Structural arrangement, coordination

Complex ions, also called coordination complexes, have well-defined stoichiometries and structural arrangements. Usually, the formula of a coordination complex is enclosed in brackets to show that the metal and all its ligands form a single structural entity. When an ionic coordination complex is isolated from aqueous solution, the product is composed of the complex ion and enough counter-ions to give a neutral salt. In the chemical formula, the counter-ions are shown outside the brackets. Examples include the sulfate salt of [Ni (NH3)g, ... 

A diverse coordination chemistry is emerging for bismuth(III) made possible by a spacious and flexible coordination environment, allowing for coordination numbers in excess of 9. Although the available data are still limited, distinct trends are evident, and the polymeric solid-state features that may be assumed on the basis of high coordination numbers can be mediated by appropriate selection of organic-based ligands. The unusual structural arrangements observed for many types of complex may prove to be representative as the number of examples of such systems increases. 

The subsequent Figs. 3.29 (a)-(d) correspond to an analysis of the structure carried out in order to show the different local atomic arrangements (coordinations around the atoms in the two crystal sites). 

Each of the four organic moieties bridges between an equatorial and an axial copper atom through its C(l) atom, while the nitrogen atom in the substituent is coordinated to an adjacent equatorial copper atom. The two bromine atoms bridge, at opposite sites, between two equatorial copper atoms. This structural arrangement has the consequence that the aggregate incorporates two distinct types of... 

There are six subunits in the asymmetric unit of the Panuliris structure, arranged in a particle best described as a trimer of dimers. The 3-2 symmetry was good enough to be useful in a phase extension technique commonly used in the structure determination of highly symmetric viruses. Unfortunately, these crystals diffract only to 3.2 A, so that there cannot be a high level of detail available for description of the active site. Nevertheless, because there are six independent copies of the molecule in the asymmetric unit, there is more information than might normally be available at this resolution. The structure has been carefully refined at this resolution, with and without the 3-2 symmetry restraint. The estimated coordinate error is —0.35 A. The overall R is 0.201 for data between 8 and 3.2 A. Surprisingly, while the overalls for subunits 1 and... 

AB2 structures. Fluorides and oxides of the formula AB2, which are distinctly ionic, crystallize in structures determined by size considerations. As in the case of AB structures, it is the coordination geometry of anions around the cation that determines the structural arrangement. The coordination may be 8-, 6-, or 4-fold, fixing the corresponding anion coordination numbers to 4,3 or 2. We thus have the following structures for ionic AB2 compounds fluorite (8 4), rutile (6 3) and silica (4 2) and these structures are shown in Fig. 1.7. 

By analogy to the zinc structure, the coordination sphere around the silver(II) ion was anticipated to contain four sulfur atoms from two dialkyl dithiocarbamates in a square planar arrangement. Dimerization would occur by interaction via two Ag—S bridges (8S).538... 

Heteropolyanions and isopolyanions are polymeric oxoanions (polyoxometalates) (2, 3, 5, 6). The structure of a heteropolyanion or polyoxoanion molecule itself is called a primary structure (5, 6, 77). There are various kinds of polyoxoanion structure (Section II.A. 1). In solution, heteropoly anions are present in the unit of the primary structure, being coordinated with solvent molecules and/ or protonated. Most heteropolyanions tend to hydrolyze readily at high pH (Section 1I.C). Protonation and hydrolysis of the primary structure may be major structural concerns in solution catalysis. Heteropoly compounds in the solid state are ionic crystals (sometimes amorphous) consisting of large polyanions, cations, water of crystallization, and other molecules. This three-dimensional arrangement is called the secondary structure. For understanding catalysis by solid heteropoly compounds, it is important to distinguish between the primary structure and the secondary structure (5, 6, 17). Recently, it has been realized that, in addition... 

The sheets formed by the apices of the tetrahedra are completed by hydroxyls and magnesium ions in octahedral coordination link the sheets. The one structural arrangement has nine octahedral sites and the other only eight. Both structures have channels on both sides and top and bottom of each ribbon which contains water molecules (zeolitic water). Additional water is bound to the edge of the ribbons and hydroxyls occur in the structure proper. 

Both metals form a series of MF3 modifications which are isotypic to each other. In general, in these MF3 compounds, the coordination number of the cation is 6, and the structural arrangement can be described in terms of a three dimensional array of corner-sharing octahedra. 

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