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Title: New honeycomb iridium( v ) oxides: NaIrO 3 and Sr 3 CaIr 2 O 9

Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
OSTI Identifier:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Dalton Transactions; Journal Volume: 44; Journal Issue: 47
Country of Publication:
United States

Citation Formats

Wallace, David C., and McQueen, Tyrel M. New honeycomb iridium( v ) oxides: NaIrO 3 and Sr 3 CaIr 2 O 9. United States: N. p., 2015. Web. doi:10.1039/C5DT03188E.
Wallace, David C., & McQueen, Tyrel M. New honeycomb iridium( v ) oxides: NaIrO 3 and Sr 3 CaIr 2 O 9. United States. doi:10.1039/C5DT03188E.
Wallace, David C., and McQueen, Tyrel M. 2015. "New honeycomb iridium( v ) oxides: NaIrO 3 and Sr 3 CaIr 2 O 9". United States. doi:10.1039/C5DT03188E.
title = {New honeycomb iridium( v ) oxides: NaIrO 3 and Sr 3 CaIr 2 O 9},
author = {Wallace, David C. and McQueen, Tyrel M.},
abstractNote = {},
doi = {10.1039/C5DT03188E},
journal = {Dalton Transactions},
number = 47,
volume = 44,
place = {United States},
year = 2015,
month = 1
  • Sodium iridium (V) oxide, NaIrO{sub 3,} was synthesized by a high pressure solid state method and recovered to ambient conditions. It is found to be isostructural with CaIrO{sub 3}, the much-studied structural analog of the high-pressure post-perovskite phase of MgSiO{sub 3}. Among the oxide post-perovskites, NaIrO{sub 3} is the first example with a pentavalent cation. The structure consists of layers of corner- and edge-sharing IrO{sub 6} octahedra separated by layers of NaO{sub 8} bicapped trigonal prisms. NaIrO{sub 3} shows no magnetic ordering and resistivity measurements show non-metallic behavior. The crystal structure, electrical and magnetic properties are discussed and compared tomore » known post-perovskites and pentavalent perovskite metal oxides. -- Graphical abstract: Sodium iridium(V) oxide, NaIrO{sub 3}, synthesized by a high pressure solid state method and recovered to ambient conditions is found to crystallize as the post-perovskite structure and is the first example of a pentavalent ABO{sub 3} post-perovskite. Research highlights: {yields} NaIrO{sub 3} post-perovskite stabilized by pressure. {yields} First example of a pentavalent oxide post-perovskite. {yields} Non-metallic and non-magnetic behavior of NaIrO{sub 3}.« less
  • N{sup 5}-Carboxyaminoimidazole ribonucleotide mutase (N{sup 5}-CAIR mutase or PurE) from Escherichia coli catalyzes the reversible interconversion of N{sup 5}-CAIR to carboxyaminoimidazole ribonucleotide (CAIR) with direct CO{sub 2} transfer. Site-directed mutagenesis, a pH-rate profile, DFT calculations, and X-ray crystallography together provide new insight into the mechanism of this unusual transformation. These studies suggest that a conserved, protonated histidine (His45) plays an essential role in catalysis. The importance of proton transfers is supported by DFT calculations on CAIR and N{sup 5}-CAIR analogues in which the ribose 5'-phosphate is replaced with a methyl group. The calculations suggest that the nonaromatic tautomer of CAIRmore » (isoCAIR) is only 3.1 kcal/mol higher in energy than its aromatic counterpart, implicating this species as a potential intermediate in the PurE-catalyzed reaction. A structure of wild-type PurE cocrystallized with 4-nitroaminoimidazole ribonucleotide (NO{sub 2}-AIR, a CAIR analogue) and structures of H45N and H45Q PurEs soaked with CAIR have been determined and provide the first insight into the binding of an intact PurE substrate. A comparison of 19 available structures of PurE and PurE mutants in apo and nucleotide-bound forms reveals a common, buried carboxylate or CO{sub 2} binding site for CAIR and N{sup 5}-CAIR in a hydrophobic pocket in which the carboxylate or CO{sub 2} interacts with backbone amides. This work has led to a mechanistic proposal in which the carboxylate orients the substrate for proton transfer from His45 to N{sup 5}-CAIR to form an enzyme-bound aminoimidazole ribonucleotide (AIR) and CO{sub 2} intermediate. Subsequent movement of the aminoimidazole moiety of AIR reorients it for addition of CO{sub 2} at C4 to generate isoCAIR. His45 is now in a position to remove a C4 proton to produce CAIR.« less
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  • The high-pressure phase of iridium-based compound Ba{sub 3}CaIr{sub 2}O{sub 9} was synthesized using high-pressure sintering. Being different from the distorted hexagonal BaTiO{sub 3} structure of the ambient Ba{sub 3}CaIr{sub 2}O{sub 9}, the high-pressure phase crystals into the 1:2 B-site-ordered perovskite structure with the space group P-3m1 (Z=1). Through fitting the X-ray powder diffraction (XRD) data with Rietveld analysis, in which the obtained R{sub p}, R{sub wp}, and R{sub exp} factors are 7.49%, 11.4%, and 4.82%, respectively, the lattice parameters are a=5.8296(1) A and c=7.1659(2) A. The atomic coordinates and the main interatomic distances and bond angles were also obtained. Themore » relationship of electrical resistivity versus temperature shows that the high-pressure phase of Ba{sub 3}CaIr{sub 2}O{sub 9} is a semiconductor in the temperature range of 5-300 K. The measurement of temperature dependence of magnetic susceptibility indicates that it is paramagnetic. - Graphical Abstract: The high-pressure form of iridium-based perovskite Ba{sub 3}CaIr{sub 2}O{sub 9} crystals into the 1:2 B-site-ordered perovskite-type structure, with the ordered arrangement of Ca and Ir ions in B-site.« less
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