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Structural variety in iridate oxides and hydroxides from hydrothermal synthesis

DOI: 10.1039/c1sc00192b DOI Help

Authors: Kripasindhu Sardar (University of Warwick) , Janet Fisher (Johnson Matthey plc) , David Thompsett (Johnson Matthey plc) , Martin Lees (University of Warwick) , Guy J. Clarkson (University of Warwick) , Jeremy Sloan (University of Warwick) , Reza J. Kashtiban (University of Warwick) , Richard Walton (University of Warwick)
Co-authored by industrial partner: Yes

Type: Journal Paper
Journal: Chemical Science , VOL 2 (8) , PAGES 1573-1578

State: Published (Approved)
Published: May 2011
Diamond Proposal Number(s): 2451

Abstract: We report the results of an exploratory synthetic study of iridium-containing materials using hydrothermal methods from simple metal salts. Three alkali-earth iridium hydroxides are isolated as phase-pure samples and their structures examined by single-crystal or powder diffraction methods: each contains Ir(IV)-centred octahedra, isolated from each other and sharing bridging hydroxides or fluoride with alkali-earth (Ca, Sr or Ba) centres. One of these hydroxides, Ca(2)IrF(OH)(6)center dot OH, possesses a unique open structure, consisting of a positively-charged framework that has one-dimensional channels in which infinite chains of hydrogen-bonded hydroxide anions are encapsulated. The addition of hydrogen peroxide or sodium peroxide to otherwise identical hydrothermal reactions yields dense oxide materials in which iridium is found in an oxidation state between +4 and +5: the novel oxide Na(0.8)Sr(2.2)Ir(3)O(10.1) has a KSbO(3)-type structure with an iridium oxidation state of +5, while the new pyrochlore (Na(0.27)Ca(0.59))(2)Ir(2)O(6)center dot 0.66H(2)O contains iridium with an average oxidation state close to +4.5. Our results illustrate the utility for hydrothermal synthesis in the discovery of novel complex structures that may be inaccessible using conventional high-temperature synthesis, with control of the metal oxidation state possible with judicious choice of reagents.

Subject Areas: Chemistry, Materials


Instruments: B18-Core EXAFS