Bisoxalateiridium Acid, a New Rare Example of a Crystal Complex Acid with the \({{\text{H}}_{5}}\text{O}_{2}^{+}\) Cation, and Its Sodium Salt

New coordination compounds, sodium trans-bis(oxalato)diaqua-iridate(III) dihydrate Na[Ir(H₂O)₂(C₂ O₄)₂]·2H₂O and trans-bis(oxalato)diaquairidic acid H₅O₂[Ir(H₂O)₂(C₂O₄)₂], are prepared. The substances are characterized by single-crystal XRD, powder XRD, and IR spectroscopy. Crystal data for Na[Ir(H₂O)₂(C₂O₄)₂]·2H₂O: \(P\bar{1}\) space group, a = 5.2456(7) Å, b = 6.4999(8) Å, c = 8.237(1) Å, α = 98.162(6)°, β = 92.005(6)°, γ = 112.043(4)°, Z = 1; for H₅O₂[Ir(H₂O)₂(C₂O₄)₂]: \(P\bar{1}\) space group, a = 4.6903(2) Å, b = 6.0053(3) Å, c = 9.1527(5) Å, α = 75.843(2)°, β = 84.270(2)°, γ = 82.413(2)°, Z = 1. The coordination sphere of iridium is a distorted octahedron. The Na[Ir(H₂O)₂(C₂O₄)₂]·2H₂O structure is similar to those of MC₂O₄·2H₂O divalent metal oxalates (M = Mn, Fe, Co, Ni, Cu, Zn). The \({{\text{H}}_{\text{5}}}\text{O}_{2}^{+}\) Zundel cation in the trans-bis(oxalato)iridic acid is located discretely.