Coordination Polyhedra RhX6 (X = F,Cl, Br) in Crystal Structures

Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analyses of compounds containing complexes [Rh _a X _n ] ^z– (X = F, Cl, Br). It was found that, irrespective of oxidation number (+3, +4, or +5), rhodium atoms always exhibit the coordination number 6 with respect to the halogen atoms and have octahedral coordination. The influence of site symmetry and the valence state of Rh on the distortion of RhX₆ octahedra are considered. The electronic configuration of the Rh atoms is shown to influence the symmetry of their valence-force field within the crystal structure.     

The IrX6 Coordination Polyhedra (X = F,Cl, Br) in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analysis of compounds containing [Ir _a X _b ] ^z– complexes (X = F, Cl, or Br). The coordination number of Ir atoms with respect to halogen atoms was found to be 6, irrespective of the oxidation state (III, IV, or V), and the coordination polyhedra formed by Ir were found to be always octahedra. The influence of the site symmetry and the valence state of the Ir atoms on the distortion of the IrX₆ octahedra is considered. It is shown that characteristics of the VDP of Ir atoms can be used for quantitative estimation of the crystal-chemical role of Ir atoms in the halide structures.     

The RhX n (X = S,Se, Te) Coordination Polyhedra in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were applied to crystal-chemical analysis of all known compounds whose structures contain rhodium atoms surrounded by chalcogen atoms. The influence of the rhodium valence state and the nature of the chalcogen on the main features of Rh stereochemistry are discussed. Rhodium atoms exhibit coordination numbers of 6, 5, or 4 with respect to S, Se, or Te atoms; in addition to the bonds with chalcogens, rhodium can form 1 to 4 bonds with metal atoms. The VDP volume for Rh(III), Rh(2.67), and Rh(II) atoms in selenides and tellurides very weakly depends on the valence state, whereas in the case of sulfides, the volume increases rather regularly with a decrease in the metal oxidation number from Rh(III) to Rh(I).     

Zur Kristallchemie der Oxorhodate

On the Crystal Chemistry of Oxorhodates The review gives a view to the crystal chemistry of oxorhodates. In comparison to the chemistry of other precious metals rhodium shows a dominant octahedral coordination in oxides and oxorhodates. Starting with the oxides Rh₂O₃, hp‐Rh₂O₃ and RhO₂ it will be shown that the exclusively octahedral coordination of rhodium turns up in oxorhodates. Oxorhodates take over the crystal chemistry of Delafossites, of the K₂NiF₄‐typ and its variants. Oxorhodates form stacking variants, “one dimensional oxides”, perowskites, pyrochlores, hollandites and spinells. Something remarkable is the Perrhenat like network in URh₂O₆ and a modified SrCr₂O₄‐type, observed in β‐Sr_0,97Rh₂O₄. Pb₃Rh₇O₁₅ is remarkable because of incorporation of one sided open Pb(1)O₄ and Pb(2)O₆ polyhedra into the RhO₆‐octahedra network. The open polyhedra are closed by lone pairs, forming Pb(1)O₄LP(1) (trigonal bipyramid) and Pb(2)O₆LP(2) (capped trigonal prism). The positions of lone pairs (e^2? point charge) are verified by calculations of Madelung parts of lattice energy.     

LaRhAl,La<Subscript>3</Subscript>Rh<Subscript>3</Subscript>Al<Subscript>4</Subscript>, and Ce<Subscript>5</Subscript>Rh<Subscript>5</Subscript>Al<Subscript>6</Subscript> as a new family of ternary aluminides

The structures of three aluminides of similar composition are determined via X-ray diffraction. The structures consist of coordination polyhedra built of rhodium atoms that form alternating layers extending perpendicular to the short cell parameter. Compound Ce₅Rh₅Al₆ is built of fragments of the structures of LaRhAl and La₃Rh₃Al₄ in a ratio of 1: 1.     

Characteristic Features of the Rhodium Stereochemistry in the Structure of Carbonyls and Organometallic Compounds

Characteristics of the Voronoi–Dirichlet polyhedra (VDP) were used to carry out crystal chemical analysis of 160 compounds containing 308 RhC _n or RhC _n Rh _m coordination polyhedra. The volume of the rhodium VDP virtually does not depend on the coordination number (C.N.), which varies from 4 to 12, in spite of the pronounced variation of the Rh–C (1.72–2.83 Å) and Rh–Rh (2.55–2.97 Å) bond lengths. It is shown that the VDP parameters allow one to estimate quantitatively the main features of rhodium stereochemistry irrespective of the nature (Rh or C) and the number (n varies from 3 to 12 and m varies from 0 to 6) of atoms in the first coordination sphere.     

The Coordination Polyhedra BC<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> in Crystal Structures

The method of intersecting spheres and Voronoi–Dirichlet polyhedra are used for crystal chemical analysis of 3817 structures comprising 4533 crystallographically nonequivalent sorts of boron atoms contained in BC_n coordination polyhedra. In these coordination polyhedra, boron has coordination numbers (CNs) from 2 to 6, the CN 4 being most typical. With increasing boron CN, the average B–C interatomic distances of the BC_n polyhedra increase by 0.01–0.13 Å, while the average radii of the spheres whose volumes are equal to the volumes of the Voronoi–Dirichlet polyhedra of boron atoms virtually do not vary within the determination error. The characteristic features of intermolecular contacts in the structures of two crystalline hydrates, Fe[B(CN)₄]₂ · 2H₂O and Fe[B(CN)₄]₃ · 6H₂O, are considered according to the method of Voronoi–Dirichlet molecular polyhedra.     

The Coordination Polyhedra OsN n in Crystal Structures

Characteristics of the Voronoi-Dirichlet polyhedra were used to perform the crystal-chemical analysis of 53 compounds containing osmium atoms surrounded by nitrogen atoms. Depending on the metal oxidation state, which varies from Os(II) to Os(VII), the coordination polyhedra formed by osmium atoms can be octahedra or trigonal prisms (OsN₆), square pyramids (OsN₄Os), tetrahedra (OsN₄), or triangles (OsN₃). The parameters of the Voronoi-Dirichlet polyhedra allow one to estimate quantitatively the main stereochemical features of Os atoms, depending on their oxidation state, and in controversial cases, they can be used to determine the oxidation state of osmium in the crystal structures.     

The Coordination Polyhedra PdX n (X = Cl,Br, I) in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analysis of 106 compounds containing palladium atoms surrounded by halogen atoms. Depending on the oxidation number (2 or 4), Pd atoms can bind 4 to 6 X atoms (X = Cl, Br, I) and form PdX _n coordination polyhedra shaped like octahedra or square pyramids (n = 6), square pyramids (n = 5), or squares (n = 4). A lone electron pair on Pd(II) was found on the basis of X-ray diffraction data. The influence of the palladium valence state on the key stereochemical features of palladium halide complexes is considered in terms of the 18-electron rule. The tendency of palladium atoms to Pd···H aghostic interactions was noted.     

Coordination Polyhedra TiOn in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analysis of 532 compounds containing 940 crystallographic sorts of titanium atoms in TiO _n coordination polyhedra. It was found that Ti(IV) or Ti(III) atoms can coordinate four to eight oxygen atoms. For a constant valence state and a constant coordination number (C.N.) of titanium, the Ti–O bond lengths vary by 0.1–1.0 Å. At C.N. #gt; 5, the volume of the metal VDP remains virtually unchanged; when the C.N. decreases to 4, the VDP volume increases by 2–3 ų. For a constant C.N., Ti(IV) Ti(III) transition is accompanied by an increase in the VDP volume of metal atoms of 0.5–1.9 ų. The VDP characteristics of the Ti atoms can be used to determine their valence state and to identify the titanium–metal bonds in the structures of compounds.     

The activity and thermal stability of RhOx/CeO2 nanocomposites prepared by radio-frequency plasma sputtering

The model RhO_x/CeO₂ systems were prepared by radio-frequency (RF) plasma sputtering of Rh electrode in O₂ or Ar/O₂ atmosphere. Thermal stability of the systems and their reaction probability towards CO oxidation were studied by X-ray photoelectron spectroscopy. It was shown that the small oxidized Rh nanoparticles on the CeO₂ surface (RhO_x/CeO₂) obtained by RF sputtering in O₂ have spectroscopic characteristics close to those of Rh³⁺ ions highly dispersed in ceria lattice. The RhO_x/CeO₂ system remains stable upon heating in vacuum at 450°C and shows reactivity towards CO oxidation at T > 200°C. RF sputtering in Ar/O₂ atmosphere results in the formation of larger rhodium nanoparticles that are close to Rh₂O₃ oxide. The Rh₂O₃/CeO₂ system demonstrates lower activity in CO oxidation and cannot be reduced at a temperature below 300°C.     

Crystal structures of three complexes structurally similar to KTbW(CN)8 · 7H2O

Three complexes that crystallize into structures like KTbW(CN)₈ · 7H₂O (triclinic crystal system, space group P $ \bar 1 $ ) were structurally characterized by X-ray diffraction: KYMo(CN)₈ · 7H₂O, a = 7.6371(5), b = 9.2569(6), c = 14.4976(2) Å, α = 80.782(6)°, β = 87.644(5)°, γ = 77.645(5)°, V = 988.23(11) ų, Z = 2, ρ_calcd = 1.876 g/cm³; KHoW(CN)₈ · 7H₂O, a = 7.5887(4), b = 9.2232(5), c = 14.4479(9) Å, α = 80.709(5)°, β = 87.525(5)°, γ = 77.457(5)°, V = 974.12(10) ų, Z = 2, ρ_calcd = 2.462 g/cm³; KErW(CN)₈ · 7H₂O, a = 7.6180(5), b = 9.2356(6), c = 14.4903(11) Å, α = 80.655(6)°, β = 87.492(6)°, γ = 77.557(6)°, V = 982.29(13) ų, Z = 2, ρ_calcd = 2.449 g/cm³. The coordination polyhedra of the d element atoms [M(CN)₈] (M⁴⁺ = Mo and W) are dodecahedra; the coordination polyhedra of the rare-earth metal atoms [RN₄(OH₂)₄] (R³⁺ = Y, Ho, and Er) are tetragonal antiprisms. Four bridging cyano groups are coordinated to the W/Mo and rare-earth metal atoms through the C and N atoms, respectively, to form a polymeric 3D structure involving potassium atoms. The coordination polymers can be formulated as {[K(H₂O)][R(H₂O)₄][M(CN)₈] · 2H₂O} _n (R³⁺ = Y, M⁴⁺ = Mo; R³⁺ = Ho and Er, M⁴⁺ = W).     

Coordination Polyhedra OsXn(X = F, Cl, Br, I) in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analysis of compounds containing complexes [Os _a X _b ] ^z–(X = F, Cl, Br, I). Atoms of Os(V) at X = F and Cl, of Os(IV) at X = Cl, Br, and of Os(III) at X = Br were found to exhibit a coordination number of 6 with respect to the halogen atoms and to form OsX₆octahedra. The coordination polyhedra of Os(III) for X = Cl, I are square pyramids OsX₄. Each Os(III) atom forms one Os–Os bond; as a consequence, the OsBr₆octahedra share a face in forming Os₂Br^3– ₉complexes, while the OsX₄pyramids (X = Cl, I) dimerize to produce [X₄Os–OsX₄]^2–ions. The influence of the valence state of the Os atoms and of the nature of the halogen atoms on the composition and structure of the complexes formed and some characteristics of the coordination sphere of Os were considered.     

{μ‐PbSe}: A Heavy CO Homologue as an Unexpected Ligand

Reactions of [K(18‐crown‐6)]₂[Pb₂Se₃] and [K([2.2.2]crypt)]₂[Pb₂Se₃] with [Rh(PPh₃)₃Cl] in en (ethane‐1,2‐diamine) afforded ionic compounds with [Rh₃(PPh₃)₆(μ₃‐Se)₂]^? and [Rh₃(CN)₂(PPh₃)₄(μ₃‐Se)₂(μ‐PbSe)]^3? anions, respectively. The latter contains a PbSe ligand, a rather uncommon homologue of CO that acts as a μ‐bridge between two Rh atoms. Quantum chemical calculations yield a significantly higher bond energy for PbSe than for CO, since the size of the ligand orbitals better matches the comparably rigid Rh‐Se‐Rh angles and the resulting Rh???Rh distance. To rationalize the bent coordination of the ligand, orbitals with significant ligand contributions and their dependence on the bonding angle were investigated in detail.     

The EuOnCoordination Polyhedra in Crystal Structures

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform crystal-chemical analysis of the compounds studied to date containing EuO _n polyhedra. The Eu(III) and Eu(II) atoms were found to have coordination numbers (C.N.s) from 6 to 12 with respect to oxygen. The Eu(III) Eu(II) transition entails an increase in the VDP volume by, on average, 4 ų. For a constant valence state of europium, the VDP volume barely depends on the C.N., although the Eu–O interatomic distances change by 0.72 Å for Eu(III)-containing structures and by 0.59 Å for Eu(II)-containing structures.     

Spatial Separation of Covalent,Ionic, and Metallic Interactions in Mg11Rh18B8 and Mg3Rh5B3

The crystal structures of Mg₁₁Rh₁₈B₈ and Mg₃Rh₅B₃ have been investigated by using single‐crystal X‐ray diffraction. Mg₁₁Rh₁₈B₈: space group P4/mbm; a=17.9949(7), c=2.9271(1) Å; Z=2. Mg₃Rh₅B₃: space group Pmma; a=8.450(2), b=2.8644(6), c=11.602(2) Å; Z=2. Both crystal structures are characterized by trigonal prismatic coordination of the boron atoms by rhodium atoms. The [BRh₆] trigonal prisms form arrangements with different connectivity patterns. Analysis of the chemical bonding by means of the electron‐localizability/electron‐density approach reveals covalent B? Rh interactions in these arrangements and the formation of B? Rh polyanions. The magnesium atoms that are located inside the polyanions interact ionically with their environment, whereas, in the structure parts, which are mainly formed by Mg and Rh atoms, multicenter (metallic) interactions are observed. Diamagnetic behavior and metallic electron transport of the Mg₁₁Rh₁₈B₈ and Mg₃Rh₅B₃ phases are in agreement with the bonding picture and the band structure.     

Study of the state of rhodium in the potassium rhodiumundecatungstosilicate/alumina system by diffuse-reflectance IR spectroscopy

Adsorption of CO on the catalytic system K₅[SiW₁₁RhO₃₉]/Al₂O₃ was studied by diffuse-reflectance IR spectroscopy. The electronic state of rhodium and thermal stability of the system in the redox cycles were studied. The oxidized heteropolycompound (HPC) contains the charged forms Rh⁺, Rh²⁺, and Rh³⁺. Their ratio strongly depends on the pre-treatment temperature of the sample. In the reduced HPC two main forms of rhodium exist: the ionic Rh⁺ and metallic Rh⁰. The supported HPC structure is stable in an oxidative medium at temperatures below ∼900 K. The properties of the K₅[SiW₁₁RhO₃₉]/Al₂O₃ system are retained in the redox cycles up to ∼670 K, and the highly dispersed state of rhodium is observed up to 900 K.     

Coordination polyhedra LnFn (Ln = La-Lu) in crystal structures

Voronoi-Dirichlet (VD) polyhedra and the intersecting spheres method are used to study stereochemical features of lanthanides (Ln) surrounded by fluorine atoms in the structures of 118 compounds. The coordination numbers of Ln atoms range from 6 to 12. Nine types of coordination polyhedra LnF_n are found; depending on the CN of Ln, the Ln-F bond length can change by 0.2–0.7 Å. Despite the considerable differences in bond lengths, the volume of the VD polyhedra of Ln atoms depends only on their nature and oxidation state. The change in the radii of the spherical domains whose volume is equal to that of the VD polyhedra of Ln atoms shows the tetrad effect.     

The Coordination Polyhedra IrN n in Crystal Structures

Characteristics of the Voronoi–Dirichlet polyhedra were used to perform the crystal-chemical analysis of compounds containing iridium atoms surrounded by nitrogen atoms. The coordination polyhedra formed by Ir(III) atoms are always octahedra (IrN₆), whereas the Ir(2.5) and Ir(II) atoms occurring only in binuclear clusters form the IrN₄Ir ( is the vacancy) and IrN₅Ir quasi-octahedra. The parameters of the Voronoi–Dirichlet polyhedra allow one to estimate quantitatively the main stereochemical characteristics of iridium atoms, depending on their valence state.     

Crystal structure of neptunium(IV) N,N-diethyl dithiocarbamate Np[S2CN(C2H5)2]4

Crystal structure of Np[S₂CN(C₂H₅)₂]₄ has been determined. The environment of the Np atom is formed by eight sulfur atoms. The coordination polyhedron of the Np atom is a dodecahedron. The Np-S bond lengths vary from 2.782(2) to 2.812(2) Å (average 2.795 Å). Two independent (H₅C₂)₂NCS ₂ ^? anions are characterized by different orientations of the diethylcarbamate fragments. A comparison of the geometric characteristics of the coordination polyhedra of the compounds An[S₂CN(C₂H₅)₂]₄ (An = Th, Np) and Np(S₂CN(C₂H₅)₂)₄][N(C₂H₅)₄ shows that the average Np-S bond lengths in the coordination polyhedra decrease by the same value on going from Th⁴⁺ to Np⁴⁺ and from Np³⁺ to Np⁴⁺.