Coordination compounds definition

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...

The chief aim of this Formula Index, like that of other formula indexes, is to help in locating specific compounds, or even groups of compounds, that might not be easily found in the Subject Index, or in the case of compounds in tables or of many complex coordination compounds, not to be found at all in the Subject Index. All specific compounds, or in some cases ions, with definite formulas (or even a few less definite) are entered in this index, whether entered specifically in the Subject Index or not. As in the latter index, boldface type is used for formulas of compounds or ions whose preparations are described in detail, in at least one of the references cited. 

Perhaps the greatest area in which the Lewis acid-base approach is most useful is that of coordination chemistry. In the formation of coordination compounds, Lewis acids such as Cr3+, Co3+, Pt2+, or Ag+ bind to a certain number (usually 2, 4, or 6) of groups as a result of electron pair donation and acceptance. Typical electron pair donors include H20, NH3, F , CN , and many other molecules and ions. The products, known as coordination compounds or coordination complexes, have definite structures that are predictable in terms of principles of bonding. Because of the importance of this area of inorganic chemistry, Chapters 16 through 22 in this book are devoted to coordination chemistry. 

Thus, Lewis s definition is a much broader definition that includes coordination compound formation as acid-base reactions, besides Arrhenius and Lowry-Bronsted acids and bases. Examples ... 

No strict definition of coordination compound will be followed for the compounds of these two groups, but coverage will be concentrated on those compounds where inter-group relationships are most obvious. In particular, the halogen oxides and derived oxo ions will not be considered. 

The Lewis definition thus encompasses all reactions entailing hydrogen ion. oxide ion. or solvent interactions, as well as the formation of acid-base adducts such as R,NBF, and all coordination compounds. Usage of the Lewis concept is extensive in both inorganic and organic chemistry, and so no further examples will be given here, but many will be encountered throughout the remainder of the book.11... 

By careful control of the conditions of the reaction one can obtain preferentially oxidation of sulfur to its four coordinate oxidation state and by using a second set of conditions one can obtain the oxidation to the six-coordinate sulfur species. The dynamic NMR study of SF3CF2SF3 is currently in progress in collaboration with A. H. Cowley (60). This differentiation of oxidation states is extremely promising, and work in progress shows that this is not at all an isolated situation. Mercaptans and other organosulfur compounds definitely exhibit this capacity in fluorine reactions. 

At present, the ligand selection is being carried out mainly to create complexes of definite type, control of their stereochemistry and stereodynamics of coordination compounds, their physicochemical and practically useful properties. 

A change of salt anions allows us to carry out controlled syntheses of definite types of coordination compounds. Thus, metal halides are widely used to prepare molecular (Sec. 3.1.1.1) and ti-complexes (Sec. 3.1.1.3). Metal acetates are mostly applied in the syntheses of metal chelates and, especially, inner-complex compounds (Sec. 3.1.1.2). Di- and polynuclear structures are formed under use of the anions mentioned above, which, in some cases, determine (see Sec. 3.1.1.4) a type and donor centers of bridge fragments. At the same time, the mentioned approach to choice of salts of metal complex-formers has many exceptions, although it is useful. 

To synthesize coordination compounds of definite type, the following properties of a solvent should be taken into account, additionally to its capacity to dissolve ligands and metal sources physical properties (mainly dielectric constant, dipole moment, boiling and melting points) and chemical ones (solvation activity, including acid-base characteristics, specific interaction) [208,222-229],... 

As a result of interaction of 843 and pyridine, the adduct 845 is formed [53], The structures of coordination compounds 844 and 845 were proved by x-ray diffraction. As shown above (Sec. 3.4.3.2), the direct ammonia synthesis [55,56] with participation of various ligands (especially aliphatic, aromatic, and heterocyclic amines, aminoalcohols), elemental metals (or their oxides), and NH4SCN in mostly non-aqueous media, opens definite possibilities for obtaining thiocyanate complexes. In this respect, transformation (4.9) should be mentioned [57] ... 

Infrared and NMR-spectral analysis, and x-ray diffraction data, testify [42-54] that in case of complexes of the already discussed pseudohalide ions, the competitive coordination can be explained by the HSAB principle hard Pearson acids are bound with hard N-center, and soft acids with soft X- donor (S, Se) centers. This situation allows us to obtain directly the coordination compounds of pseudohalides with a definite localization mode of the coordination bond, i.e., to carry out the regioselective synthesis on the basis of the higher stability of complexes which are obtained as a result of hard-hard or soft-soft interactions [2]. 

Metal carbonyl complexes are an interesting series of coordination compounds in which the ligands are CO molecules, and in many cases the metals are present in a zero oxidation state. In these complexes, both the metal and ligand are soft according to the Lewis acid-base definitions. Although the discussion at first will be limited to the binary compounds containing only metal and CO, many mixed complexes are known that contain both CO and other ligands. 

Since the analyte is often present in quite a complex matrix comprising other elements or substances that may or may not interfere with any projected method of determination, and may indeed be quite a minor constituent of the whole sample, these considerations will effectively dominate the working details of any analytical procedure. There can therefore be no case for prescribing a single definitive method for (say) nickel that would be universally applicable to its determination in alloys see Alloys), organometallic compounds see Organometallic Complexes), inorganic salts see Ionic Bonds), or coordination compounds see Coordination Complexes), to its presence as a trace constituent see Trace Element) in maize or other plant products, or in natural waters or effluents. 

One definition of a metal complex or coordination compound is "a compound formed from a Lewis acid and a Bronsted base a Lewis acid being an electron pair acceptor and a Bronsted base a proton acceptor. Thus the interaction of the Lewis acid metal centre in Ni(C104)2 with the Bronsted base ammonia to form a complex according to equation 4.1... 

A large number of covalently linked systems are currently being synthesized and investigated, differing in the nature of A, B, and L, as well as in the number of functional units in the supramolecular system (nuclearity). It is common to call simple two-component donor-acceptor systems such as that of Eq. 2 dyads , and progressively more complex systems triads , tetrads , pentads , etc.. Systems where all the A and B units are organic molecules are dealt with in Chapter 1 of this section. The present chapter deals with systems where at least one of the A/B functional units is a transition metal coordination compound. From this definition, however, are excluded (a) systems where A and/or B are porphyrins or related species (dealt with in Chapter 2) and (b) systems of high nuclearity with dendritic structures (dealt with in Chapter 9). 

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