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A number of new quaternary iridium based hydrides and deuterides AAeIrH/D(6) (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-Hagg X-ray and neutron powder diffraction and a new cubic structure type was found. The structure is described in space group F (4) over bar 3m, but related to the K(2)PtCl(6) type structure. The new structure can be described as consisting of cubes of A(+) and Ae(2+) ions, where the A(+) and Ae(2+) ions alternates so that they occupy opposite corners in the cube. Every second cube contains a regular octahedral [Ir(III)H(6)](-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)H(6)](-3) complex with different counterions. These were also compared with the corresponding stretching frequencies for Fe(II)H(6), Ru(II)H(6), Os(II)H(6), and Ir(II)H(5) 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.

Mg2Na2NiH6 was synthesized by reacting NaH and Mg2NiH4 at 310 degrees C under hydrogen pressure. The novel structure type was refined from neutron-diffraction data in the orthorhombic space group Pnma (No. 62), with unit cell dimensions of a = 11.428(2), b = 8.442(2), and c = 5.4165(9) Angstrom and a unit cell volume = 523 Angstrom(3) (Z = 4). The structure can be described by (Mg2H2)(2+) layers intersected by (Na2NiH4)(2-) layers. The [NiH4](4-) complex is approximately tetrahedral, indicating formal zerovalent nickel. This is the first example of a solid-state hydride where a [NiH4](4-) complex is directly stabilized by alkali metal ions instead of the more polarizing Mg(2+) ions. A rather long nickel-hydrogen bond distance of 1.65 Angstrom indicates a weaker Ni-H bond as a result of the weaker support from the less polarizing alkali metal counterions.