Coordination compounds Dr. Peter Warburton

All media copyright of their respective owners2 Complex ions AgCl(s) + 2 NH 3 (aq) → [Ag(NH 3 ) 2 ] + (aq) + Cl - (aq)

All media copyright of their respective owners3 Theory of coordination compounds Compounds made up of simpler compounds are called coordination compounds. Alfred Werner

All media copyright of their respective owners4 Coordination compounds Coordination compounds contain complex ions which are polyatomic cations or anions composed of: a central metal ion and ligands

All media copyright of their respective owners5 Werner’s theory of coordination compounds [Co(NH 3 ) 6 ]Cl 3 and [CoCl(NH 3 ) 5 ]Cl 2 Two compounds made of the same chemicals, yet they look different, and react differently with silver nitrate.

All media copyright of their respective owners6 Werner’s theory [Co(NH 3 ) 6 ]Cl 3 → [Co(NH 3 ) 6 ] Cl - [CoCl(NH 3 ) 5 ]Cl 2 → [CoCl(NH 3 ) 5 ] Cl - Two types of valence or bonding capacity. Primary valence. Based on the number of e - an atom loses in forming the ion. Secondary valence. Responsible for the bonding of other groups, called ligands, to the central metal atom.

All media copyright of their respective owners7 Cobalt coordination compounds In all these compounds the central cobalt ion of the complex ion (the square brackets) has SIX ligands around it.

All media copyright of their respective owners8 Cobalt coordination compounds The number of nitrate groups depends on the charge of the complex ion, which depends on the charges of the central ion and the ligands.

All media copyright of their respective owners9 Coordination number Coordination number – # of points of attachment by ligands to the metal ion

All media copyright of their respective owners10 Coordination sphere Coordination sphere – the central metal ion and the ligands [CoCl(NO 2 )(NH 3 ) 4 ] +

All media copyright of their respective owners11 Problem What are the coordination number and oxidation state of Ni in the complex ion [Ni(CN) 4 I] 3- ? Answer: The coordination number is 5. The oxidation state of Ni is +2.

All media copyright of their respective owners12 Problem Write the formula of a complex ion with cyanide ion ligands, an iron ion with an oxidation state of +3, and a coordination number of 6. Answer: [Fe(CN) 6 ] 3-

All media copyright of their respective owners13 Ligands Ligands are Lewis bases – electron pair donors. They donate electrons to the metal ion, which acts as a Lewis acid – electron pair acceptor.

All media copyright of their respective owners14 Ligands Monodentate ligands Use one pair of electrons to form one point of attachment to the metal ion. Bidentate ligands Use two pairs of electrons to form two points of attachment to the metal ion. Tridentate, tetradentate, … See Tables 24.2 and 24.3

All media copyright of their respective owners15 Formulas for complex ions The complex ion is in square brackets! Metal ion first Anions next – in alphabetical order BY CHEMICAL SYMBOL if there are more than one kind Neutral ligands last – in alphabetical order BY CHEMICAL SYMBOL if there are more than one kind Overall charge of the complex ion outside of brackets

All media copyright of their respective owners16 Formulas for complexes Check to see if the rules have been followed in the complexes of these coordination compounds.

All media copyright of their respective owners17 Problem What would the formula be for the following complex? Answer: [CrBr 2 (H 2 O) 2 (NH 3 ) 2 ] +