1. Transition Metal Complexes

2.  A covalent bond is a shared pair of electrons  Usually the two atoms involved in the covalent bond each contribute one electron  Definition: In a co-ordinate bond, one atom donates both of the electrons in the shared pair of electrons  In order for a co-ordinate bond to form there must be a lone pair of electrons on one of the atoms  A co-ordinate bond is represented by an arrow, →

3.  Definition: A complex is a central metal ion surrounded by ligands  Definition: A ligand is an ion or molecule that can donate a lone pair of electrons to the central metal ion  The ligand donates its lone pair of electrons to the metal ion forming a co-ordinate bond  The ligand must have a lone pair of electrons

4.  Ligands can be negative ions such as:  Halide ions - Chloride ions, :Cl -, Bromide ions, :Br -  Hydroxide ion, :OH -  Cyanide ion, :CN -  Ligands can also be neutral molecules which contain more than one lone pair of electrons such as:  Ammonia, :NH 3  Water, H 2 O: The oxygen atom in water has two lone pairs of electrons

5.  A ligand that can donate one lone pair of electrons is a unidentate ligand  A ligand that can donate two lone pairs of electrons is a bidentate ligand  A ligand that can donate more than two lone pairs of electrons is a multidentate ligand  Even although water has two lone pairs of electrons, it can only donate one pair of electrons  Therefore water is a unidentate ligand O HH : :

6.  Definition: The co-ordination number is the number of pairs of electrons donated to the central metal ion  Co-ordination numbers are 2, 4 or 6 ComplexCo-ordination number [Ag(NH 3 ) 2 ] + [CuCl 4 ] 2- [Cu(H 2 O) 6 ] 2+ [FeCl 4 ] 2- [Cu(H 2 O) 4 (OH) 2 ] [Ag(H 2 O) 2 ] + 2 4 6 4 6 2

7.  The central metal ion has a positive charge  The overall charge on the complex depends on the charge of the metal ion and the charge on the ligands  Example: [Cu(H 2 O) 6 ] 2+  Overall charge = 2+  Oxidation state of copper = +2  Remember water is a neutral ligand

8. ComplexOverall chargeOxidation state of metal ion [Ag(NH 3 ) 2 ] + [Cu(H 2 O) 6 ] 2+ [CuCl 4 ] 2- [V(H 2 O) 6 ] 3+ [Cu(H 2 O) 4 (OH)] [Ag(CN) 2 ] - [NiCl 4 ] 2- [CrCl 2 (H 2 O) 4 ] + 1++1 2+ +2 2-+2 3+ +3 0+2 1- +1 2-+2 1+ +3

9.  Silver forms complexes with a co-ordination number of 2  The shape of the complex is linear  Example: Tollens’ reagent (Test for aldehydes)  Tollen’s reagent contains the complex, [Ag(NH 3 ) 2 ] +  There are two ammonia ligands each donating one lone pair of electrons to the Ag + ion [H 3 N: → Ag + ← :NH 3 ] +

10.  When Tollen’s reagent is warmed with an aldehyde, the silver(I) ion (Ag + ) is reduced to silver atoms (Ag) producing a silver mirror  Ketones do not reduce the silver(I) ion and no silver mirror is formed