Investigation of Counterion Influence on an Octahedral IrH₆-Complex in the Solid State Hydrides AAeIrH₆ (A = Na, K and Ae = Ca, Sr, Ba, and Eu) with a New Structure Type

A number of new quaternary iridium based hydrides and deuterides AAeIrH/D₆ (where A = Na and K; Ae = Ca, Ba, Sr, and Eu) have been synthesized by direct combination of the alkali, alkaline earth or europium binary hydrides/deuterides and iridium powder. The crystal structures were determined by Guinier–Hägg X-ray and neutron powder diffraction and a new cubic structure type was found. The structure is described in space group F4̅3m, but related to the K₂PtCl₆ type structure. The new structure can be described as consisting of cubes of A⁺ and Ae²⁺ ions, where the A⁺ and Ae²⁺ ions alternates so that they occupy opposite corners in the cube. Every second cube contains a regular octahedral [Ir­(III)­H₆]⁻³-complex and the adjacent is empty. Solid-state IR spectroscopy was used to determine the Ir-allowed stretching and bending frequencies for the [Ir­(III)­H₆]⁻³ complex with different counterions. These were also compared with the corresponding stretching frequencies for Fe­(II)­H₆, Ru­(II)­H₆, Os­(II)­H₆, and Ir­(II)­H₅ complexes in similar solid state hydrides, which increased when going from Fe through Ru, Os to Ir. The frequencies scaled almost linearly with the inverse of size of the cube surrounding the complexes but showed no significant dependence of the formal oxidation state or the experimentally obtained Ir–D distances. However, this was mainly because of difficulties in obtaining enough accurate atomic positions. The ab initio DFT calculations could reproduce the stretching frequencies within a few 10 cm^–1, indicating that experimental vibrational frequencies offer a sensitive test of DFT results.