23.2 Complex formation and shape of complex ions Flashcards
What bonds can all transition metals form and how
. Co-ordinate bonds: When one atom in a covalent bond provides both the electrons.
By accepting electron pairs from other ions or molecules.
So the bonds that form are dative/coordinate bonds.
What is a ligand
Give 4 examples
A ion or molecule with a lone pair of electrons, that forms a co-ordinate bond with a transition metal.
H20: :NH3 :Cl- :CN-
What is a complex ion
What is its coordination number
When 2, 4 or 6 ligands bond to a transition metal ion.
Its coordination number is the number of co-ordinate bonds to ligands that surround the d block metal ion
What is the shape called when 6 ligands bond to a transition metal ion
What are the angles?
What is the coordination number
Octahedral shape
90 degrees
They have six as a coordination number.
Eg [Co(NH2)6]3+
What are the two possible shapes for a transition metal ion with 4 ligands.
And what are the angles in these
What would the coordination number be
. Tetrahedral in most cases
Eg Co(Cl4)2-
Angles are 109.5 degrees
However with the metals nickel and platinum, they form square planar
Eg [NiCN4]2-
Angles are 90 degrees
What shape are transition metal ions with two ligands attached?
What are the angles
What is the coordination number
What ion does this occur in
Linear shape
180 degrees
Coordination number is 2
This occurs in Ag+ complexes
What are aqua ions
. If you dissolve the salt of a transition metal in water, eg copper sulfate, the positively charged metal ion becomes surrounded by water molecules acting as ligands.
Normally there are 6 water molecules in an octahedral arrangement.
The oxygen from the water bonds to the metal ion
What are unidentate ligands
. A ligand (particle with a lone pair of electrons that bonds to metals by dative bond) that forms one co-ordinate bond to a metal ion.
What are multidentate ligands
- Ligands that form two or more
co-ordinate bonds to a metal ion.
They have more than one atom with a lone pair of electrons which can bond to a transition metal ion.
An example of a bidentate ligand is
Ethene-1,2-diamine, and it binds to chromium 3+ ion.
Describe the structure of the ligand
And forms complex
(Cr(NH2CH2CH2NH2)3 3+
Explain how this occurs
. Each nitrogen has a lone pair of electrons which can form a co-ordinate bond to the metal ion, there are 2 nitrogen’s on each ligand.
. So overall there are 3 ligands that can bind to the chromium ion as each can form 2 coordinate bonds
H2N: - CH2 - CH2 - :NH2
It is a neutral ligand and the chromium ion has a 3+ charge so the complex ion has an overall 3+ charge
What is the structure of the bidentate ligand
ethanedioate
Bonds with chromium 3+ also, so what is this complex
(C2O4)2- so the ligand has a 2- charge
[Cr(C2O4)3] 3-
It is overall 3- because each ligand brings the overall charge of the 3+ down to 3-
What is the bidentate ligand
Benzene 1,2-diol
What is the formula
Benzene 1,2 diol is a neutral ligand also
Has two oxygens on it, each with a lone pair to form co-ordinate bond
C6H6O2
Is the formula of it
But it is shaped as a hexagon ring
What is the multidentate ligand EDTA4-
And how many bonds does it form
What ligand does it act as
. It forms 6 bonds
And it acts as a hexadentate ligand.
It uses lone pairs on 4 oxygen and both nitrogen atoms
What are complex ions with multidentate ligands
What are they used for
Called chalates
Can be used to effectively remove d block metal ions from a solution.
What is the chelate effect
(when EDTA4- is added to an aqua ion)
. When a hexadentate ligand eg EDTA is added to a solution of a transition metal salt, the EDTA will replace all six water ligands in the aqua ion
[Cu(H20)6]2+(aq) + EDTA4-(aq)
This makes [CuEDTA]2-(aq) + 6H20(l)
In this equation, two species are replaced by seven, as there are 7 products.
This increase in particles causes a significant increase in entropy which drives the reaction to the right.
For this reason, chelate complexes with multidentate ligands are favoured over complexes with monodentate ligands
What does the polydentate porphyrin do in haemoglobin
Haemoglobin carries oxygen around body from the lungs.
Molecule consists of Fe2+ ion with a coordinate number 6.
Four of the coordination sites are taken up by a ring system celled a porphyrin which acts as a tetradentate ligand.
This complex is called a haem.
Describe the structure of porphyrin in haemoglobin
How is carbon monoxide affecting the Fe2+
Fe2+ ion binds to 4 :N , a globin, and an O2 or H2O
It first binds to 4 :N but below the plane of this ring is a fifth nitrogen atom acting as a ligand, and it is part of a complex called globin.
The Fe2+ to O2 bond is weak as :O2 is not a very good ligand, allowing the molecule to easily give up to its cells.
However, when a better ligand than oxygen binds, it binds irreversably to the fe2+ so destroys the oxygen carrying site.
This explains the poisonous effect of carbon monoxide
What ligands have a negative charge
:Cl- ions
Eg in [CoCl4]2- ion, with 4 ligands it is a tetrahedral .
Compare the complex ions of [Co(NH3)6]3+ ion and the [CoCl4]2- ion.
- [Co(NH3)6]3+ ion has 6 ligands and is an octahedral shape.
An octahedron has six points but eight faces.
Metal ion Co3+ has a charge of +3 and the ligands are all neutral. So complex ion has an overall charge of +3
In [CoCl4]2- ion, the metal ion is Co2+ so has a 2+ charge, and there are four 1- ions, the overall charge is -2.
It is a tetrahedral shape, and so is different from other cobalt complex. The :Cl- ions are larger ligands than the ammonia molecules so fewer ligands can fit around the central metal ion.
What shape complex is [Ag(NH3)2]+:
What is the name of the solution, where is it used
Eg aldehydes and ketones
What is the name of the test.
Linear complex
The solution containing it is called Tollens’ reagent. It is used in organic chemistry to distinguish aldehydes from ketones.
The aldehydes reduce the [Ag(NH3)2]+ to Ag (metallic silver) while ketones do not.
The silver forms a mirror on the surface of the test tube, giving the name of the test.
Called the silver mirror test
What is an isomer
What two types of isomers can transition metal complexes form
Compounds with the same molecular formula but with different arrangements of their atoms in space.
Geometrical isomers
Optical isomers
Describe the two types of geometrical isomers
What ligands does this occur in
What shape complexes
Do different geometrical isomers have different chemical properties in cisplatin for example
Cis-Trans
Occurs for monodentate ligands
Occurs in octahedral and square planar complexes
Yes, they will eg cisplatin is an anti cancer drug which is a cis isomer, whilst the trans isomer of it does nothing
Describe the structure of cisplatin
Formula [Pt(Cl)2(NH3)2]
It is the square planar complex of platinum
Anti cancer drug
It is chiral so only the cis isomer works to cure disease, the trans one doesn’t affect cancer
Describe cis isomers of mono-dentate ligands
Eg in an octahedral complex ion, the same ligands are next to each other
Same with a square planar complex
Describe trans isomers of
mono-dentate ligands
Eg in octahedral, the same ligands go opposite each other
Same with in square planar
When does optical isomerism occur
When there are two or more bi-dentate ligands in a complex
The two isomers are non-superimposable mirror images of each other
so are non identical in mirror images
Do the properties change in optical isomers
They are said to be chiral, so they have identical chemical properties, but can be distinguished by their effect on polarised light.
One isomer will rotate the plane of polarisation of polarised light clockwise, and the other anticlockwise
