Hydrothermal Synthesis, Crystal Structure, and Magnetism of Na₂[Ir(OH)₆] and its Dehydration to Na₂IrO₃

Abstract

Yellow single-crystals of Na 2 [Ir(OH) 6 ] were obtained by hydrothermal synthesis in 20 m sodium hydroxide solution at 473 K within 5 hours. X-ray diffraction on a single-crystal revealed the trigonal space group R � 3 (no. 148) with lattice parameters a = 582.76(3) pm and c = 1399.30(8) pm at 100(1) K. Na 2 [Ir(OH) 6 ] crystallizes in a hettotype of Mg(OH) 2 (brucite) and is isostructural to Na 2 [Sn(OH) 6 ]. The oxygen atoms are arranged in a hexagonal close packing, Na + and Ir 4 + ions occupy the octahedral voids in every second layer in an ordered manner, the voids of the next layers remain empty. The hydroxidometalate layer can be seen as isolated [Ir(OH) 6 ] 2À octahedra, which are embedded in a honeycomb net of alkali metal cations. Temperature-dependent magnetic measurements revealed paramagnetic behavior with an effective moment of 1.9 μ B per iridium ion. The thermal decomposition of Na 2 [Ir(OH) 6 ] in air starts at about 220°C and results in pure Na 2 IrO 3.

Oxohydroxo‐Tellurates(VI) K2[TeO2(OH)4] and K2[Fe2TeO6(OH)2] ⋅ 2H2O from Alkaline Hydroflux

“…The cubic K 2 PtCl 6 structure type or less symmetric variants of it are often adopted, e. g., in the case of K 2 [OsO 2 (OH) 4 ] [49] . Alternatively, the lower charged A cations are located between the [ MX ] 6 octahedra in the same layer, such as in the hexahydroxoiridate(IV) Na 2 [Ir(OH) 6 ] [39] . In K 2 [TeO 2 (OH) 4 ], the hydrogen bonding system forms a comparatively dense 4 4 net that prevents the entry of potassium cations.…”

“…The work of zur Loye [15,16,[19][20][21][22][23][24][25][26][27][28] and the recent contributions by us [29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] give an impression of the potential of the hydroflux method. In just a few years, almost 100 new compounds were found in already extensively explored systems.…”

Recycling organoiridium waste to [(1,5-cyclooctadiene)IrCl]2

“…Oxidation in an acidic solution was not a practical approach on our hands: these conditions give persistent organic derivatives of Ir(IV) rather than converging the system to the desired IrCl 6 2− . By requires hydrothermal conditions (20 M NaOH, 200 °C), 21 while full hydrolysis to 2 happens readily at pH 7-9.…”

“…In a strongly alkaline media, iridium( iv ) exists primarily as a mixture of 2 and Ir(OH) 6 2− with the equilibrium favoring the former. Full dissolution to Ir(OH) 6 2− requires hydrothermal conditions (20 M NaOH, 200 °C), 21 while full hydrolysis to 2 happens readily at pH 7–9. (2) Adding a fresh portion of NaClO to the completed reaction actively evolves O 2 at 70–100 °C.…”