Nomenclature of Coordination Complexes

If pressed for time, you re better off skipping this section in favor of another more important section, but if you have the luxury of time, read on. The name of a coordination complex has come up on the multiple-choice test before. There is an established set of rules for naming these compounds that has been developed by the IUPAC, and it consists of the following five parts  

Q When naming salts, the name of the cation is given before the name of the anion (this is the same as the other nomenclature rules). 

Q The name of the complex ion, whether it is an anion, cation, or neutral, is written as two parts that are combined into one word. The first part consists of the name of the ligand, and the second part, the name of the metal ion. If more than one of the same type of ligand appears, Greek prefixes are used to indicate the number of times the ligand occurs. A Roman numeral is used to indicate the charge on the cation. For instance, the name of the ion in the previous example, Fe(CN)64, is hexacyanofer-rate (II) ion. 

The prefix hexa- represents the six cyanide ligands, the anion appears before the cation, and the Roman numeral (II) in parentheses indicates the 2+ charge on the iron ion. 

Q One thing you may have noticed in the previous example is the ending -o on the end of cyano. Most anionic ligands are written with an -o ending, like chloro, bromo, cyano, and oxo. Neutral ligands are usually given the name of the molecule. A few notable exceptions to this are NH3, known as ammine H20, known as aqua and CO, known as carbonyl. 

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Nomenclature of Coordination Compounds Table 13 Compounds Containing Complex Anions... 

Complex ions combine with cations or anions to form coordination complexes. These complex ions usually consist of a transition metal ion attached to ligands. You should be familiar with the basic nomenclature for coordination complexes. 

The r0 values are listed in Table II. The V(V) values are calculated from V(IV) values using the d-electron correction described by Brown (43). Specifically, 0.020 is added to the V(IV) values. The BVS results are tabulated along with the known oxidation state and the coordination environment (Table III). For the most part, the original nomenclature of these complexes has been retained details are available in the references. 

Alkenes, arenes and other unsaturated molecules attach to central atoms, using some or all of their multiply bonded atoms, to give organometallic complexes. While there are many similarities between the nomenclature of coordination and organometallic compounds, the latter differ from the former in clearly definable ways. Organometallic complexes are therefore treated separately in Chapter IR-10. 

Here are a few examples of using lUPAC nomenclature for writing the formulae and names of coordination complexes. 

The nomenclature of compounds containing complex ions is more involved than that of the simple inorganic compounds considered in earlier chapters. We will see first how complex ions are named and then look at the nomenclature of coordination compounds. 

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...

Originally, compounds containing coordination complexes were given common names such as Prussian blue (KFe[Fe (CN)g ]), which is deep blue, or Reinecke s salt (NH4[Cr (NH3)2 (NCS)4]), named for its first maker. Eventually, coordination compounds became too numerous for chemists to keep track of all the common names. To solve the nomenclature problem, the International Union of Pure and Applied Chemistry (lUPAC) created a systematic procedure for naming coordination compounds. The following guidelines are used to determine the name of a coordination compound from its formula, or vice versa ... 

The sections are divided by the coordination number of the reacting ion defined as the number of donor atoms that interact with the metal. The nomenclature used for the ligands is L for neutral molecules that act as ligands and X for anions that act as ligands. Most of the examples in this section will involve cations [ML ]+ or [MX ]+, but there will be a short section on bare metal anions, M . The anions of more complexity than M will be discussed in Section IV on clusters. Many reactions produce an initial product that continues to react resulting in further coordi-native changes and possibly redox changes. Tables I and II will indicate the initial reaction product and other major reaction products. 

We illustrate the nomenclature introduced above in an example taken from coordination chemistry. In fact, equilibrium species of interesting complexity are commonly encountered in coordination chemistry and to a large extent coordination chemists have developed the principles of equilibrium studies. Consider the interaction of a metal ion M (e.g. Cu2+) with a bidentate ligand L (e.g. ethylenediamine, en) in aqueous solution. For work in aqueous solution the pH also plays an important role and thus, the proton concentration H (=[ff+]), as well as several differently protonated species, need to be taken into account. Using the nomenclature commonly employed in coordination chemistry, there are three components, M, L, and H. In aqueous solution they interact to form the following species, HL, H2L, ML, Mia, ML3, MLH, MLH1 and OH. (In fact, more species are formed, e.g. ML2H 1, but the above selection will suffice now.) The water molecules are usually not defined as additional components. The concentration of water is constant and its value is taken into the equilibrium constants. 

This chapter presents a concise overview of the present conventions in coordination nomenclature. Generally, the IUPAC rules and recommendations have been followed. For the cases where the IUPAC practices seemed to be out of date or incomplete, the author has drawn upon the vast expertise in nomenclature available at Chemical Abstracts Service. Sections 3.2.3 and 3.4 deal with ligand locant notation and the numbering of polynuclear complexes may be considered provisional. These concepts are still under active consideration in the various national and international nomenclature commissions and committees. The presentation is relatively brief, but it is hoped that the nomenclature principles are evident, especially when examples presented are closely... 

The nomenclature pattern established in binary nomenclature is also used to indicate the composition of more complex entities, including ionic coordination compounds. Electropositive constituents are cited in alphabetical order before the electronegative constituents, which are also cited in alphabetical order. For examples see Table 2. 

The conversion from a connection table to other unambiguous representations is substantially more difficult. The connection table is the least structured representation and incorporates no concepts of chemical significance beyond the list of atoms, bonds, and connections. A complex set of rules must be applied in order to derive nomenclature and linear notation representations. To translate from these more structured representations to a connection table requires primarily the interpretation of symbols and syntax. The opposite conversion, from the connection table to linear notation, nomenclature, or coordinate representation first requires the detailed analysis of the connection table to identify appropriate substructural units. The complex ordering rules of the nomenclature or notation system or the esthetic rules for graphic display are then applied to derive the desired representation. 

The separation of coordination compounds into four types, as described above (a) encompasses practically all types of complexes reported in modern coordination chemistry [1,2,10,16,34,124-127] (b) is clear and informative with respect to a given molecule in a coordination compound as a whole, and does not rely on its individual portions (c) concentrates its attention on the special features of some types of metal complexes (d) follows from the modern approach to study the structures of metal complexes [16,34,125,126], together with their systematic nomenclature [122,123]. 

Per Section 1-10.6.2.2. of [48] "In the nomenclature of polydentate chelate complexes, single ligating atom attachments of a polyatomic ligand to a coordinating centre are indicated by the italic element symbol preceded by the Greek letter kappa, k."... 

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