Complexes central atom

In empirical formulas of inorganic compounds, electropositive elements are listed first [3]. The stoichiometry of the element symbols is indicated at the lower right-hand side by index numbers. If necessary, the charges of ions are placed at the top right-hand side next to the element symbol (e.g., S "). In ions of complexes, the central atom is specified before the ligands are listed in alphabetical order, the complex ion is set in square brackets (e.g., Na2[Sn(OH)+]). 

Other Polyatomic Anions. Names for other polyatomic anions consist of the root name of the central atom with the ending -ate and followed by the valence of the central atom expressed by its oxidation number. Atoms and groups attached to the central atom are treated as ligands in a complex. 

Chelates are often named merely as a complex, eg, cadmium complex with acetylacetone. A common practice ia the Hterature is to give the symbol of the central atom and an abbreviation for the ligand with or without an iadication of ionic charges, oxidation states, stmcture, or counterions, as ia the foUowiag Pb-EDTA, Cacit , Cu(en)2, Co(II)-(phen), [Cu(dipy)2]S04, [Ru(dipy)2(en)], and Na[Co(acac)2]. Ligand abbreviations are given ia Table 1. 

No completely general and quantitative theory of the stereochemical activity of the lone-pair of electrons in complex halides of tervalent As, Sb and Bi has been developed but certain trends are discernible. The lone-pair becomes less decisive in modifying the stereochemistry (a) with increase in the coordination number of the central atom from 4 through 5 to 6, (b) with increase in the atomic weight of the central atom (As > Sb > Bi), and (c) with increa.se in the atomic weight of the halogen (F > Cl > Br > 1). The relative energies of the various valence-Ievel orbitals may also be an important factor the F(a) orbital of F lies well below both the s and the p valence... 

We saw in Chapter 7 that octahedral geometry is characteristic of many molecules (e.g., SF6) in which a central atom is surrounded by six other atoms. (Remember, an octahedron has eight sides, which is irrelevant here it has six comers, which is important) All complex ions... 

Octahedral Having the symmetry of a regular octahedron. In an octahedral species, a central atom is surrounded by six other atoms, one above, one below, and four at the comers of a square, 176 complex in transitional metals, 418-420 geometric isomerism, 415 Octane number, 584... 

One of the most important parameters that defines the structure and stability of inorganic crystals is their stoichiometry - the quantitative relationship between the anions and the cations [134]. Oxygen and fluorine ions, O2 and F, have very similar ionic radii of 1.36 and 1.33 A, respectively. The steric similarity enables isomorphic substitution of oxygen and fluorine ions in the anionic sub-lattice as well as the combination of complex fluoride, oxyfluoride and some oxide compounds in the same system. On the other hand, tantalum or niobium, which are the central atoms in the fluoride and oxyfluoride complexes, have identical ionic radii equal to 0.66 A. Several other cations of transition metals are also sterically similar or even identical to tantalum and niobium, which allows for certain isomorphic substitutions in the cation sublattice. 

Since the coordination number of tantalum or niobium in fluoride and oxyfluoride compounds cannot be lower than 6 due to steric limitations, further decrease of the X Me ratio (lower than 6) leads to linkage between complex ions in order to achieve coordination saturation by sharing of ligands between different central atoms of the complexes. The resulting compounds have X Me ratios between 6 and 4, and form crystals with a chain-type structure. 

Sharing of an oxygen atom by two central atoms in compounds with chain-type structures weakens the binary Nb=0 bond compared to the corresponding bond in pure isolated ions such as NbOF52 This phenomenon affects the vibration spectra and increases wave numbers of NbO vibrations in the case of isolated oxyfluoride complex ions. Table 31 displays IR absorption spectra of some chain- type compounds. Raman spectra are discussed in [212],... 

Vibration spectra of fluoride and oxyfuoride compounds correspond to X Me ratios, especially in the case of island-type structure compounds. Analysis of IR absorption spectra provides additional indication of the coordination number of the central atom. Fig. 45 shows the dependence on the X Me ratio of the most intensive IR bands, which correspond to asymmetric Me-F modes in fluoride complexes, as well as v(Me=0) and v(Me-F) in oxyfluoride complexes. Wave numbers of TaF5, NbF5 and NbOF3 IR spectra were taken from [283-286]. 

Changes in the charge of the central atom also strongly affect the metal-ligand bond length and the ionic-covalent share in fluoride complexes, which in turn impact the vibration spectra. Fig. 46 shows the dependence of asymmetric valence vibrations on the charge of the central atom. The spectral data for Mo, W, Zr, Hf fluoride compounds were taken from [71,115,137]. 

Fluorine ions form the first coordination sphere around the tantalum ion, which is the central atom of the complex. Potassium ions form the second coordination sphere, which significantly affects the geometry and force field of the first coordination sphere. The melting of K2TaF7 leads to the dissociation of the compound into ions, as follows ... 

The way that atoms or molecules are arranged in space around a central atom has a great influence on whether a given complex aggregate is stable enough to be observed. What kinds of arrangements are found in complex ions What... 

In addition to the tetrahedral and octahedral complexes mentioned above, there are two other types commonly found—the square planar and the linear. In the square planar complexes, the central atom has four near neighbors at the corners of a square. The coordination number is 4, the same number as in the tetrahedral complexes. An example of a square planar complex is the complex nickel cyanide anion, Ni(CN)4-2. 

In a linear complex, the coordination number is 2, corresponding to one group on each side of the central atom. The silver-ammonia complex, which generally forms when a very slightly soluble silver salt such as silver chloride dissolves in aqueous ammonia, is an example, as shown in Figure 22-6. Another example of a linear com-... 

The structure theory of inorganic chemistry may be said to have been bom only fifty years ago, when Werner, Nobel Laureate in Chemistry in 1913, found that the chemical composition and properties of complex inorganic substances could be explained by assuming that metal atoms often coordinate about themselves a number of atoms different from their valence, usually four atoms at the comers either of a tetrahedron or of a square coplanar with the central atom, or six atoms at the comers of an octahedron. His ideas about the geometry of inorganic complexes were completely verified twenty years later, through the application of the technique of x-ray diffraction. 

The X-ray absorption fine structure (XAFS) methods (EXAFS and X-ray absorption near-edge structure (XANES)) are suitable techniques for determination of the local structure of metal complexes. Of these methods, the former provides structural information relating to the radial distribution of atom pairs in systems studied the number of neighboring atoms (coordination number) around a central atom in the first, second, and sometimes third coordination spheres the... 

The complexes of aromatic hydroxy carboxylic acids (salicylic acid and its isomers) with [Bu2Sn(IV)] and [Ph3Sn(IV)] were obtained. The FT-IR and Raman spectra clearly demonstrated that the organotin(IV) moieties react with the O, O) atoms of the ligands. It was found that in most cases the -COO group chelated to the central atoms, but monodentate coordination was also observed. The complexes probably have polymeric structures. 

The FT-IR spectroscopic measurements shown that in most cases the -COO or -0 groups formed a bridge between two Sn central atom, and polymerization occurred. The pqs approximations proved the formation of complexes with Oh, Tbp, and structures. H NMR measurements performed in DMSO solution have shown that the polymeric structure of the complexes does not persist in solution, and depolymerization occurs.. ... 

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