Neutral ligands, naming

Neutral ligand names, with the exception of NH3 (ammine), H20 (aqua), CO (carbonyl) and NO (nitrosyl), are expressed in coordination nomenclature by their unmodified names. The ligand names for all neutral ligands except for the four listed above are enclosed in punctuation (parentheses - ( ), square brackets - [ ], and braces - ). For examples see Table 3. 

Neutral and Cationic Ligands. Neutral and cationic ligands are used without change in name and are set off with enclosing marks. Water and ammonia, as neutral ligands, are called aqua and ammine, respectively. The groups NO and CO, when linked directly to a metal atom, are called nitrosyl and carbonyl, respectively. 

Neutral ligands, such as H2NCH2CH2NH2 (ethylenediamine), have the same name as the molecule, except for HzO (aqua), NH (ammine), CO (carbonyl), and NO (nitrosyl). 

The chemical symbols of anionic ligands precede those of neutral ligands in the chemical formula of the complex (but not necessarily in its name). Thus, Cl precedes H20 and NH3. 

If the ligand is an anion, add the suffix -o to the stem name bromo (Br), cyano (CN ),and hydroxo (OH). The simplest neutral ligands have special names aqua (H2O), ammine (NH3), and carbonyl (CO). Other neutral ligands retain their usual names. Some common ligands and their names appear in Table 20-3. 

It is interesting to note that both Te42+ and neutral Te4 rings have been characterized as ligands, namely in the respective complexes [Te4 Nb30l6(Te2)2 ] [26] and [Te4 Cr(CO)s 4] [27]. As we will see in Section 2.7.3, effectively isolated Te4 rings are present in the anionic network of Cs4Te28 [8]. 

The names of anionic ligands always end in an o. Neutral ligands are basically unchanged. Two common exceptions in the case of neutral ligands are NH3 = ammine (note the double m), and H20 = aqua. Other common ligands and their names are listed in Appendix C. 

Both categories of sp-hybridized neutral carbon ligands, namely the all-carbon-substituted and heteroatom-conjugated allenylidene and cumulenylidene ligands, are presented in great detail by V. Cadiemo and S. E. Garcia-Garrido in the sixth and seventh chapters of this volume, respectively. 

Additive nomenclature1 is based on the combination of element names or roots of element names and/or ligand names. The simplest and oldest additive nomenclature is binary nomenclature that expresses two components, e.g. sodium chloride. The cationic or electropositive portion of the compound expressed in a binary name is the element name unchanged or a group name ending in -ium , and the anionic or electronegative portion of a compound expressed in the name ends in -ide, -ite or -ate. The proportions of cations and anions in neutral compounds are indicated by Stock numbers or simple or multiplicative prefixes (see Section 3.3.2). Additive nomenclature denotes composition. For examples see Table 1. 

Anionic Ligand Ligand Name Neutral Ligand Ligand Name... 

Some neutral ligands are given special names—ammine for NH3, aqua for H2O, carbonyl for CO. 

Naming of Ligands The central metal ion in a complex is surrounded by positive or negative or neutral ligands. 

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. 

In naming ligands, an o is added to the root name of an anion. For example, the halides as ligands are called fluoro, chloro, bromo, and iodo hydroxide is hydroxo and cyanide is cyano. For a neutral ligand the name of the molecule is used, with the exception of H20, NH3, CO, and NO, as illustrated in Table 20.14. 

In an older system the negatively charged ligands were named first, followed by neutral ligands, with positively charged ligands named last. We will follow the newer convention in this text. 

Anionic ligands are given an o suffix. Neutral ligands retain their usual name. Coordinated water is called aqua and coordinated ammonia is called ammine. 

Anionic ligands are named by replacing the usual ending with the suffix -o. The names of neutral ligands are unchanged. Exceptions to the latter rule are aqua (for water), ammine (for NH3), and carbonyl (for CO) (see Table 8.4). 

Ligand formula Systematic name as anionic ligand Systematic name as neutral ligand Acceptable alternative name... 

---