Coordination compounds atoms 64

In the following year, 1905, Werner published his great book on coordination chemistry, and this had a powerful influence on Lewis. Werner proposed that in coordination compounds, atoms or groups of atoms surrounded a central atom to form an electrically charged ion or a neutral compound, and the geometrical or structural theory seemed to fit very nicely with Lewis s ideas. All that was needed (and it was a big all ) was a clearer picture of the electrical nature of atoms. 

Besides structure and substructure searches, Gmclin provides a special search strategy for coordiuation compouuds which is found in no other database the ligand search system, This superior search method gives access to coordination compounds from a completely different point of view it is possible to retrieve all coordination compounds with the same ligand environment, independently of the central atom or the empirical formula of the compound. 

Naming a Coordination Compound. To name a coordination compound, the names of the ligands are attached directly in front of the name of the central atom. The ligands are listed in alphabetical order regardless of the number of each and with the name of a ligand treated as a unit. Thus diammine is listed under a and dimethylamine under d. The oxidation number of the central atom is stated last by either the oxidation number or charge number. 

The participation of phosphoms d orbitals in the five- and six-coordinate compounds provides increased polarizabiUty, nucleophilicity, and ionic character. In fact, compounds such as phosphoms pentachloride [10026-13-8] 5) thought to have considerable ionic character. The CJ-bond orders between the phosphoms atom and its constituents in the higher coordinate compounds maybe less than one. 

Much effort has been placed in the synthesis of compounds possessing a chiral center at the phosphoms atom, particularly three- and four-coordinate compounds such as tertiary phosphines, phosphine oxides, phosphonates, phosphinates, and phosphate esters (11). Some enantiomers are known to exhibit a variety of biological activities and are therefore of interest Oas agricultural chemicals, pharmaceuticals (qv), etc. Homochiral bisphosphines are commonly used in catalytic asymmetric syntheses providing good enantioselectivities (see also Nucleic acids). Excellent reviews of low coordinate (coordination numbers 1 and 2) phosphoms compounds are available (12). 

Other types of bonding include donation by Ligand TT-orbitals, as in the classical Zeiss s salt ion [Pt( 7 -CH2=CH2)Cl3] [12275-00-2] and sandwich compounds such as ferrocene. Another type is the delta (5) bond, as in the Re2Clg ion, which consists of two ReCl squares with the Re—Re bonding and echpsed chlorides. The Re—Re 5 bond makes the system quadmply bonded and holds the chlorides in sterically crowded conditions. Numerous other coordination compounds contain two or more metal atoms having metal—metal bonds (11). 

A coordination compound, or complex, is formed when a Lewis base (ligand) is attached to a Lewis acid (acceptor) by means of a lone-pair of electrons. Where the ligand is composed of a number of atoms, the one which is directly attached to the acceptor is called the donor atom . This type of bonding has already been discussed (p. 198) and is exemplified by the addition compounds formed by the trihalides of the elements of Group 13 (p. 237) it is also the basis of much of the chemistry of the... 

The complex 23 is the first X-ray structurally characterized metal coordination compound with a benzochalcogenazole ligand in which chalcogen behaves as the ligating atom. 

Compound [PtCl( Bu2PCMe2CH2)2l reacts with pyrazole or 3,5-dimethyl-pyrazole in the presence of sodium hydroxide to form 242 (R = H, Me) [84ICA (82)L9]. The chelate ring is not planar in this case, and the trans strucmre of the pyrazolate derivative was demonstrated. Tlie four-coordinated platinum atoms are characterized by a distorted square-planar coordination. 

The physical and chemical properties of complex ions and of the coordination compounds they form depend on the spatial orientation of ligands around the central metal atom. Here we consider the geometries associated with the coordination numbers 2,4, and 6. With that background, we then examine the phenomenon of geometric isomerism, in which two or more complex ions have the same chemical formula but different properties because of their different geometries. 

Vitamin B12 is a coordination compound with cobalt as its central atom. It contains 4.4% cobalt by mass and has a molar mass of 1.3 X 103 g/mol. How many cobalt atoms are in a molecule of vitamin B12 ... 

Earlandite structure, 6,849 Edge-coalesced icosahedra eleven-coordinate compounds, 1, 99 repulsion energy coefficients, 1,33,34 Edta — see Acetic acid, ethylenediaminetetra-Effective atomic number concept, 1,16 Effective bond length ratios non-bonding electron pairs, 1,37 Effective d-orbital set, 1,222 Egta — see Acetic acid,... 

The hydrated ion [Cu(H20)6]2+ is an example of a complex, a species consisting of a central metal atom or ion to which a number of molecules or ions are attached by coordinate covalent bonds. A coordination compound is an electrically neutral compound in which at least one of the ions present is a complex. However, the terms coordination compound (the overall neutral compound) and complex (one or more of the ions or neutral species present in the compound) are often used interchangeably. Coordination compounds include complexes in which the central metal atom is electrically neutral, such as Ni(CO)4, and ionic compounds, such as K4[Fe(CN)6]. 

Many complexes and coordination compounds exist as isomers, compounds that contain the same numbers of the same atoms but in different arrangements. For example, the ions shown in (13a) and (13b) differ only in the positions of the Cl ligands, but they are distinct species, because they have different physical and chemical properties. Isomerism is of more than academic interest for example, anticancer drugs based on complexes of platinum are active only if they are the correct isomer. The complex needs to have a particular shape to interact with DNA molecules. 

Figure 16.18 summarizes the types of isomerism found in coordination complexes. The two major classes of isomers are structural isomers, in which the atoms are connected to different partners, and stereoisomers, in which the atoms have the same partners but are arranged differently in space. Structural isomers of coordination compounds are subdivided into ionization, hydrate, linkage, and coordination isomers. 

The processes (11) and (12) have been studied by means of the MINDO/3 method optimizing the geometry with respect to the cartesian coordinates of the model compound atoms. The reaction enthalpies AH , calculated for the reactions (11) and (12) are to be seen in Table 11. 

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