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DOE OSTI2020

Materials Data on SiPb4(ClO)4 by Materials Project

Pb4Si(OCl)4 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are four inequivalent Pb2+ sites. In the first Pb2+ site, Pb2+ is bonded in a 2-coordinate geometry to two O2- and three Cl1- atoms. There are one shorter (2.34 Å) and one longer (2.38 Å) Pb–O bond lengths. There are a spread of Pb–Cl bond distances ranging from 2.84–3.27 Å. In the second Pb2+ site, Pb2+ is bonded in a 6-coordinate geometry to two O2- and seven Cl1- atoms. There are one shorter (2.41 Å) and one longer (2.56 Å) Pb–O bond lengths. There are a spread of Pb–Cl bond distances ranging from 2.90–3.65 Å. In the third Pb2+ site, Pb2+ is bonded in a 2-coordinate geometry to two O2- and three Cl1- atoms. There are one shorter (2.30 Å) and one longer (2.33 Å) Pb–O bond lengths. There are a spread of Pb–Cl bond distances ranging from 2.93–3.18 Å. In the fourth Pb2+ site, Pb2+ is bonded in a 8-coordinate geometry to three O2- and five Cl1- atoms. There are a spread of Pb–O bond distances ranging from 2.52–2.59 Å. There are a spread of Pb–Cl bond distances ranging from 3.05–3.34 Å. Si4+ is bonded in a tetrahedral geometry to four O2- atoms. There is three shorter (1.65 Å) and one longer (1.66 Å) Si–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to two Pb2+ and one Si4+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to three Pb2+ and one Si4+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to two Pb2+ and one Si4+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to two Pb2+ and one Si4+ atom. There are five inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 4-coordinate geometry to five Pb2+ atoms. In the second Cl1- site, Cl1- is bonded in a 5-coordinate geometry to five Pb2+ atoms. In the third Cl1- site, Cl1- is bonded in a 3-coordinate geometry to three Pb2+ atoms. In the fourth Cl1- site, Cl1- is bonded in a distorted square co-planar geometry to four Pb2+ atoms. In the fifth Cl1- site, Cl1- is bonded in a 6-coordinate geometry to six Pb2+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Origin of the isotopic composition of natural perchlorate: Experimental results for the impact of reaction pathway and initial ClO x reactant

Natural perchlorate (ClO 4 - ) exists in many places on Earth, in lunar regolith, meteorites, and on the surface of Mars. Terrestrial natural ClO 4 - has widely variable Cl and O stable isotopic compositions (δ 37 Cl, δ 18 O, Δ 17 O). The δ 18 O and Δ 17 O values of ClO 4 - from the most hyper-arid locations co-vary. ClO 4 - from less arid areas has relatively little 17 O excess and poor Δ 17 O-δ 18 O correlation. ClO 4 - from the Atacama Desert has unusually low δ 37 Cl (<-10‰) and exhibits a positive correlation between δ 37 Cl and δ 18 O, while the δ 37 Cl of ClO 4 - from all other locations varies between -5 and +7‰ with no δ 37 Cl-δ 18 O covariation. To evaluate the impact of different precursors (ClO x ) and reaction pathways on the isotopic composition of ClO 4 - , we measured the isotopic composition of ClO 4 - produced in the laboratory by UV or O 3 mediated aqueous oxidation of Cl-, OCl-, ClO2-, and ClO2° as well as O 3 mediated oxidation of dry NaCl. ClO x oxidation in aqueous or dry systems enriched in O 3 produced ClO 4 - with Δ 17 O values that generally increased with the number of O atoms required and included evidence that the site-specific 17 O anomaly in O 3 was preferentially transferred to ClO 4 - . Based on the inferred number of O atoms sourced from O 3 , and known Cl and O reaction pathways, it appears that ClO 2 ° and ClO 3 * were required intermediates in the production of ClO 4 - in the O 3 experiments. ClO x aqueous oxidation by UV irradiation produced ClO 4 - with a large range of δ 18 O values and little or no 17 O anomaly. ClO 3 - was produced to a much greater extent than ClO 4 - in all experiments except dry oxidation of NaCl by O 3 . The isotopic composition of ClO 3 - was distinct from that of ClO 4 - produced from the same initial reactants. Combined results of O 3 and UV mediated reactions largely bracketed the range of natural ClO 4 - δ 18 O and Δ 17 O values as well as δ 37 Cl values of non-Atacama natural samples, but no conditions produced the low δ 37 Cl values of Atacama ClO 4 - . Finally, our results indicate that variation in production mechanisms, possibly combined with isotopically variable precursors, could be responsible for much of the observed isotopic variation in natural ClO 4 - and ClO 3 - .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗