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.     

Crystallochemical Analysis of Rare-Earth Halogen-Containing π-Complexes

Ninety-six halogen-containing -complexes of rare-earth elements were studied to reveal how the volume of the area of action of the Ln atom in coordination polyhedra LnC _n X _m (X = F, Cl, Br) depends on its nature, coordination and oxidation numbers, and on the number of Ln–X bonds. A method was proposed for estimating the ligand sizes in the coordination sphere by making use of the molecular Voronoi–Dirichlet polyhedra. The effect of the ligand sizes on the stability of -complexes and formation of aghostic contacts in their structures was analyzed.     

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.     

Xas study of actinide solvent extraction compounds. ii: UO(NO)(L) (with L=tri-isobutylphosphate, tri-n-butylphosphate, trimethylphosphate and triphenylphosphate)

In the back-end of the nuclear fuel cycle, liquid–liquid extraction is the selected separation method. For an improved design of new extracting agent, the knowledge of the coordination polyhedra of the metal ions is important. In this paper, we investigated the coordination sphere of a series of uranyl complexes with selected organophosphorus extracting molecules: UO₂(NO₃)₂L₂ (with L=tri-iso-butylphosphate, tri-n-butylphosphate, trimethylphosphate and triphenylphosphate) using X-ray absorption spectroscopy. FEFF7 calculations of the EXAFS spectra corresponding to the model compound UO₂(NO₃)₂(TiBP)₂ (with TiBP=tri-iso-butylphosphate) for which the crystal structure is known led to a multiple scattering approach of the data fitting. EXAFS results show subtle U–O(P) bond distance differences between the different complexes that are discussed in terms of both electronic and steric effects of L. These results are discussed with regards to the extraction ability of L. In the same time, exploratory work has been attempted in order to evaluate U–O–P bond angle variations as a function of L using multiple photon-scattering paths. Satisfactory values have been obtained compared to the crystallographic data.     

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 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.     

Stereochemistry of Pb(II) Complexes with Aminopolycarboxylic Ligands. The Role of a Lone Electron Pair

The structures of complex anions of Pb(II) coordination compounds (complexonates) with monoamino-, diamino-, and polyaminopolycarboxylic acids as ligands were interpreted in terms of a model of the valence shell electron pair repulsion. A lone electron pair (E) in all structurally studied Pb(II) complexonates with carboxyl-containing complexones was shown to be stereochemically active, and the structure of Pb coordination polyhedron was found to depend on both the ligand dentate number and on its degree of protonation. As the ligand dentate number increased, the coordination number (C.N.) of a central atom changed from 4 + E for monoamine complexonates to 6 + E for diamine and triamine complexonates. With allowance for secondary bonds in the structure, the C.N. of the Pb atom increased to 7–9. The Pb(II) complexonates with nitrilotriacetic acid exhibit the formation of a new type of coordination polyhedron for post-transition elements in a low-valent state with five electron pairs in a valence shell (including one lone electron pair), i.e., the ψ-trigonal bipyramid with E in the axial position.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 483–494.Original Russian Text Copyright © 2005 by Davidovich.     

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

The Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to perform a crystal-chemical analysis of compounds whose structures contain Os atoms surrounded by chalcogen atoms. Depending on the valence state, Os atoms bind four to seven X atoms (X = O, S, Se, Te) forming OsX _n coordination polyhedra which can be tetrahedra (n = 4), trigonal bipyramids or square pyramids (n = 5), octahedra (n = 6), or pentagonal bipyramids (n = 7). In some compounds, pairs of OsO₆ octahedra share edges to form Os–Os bonds. The influence of the Os valence state and the nature of the chalcogen atom on the composition and structure of the [Os _a X _b ] groups is discussed. On the basis of analysis of the crystal-structural data from the standpoint of the 18-electron rule, dependences of the Os–O and Os–Os bond orders on the bond lengths are proposed.     

Systematization of the effective ionic charges in the oxides,oxide fluorides,and fluorides of the rare earth metals

Conclusion We can compare the values obtained above and in [9] for the effective ionic charges e^* for all three types of REM compound examined: fluorides, oxides, and oxide fluorides.In spite of the difference in composition, all these substances can be divided into two groups by separating the cubic (or pseudo-isotropic) crystals and the anisotropic compounds. The average values of the effective charges for each of the structural groups are given in Table 7, which also gives in parentheses the values of the ionic character of the bond, calculated according to Pauling's scheme with allowance for only the nearest homogeneous coordination sphere (for example, for CN=5 instead of 11 for the hexagonal LnF₃, etc.).It can be seen from the Table that the effective charges increase on going from the oxides to the fluorides of the REM, as expected in view of the fact that the electronegativity of fluorine is greater than that of oxygen. In all cases, the increase in the values of e^*, noted above, is observed on going from the anisotropic to the cubic crystals of these compounds. This last feature can be attributed to a decrease in the immediate coordination sphere around the REM atoms with change in the structure of the crystal; in this case the coordination sphere is understood to consist of the nearest ligands. Calculation of the degree of ionic character by the EN method with allowance for only the atoms situated at the shortest distances shows much better agreement with experiment than the classical calculation using the formal CN [8].All-Union Scientific-Research Institute for Physicotechnical and Radiotechnical Measurements. Translated from Zhurnal Strukturnoi Khimii, Vol. 14, No. 3, pp. 541–547, May–June, 1973.     

The SmO n Coordination Polyhedra in Crystal Structures

Crystal-chemical analysis of all compounds studied to date and containing SmO _n coordination polyhedra was performed using the methods of Voronoi–Dirichlet polyhedra (VDP) and intersecting spheres. It was shown that the coordination number (CN) of Sm(III) atoms with respect to oxygen varies from 4 to 12 and the CN of Sm(II) is 5, 7, or 9. The Sm(III) Sm(II) transition was found to entail an increase in the VDP volume by, on average, 2.8 ų, whereas for a constant oxidation state of Sm, the VDP volume barely depends on the CN, although the Sm–O interatomic distances vary by 0.83 Å for Sm(III)-containing crystals and by 0.39 Å for Sm(II)-containing crystals. The results of analysis of the topology of [Sm _a O _b ] groups in the crystal structure are presented.     

The coordination polyhedra KCl<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript> in the crystal structures

The Voronoi-Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to carry out crystal chemical analysis of 141 chlorides containing 245 crystallographic sorts of potassium atoms in the KCl_n coordination polyhedra. The potassium atoms in the crystal structures can coordinate 6 to 12 chlorine atoms, the K-Cl bond lengths varying from 2.81 to 3.91 Å. The radius of spherical domains whose volume coincides with the volume of potassium VDP was found to be virtually independent of the coordination number or the shape of the coordination polyhedron, being equal to 1.93(4) Å. The VDP characteristics were used to analyze the stereochemical features of potassium in the crystal structures.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 1, 2005, pp. 72–80.Original Russian Text Copyright © 2005 by Bikanina, Shevchenko, Serezhkin     

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 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.     

Coordination formulation of tetrahedrally close packed structures: An addendum to the observations of Yarmolyuk and Kripyakevich

Ya. P. Yarmolyuk and P. I. Kripyakevich (Kristallographiya 19, 539 (1974)) showed that all tetrahedrally close packed (t.c.p.) structures have coordination formulae P_pQ_qR_rX_x → (PX₂)_i(Q₂R₂X₃)_j (R₃X)_k, where P, Q, R, and X represent coordination numbers (CN) 16, 15, 14, and 12 polyhedra respectively: p, q, r, and x indicate the numbers of such polyhedra in the unit cells of t.c.p. structures and i, j, and k are positive integers. We propose and demonstrate a limitation to the above formulation: if i ≥ 1 and k ≥ 1, then j ≥ 1 (or if both p> 0 and r> 0, then q> 0). We give reasons for this and discuss the Aufbauprinzip of t.c.p. structures and the results of C. B. Shoemaker and D. P. Shoemaker (Acta Crystallogr. B 42, 3 (1986)).     

Tetraaryl-methane analogues in group 14—V. Distortion of tetrahedral geometryin terms of through-space π–π and π–σ interactions andNMR sagging in terms of π–σcharge transfer

44 members of thecompound series Ph_4−nMR_n (M=Si, Ge, Sn, Pb; R=o-, m-, p-Tol; n=0–4) were synthesized (15 newcompounds). The crystal structures of Ph₃Sn (o-Tol) and PhSn (o-Tol)₃ were determined and compared to 16 known structures. Subject to the distanced (M–C), an interplay between through-space π–π repulsion and π–σ attraction leads to either elongated or compressed tetrahedral geometry. ²⁹ Si-, ¹¹⁹ Sn- and ²⁰⁷ Pb-NMR chemical shifts were determined in solution and in the solid state. ⁷³ Ge chemical shifts were measured only in solution. Anupfield or downfield sagging of the chemical shifts along each series is rationalized in terms of a π–σcharge transfer which is constrained by torsion of the aromatic groups.     

Coordination Polyhedra RuXn (X = O,S, Se,Te) in Crystal Structures

Crystal-chemical analysis of 312 compounds containing complexes [Ru _a X _b ] ^z– (X = O, S, Se, Te) is performed using Voronoi–Dirichlet polyhedra (VDP) and the method of intersecting spheres. In most of these complexes, Ru atoms have coordination number (CN) 6 and form RuX₆ octahedra. However, only with respect to oxygen do the Ru(V)–Ru(VII) atoms exhibit CN 5 or 4 with trigonal-bipyramidal and tetrahedral coordination, respectively.The effect of the valence state of the Ru atoms on their stereochemistry is considered. The important role of the Ru–Ru interactions in the structure of the Ru(II)–Ru(V) compounds is established. As a result of the Ru–Ru interactions, the RuX₆ octahedra are linked through a face or common edge or give O₅Ru–RuO_- dimers in which every metal atom occupies one of the vertices of an octahedron formed by the neighboring Ru atom.The dependence of the Ru–Ru and Ru–O bond orders on their lengths is established on the basis of a crystal-structure analysis and the 18-electron rule.     

Chemical applications of topology and group theory

Possible convex polyhedra for three-dimensional water networks in clathrate and semiclathrate hydrates are discussed in this paper. All such polyhedra have all vertices of order three. Therefore, the number of vertices (v), edges (e), and faces (f) must satisfy the equalities e=3v/2 and f=(4+v)/2. Possible polyhedra of this type with exclusively quadrilateral, pentagonal, and hexagonal faces and with up to 18 faces are examined. Many of these polyhedra are duals of various triangulated coordination polyhedra studied in previous papers of this series. In order to minimize angular strain, polyhedra with the maximum number of pentagonal faces are favored for water networks in clathrate and semiclathrate hydrates subject to the presence of sufficiently large cavities to accommodate the guest molecule.

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Zusammenfassung In dieser Arbeit werden mögliche konvexe Polyeder für dreidimensionale Wasser-Netzwerke in Klathrat- und Semiklathrathydraten diskutiert. Daher muß die Anzahl der Scheitelpunkte (v), Kanten (e) und Flächen (f) den Gleichungen e=3v – und f=(4+v) – genügen. Es werden mögliche Polyeder dieses Typs mit bis zu 18 Flächen, die ausschließlich quadrilateral, pentagonal und hexagonal sein sollen, untersucht. Viele dieser Polyeder sind Zwillinge von verschiedenen, aus Dreiecken zusammengesetzten Koordinationspolyedern, die in früheren Arbeiten dieser Reihe untersucht wurden. Um die Winkeldeformation auf ein Mindestmaß zurückzuführen, werden im Falle von Wassernetzwerken in Klathrat- und Semiklathrathydraten Polyeder mit der maximalen Anzahl von pentagonalen Flächen bevorzugt, weil so ausreichend große Hohlräume zur Aufnahme des Gastmoleküls entstehen.

     

Characteristic Features of Platinum Stereochemistry in the Structures of Organometallic Compounds

The Voronoi-Dirichlet polyhedra (VDP) and the method of intersecting spheres were used to carry out crystal chemical analysis of 85 compounds containing 124 PtC _n or PtC _n Pt _m coordination polyhedra in which the Pt-C and Pt-Pt bond lengths vary in the 1.82-2.43 and 2.58-2.98 Å ranges. The main stereochemical features of platinum are discussed depending on the nature (C or Pt) and the number (n varying from 1 to 10; m varying from 0 to 9) of atoms in the first coordination sphere. It is shown that the VDP parameters can be used to identify the aghostic Pt···H-C interactions in the crystal structure.     

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

Using the Voronoi–Dirichlet partition procedure and the method of intersecting spheres, it is demonstrated that in the crystal structures of chalcogen-containing compounds, Pt(IV) atoms form only PtX₆ octahedra (X = S, Se, Te), whereas in the case of Pt(III) and Pt(II), square coordination by X atoms is typical. The Pt(II) atoms can also form PtX₅ square pyramids (X = S, Se), PtS₆ octahedra, and PtTe₃Pt₃ quasi-octahedra in which a platinum atom is located in the trans-position to each coordinated tellurium atom. It was found that Pt(II) atoms in the PtX₄ squares (X = S, Se), unlike square-coordinated Pt(III) atoms, can form one or two Pt–M bonds (M is a d metal) and 1 to 4 secondary Pt–Q bonds, where Q is an s metal or hydrogen. The main features of platinum stereochemistry depending on the metal valence state and coordination number (CN) and on the nature of the chalcogen atom were quantitatively characterized in terms of the Voronoi–Dirichlet polyhedra.