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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.

A new quaternary magnesium based alloy (La0.65Ca0.35)(Mg1.32Ca0.68)Ni9 and its hydride have been synthesized and their crystal structures were determined by Guinier–Hagg X-ray powder diffraction. The compound has a hexagonal structure and is isostructural with LaMg2Ni9 (AB2C9 type), in which Ca partially occupies both A and B sites. The hydrogen absorption/desorption properties were determined by pressure–composition isotherms and compared with LaMg2Ni9. (La0.65Ca0.35)(Mg1.32Ca0.68)Ni9 absorbs ∼1.87 wt.% H2 at ∼3.3 MPa H2 and 283 K.

A new calcium substituted palladium hydride, CaPd3H, has been synthesized and the metal structure was found to be of the Ni3Ti (D024) type. From a Guinier-Hagg X-ray powder diffraction pattern the unit cell dimensions were determined to be a = 5.8617(2) and c = 9.7793(6) A. Resistance measurements did not reveal any superconducting transition, but the alloy has metallic character. From considerations of bonding distances in the binary hydrides, the hydrogen atoms are restricted to the octahedral site coordinated by six palladium atoms. The experimental results were confirmed by theoretical calculations on the electronic structure, using the LMTO method. The d-electron bands are filled at the CaPd3H composition, thus limiting the hydrogen occupancy to only one H atom per formula unit.

A new hexagonal intermetallic phase has been detected in a LaMg 2 Cu 2 preparation, which absorbs large quantities of hydrogen (∼2.4 wt.%). The dissociation pressure of the hydride reaches nearly ∼0.4 atmosphere at 170°C. The hydrogen absorption/desorption properties have been determined by thermal analysis and pressure–composition isotherms.

New ternary magnesium-based alloys, YMg2Ni9 and (Y0.5Ca0.5)(MgCa)Ni9 have been synthesized and their crystal structures were determined by Guinier–Hagg X-ray powder diffraction. The compounds are a hexagonal and isostructural with LaMg2Ni9 (AB2C9 type), in which Y is uniquely at the A site as in YMg2Ni9, and Ca partially occupies both A and B sites. The hydrogen absorption/desorption properties were determined by pressure–composition isotherms. YMg2Ni9 does not absorb hydrogen, whereas (Y0.5Ca0.5)(MgCa)Ni9 absorbs ∼2 wt.% H2 at ∼3.3 MPa and 263 K.

A new ternary magnesium-based alloy CaMg 2 Ni 9 has been synthesized, and its crystal structure was determined by Guinier–Hagg X-ray and neutron powder diffraction. The compound has a hexagonal structure and is isostructural with LaMg 2 Ni 9 type, with Ca at the La atom site. The hydrogen absorption/desorption properties have been determined by thermal analysis and pressure–composition isotherms. The electrochemical properties of the alloy were also examined.

In the structure of the title compound, (NH4)8[Cu4(C2O4)8(H2O)2]·4H2O, isolated tetramers of [Cu(ox)2]2+ (ox is oxalate) are present. Each CuII ion coordinates to four O atoms in two oxalate ligands and to two more distant O atoms in a neighbouring oxalate ligand or a water molecule. An extensive hydrogen-bonding network connects the tetramers to two unique solvent water molecules and four ammonium ions.

A number of new ternary magnesium based alloys, RMg2Ni9 (where R=La, Ce, Pr, Nd, Sm and Gd), have been synthesized by reacting a mixture of MgNi2 with RNi5 intermetallic compounds or by direct combination of the elements in the atomic ratio R:Mg:Ni=1:2:9. The crystal structure, determined by Guinier-Hagg X-ray powder diffraction, is related to the hexagonal PuNi3 type. All interatomic distances are close to the corresponding ones in (C15) MgCu2, (C14) MgZn2, (C36) MgNi2, RNi3 and RNi5 of metallic-type bonding.

The new title hydrides and the corresponding deuterides are prepared from mixtures of the alkali, alkaline earth, or europium binary hydrides/deuterides, and Ir powder (5 MPa H2/D2, 400 °C).

A new ternary hydride, Ba 3 Ir 2 H 12 , has been synthesized by reacting a mixture of BaH 2 and iridium powders in a hydrogen atmosphere. The crystal structure was determined by combining Guinier-Hagg X-ray powder diffraction and neutron diffraction data from a deuterated compound. The structure was refined (space group, P-3m1 ; a = 5.4865(3) A and c = 8.8459(10) A ; Z = 1 ). The unit cell contains two slightly distorted [IrH 6 ] 3− octahedra which form a La 2 O 3 -type structure with the three Ba 2+ counterions. Two different Ir-H bond lengths were refined with neutron diffraction data from Ba 3 Ir 2 D 12 : 1.60(1) A and 1.77(2) A.

New ternary magnesium-based alloys, YMg2Ni9 and (Y0.5Ca0.5)(MgCa)Ni9 have been synthesized and their crystal structures were determined by Guinier–Hagg X-ray powder diffraction. The compounds are a hexagonal and isostructural with LaMg2Ni9 (AB2C9 type), in which Y is uniquely at the A site as in YMg2Ni9, and Ca partially occupies both A and B sites. The hydrogen absorption/desorption properties were determined by pressure–composition isotherms. YMg2Ni9 does not absorb hydrogen, whereas (Y0.5Ca0.5)(MgCa)Ni9 absorbs ∼2 wt.% H2 at ∼3.3 MPa and 263 K.

Yttrium tricopper dialuminium, YCu3Al2, is isostructural with hexagonal CaCu5, in which each Cu atom at the 3g(½,0,½) position in space group P6/mmm (No. 191) is partially replaced by an Al atom. The hydrogen-uptake properties are usually enhanced in other AB5 structures by aluminium substitution. YCu5 does not show any hydrogen absorption, and the goal of the present work is to investigate whether aluminium substitution could expand the metal-atom lattice enough to provide better interstitial positions for hydrogen storage. However, no enthalpy change was observed up to 773 K under 3 MPa static H2 pressure by differential thermal analysis (DTA) for the title compound. The compound does not show any significant hydrogen absorption/desorption in the pressure-composition isotherms (P–C–T diagrams) in the temperature range 298–673 K under 3.3 MPa H2 pressure.

Two new hydrides, Li 2 PdH 2 and K 2 PdH 4 , are compared with Na 2 PdH 2 . Both Li 2 PdH 2 and Na 2 PdH 2 are found to be metals and their structures are characterized by linear, formally zero-valent PdH 2 complexes in an alkali atom framework. The structures are isomorphous with Na 2 HgO 2 . The palladium-hydrogen bond length is 1.68 A. The usual stabilization mechanism for a low formal oxidation state, by back donation to orbitals on the ligand, is inoperative when hydrogen is the only ligand and the metallic properties of Li 2 PdH 2 and Na 2 PdH 2 are attributed to a stabilization mechanism in which electrons are delocalized into a conduction band. In K 2 PdH 4 , with the Na 2 PtH 4 type structure, the larger and more electropositive potassium atom allows a more common four-coordinated d 8 square planar palladium complex to be formed. The palladium-hydrogen bond length is 1.63 A. The electrons are localized and K 2 PdH 4 is a yellow-green non-conducting powder.

A number of new ternary magnesium based alloys AMgNi 4 (where A=Ca, La, Ce, Pr, Nd, and Y) have been synthesized by direct combination of the elements in the atomic ratio A:Mg:Ni=1:1:4. The crystal structures were determined by Guinier–Hagg X-ray powder diffraction. The compounds have a cubic SnMgCu 4 (AuBe 5 type) structure, which is related to the (C 15 ) MgCu 2 structure. All interatomic distances indicate metallic-type bonding.

A new ternary hydride, Ba 3 Ir 2 H 12 , has been synthesized by reacting a mixture of BaH 2 and iridium powders in a hydrogen atmosphere. The crystal structure was determined by combining Guinier-Hagg X-ray powder diffraction and neutron diffraction data from a deuterated compound. The structure was refined (space group, P-3m1 ; a = 5.4865(3) A and c = 8.8459(10) A ; Z = 1 ). The unit cell contains two slightly distorted [IrH 6 ] 3− octahedra which form a La 2 O 3 -type structure with the three Ba 2+ counterions. Two different Ir-H bond lengths were refined with neutron diffraction data from Ba 3 Ir 2 D 12 : 1.60(1) A and 1.77(2) A.

Yttrium tricopper dialuminium, YCu(3)Al(2), is isostructural with hexagonal CaCu(5), in which each Cu atom at the 3g((1/2),0,(1/2)) position in space group P6/mmm (No. 191) is partially replaced by an Al atom. The hydrogen-uptake properties are usually enhanced in other AB(5) structures by aluminium substitution. YCu(5) does not show any hydrogen absorption, and the goal of the present work is to investigate whether aluminium substitution could expand the metal-atom lattice enough to provide better interstitial positions for hydrogen storage. However, no enthalpy change was observed up to 773 K under 3 MPa static H(2) pressure by differential thermal analysis (DTA) for the title compound. The compound does not show any significant hydrogen absorption/desorption in the pressure-composition isotherms (P-C-T diagrams) in the temperature range 298-673 K under 3.3 MPa H(2) pressure.