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The d-block Coordination Chemistry
Objectives Must Explain and use the terms ligand/complex/complex ion and ligand substitutions. Should Describe the formation of complexes in terms of dative (coordinate) bonding and shapes of complexes. Could Describe ligand substitution reactions using examples.
Transition metal ions in solution • When a transition metal compound such as cobalt chlorideis dissolved in water it becomes Co3+ and Cl- ions. • The Co3+ ions attract water molecules around them to form something we call a complex.
Charged or not? • If the complex is charged then it is called a complex ion For example The overall charge is the sum of the charge on the metal ion + charges on the ligands
How do we write complexes down? • The symbol formula for this complex is • [Co(H2O)6]3+ • Remember square brackets • Remember overall charge • Its name is hexaaqua cobalt III
AfL – using whiteboards Write the symbol formula for:
Ligands and bonding • The molecules which bond to the metal ions are called ligands • Complexes form because the lone pairs of the ligand can bond with the metal ion. • Transition metals have more available orbitals so they can bond with a large number of ligands. • The number of ligands is called the coordination number
AfL – test your understanding • What is the ligand and coordination number in each case:
Coordinate (dative) bonding • When the lone pairs of the ligand bond to the metal we call this coordinate bonding. • It works with d-metals because of the metal’s electronic structure. Empty orbitals mean that the lone pair electrons have somewhere to go.
Shapes of complexes • The shapes of complexes are determined by the number and type of ligands. • Complexes with 6 ligands are usually octahedral • Can you draw an octahedral [Cu(H2O)6]2+ complex?
Shapes of complexes • The shapes of complexes are determined by the number and type of ligands. • Complexes with 4 ligands are usually tetrahedral • Can you draw an tetrahedral [Cu(Cl)4]2- complex?
Square planar • Some complexes are square planar. • Draw a square planar [Ni(CN)4]2- complex.
Polydentate ligands • Some ligands can bond to the metal more than once. • Each molecule of ethandioate bonds to the metal twice. • Each molecule of EDTA4- bonds to the metal six times.
Stability • Ligands can be exchanged in substitution reactions because they are labile (can attach on and off). • Example of a reaction between copper in water and copper in concentrated HCl: [Cu(H2O)6]2++ HCl [Cu(Cl)4]2- (blue)(yellow)
Colour changes http://www.chemguide.co.uk/inorganic/complexions/ligandexch.html
Other substitution reactions [Cu(H2O)6]2++ HCl [Cu(Cl)4]2-+ 6H2O [Cu(H2O)6]2++ NH3 [Cu(NH3)4(H2O)2]2++ 4H2O [Fe(H2O)6]3++ SCN-[Fe(H2O)5SCN]2++ H2O