Solid-state and solution-state self-association of dimethylarsinic acid: IR, NMR and theoretical study

Preparation of magnetic composites and their dimethyl arsonic acid adsorption performances

Dimethyl arsonic acid, the most common organic arsenic pollutant, is widely present in the environment and seriously threatens the safety of drinking water. Syntheses of magnetite, magnetic bentonite, and magnetic ferrihydrite via hydrothermal methods, and the magnetic composites were examined using XRD, BET, VSM, and SEM. SEM images revealed that many monodispersible pellets were attached to the surface of magnetic bentonite. The magnetic ferrihydrite contained abundant pores and had a rich pore structure, which expanded the specific surface area of the original magnetite. The specific surface areas of the magnetic bentonite and magnetic ferrihydrite were 65.17 and 220.30 m²·g^-1, respectively. The adsorption kinetics and adsorption isotherms of dimethyl arsonic acid on magnetic composites were studied. The adsorption of dimethyl arsonic acid on the magnetic composites conformed to the pseudo-second-order model and Freundlich isothermal adsorption model. By comparing the isotherms of the adsorption of dimethyl arsonic acid by the magnetic composites at pH values of 3, 7, and 11, respectively, it was found that the adsorption of dimethyl arsonic acid was the greatest at neutral pH of 7. The adsorption mechanism was analyzed via zeta potential determination, Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). The zeta potential results revealed that magnetic bentonite electrostatic activity occurred with dimethyl arsonic acid, and the magnetic ferrihydrite indicated a coordination complex with dimethyl arsonic acid. The XPS results revealed that the Fe-O bonds on the surfaces of the magnetic ferrihydrite had coordination complexation effects on the As-O of the dimethyl arsonic acid.

Evolution of vibrational bands upon gradual protonation/deprotonation of arsinic acid H2As(O)OH in media of different polarity

This computational work is devoted to the investigation (MP2/def2-TZVP) of the geometry and IR parameters of arsinic acid H₂AsOOH and its hydrogen-bonded complexes under vacuum and in media with different polarity. The medium effects were accounted for in two ways: (1) implicitly, using the IEFPCM model, varying the dielectric permittivity (ε) and (2) explicitly, by considering hydrogen-bonded complexes of H₂As(O)OH with various hydrogen bond donors (41 complexes) or acceptors (38 complexes), imitating a gradual transition to the As(OH)₂⁺ or AsO₂^- moiety, respectively. It was shown that the transition from vacuum to a medium with ε > 1 causes the As(O)OH fragment to lose its flatness. The solvent polar medium introduces significant changes in the geometry and IR spectral parameters of hydrogen-bonded complexes too: as the polarity of a medium increases, weak hydrogen bonds become weaker, and strong and medium hydrogen bonds become stronger; in the case of a complex with two hydrogen bonds cooperativity effects are observed. In almost all cases the driving force of these changes appears to be preferential solvation of charge-separated structures. In the limiting case of complete deprotonation (or conversely complete protonation) the vibrational frequencies of ν_AsO and ν_As-O turn into ν_As-O(asym) and ν_As-O(sym), respectively. In the intermediate cases the distance between ν_AsO and ν_As-O is sensitive to both implicit solvation and explicit solvation and the systematic changes of this distance can be used for estimation of the degree of proton transfer within the hydrogen bond.

Isotope Effects on Chemical Shifts in the Study of Hydrogen Bonds in Small Molecules

This review is giving a short introduction to the techniques used to investigate isotope effects on NMR chemical shifts. The review is discussing how isotope effects on chemical shifts can be used to elucidate the importance of either intra- or intermolecular hydrogen bonding in ionic liquids, of ammonium ions in a confined space, how isotope effects can help define dimers, trimers, etc., how isotope effects can lead to structural parameters such as distances and give information about ion pairing. Tautomerism is by advantage investigated by isotope effects on chemical shifts both in symmetric and asymmetric systems. The relationship between hydrogen bond energies and two-bond deuterium isotope effects on chemical shifts is described. Finally, theoretical calculations to obtain isotope effects on chemical shifts are looked into.

Self-association of diphenylpnictoginic acids in solution and solid state: covalent vs. hydrogen bonding

Triphenylpnictogens were oxidized to access diphenylpnictioginic acids Ph₂XOOH (X = P, As, Sb, Bi). It was shown that oxidation with chloramine-T does not lead to the cleavage of a C-pnictogen bond. The preliminary reductive cleavage with sodium in liquid ammonia followed by the oxidation with hydrogen peroxide was successfully utilised for the synthesis of diphenylphosphinic and diphenylarsinic acids. It was shown that in solid state (by means of XRD), all diphenylpnictoginic acids form polymeric chains. Diphenylbismuthinic and diphenylantimonic acids form polymeric covalent adducts, while diphenylphosphinic and diphenylarsinic chains are associated through hydrogen bonding. Unlike diphenylphosphinic acid, diphenilarsinic acid forms two polymorphs of hydrogen-bonded infinite chains. In solution in a polar aprotic solvent diphenylarsinic acid, similarly to dimethylarsinic, forms hydrogen-bonded cyclic dimers together with a small amount of cyclic trimers.