Probing Vibrational Dynamics of Hydrogen-Bonded Inclusion Compounds with Inelastic Neutron Scattering and Ab Initio Calculations

Abstract

Guanidinium organodisulfonates form lamellar host lattices in which adjacent two-dimensional hydrogenbonded sheets consisting of topologically complementary guanidinium cations (G) and sulfonate moieties (S) are connected by the organodisulfonates, which serve as pillars that support inclusion cavities, between the sheets, which are occupied by guest molecules. Inelastic neutron scattering (INS) at low energies (35-120 meV or 280-970 cm -1 ) has been performed to probe the lattice dynamics of selected GS inclusion compounds. The pillars and the guests can be easily interchanged to produce inclusion compounds with various host-guest compositions, which can have different solid-state architectures but with retention of lamellar character. The specific host-guest combinations were chosen to evaluate the influence of the host environment on the vibrational modes of the guests, with particular attention paid to the role of pillar-guest isomorphism and lattice architecture. The multicomponent character of these materials enables selective isotopic labeling (hydrogen or deuterium) of the componentssguanidinium ion, organodisulfonate pillar, and guest molecules so that specific features in the INS spectra of the inclusion compounds can be assigned unambiguously to each component. These assignments are corroborated by ab initio density functional theory calculations for free, isolated guest molecules, which also define the specific molecular motions associated with each feature in the INS data. The INS spectra produced by the ab initio calculations are in excellent agreement with the experimental data, illustrating the accuracy of the assignments while also demonstrating the reliability of the calculations for predicting INS spectra and lattice dynamics. Overall, the contributions to the INS spectra from the guest molecules do not differ appreciably from those observed for crystals of the pure guests or predicted by ab initio calculations. This demonstrates that the host lattices examined here do not appreciably influence the dynamic behavior of the guest molecules, most likely reflecting the absence of strong hostguest interactions, specifically between the organodisulfonate pillars and the guests.

Dipotassium biphenyl-4,4′-disulfonate dihydrate: a coordination polymer

“…2). This is somewhat analogous to the 2-D but hydrogen-bonded guanidinium-BPDS open framework structures (Swift et al, 1998;Pivovar et al, 2002) which accommodate interstitial inert aromatic molecules. With (I), the water molecules are similarly accommodated in the interstitial spaces along the crystallographic mirror planes in linear head-to-tail interactions (Table 1) and also link the coordination polymer chains.…”

“…For other 4,4 0 -biphenyldisulfonate crystal structures, see: Swift et al (1998); Liao et al (2001); Cai et al (2001); Usuki et al (2002). For related literature, see: Pivovar et al (2002). For synthesis, see: Feldmann (1931).…”

“…Compounds of 4,4′-biphenyldisulfonic acid (BPDS) are not numerous in the crystallographic literature. The guanidinium salts have been used for the generation of 2-D structures for the formation of crystalline clathrates with aromatic hydrocarbons (Swift et al, 1998;Pivovar et al, 2002). The bis(alaninium) salt is also known (Liao et al, 2001).…”