F. Bonhomme

New ternary and quaternary metal hydrides with K2PtCl6-type structures

Abstract The ternary alkaline earth transition metal hydrides Ca 2 FeH 6 , Sr 2 FeH 6 , Eu 2 FeH 6 , Mg 2 RuH 6 , Mg 2 OsH 6 and Ca 2 OsH 6 were synthesized from metal mixtures at 450–500°C and 70–130 bar H 2 pressure. They crystallize with the f.c.c. K 2 PtCl 6 structure type and contain octahedral [TH 6 ] 4− (T = Fe, Ru, Os) hydride complexes with bond distances [T-D] = 1.618(5) A (Ca 1.98 Mg 0.02 FeD 6 ), 1.673(4) A (Mg 2 RuD 6 ), 1.682(2) A (Mg 2 OsD 6 ) and 1.728(5) A (Ca 1.92 Mg 0.08 OsD 6 ) as refined from neutron powder diffraction of magnesium-containing deuterides. In systems containing two alkaline earth elements quaternary hydrides with primitive cubic structures are formed in which the alkaline earth atoms are ordered. Preliminary neutron data on iron-based CaMgFeD 6 and nickel-based CaMgNiD 4 confirm the presence of octahedral [FeD 6 ] 4− and tetrahedral [NiD 4 ] 4− complexes respectively.

Hexamagnesium dicobalt undecadeuteride Mg6Co2D11: containing [CoD4]5− and [CoD5]4− complex anions conforming to the 18-electron rule

Abstract Mg6Co2D11 crystallizes in space group Pnma, a=8.1000(2) A , b=10.0643(2) A , c = 18.5664(4) A , V = 1513 A 3 , Z = 8. The partly disordered structure contains 14 symmetry-independent deuterium atoms, of which 9 are coordinated to cobalt in square-pyramidal [CoD5]4− and saddle-like [CoD4]5− complex anions, and 5 are bonded to magnesium only. The Co-D bond distances range between 1.52(1) A and 1.62(2) A. The limiting ionic formula can be written as 4Mg6Co2D11=5MgD219Mg2+2[CoD5]4−6[CoD4]5−. The 63-parameter structure was solved ab initio and refined from joint synchrotron and neutron high resolution powder diffraction data.

Orthorhombic dimagnesium ruthenium tetrahydride containing a diamagnetic [RuH4]4- complex anion with C2v symmetry

Abstract Dimagnesium ruthenium tetrahydride (Mg 2 RuH 4 ) and its deuteride were synthesized by the reaction of magnesium with ruthenium under a hydrogen (deuterium) pressure and characterized by X-ray and neutron powder diffraction. The compound crystallizes in the orthorhombic space group Cmcm . The structure contains a new 16-electron low spin [RuD 4 ] 4 complex anion of C 2v symmetry which derives from the octahedral 18-electron [RuD e ] 4- complex anion in Mg 2 RuD 6 by removal of two cis deuterium ligands.

Synthesis and crystal structure refinement of cubic Mg6.8 Y

Abstract The crystal structure of the Mg-rich compound in the Mg-Y system was determined on a single crystal. Refinement showed its composition to be Mg6.8-Y. The crystal structure is a variant of the cubic α-Mn-type (space group I 4 3m). In contradistinction to a previous structure report we found that the 8c site shows mixed occupancy, whereas the 2a site is exclusively occupied by Y.

Tetragonal Zr2CoD5 with filled Al2Cu-type structure and ordered deuterium distribution

Abstract Tetragonal Zr 2 CoD 5 (measured composition, Zr 2 CoD 4.82(1) ; space group symmetry P4/ncc; a= 6.9251(5) A , c= 5.6462(6) A ; T= 298 K ; Z= 4 ; refined composition Zr 2 CoD 5.05(2) ) was synthesized from intermetallic Zr 2 Co (Al 2 Cu-type structure; space group symmetry I4/mcm; a = 6.3642(4) A , c = 5.5204(3) A ) by reaction with deuterium at 398 K and 15 bar pressure. Neutron powder diffraction shows that deuterium fills tetrahedral [Zr 4 ] and [Zr 3 Co] interstices in an ordered way. Cobalt is surrounded by deuterium in an approximately square-planar configuration with CoD bond distances of 1.663(2) A. The shortest ZrD bond and DD contact distances are 2.044(1) A and 2.092(1) A respectively. The compound decomposes at 773 K and 1 bar H 2 pressure into ZrH 2 and ZrCo 2 .

Tetragonal trimagnesium ruthenium trideuteride, Mg3RuD3, containing dinuclear [Ru2D6]12- complex anions

Abstract Trimagnesium ruthenium trihydride, Mg 3 RuH 3 , and its deuteride were synthesized by reaction of magnesium and ruthenium powders at 883 K and 9 bar hydrogen (deuterium) pressure and structurally characterized by X-ray and neutron powder diffraction; space group P4 2 /mnm, a = 7.2729(4) A , c = 6.9302(7) A ( deuteride , T = 298 K ), Z = 4 . The structure can be described in terms of [Ru 2 D 6 ] 12− dianions in which deuterium surrounds ruthenium in a distorted T-shaped configuration with bond distances Ru-D = 1.712(4) A (2×) and 1.709(9) A (1×) and bond angles D-Ru-D = 170.3(3)° and 94.7(2)°. The Ru-Ru distance is 3.310(4) A.

Cubic Mg29Ir4 crystallizing with an ordered variant of the Mg6Pd-type structure

Abstract Mg29Ir4 was synthesised by solid state reaction at 500°C and characterised by X-ray powder diffraction. Its structure (space group F 4 3m, a = 20.1148(3) A , Z = 12 ) corresponds to a fully ordered variant of the Mg6Pd type.

Hydrogen-stabilized Mg2RhH1.1 with filled Ti2Ni-type structure

Mg2RhH1.1 is the first example for a hydrogen stabilized binary metal compound with filled Ti2Ni-type structure. Its composition was refined from X-ray and neutron powder diffraction data on the deuteride and found to be Mg2RhD1.1. The deuterium atoms in the structure occupy octahedral holes formed by Mg atoms and tetrahedral holes formed by Mg and/or Rh atoms. Retrieval of hydrogen by desorption destabilizes the structure and leads to a hitherto unknown binary metal compound of composition Mg2Rh which crystallizes with the Ti2Pd-type structure, a branch of the MoSi2-type structure.

Orthorhombic Mg4IrD5 with disordered deuterium distribution

Mg4IrH5 and its deuteride was synthesized by the reaction of magnesium and iridium powders with hydrogen (deuterium) at high pressure (41–100 bar) and high temperature (723–783 K). The structure was determined by X-ray and neutron powder diffraction. This compound crystallizes with a new structure type with orthorhombic symmetry (space group Imma, cell parameters a = 4.8110(3) A, b = 8.9624(6) A, c = 10.8970(8) A, Z = 4, hydride, T = 298 K). It contains two deuterium sites: one is disordered with an occupancy of 75% and surrounds iridium in a distorted square planar configuration with distances [IrD] = 1.69 A; the other is ordered and is coordinated by magnesium in a distorted tetrahedral configuration.

MgRhD1-x, a new interstitial deuteride containing square planar [Rh4D4] rings with nearly linear RhDRh bridges

Abstract The title compound was investigated by neutron powder diffraction at various deuterium pressures. It has metallic character and crystallizes with a tetragonally deformed CsCl-type metal arrangement (MgRhD 0.94(2) : space group P4/mmm; Z=4, a=6.395(1) A , c = 3.2368(7) A at p = 39 bar and T= 298 K ). The rhodium atoms are connected to four-membered planar rings via deuterium atoms with bond distances [Rh-D] = 1.708(4) A and bond angles [D-Rh-D] = 87.5(7)° and [Rh-D-Rh] = 177.5(9)°. Two-thirds of the magnesium atoms are bonded to deuterium at distances in the range [Mg-D] = 2.23–2.33 A .