Coordination type

Fig. 2. Classification/nomenclature of host—guest type inclusion compounds, definitions and relations (/) coordinative interaction, (2) lattice barrier interaction, (J) monomolecular shielding interaction (I) coordination-type inclusion compound (inclusion complex), (II) lattice-type inclusion compound (multimolecular/extramolecular inclusion compound, clathrate), (III) cavitate-type inclusion compound (monomolecular/intramolecular inclusion...

Type 2 coordination is more prevalent and commonly used for all industrial applications. Below, we concentrate on coordination Type 2, permitting the least damage and longer service life. This coordination can safely withstand normal fluctuations in system parameters and operating conditions during normal working. It is always advisable to verify the authenticity of the coordination in a laboratory. For procedure, to establish the type of co-ordination, refer to lEC 60298. To achieve the required precise coordination we discuss a few typical cases below. 

There are two ways to further reduce the X Me ratio to a value lower than 3. The first is to arrange simple similar to coordination type structure that requests steric similarity of all cations so as to be able to occupy octahedral voids. This method will be discussed separately. The second way is to arrange the linking of the octahedrons so as to render additional structural elements, namely pentagonal "blocks". 

Crystal chemistry ofTa and Nb fluorides - Compounds with coordination-type 109... 

The steric similarity of oxygen and fluorine ions enables the formation of coordination-type structures in some tantalum and niobium oxyfluoride compounds. 

The lowest coordination number of tantalum or niobium permitted by crystal chemistry formalism is 6, which corresponds to an octahedral configuration. X Me ratios that equal 3, 2 or 1 can, therefore, be obtained by corresponding substitutions in the cationic sub-lattice. A condition for such substitution is no doubt steric similarity between the second cation and the tantalum or niobium ion so as to enable its replacement in the octahedral polyhedron. In such cases, the structure of the compound consists of oxyfluoride octahedrons that are linked by their vertexes, sides or faces, according to the compound type, MeX3, MeX2 or MeX respectively. Table 37 lists compounds that have a coordination-type structure [259-261]. 

Typical examples of compounds with a coordination-type structure are Nb02F and Ta02F, which crystallize in a Re03 type structure [233, 243]. Oxygen and fluorine ions are statistically distributed in the anionic sub-lattice. The compounds are characterized by X Me = 3 and can be described as MeX3 type compounds. 

Table 37. Fluoride and oxyfluoride compounds with coordination-type structures...

The family of coordination-type compounds contains only compounds with ions that can occupy octahedral positions. It is obvious that the X Me ratio for this type of compound cannot be greater than 3. 

When X Me < 3 two possibilities exist coordination-type structure (3, 2, 1) or blocks (2.67), when the stoichiometry of the compounds does not correspond to the formation of any coordination- type compound. 

Me02F Coordination-type structures Shared vertexes - MeX3... 

Framework-type structure Coordination-type structure... 

Tantalum and niobium fluoride compounds that crystallize in coordination-type structures also seem to be perspective candidates for the investigation of ferroelectric properties. Ravez and Mogus-Milancovic [404] showed that some fluoride and oxyfluoride compounds with crystal structures similar to the Re03 type exhibit ferroelastic properties. For instance, ferroelastic properties were found in some solid solutions based on Nb02F and Ta02F [405,406]. 

Self-Test 5.7A (a) How many AgJ" ions are present in the AgCl unit cell (b) What is the coordination type of AgCl ... 

Structure type Binary representatives Ternary representatives. Boron coordination Type of boron defects... 

Reactions of metal halides with polysulfide dianions are useful methods for the synthesis of polysulfido complexes of main group elements and transition metals. In most of these reactions, similarly to other methods, the chain lengths and coordination types of the polysulfide ligands depend on the other ligands coordinated to the metal, on the ratio between the metal and sulfur, on the reaction temperature, and other parameters. 

Depending on the level of interaction between these organic-inorganic phases, hybrid materials can either possess weak interaction between these phases such as van der Waals, hydrogen bonding, or electrostatic interaction [7,8], or be of strong, chemically bonded (covalent or coordinate) types [9]. 

Dynamic Mechanical Properties. The dynamic mechanical properties of branched and linear polyethylene have been studied in detail and molecular interpretation for various transitions have already been given, although not necessarily agreed upon in terras of molecular origin.(52-56) Transitions for conventional LDPE (prepared by free radical methods) when measured at low frequencies, are located around +70°C, -20°C and -120°C and are assigned to o, 5, and y transitions respectively. (53) Recently Tanaka et al. have reported the dynamic mechanical properties for a sample of HB which was also prepared by anionic polymerization, but contrary to our system the hydrogenation of the polybutadiene was carried out by a coordinate type catalyst.(12) The transitions reported for such a polymer at 35 Hz are very similar to those of LDPE.(12)... 

Copper(II) triflate is quite inefficient in promoting cyclopropanation of allyl alcohol, and the use of f-butyl diazoacetate [164/(165+166) = 97/3%] brought no improvement over ethyl diazoacetate (67/6 %)162). If, however, copper(I) triflate was the catalyst, cyclopropanation with ethyl diazoacetate increased to 30% at the expense of O/H insertion (55%). As has already been discussed in Sect. 2.2.1, competitive coordination-type and carbenoid mechanisms may be involved in cyclopropanation with copper catalysts, and the ability of Cu(I) to coordinate efficiently with olefins may enhance this reaction in the intramolecular competition with O/H insertion. 

From a structural point of view the complexes with tertiary stibine ligands are very uniform. The predominant type is rj coordination (type 1), with electron pair donation of the Sb atom to the metal centre.1,2,6,8 However, complexes with bridging stibine ligands (type 2) are also known.13,14 (Scheme 1). 

All structures in this family contain icosahedra and at least one other coordination type. Frank and Kasper demonstrated that structures formed by the interpenetration of the four polyhedra contain planar or approximately planar layers of atoms primary layers made by tessellation of triangles with hexagons and/or pentagons, and intervening secondary layers of triangles and/or squares. For a classification and coding of the nets and of their stacking, see Pearson (1972) and also Shoemaker and Shoemaker (1969) or Frank and Kasper (1958, 1959). 

Several structural types, corresponding to about 5500 binary compounds and alloys, were considered 147 structure types were classified as 97 coordination types. The applications of these maps, which, in the most favourable cases make it possible to predict not only the CN and polyhedron but also the structure type or a limited number of possibilities, were discussed. The possible extension to ternary and quaternary phases was also considered. 

Compare these data with those reported for the tI12-ThSi2 type which belongs to the same coordination type . 

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