Structural Investigation of Pd(II) in Concentrated Nitric and Perchloric Acid Solutions by XAFS

Abstract

XAFS spectra of palladium (II) 2+ square-planar aqua ion in strong perchloric acid, the use of an FEFF6 theoretical approach led to a first-shell Pd-O w distance of 2.00 (1) Å and a Debye-Waller (DW) factor of σ 2 ) 0.0030 (3) Å 2 . Four water molecules are tightly bound to the Pd 2+ ion in the equatorial plane, while two (or one) axial water molecules are weakly bound to the metal ion at 2.5 Å with a DW factor of 0.015 (5) Å 2 . For highly concentrated mixtures (4-6 M HNO 3 ) and for pure concentrated (4-6 M) nitric acid as well as for crystalline powder Pd(NO 3 ) 2 (H 2 O) 2 , the XAFS spectra are very similar and are determined by the mixed nitric complex Pd(NO 3 ) 2 (H 2 O) 2 : four Pd-O near-equivalent distances of 2.01 (1) Å from two H 2 O and two NO 3 molecules with a total DW factor of σ 2 ) 0.0037 (3) Å 2 . Moreover, two Pd---N distances of 2.8-2.9 Å were determined in the second coordination shell.

Studies on the feasibility of electrochemical recovery of palladium from high-level liquid waste

“…2, also exhibits a bathochromic shift with increase in the concentration of nitric acid due to nitrate complexation. Purans et al [14] studied the structure and speciation of Pd 2+ in nitric and perchloric acid medium. The stability constants for the complexation of palladium (II) ion with nitrate ions in nitric acid medium, derived from solvent extraction data, were reported by Tarapcik [15].…”

Aquanitrato Complexes of Palladium, Rhodium, and Platinum: A Comparative 15N NMR and DFT Study

“…Tarapčik reported stability constants for all nitrato complexes of Pd in Pd II _NASs calculated from the results of solvent extraction experiments . Taking into account the structural data on palladium nitrato complexes, an XAFS investigation of Pd II _NASs was carried out with [HNO 3 ] in the range of 1–6 m …”

“…Fitting of the experimental data yields stability constants 1 and 2 , which corrected to ionic strength (I) values of 1.49 and 0.45 for a solution with I = 3 M. [26] Tarapčik reported stability constants for all nitrato complexes of Pd in Pd II _NASs calculated from the results of solvent extraction experiments. [27] Taking into account the structural data on palladium nitrato complexes, an XAFS investigation of Pd II _NASs was carried out with [HNO 3 ] in the range of 1-6 M. [28] While speciation in Pd II _NASs with low to high concentrations of HNO 3 (0.1 up to 6 M) are well studied, no information is available on species distribution in solutions with high HNO 3 contents (> 6 M), where homoleptic nitrato complexes should exist. To cover the widest spectrum of HNO 3 concentrations, NMR spectroscopy on the nuclei of ligand atoms can be very informative.…”

Mechanism of Palladium(II) Adsorption from Nitric Acid Solutions by a Styrene-Divinylbenzene Copolymer Functionalized with <i>N,N,N</i>-Trimethylglycine

“…(1) According to a previous report [23], the small peak results from multiple scatterings related to N and distal O atoms in the NO 3 − coordinating to Pd(II) in a unidentate manner. Since the Fourier-transformed spectra of Pd(II) in AMP03 and 7.0 M HNO 3 solution were similar to each other, we concluded that the adsorbed Pd(II) species was coordinated to NO 3 − .…”