The Solid‐State Lanthanoid‐Assisted Hydrolysis of the Solvolytically “Inert” [AsF₆]⁻ Ion

Abstract

Results of elemental chemical analyses of the coordination compounds of the type LnFn(AsF6)3‐n (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) indicated unexpectedly low stability of the generally highly hydrolytically stable [AsF6]− ion. Experiments conducted on model compounds of the type NdFn(AsF6)3‐n have shown that hydrolysis proceeded instantaneously during the reaction of the solid compound with water. The ligand substitution catalysis of the compounds is explained in terms of the distortion of the [AsF6]− octahedra earlier shown by vibrational spectroscopy. The study contrasts formally related reactions on the solid−solvent interface as opposed to those in homogeneous solution. A new look at some long studied and well‐known inorganic species is offered. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

The Redox Chemistry of SbF6− Ion

“…We showed earlier that AsF 6 Ϫ , a lighter valence isoelectronic analogue of SbF 6 Ϫ , is destabilized with regard to hydrolysis by multiply-charged cations. [12] The same destabilization mechanism may also apply to reduction processes. qϩ ion where w and x are left intentionally unstated because of our admitted ignorance of the constitution of such complex ions in solution.…”

“…[8Ϫ10] Additional knowledge concerning the chemistry and properties of these compounds in aqueous media [11,12] was gained from the introduction and development of these analytical methods.…”

Ion Selective Electrode Determination of Free Versus Total Fluoride Ion in Simple and Fluoroligand Coordinated Hexafluoropnictate (PnF6−, Pn = P, As, Sb, Bi) Salts

“…As reported the rate of aqueous hydrolysis of hexafluoropnictate(V) ions is negligible for PF 6 − and AsF 6 − while SbF 6 − ion hydrolyses to [SbF 2 (OH) 4 ] − ion; Bi(V) oxidizes water and so we cannot make any further comparisons with the lighter pnictogens [16]. Hydrolysis of AsF 6 − ion was detected after suspending solid rare earth(III) fluoroarsenates(V) coordination compounds in water, a phenomenon that was explained with distortion of AsF 6 − ion in these salts [17] earlier indicated by spectroscopic data [3].…”

“…Typical examples are represented with the alkaline earth fluorides or rare earth(III) fluorides [17]. In these types of compounds the amount of determined F f − didn't exceed 0.1-0.5% which is in the range of the error of the analytical procedure for fluoride at low levels.…”

Ca(AsF3)(AsF6)2: the first alkaline earth metal cation coordinated to AsF3

“…The total fluoride content (F t À ) was determined after decomposition of the sample by fusion with KNaCO 3 [20,21]. The content of free fluoride (F f À ) was determined in an aqueous solution of the sample [21,22] by direct potentiometry using a fluoride ion selective electrode [20] prior to the total decomposition by fusion with KNaCO 3 and subsequent determination of arsenic content in the form of As(V) by iodometric titration. The sample for total arsenic (As t ) determination was evaporated to dryness in highly alkaline media.…”