Optical probes of interlamellar redox chemistry: Intercalation of the Creutz-Taube complex into hydrogen uranyl phosphate

Abstract

Hydrogen uranyl phosphate (HUP) can be intercalated by the Creutz-Taube (C-T) complex, {[Ru(NH 3) 5] 2(μ-pyrazine)} 5+, to yield hydrated, partially-substituted lamellar solids, H(C-T)UP, of approximate composition H 1−5 x (C-T) x UO 2PO 4 (0.001< x<0.01). The more crystalline samples exhibited an X-ray powder pattern similar to that of HUP: the structure can be indexed in tetragonal symmetry and possesses an interlamellar spacing of ∼8.69 Å. The absorption spectrum of H(C-T) UP appears to be a simple superposition of bands due to the UO 2+ 2 moiety and the C-T complex. Photoluminescence (PL) of H(C-T) UP is quenched relative to HUP; PL decay curves are nonexponential and span a shorter time domain relative to HUP. Exposure of H(C-T) UP to Br 2 vapor causes the purple solid to become yellow. The spectral changes are consistent with redox chemistry wherein the intercalated C-T complex undergoes oxidation. For most samples examined, the PL decay times were enhanced upon oxidation.