Cation names coordination compounds

To name coordination compounds, you follow a series of general rules based on the system originally proposed by Werner. As with all salts (see Section 3.5), the name of the cation goes before the name of the anion. 

In naming coordination compounds, we use the name of the cation followed by the name of the anion. To name a complex ion we use the guidelines outlined in Section 24.3. 

Coordination compounds are named in much the same way as simple ionic compounds. The cation is named first, followed by the anion. Examples include... 

The name of a coordination compound (as distinct from a complex cation or anion) is built in the same way as that of a simple compound, with the cation named before the anion ... 

How do we name the coordination compound [Co(NH3)3(H20)3]2(S04)3 First, we note that the charge on the complex cation must be +3 to ensure charge neutrality of the compound (there are three S042- ions for every two complex ions). Therefore, the complex cation is fCo(NH3)3(H20)3J3+. Because all the ligands are neutral, the cobalt must be present as cobalt(III). I It follows that the name of the cation is triamminetriaquacobalt(III), so the compound is triamminetriaquacobalt(III) sulfate. 

In naming a coordination compound, the cation is named first followed by the name of the anion. One or both of these ions may be complex ions. 

In formulae and names of salts, double salts and coordination compounds, cations precede anions. Ordering within each of these groups is alphabetical, cf. Section IR-2.15.2. 

Werner also described and named the various other types of isomerism observed in coordination compounds. These are ionisation isomerism, displayed by [Co(NH3)5C1]S04 and [Co(NH3)5S04]Cl hydrate isomerism, for example [Cr(H20)5]Cl3 and [Cr(H20)5Cl]Cl2.H20 and coordination isomerism, which occurs when both cation and anion are complexes, for example [Co(NH3)5][Cr(CN)6] and [Cr(NH3)5][Co(CN)6] Werner also explained one case of what is now known as linkage isomerism in [Co(NH3)5N02]Cl2 and [Co(NH3)50NO]Cl2, where the NO2 ligand has two possible sites of attachment to the metal atom. It was many years before other linkage isomers were prepared. 

The specific combination of ions in a coordination compound is the key to writing its formula and name. A coordination compound can consist of a complex cation with simple anionic counter ions, a complex anion with simple cationic counter ions, or even a complex cation with complex anion as counter ion. 

Thousands of coordination compounds are now known. A systematic method of naming such compounds, or nomenclature, needs to provide basic information about the structure of a coordination compound. What is the metal in the complex Does the metal atom occur in the cation or the anion What is the oxidation state of the metal What are the ligands You can answer these questions by following the rules of nomenclature agreed upon by the International Union of Pure and Applied Chemistry (lUPAC). These rules are essentially an extension of those originally given by Werner. 

Ionic coordination compounds are named by first naming the cation and then the anion. Complex ions are named by listing the ligands in alphabetical order, followed by the metal and its oxidation state (as... 

In names and formulas of coordination compounds, cations come first followed by anions. This is the same order as in simple ionic compounds like NaCl for sodium chloride. For example, the formula [Pt(NH3)4][PtCl4] represents the coordination compound tetraammineplatinum(II) tetrachioridoplati-nate(ll). 

This compound consists of cations and complex anions having the formula [Fe(CN)6] . Each cyanide ion carries a charge of 1—, so the oxidation state of the iron must be +3. The Latin-based name "ferrate" is used because the complex ion is an anion. The name of the anion is hexacyanidoferrate(III) ion. The coordination compound is potassium hexacyanidoferrate(III). 

When the radius ratio of an ionic compound is less than about 0.4, corresponding to cations that are significantly smaller than the anion, the small tetrahedral holes may be occupied. An example is the zinc-blende structure (which is also called the sphalerite structure), named after a form of the mineral ZnS (Fig. 5.43). This structure is based on an expanded cubic close-packed lattice of the big S2 anions, with the small Zn2+ cations occupying half the tetrahedral holes. Each Zn2+ ion is surrounded by four S2 ions, and each S2" ion is surrounded by four Zn2+ ions so the zinc-blende structure has (4,4)-coordination. 

In the complex [Co(NH3)6]Cl3, the cation is [Co(NH3)6]3+, and it is named first. The coordinated ammonia molecules are named as ammine, with the number of them being indicated by the prefix hexa. Therefore, the name for the compound is hexaamminecobalt(III) chloride. There are no spaces in the name of the cation. [Co(NH3)5C1]C12 has five NH3 molecules and one CN coordinated to Co3+. Following the rules just listed leads to the name pentaamminechlorocobalt(III) chloride. Potassium hexacyanoferrate(III) is K3[Fe(CN)6j. Reinecke s salt, NH4[Cr(NCS)4(NH3)2], would be named as ammonium diamminetetrathiocyanatochro mate (III). In Magnus s green salt, [Pt(NH3)4][PtCl4], both cation and anion are complexes. The name of the complex is tetraammineplatinum(II) tetrachloroplatinate(II). The compound [Co(en)3](N03)3 is named as tris(ethylenediamine)cobalt(III) nitrate. 

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