The thermal dehydration of high-surface-area (ca. 180 m2 g-') tin(1v) oxide gel has been studied by thermogravimetric analysis and infrared spectroscopy in the temperature range 293-673 K. The thermogravimetricanalysis data show that two types of physisorbed water are present, one which is largely removed by evacuation at ambient temperature and a more strongly held type which is removed by evacuation at 373-423 K. Further mass loss occurring at higher temperatures is due to the condensation of hydroxyl groups on the surface of the oxide particles. The amount of physisorbed molecular water present on the freshly prepared gel corresponds to a ca. three-monolayer coverage, reducing to ca. 0.74 of a monolayer after evacuation at 295 K, and is totally removed after evacuation at 423 K. The surface concentration of hydroxyl groups is determined to be 19.8 nm-2 at 423-473 K, falling to 16.2 nmP2 at 573 K and 13.0 nm-2 at 673 K. Infrared spectra confirm that physisorbed molecular water [v (OH) 3800-2000 cm-I, &OH) 1640 cm-'1 is removed by 423 K. Isolated and hydrogen-bonded surface hydroxyl groups give rise to stretching modes at 3640 cm-l (sharp) and 3500 cm-' (very broad), respectively. Surface hydroxyl deformation bands are found at 870, 940, 1175 and 1245 cm-l. The bands at 870 and 950 cm-' are removed on evacuation by 473 and 523 K, respectively. The deformation bands at 1175 and 1245 cm-' which remain at 523 K are assigned to isolated surface hydroxyl groups. The band at 770 cm-', which increases in intensity during dehydration, is assigned to surface Sn-0-Sn linkages formed by the dehydroxylation process. The results are interpreted in terms of hydroxylated exposed [loo], [loll (both of which contain clusters of three hydroxyl groups attached to each surface tin atom) and [110] (which contains both isolated and geminal pairs of hydroxyl groups attached to surface tin atoms) crystal planes of the rutile structure, the former predominating.A knowledge of the chemical nature of the surface of tin(1v) oxide and its binary mixtures with other oxides such as Sn0,-

The addition of Ta0.01Nb0.03Ti0.96O2 improves the electrocatalytic activity and stability of carbon for the oxygen reduction reaction.

The adsorption of trifluoroacetic acid, 1,1,1,3,3,3-hexafluoropropan-2-one, 1,l ,l-trifluoropropan-2-one, 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol on tin(iv) oxide gel has been studied by infrared spectroscopy. Trifluoroacetic acid is adsorbed as both hydrogen-bonded molecular trifluoroacetic acid and surface trifluoroacetate, the former being totally converted into the latter by 533 K. The surface trifluoroacetate decarboxylates by 673 K to give surface trifluoromethoxide. Both of the ketones 1,1,1,3,3,3-hexafluoropropan-2-one and 1,1,1-trifluoropropan-2-one are chemisorbed as surface hemiacetal species by interaction with a surface hydroxyl group. These undergo subsequent thermal decomposition to give, respectively, surface trifluoroacetate and a mixture of surface trifluoroacetate and surface acetate. The two alcohols 2,2,2-trifluoroethanol and 1,1,1,3, 3,3-hexafluoropropan-2-ol are chemisorbed as surface alkoxy species which thermally decompose to surface formate and surface trifluoromethoxide in the case of the former and additionally in the case of the latter, surface trifluoroacetate. The thermal stability of the surface carboxylates is in the order: surface acetate > surface trifluoroacetate > surface formate.

Attempts to prepare rhenium hexachloride by the method described by Colton (2) have been unsuccessful. The products of the reaction were always impure rhenium oxotetrachloride and rhenium pentachloride. A compound of rhenium(VI), ReOCI40PCl3, is shown to have a structure analogous to that of rhenium(V) ions [ReOX4.L]-in which the ligands are in a pseudooctahedral arrangement with L trans to the 0x0-group (3). Reactions of ReOCI, and ReOCI4-OPCI, with pyridine and 2,2'-dipyridyl are described, and a scheme is proposed for the reactions of the products. Two stable complexes of perrhenyl chloride with the above amines have been obtained.

We have been unable t o prepare TcCI, by the method published previously even though our reaction between Tc and CI, gave products which appeared the same. Tc0,CI and TcOCI, have been prepared and fully characterized for the first time.11 a ete impossible de preparer TcCI, par la methode precedemment publiee, m@me si la reaction entre Tc et CI, conduit a des produits qui semblent les m&mes. Les composes Tc0,CI et TcOCI, ont ete prepares et caracterises sans ambigui'tt pour la premiire fois.