Mixed‐Metal Monophosphate Tungsten Bronzes Containing Rhodium and Iridium

Solution combustion synthesis followed by annealing in air led to the MPTB‐related phosphates (Rh 1/6 W 5/6 O 3 ) 8 (PO 2 ) 4 , (Ir 1/6 W 5/6 O 3 ) 8 (PO 2 ) 4 ( a =5.258(2) Å, b =6.538(3) Å, c =17.322(8) Å), (Rh 1/9 W 8/9 O 3 ) 12 (PO 2 ) 4 and (Rh 2/21 W 19/21 O 3 ) 14 (PO 2 ) 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 : P 2 1 2 1 2 1 , Z =1, a =5.2232(3) Å, b =6.4966(3) Å, c =17.3819(9) Å, R 1 =0.032, wR 2 =0.075 for 1714 unique reflections, 1524 with F o >4 σ ( F o ), 66 variables, 1 constraint, composition from refinement (Rh 0.15 W 0.85 O 3 ) 8 (PO 2 ) 4 ; (Rh,W)‐MPTB at m =7 : P 2 1 / n , Z =1, a =5.2510(4) Å, b =6.4949(5) Å, c =26.685(2) Å, β =90.30(1)°, R 1 =0.060, wR 2 =0.163 for 2074 unique reflections, 1894 with F o >4 σ ( F o ), 100 variables, comp. from ref. (Rh 0.07 W 0.93 O 3 ) 14 (PO 2 ) 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 W 5+ besides Rh 3+ and W 6+ . Results of the ligand field analysis for the reference material Rh(PO 3 ) 3 , which is containing the octahedral chromophore [Rh III O 6 ], are reported ( Δ o =23200 cm −1 , B =490 cm −1 ).