Halogenated derivatives of Bi0H10-2 and 2 2-2 have been prepared by reaction of these anions with chlorine, bromine, or iodine and by reaction of Bi2HI2-2 with hydrogen fluoride, hydrogen chloride, or fluorine. These derivatives are exceedingly resistant toward thermal degradation and chemical attack.

General Radio Type 1231-B amplifier and null-detector. Conductivity cells were immersed in an oil thermostat maintained at 25 ± 0.002°, the temperature of which was checked periodically with a calibrated resistance thermometer.

The hydrolysis equilibrium constant of chlorine was measured from 0 to 45°u sing a conductivity method. The value at 25°of (3.94 ± 0.02) X 10-4 is compared with previous results. In agreement with the observations of earlier investigators, the reaction was found to have a positive AH0 which changes rapidly with temperature, corresponding to a value of ACP°o f approximately -93 cal. mole-1 deg.-1. It is argued that this value arises primarily from the properties of Cl2(aq) and the significance of the large heat capacity of this species is discussed in terms of plausible models. A picture based on a gas hydrate-like structure, which undergoes a progressive breakdown with increasing temperature, is contrasted with a model consisting of two species, one of which is more hydrated than the other. Evidence for the latter comes from spectral changes, while the former model is supported by the similarity7 in behavior of the partial molal heat capacity of other non-polar gases in water.

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The transition state for the electron-transfer reaction of cis-difluorotetra-aquochromium (111) ion with chromium(1I) ion which involves two fluoride ions acting as bridging groups is not detected. Reaction by this pathway is very much slower than by the pathway involving a single fluoride ion acting as the bridging group. The values of AH* and AS* for the reactions of chromium(II) ion with cis-difluorotetra-aquochromium(II1) ion and with monofluoropenta-aquochromium(II1) ion are very similar.Bridged transition-states have been demonstrated to provide the predominant reaction pathway for many oxidation-reduction reactions involving metal ions.1 What of the possibility of a transition-state in which two anions act as a bridge between the reacting metal ions ? Although transition-states containing two anions are known for such reactions, e.g. the transition-states (Fe2C12+)* 2 and (Fe2F;+)+ 3 for the iron(I1)-iron(II1) exchange, it cannot be assumed, as has been suggested,4 that these reactions proceed by transition-states in which both anions act as bridging groups. The present study was designed to investigate this question for the reaction of chromium(1I) ion and cis difluorotetra-aquochromium(II1) ion ; because of the inertness of chromium(II1) species, this system is one which can be expected to provide unequivocal information. That a fluoride-bridged transitionstate does provide the easiest pathway for the " electron-transfer " between chromium(I1) and monofluoropenta-aquochromium(I1I) has been shown by the occurrence of chromium exchange between these two species unaccompanied by a q ~a t i o n . ~ Chromium(I1) can be expected to catalyze the aquation of each isomer of difluorotetra-aquochromium(II1) ion by a path which involves a transition-state analogous to that for the exchange of chromium(I1) and monofluoropenta-aquochromium(II1) ion with a single fluoride ion acting as the bridging group,