Fluorides and fluoro acids. 30. Crystal structures of acid hydrates and oxonium salts. 34. Trifluoroacetic acid tetrahydrate: a unique change from an ionic to a molecular crystal structure on deuteration

Abstract

7435thylcyclohexane-d13 6 1.36. ,lP spectra were referenced relative to 85% H3P04 at 6 = 0. of quencher to the cuvette with a microliter syringe (Et3SiH, cyclopentene) or by employing stock solutions (PMe,, 'BuNC). In the latter case, a measured quantity of gas was condensed into a measured volume of cyclohexane on a high-vacuum line. The absorbances of the solutions for flash photolysis experiments were in the range 0.5-1.0 at 308 nm. Variable-temperature measurements were made by replacing the standard sample holder by an insulated holder mount4 on a block through which thermostat4 water was circulated.Steady-State Photolysis. Steady-state photolysis experiments were usually performed in NMR tubes in situ. NMR spectra were recorded on a Bruker MSL 300-MHz spectrometer. lH spectra were referenced to solvent peaks as follows: CLDSH 6 7.13, cyclohexane-dll 6 1.38, meAcknowledgment. We are grateful to Dr. 0. Traverso and Dr. L. D. Field for helpful discussions and for disclosing data prior to publication, to D~, s. E. J , ~~u for advice on optics, to D. ~~f i for his work in interfacing and development of software, and to Prof. and Dr. M. George for carrying Out the time-resolved IR experiment. W e acknowledge the support of The Fulbright Commission, The Royal Society, SERC, NATO, British Gas, and the E C Commission.Abstract: Trfiuoroacetic acid has been found from DTA, DSC, and temperature-dependent X-ray powder diffraction to form, besides other stable and metastable hydrates, both an undeuterated (reinvestigation) and perdeuterated stable tetrahydrate.

Rhodium and Iridium Complexes Derived fromtrans-[MCl(CO)(PPh3)2] (M = Rh, Ir) and Pyridine-2-thiolate or 4,6-Dimethylpyrimidine-2-thiolate Ligands:S-Monodentate Coordination versusS,N-Chelation andS,N-Bridging; Reactivity oftrans-[Ir(‘Spy’)(CO)(PPh3)2] andtrans-[Ir(‘SpymMe2’)(CO)(PPh3)2] towards Acid

“…The sulfur atom of the four-membered IrϪSϪCϪN heterocycle is trans with respect to IrϪH, the metal-bound pyrimidine nitrogen atom being trans to the carbonyl group. [15] [16] The geometry, optimized for the ''best'' [17] hydrogen bond in the [H(O 2 CCF 3 ) 2 ] Ϫ anion of 5a (OϪH, 0.82 Å ; H···O, 1.71 Å ; O···O, 2.53 Å , OHO, 170.7°), is quite normal and compares well with those of earlier determinations. The planes defined by the two carboxylate fragments are twisted about the OϪH···O bond, such that the angle between them is 71.9°.…”

Die Wasserstoffbrücke im Festkörper

“…[107] Die Schwingung der O-D-Bindung hat eine niedrigere Nullpunktsenergie im Vergleich zu O-H, und die O-D-Bindung ist dadurch etwas stabiler. [109] Der Ubbelohde-Effekt wurde leider nur f¸r relativ wenige OÀH/D ¥¥¥ O-Paare experimentell untersucht, und die Details der zugrundeliegenden Effekte sind noch nicht vollst‰ndig verstanden.…”

A ground state morphed intermolecular potential for the hydrogen bonded and van der Waals isomers in OC:HI and a prediction of an anomalous deuterium isotope effect

“…[20][21][22][23][24][25][26][27][28] As a consequence of such extensive applications, investigations of anomalous isotope effects have now become the subject of intense interest and considerable focus. 41 Here, deuterium substitution has been proposed to fundamentally change hydrogen bonding in trifluoracteic tetrahydrate from a cationic layer structure of hydrogen bonded ͑H 3 O + ͑3H 2 O͒͒ enclosing F 3 CCOO − anions to a molecular hydrogen bonded ͑D 2 O͒ n layer enclosing F 3 CCO 2 H. 41 The generated potential energy surface of OC:HI can be used to determine if the OC-IH van der Waals global equilibrium minimum structure can be differentiated from its OC-HI ground state hydrogen bound structure. [33][34][35][36][37] A combination of high resolution gas phase and supersonic jet/molecular beam spectroscopic methods and application of theoretical and modeling approaches [38][39][40] can be particularly effective for phenomenologically more detailed investigations.…”