Lecture Sixteen - Coordination complexes Flashcards
What is a coordinatino xomplex, counter ions and a coordination compound?
A coordination complex consists of a central cation (metal ion) bonded to molecules or anions (called ligands).
Counter ions may be present to maintain charge balence, e.g. Cl-.
A coordination compound contains a complex and other species (counter ions).
A compound may dissociate into anions and cations in solution - can behave as an electrolyte.
Ligans remain attached to the metal ion (the counter ions dissociate).
Solutions conduct electricity.
E.g. In solution, [Co(NH3)6]Cl3 dissociates into [Co(NH3)6]3+ and 3Cl-.
Who was Alfred Werner?
The ‘father of coordination chemistry.’
Introduced to concept of coordination number, and explained the existence of optically active metal complex isomers.
Made hundereds of new compounds and studies their configuations.
Measured the physical properties of various complexes - only knew the empirical formulae of these complexes, not how they behaved.
He realised that CoCl3(NH3)6 was not a simple ‘ionic’ salt, but a ‘complex’ cation - [Co(NH3)6]Cl3.
Complex was ionic.
Oxidation state was Co(III).
Molecule was octahedral.
6 NH3 ammonia ligands - coordination number (CN) = 6.
Cl- not coordinated but ionic ‘counter ions.’
He correctly predicted that there would be two forms of CoCl3.4NH3.
One form has the two chlorides next to eachother - cis.
One form has the two chlorides opposite eachother - trans.
What is Ketpet’s theory?
Kerpet theory: Complex shapes depend on repulsion of ligands.
Geometry - depends on coordination number and nature of ligands.
Generally follow VSEPR theory - square planar geometry an exception.
Linear = 2 domor atoms.
Trigonal planar = 3 donor atoms.
Tetrahedral - 4 donor atoms (exception for some 4-coordinate complexes which are square planar).
Trigonal bipyramidal or square based pyramidal - 5 donor atoms.
Octahedreal or trigonal prismatic - 6 donor atoms.
Define:
Ligands.
Donor atoms.
Overall charge.
Oxidation state.
Counter ion.
Hydrate.
Coordination number.
Ligands - molecules/ions attahced to metal ion (neurtal or negitive).
Donor atom - atoms bonded to metal ion - must have at least one lone pair of electrons.
Overall charge - net charge of cation, ligands and counter ions.
Oxidative state - charge minus the sum of charge of ligands.
Counter ion - balances charge on complex.
Hydrate - water is present in crystal structure.
Coordination number - number of donor atoms.
