Issue 24, 2012

Electronic structure, molecular electrostatic potential and spectral characteristics of pillar[6]arene hosts and their complexes with n-octyltriethylammonium ions

Abstract

Electronic structure, charge distribution and 1H NMR in pillar[6]arene (P6) conformers, their diisobutoxy derivatives and their host–guest complexes have been investigated by employing the density functional theory. It has been shown that a P6 conformer obtained by flipping of alternate hydroquinone units turns out to be of lowest energy, owing to the hydrogen bonded network at both rims of the host. As opposed to this, a conformer void of hydrogen bonding interactions has largely been destabilized. The O–H⋯O interactions are analyzed using molecular electrostatic potential topography as a tool. Modification of a P6 host by substituting a diisobutoxy group at reactive phenols (DIBP6) renders rigid pillar-shape architecture to the host in which electron-rich regions are localized within the cavity and near portals. Complexation of n-octyltriethylammonium ions (n-OTEA) with P6 and DIBP6 reveals qualitatively different binding patterns. It has been shown that the conformer in which n-OTEA penetrates from the lower rim of the host and partially encapsulates within the P6 cavity turns out to be 1.4 kJ mol−1 lower in energy than the complex showing complete guest encapsulation. Host–guest binding patterns, viz. encapsulation or portal interactions, can be distinguished from 1H NMR chemical shifts. The shielding of ethyl and n-octyl chain protons in an n-OTEA⊂DIBP6 complex points to encapsulation of the guest which has been rationalized from natural bond orbital analyses. These inferences are in consonance with 1H NMR experiments.

Graphical abstract: Electronic structure, molecular electrostatic potential and spectral characteristics of pillar[6]arene hosts and their complexes with n-octyltriethylammonium ions

Article information

Article type
Paper
Submitted
18 Oct 2011
Accepted
28 Mar 2012
First published
29 Mar 2012

Phys. Chem. Chem. Phys., 2012,14, 8711-8722

Electronic structure, molecular electrostatic potential and spectral characteristics of pillar[6]arene hosts and their complexes with n-octyltriethylammonium ions

S. R. Peerannawar and S. P. Gejji, Phys. Chem. Chem. Phys., 2012, 14, 8711 DOI: 10.1039/C2CP23280D

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