER: Valadbeigi Y

PROVIDER: S-EPMC6645108 | biostudies-literature | 2018 Sep

REPOSITORIES: biostudies-literature

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On the Significance of Lone Pair/Lone Pair and Lone Pair/Bond Pair Repulsions in the Cation Affinity and Lewis Acid/Lewis Base Interactions.

Valadbeigi Younes Y Gal Jean-François JF

ACS omega 20180918 9

Interaction of H2O, H2S, H2Se, NH3, PH3, and AsH3 with cations H+, CH3 +, Cu+, Al+, Li+, Na+, and K+ was studied from the energetic and structural viewpoint using B3LYP/6-311++G(d,p) method. The charge transfer from the Lewis bases to the cations reduces lone pair/lone pair (LP/LP) repulsion in H2O, H2S, and H2S ...[more]

PMID: 31459241

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Project description:The high sensitivity of silole- and silafluorene-containing polymers for detecting organic nitro, nitrate, and nitramine explosives cannot be solely attributed to favorable analyte-polymer hydrophobic interactions and amplified fluorescence quenching due to delocalization along the polymer chain. The Lewis acidity of silicon in conjugated poly(silafluorene-vinylene)s is shown to be important. This was established by examining the (29)Si NMR chemical shifts (Delta) for the model trimer fragment of the polymer CH(3)-silafluorene-(trans-C(2)H(2))-silafluorene-(trans-C(2)H(2))-silafluorene-CH(3). The peripheral and central silicon resonances are up-field from a TMS reference at -9.50 and -18.9 ppm, respectively. Both resonances shift down-field in the presence of donor analytes and the observed shifts (0 to 1 ppm) correlate with the basicity of a variety of added Lewis bases, including TNT. The most basic analyte studied was acetonitrile and an association constant (K(a)) of 0.12 M(-1) was calculated its binding to the peripheral silicon centers using the Scatchard method. Spin-lattice relaxation times (T(1)) of 5.86(3) and 4.83(4) s were measured for the methyl protons of acetonitrile in benzene-d(6) at 20 degrees C in the absence and presence of the silafluorene trimer, respectively. The significant change in T(1) values further supports a binding event between acetonitrile and the silafluorene trimer. These studies as well as significant changes and shifts observed in the characteristic UV-Vis absorption of the silafluorene group support an important role for the Lewis acid character of Si in polymer sensors that incorporate strained silacycles. The nitro groups of high explosives may act as weak Lewis-base donors to silacycles. This provides a donor-acceptor interaction that may be crucial for orienting the explosive analyte in the polymer film to provide an efficient pathway for inner-sphere electron transfer during the electron-transfer quenching process.

Dataset Information

On the Significance of Lone Pair/Lone Pair and Lone Pair/Bond Pair Repulsions in the Cation Affinity and Lewis Acid/Lewis Base Interactions.

Publications

On the Significance of Lone Pair/Lone Pair and Lone Pair/Bond Pair Repulsions in the Cation Affinity and Lewis Acid/Lewis Base Interactions.

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