ESR study of the Aso radical in γ‐irradiated betaine arsenate

Arsenic Incorporation in Synthetic Struvite (NH4MgPO4·6H2O): A Synchrotron XAS and Single-Crystal EPR Study

“…Single-crystal EPR measurements show that synthetic boussingaultite does not contain any paramagnetic defect before gamma-ray irradiation but is characterized by three well-resolved arsenic-centered oxyradicals after irradiation ([AsO 4 ] 2– , [AsO 3 ] 2– , and [AsO 2 ] 2– ; Figure c). These three arsenic-centered oxyradicals are readily identified on the basis of their diagnostic 75 As hyperfine coupling constants (Table ). − Interestingly, the angular dependence of the experimental line positions (i.e., roadmaps) and the best-fit spin Hamiltonian parameters of the [AsO 3 ] 2– radical in boussingaultite are almost identical to those of an [AsO 3 ] 2– radical in arsenate-doped struvite reported by Xu (1992). Also, the same [AsO 2 ] 2– radical (Figure c) is visible in the B // c spectrum reported by Xu (1992) .…”

“…The best-fit matrices g and A ( 75 As) of Centers I–TV (Table S1) are approximately axial in symmetry and are closely comparable to those of the well-established [AsO 3 ] 2– radical (Table ). − This radical is readily linked to the diamagnetic [AsO 4 ] 3– precursor and involves the sp 3 hybridization for the unpaired electron orbital directed toward the missing O atom (Table ) . Specifically, the orientations of the unique g 3 and A 1 axes of Centers I, II, and III (Table S1) are approximately along the P–O1 bond direction (86.2°, 90°), the P–O3 bond direction (61.2°, 159.7°) and the P–O2 bond direction (23.1°, 270°), respectively.…”

Arsenic Incorporation in Colemanite From Borate Deposits: Data From Icp-Ms, -Sxrf, Xafs and Epr Analyses

“…The calculated A( 75 As)/h constant of ~2240 MHz along the b axis ( Fig. 9) is significantly smaller than those for the [AsO 4 ] 4center (Dalal et al 1972, Mao et al 2010, but is within the range reported for the [AsO 3 ] 2radical (Lin & McDowell 1964, Serway & Marshall 1966, Dalal et al 1972, Xu 1992, Pöppl et al 1994. Unfortunately, this quartet is not detectable if the magnetic field is away from the b axis, presumably because of intensity reduction related to splitting arising from magnetically nonequivalent sites.…”

“…9) is another compelling line of evidence for lattice-bound As 5+ in this mineral. The [AsO 3 ] 2radical in various hosts has been suggested to form from electron trapping on the central As atom of an [AsO 3 ]group (i.e., derived from the more common [AsO 4 ] 3group by removing an oxygen atom) during ionization irradiation (Lin & McDowell 1964, Dalal et al 1972, Xu 1992, Pöppl et al 1994. However, the substitution of As 5+ for B 3+ in borates results in a net deficiency of two electrons.…”

Arsenic Speciation in Newberyite (MgHPO4·3H2O) Determined by Synchrotron X-ray Absorption and Electron Paramagnetic Resonance Spectroscopies: Implications for the Fate of Arsenic in Green Fertilizers

“…The characteristic 75 As hyperfine coupling constants (Table ) suggest that Center I is an As-associated oxyradical of the type [AsO 3 ] 2– . ,,− The orientations of the principal g 2 and A 1 axes of Center I are approximately along the P–O2 bond direction (74.5°, 286.8°) (Figure ; Supporting Information, Table S1). The close matches of these orientations suggest that the [AsO 3 ] 2– radical formed from the diamagnetic [AsO 4 ] 3– group substituting for the [PO 4 ] 3– group in the newberyite lattice.…”