Mixed-Metal Monophosphate Tungsten Bronzes Containing Rhodium and Iridium

Incorporation of rhodium or iridium in phosphates of the MPTB structure family is possible. SXRD analysis of (Rh1/6W5/6O3)8(PO2)4 and (Rh2/21W19/21O3)14(PO2)4 reveals an unexpected distribution pattern for Rh3+ over the available metal sites. Results of further characterization by TEM, powder reflectance spectroscopy and magnetic measurements are reported.


Solution combustion synthesis followed by annealing in air led to the MPTB-related phosphates (Rh1/6W5/6O3)8(PO2)4, (Ir1/6W5/6O3)8(PO2)4 (a=5.258(2) Å, b=6.538(3) Å, c=17.322(8) Å), (Rh1/9W8/9O3)12(PO2)4 and (Rh2/21W19/21O3)14(PO2)4. Single-crystals of the mixed-metal (Rh,W)-MPTBs at m=4 and at m=7 were grown by chemical vapor transport (CVT). Their crystal structures have been refined from X-ray single-crystal data {(Rh,W)-MPTB at m=4: P212121, Z=1, a=5.2232(3) Å, b=6.4966(3) Å, c=17.3819(9) Å, R1=0.032, wR2=0.075 for 1714 unique reflections, 1524 with Fo>4σ(Fo), 66 variables, 1 constraint, composition from refinement (Rh0.15W0.85O3)8(PO2)4; (Rh,W)-MPTB at m=7: P21/n, Z=1, a=5.2510(4) Å, b=6.4949(5) Å, c=26.685(2) Å, β=90.30(1)°, R1=0.060, wR2=0.163 for 2074 unique reflections, 1894 with Fo>4σ(Fo), 100 variables, comp. from ref. (Rh0.07W0.93O3)14(PO2)4}. These structure refinements show unexpected distribution of Rh and W over the available metal sites. Further characterization (powder reflectance and magnetic measurements) of the (Rh,W)-MPTB at m=4 and at m=7 suggest for both phases a homogeneity range with respect to the Rh/W ratio and the presence of small amounts of W5+ besides Rh3+ and W6+. Results of the ligand field analysis for the reference material Rh(PO3)3, which is containing the octahedral chromophore [RhIIIO6], are reported (Δo=23200 cm−1, B=490 cm−1).
Alexander Karbstein, Markus Weber, Dominic Lahr, Dr. Jörg Daniels, Dr. Wilfried Assenmacher, Prof. Dr. Werner Mader, Dr. Frank Rosowski, Dr. Stephan A. Schunk, Prof. Dr. Robert Glaum

Eur. J. Inorg. Chem. 2021, online

© AK Glaum
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