A common metal complex is Ag(NH3)2+, formed
when Ag+ ions are mixed with neutral ammonia molecules.
Ag+ + 2 NH3 -> Ag(NH3)2+
A complex Ag(S2O3)23- is formed between silver ions and negative thiosulfate ions:
Ag+ + 2 S2O32- -> Ag(S2O3)23-
Metal complexes are also called coordination compounds. Their structures are important data and properties. Compounds having the same chemical formula but different structures are called isomers. Isomers with different geometic arrangements of ligands are called geometric isomers whereas isomers whose structures are mirror images of each other are called optical isomers. When a beam of polarized light passes optical isomers or their solutions, the plane of polarization rotates in different directions. The beam rotates to the left for one isomer, and right for its mirror image.
Werner recognized the existence of several forms of cobalt-ammonia chloride. These compounds have different color and other characteristics. The chemical formula has three chloride ions per mole, but the number of chloride ions that precipitate with Ag+ ions per formula is not always three. He thought only ionized chloride ions will form precipitate with silver ion. In the following table, the number below the Ionized Cl- is the number of ionized chloride ions per formula. To distinguish ionized chloride from the coordinated chloride, Werner formulated the Complex formula and explained structure of the cobalt complexes (See page 241 of Inorganic Chemistry by Swaddle).
|Solid||Color||Ionized Cl-||Complex formula|
Other cobalt complexes studied by Werner are also interesting. It has been predicted that the complex Co(NH2CH2CH2NH2)2ClNH3]2+ should exist in two forms, which are mirror images of each other. Werner isolated solids of the two forms, and structural studies confirmed his interpretations. The ligand NH2CH2CH2NH2 is ethylenediamine (en) often represented by en.
The images are shown on page 242 Inorganic Chemistry by Swaddle. If the triangular face of the end-amino group lie on the paper, you can draw lines to represent the en bidentate ligand. These lines will show that the two images are similar to the left-hand and right-hand screws.
From the description above, sketch the structures.
Answer these questions:
Often, several groups of the ligand are involved in a complex. The number of ligand molecules per complex is indicated by a Greek prefix: mono-, di- (or bis), tri-, tetra-, penta-, hexa, hepta-, octa-, nona-, (ennea-), deca- etc for 1, 2, 3, ... 10 etc. If the names of ligands already have one of these prefixes, the names are placed in parentheses. The prefices for the number of ligands become bis-, tris-, tetrakis, pentakis- etc.
For neutral ligands, their names are not changed, except the following few:
The names of complexes start with the ligands, the anionic ones first, followed with neutral ligands and the metal. If the complex is negative, the name ends with "ate". At the very end are some Roman numerals representing the oxidation state of the metal.
To give and remember all rules of nomenclature are hard to do. Pay attention to the names whenever you encounter any complexes is the way to learn.
A bridgin ligand is indicated by placing a m- before its name. The m- should be repeated for every bridging ligand. For example,
The structure is
(C6H5)3P Cl Cl \ / \ / Pd Pd / \ / \ Cl Cl P(C6H5)3
Answer the following questions:
(en)2Co< >Co(en)2 Cl3
The name is Bis(ethylenediamine)cobalt(III)-m- imido-m-hydroxobis(ethylenediamine)cobalt(III) ion.
When this compound dissolves in water, is the solution a conductor? What are the ions present in the solution of this compound? How many moles of chloride ions are present per mole of the compound?
When potassiumtrichloroammineplatinate(II) dissolves in water, what ions are produced? What about chloropentaamminecobalt(III) chloride?