Coordinates, atomic dependent

Diastereoisomerism is observed when two or more chiral elements appear in the same system. Isolation and characterization of enantiomers or diastereoisomers depend on the structural stability of the chiral element. Therefore the conformation of a chelate ring must generally be considered as labile. The structural stability of the configuration around the metal center and the stability of an asymmetric coordination atom depends on the nature of the central metal atom. In most cases an optically active ligand molecule can be considered as configurationally stable. The presence of a stable chiral element can induce definite chirality in another element which, taken separately, would be labile. 

Almost every metal atom can be inserted into the center of the phthalocyanine ring. Although the chemistry of the central metal atom is sometimes influenced in an extended way by the phthalocyanine macrocycle (for example the preferred oxidation state of ruthenium is changed from + III to + II going from metal-free to ruthenium phthalocyanine) it is obvious that the chemistry of the coordinated metal of metal phthalocyanines cannot be generalized. The reactions of the central metal atom depend very much on the properties of the metal. 

How does the chemical reactivity of a metal atom depend on its coordination number ... 

Schiff bases provide useful mixed donor sets. The carbonyl function of the most frequently used ligands is derived from either 1,3-dicarbonyl compounds or salicylaldehyde. Favourable combinations involve O-, N- and S-donor atoms. A range of technetium and rhenium complexes exist with bi-, tri-, tetra- and pentadentate ligands. The geometry of these complexes depends on the number and type of coordinating atoms as well as on the chain length between the donor atoms in the SchifF-base ligands. 

The availability of different metal ion binding sites in 9-substituted purine and pyrimidine nucleobases and their model compounds has been recently reviewed by Lippert [7]. The distribution of metal ions between various donor atoms depends on the basicity of the donor atom, steric factors, interligand interactions, and on the nature of the metal. Under appropriate reaction conditions most of the heteroatoms in purine and pyrimidine moieties are capable of binding Pt(II) or Pt(IV) [7]. In addition, platinum binding also to the carbon atoms (e.g. to C5 in 1,3-dimethyluracil) has been established [22]. However, the strong preference of platinum coordination to the N7 and N1 sites in purine bases and to the N3 site in pyrimidine bases cannot completely be explained by the negative molecular electrostatic potential associated with these sites [23], Other factors, such as kinetics of various binding modes and steric factors, appear to play an important role in the complexation reactions of platinum compounds. 

The Selection of Hypersurface Coordinates. Energy hypersurfaces for nonlinear molecules comprising n atoms depend parametrically on all 3n-6 internal nuclear coordinates. Considering all of them,however, would require computing times which already for medium-sized molecules would easily exceed human life-span( ), and, obviously, lead to a visualization chaos. Own experience in the design of hypersurface calculations can be summarized in the following (trivial) hints ... 

In a later study, substituted lithium phenolates were investigated in different solvents . Here, the lithium phenolates were shown to exist as monomers, dimers and tetramers, depending on the solvent and substitution pattern. It was found that the different aggregates have different QSC ranges, where the QSC is smaller for higher aggregates. It was also noted that the QSC value depends to some extent on the solvent, especially on the type of coordinating atom, i.e. O V5. N in ethers and amines, respectively. 

The nonadditivity arising from the polarization forces is the most evident. The interaction energy of two atoms depends upon the location of other atoms because the latter polarize the electronic charge distribution of both interacting atoms. For a three-atom system each pair interaction depends on coordinates of all three atoms,... 

A complex or coordination compound generally consists of one or more groups (molecules or anions) surrounding and bonded to a central metal (cation or neutral atom). Depending upon the charges on the central metal and bonded groups, the complex can be cationic, anionic, or neutral. Examples are ... 

This non-pairwise behaviour is most easily demonstrated by considering the coordination number dependence of the binding energy. It follows from eqs (5.68), (5.69), and (5.70) that the binding energy per atom of a lattice with coordination number may be written in the form... 

Why should these structures affect catalysis It is because they affect bonding. In Fig. 7.108, it can be seen that an atom on a planar site coordinates with between one and four surface atoms, depending on how it sits in the site. When it also has the opportunity to bond with further atoms at the side (i.e., against a ledge), its coordination number (and hence its bonding) increases and it gets even larger at a kink site. 

The size of an arsenic atom depends on its valence state and the number of surrounding atoms (its coordination number). When valence electrons are removed from an atom, the radius of the atom not only decreases because of the removal of the electrons, but also from the protons attracting the remaining electrons closer to the nucleus (Nebergall, Schmidt and Holtzclaw, 1976), 141. An increase in the number of surrounding atoms (coordination number) will deform the electron cloud of an ion and change its ionic radius (Faure, 1998), 91. Table 2.2 lists the radii in angstroms (A) for arsenic and its ions with their most common coordination numbers. 

The crystallochemical analysis of complexonates has been carried out and the crystallostructural role of various ligands, on the formation of different coordination modes by metal atoms, is extensively reviewed [761-763], It is established that com-plexonate ions of the diamine type are capable of forming 14 different types of coordination [761], Depending on the coordination mode present, one polydentate diaminocarboxylate ligand has the capability to bind from one to four metal atoms, producing from two to 10 coordination bonds. 

---