Study of O H···O bonded-cyclic dimer for 2,5-Dihydroxyterephthalic acid as aided by MD, DFT calculations and IR, Raman, NMR spectroscopy

Molecular Dynamics-simulated OH···O bonded-cyclic dimer structure, called Dc, has been proposed for 2,5-Dihydroxyterephthalic acid a potential organic linker in Hydrogen-bonded Organic Frameworks (HOF). Among many dimer species bound by inter-molecular OH···O bonds, Dc was chosen because of its relatively highest lifetime of 18.3 ps as indicated by the radial distribution functions (RDF). Experimentally observed intense but broad down-shifted IR absorptions peak at ∼ 3023 cm−1 and bands near 2556 cm−1 combined with staggered occurrence of IR and Raman bands in other spectral regions suggested that the proposed cyclic dimer appeared to possess an extended quasi-centrosymmetric configuration. Upon optimization of Dc at B3LYP/6-311++G(d,p) level, it yielded geometry and vibrational spectra in agreement with experimental spectra. Further, we have characterized both intra- and inter-molecular OH···O bonds in Dc using stabilization energy E(2) and other molecular orbital (MO) properties from NBO analysis. Bond critical points (BCPs) and ring critical points (RCPs) deduced from electron density (ρ(r)), its laplacian (∇2ρ(r)) and potential energy density (v(r)) using AIM calculations have provided complementary perspectives. Additionally, a combination of quantitative analysis and graphical visualization of the charge regions where non-covalent interactions occur in real space intra- and inter-molecular OH···O bonds, van der Waals and repulsive steric clash interactions have been obtained from NCI calculations.