Chemical formulas coordination compounds

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. 

The names of coordination compounds can become awesomely long because the identity and number of each type of ligand must be included. In most cases, chemists avoid the problem by using the chemical formula rather than the name itself. For instance, it is much easier to refer to [FeCl(H20)5]+ than to pen-taaquachloroiron(II) ion, its formal name. However, names are sometimes needed, and they can be constructed and interpreted, in simple cases at least, by using the rules set out in Toolbox 16.1. Table 16.4 gives the names of common ligands and their abbreviations, which are used in the formulas of complexes. 

This overview covers some of the rules for naming simple inorganic compounds. There are additional rules, and some exceptions to these rules. The first part of this overview discusses the rules for deriving a name from a chemical formula. In many cases, the formula may be determined from the name by reversing this process. The second part examines situations in which additional information is needed to generate a formula from the name of a compound. The transition metals present some additional problems therefore, there is a section covering transition metal nomenclature and coordination compounds. 

CAS CHEMICAL REGISTRY 8,000,000 compounds CHEMICAL ABSTRACTS SERVICE The world s largest file of substance information, including coordination compounds, polymers, incompletely defined substances, alloys, mixtures, and minerals. In each record, the registry number is linked to molecular structure diagram, molecular formula, CA index name, synonyms, and the ten most recent references in Chemical Abstracts. Easy crossover to the bibliographic file... 

Asymmetrical nitrido Tc(V) complexes (simply defined as heterocomplexes) are defined as coordination compounds in which two different bidentate ligands are bound to the same Tc=N group, and are represented by the general formula [Tc(N)(L)(L )]"+/0/". The attempt to develop a high-yield synthesis of these types of complexes may first appear to be prevented by basic chemical considerations. Actually, it is reasonable to expect that the reaction of two different bidentate ligands, A and B, with the same Tc=N group would always yield a statistical mixture of symmetrical and asymmetrical complexes, namely [Tc(N)(A)2], [Tc(N)(B)2] and [Tc(N)(A)(B)]. However, the peculiar properties of mixed 7r-acceptor-7r-donor ligands offered the route to the solution of this synthetic problem. The key approach can be outlined as follows. 

The misfit layer compounds are typified by materials with a formula MS +fiTS2)m, in which T is a transition metal atom, Ti, V, Cr, Nb, or Ta, and M is a large atom such as Sn, Pb, Bi, with stereochemically active electron lone pairs, or a lanthanide. The structures are built from S-T-S layers, in which the metal T takes trigonal-prismatic coordination. These layers are interleaved with layers of the halite structure, usually two or three atom layers in thickness, with composition MSx. This leads to a chemical formula of [MSx]n(71S 2)m, where n varies from approximately 1.08-1.24, and m takes values of 1-3, depending upon the nature of T and M. A typical example is the compound [(Lni/3Sr2/3S)i.5]i.i5 NbS2. In all of the misfit layer compounds, the lattice parameter of the interpolated halite layers fit one lattice parameter of the rS2 layer but not the other, so that in this direction, the... 

Fortunately the chemical formulas can be rationalized on the basis of the size of the central atoms involved it is not necessary to memorize their formulas In general, second-period atoms are hmited to a maximum total coordination number (the total coordination number counts unshared electron pairs in the p-block) of fom third and fourth-period atoms can have maximum total coordination numbers of six fifth and sixth-period atoms can exceed a total coordination number of six. These observations explain the hydrolytic inertness (and persistence in the atmosphere) of compounds such as CF4 and SFe, which contain very strongly acidic cations they also explain why the formulas of fluoro anions vary (e.g. BF4 in period 2 AlFe in period 3 WFg in period 6). Evidently, because of the influence of Jt bonding to oxygen, central atoms in 0x0 anions fail to exhibit these coordination numbers, but instead settle for lower penultimate total coordination numbers 3 in the second period, for example, COs 4 in the third and fourth periods, for example, 8104 and 0004 6 in the fifth and sixth periods. 

Thus, polymorphism with the formation of monoclinic and tetragonal modifications is typical for U- and Th-compounds with general formula BM(X04)2 (X = P, As, V). These modifications differ in the packing of the XO4 anions, the orientation of anions around a cation, and the form of the (B,M)On coordination polyhedra (n = 8 or 9). The crystal chemical formula of the BM(P04)2 phosphates and their arsenate and vanadate analogues can be written as B0.5M0.5XO4, owing to the cation disorder. 

So far, we have identified coordination compounds only by their chemical formulas, but names are also useful for many purposes. Some substances were named before their structures were known. Thus, K3[Fe(CN)g] was called potassium fer-ricyanide, and K4[Fe(CN)g] was potassium ferrocyanide [these are complexes of Fe (ferric) and Fe (ferrous) ions, respectively]. These older names are still used conversationally but systematic names are preferred to avoid ambiguity. The definitive source for the naming of inorganic compounds is Nomenclature of Inorganic Chemistry-IUPAC Recommendations 2005 (N. G. Connelly and T. Damhus, Sr., Eds. Royal Society of Chemistry, 2005). 

Much confusion in the literature on this subject has been due to the placing of too much reliance on magnetic data of dubious quality and to incorrect deductions of coordination numbers from chemical formulae. There are regrettably few examples of compounds of which both thorough magnetic and structural studies have been made. The following facts have been established ... 

Chemical nomenclature deals with names of elements and their combinations. Whereas writing the symbol or the name of an element is straightforward, a choice of which element to write first in the formula and in the name has to be made as soon as an element is associated with one or more other elements to form, for example, a binary compound. The order of citation of elements in formulae and names is based upon the methods outlined below. Furthermore, groups of atoms, such as ions, ligands in coordination compounds and substituent groups in derivatives of parent hydrides, are ordered according to specified rules. 

Since abbreviations are widely used in the chemical literature, agreement on their use and meaning is desirable. This Section provides guidelines for the selection of ligand abbreviations for application in the formulae of coordination compounds (Section IR-9.2.3.4). Some commonly used ligand abbreviations are listed in Table VII with diagrams of most of the ligands shown in Table VIII. 

The organic derivatives of silver were studied mainly by the XPS method and we have again classified the compounds studied on the basis of coordinating atoms. The numbers incorporated into chemical formulae again indicate core binding energies of relevant atoms. 

Figure 22.7 Components of a coordination compound. Coordination compounds, shown here as models (top), perspective drawings (middle), and chemical formulas (bottom), typically consist of a complex ion and counter ions to neutralize the charge. The complex ion has a central metal ion surrounded by ligands. A, When solid [Co(NH3)6]Cl3 dissolves, the complex ion and the counter ions separate, but the ligands remain bound to the metal ion. Six ligands around the metal ion give the complex ion an octahedral geometry. B, Complex ions with a central d metal ion have four ligands and a square planar geometry.

Isomers are compounds with the same chemical formula but different properties. We discussed many aspects of isomerism in the context of organic compounds in Section 15.2 it may be helpful to review that section now. Figure 22.8 presents an overview of the most common types of isomerism that occur in coordination compounds. 

From on-line coupled TG-MS and TG-FTIR measurements, in combination with quantitative chemical analysis, the chemical formula for an unknown bismuA oxalate compound was deduced to be Bi(NH4)(C204)2 3.71(6)H20 by Vanhoyland et al. [78], Solution of the crystallographic structure on the basis of X-ray powder data proved this formula to be correct. Bi is 8-fold coordinated by oxygen from the oxalate anions. Because these BiOg polyhedra do not share any edges or vertexes, an open framework is formed with water and ammoniiun molecules between. As a result, water can easily be removed, which is clearly indicated by the rapid initial mass loss in the TG cxu e. 

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