COMPLEX FORMATION Flashcards
(25 cards)
What are co-ordinate bonds? (1)
All transition metal ions can form co-ordinate bonds by accepting electron pairs from other ions or molecules.
what is a ligand? (1)
an ion or molecule with a lone pair of electrons that forms a co-ordinate bond with a transition metal is called a ligand.
what is a complex ion? (1)
when molecules form two, four or six ligand bonds to a single transition metal ion.
what is a co-ordination number? (1)
the number of co-ordinate bonds to ligands that surround a d-block metal ion.
what shape will a complex ion be if it has a co-ordination number of 6? (1)
usually octahedral
what shape will a complex ion be if it has a co-ordination number of 4? (1)
usually tetrahedral but some cane be square planar
what is an aqua ion? (1)
if you dissolve the salt of a transition metal in water, for example, copper sulphate, the positively charged metal ion becomes surrounded by water molecules acting as ligands.
What are multidentate ligands? (1)
have more than one atom with a lone pair of electrons which can bond to a transition metal ion
what are some examples of multidentate ligands? (3)
ethane-1,2-diamine
the ethanedioate ion
benzene-1,2-diol
what are chelates? (1)
complex ions with polydentate ligands
what does EDTA4- stand for? (1)
ethylenediaminetetracetate
what is the purpose of EDTA4-? (1)
this can act as a hexadentate ligand using lone pairs on four oxygen and both nitrogen atoms.
what happens when you add a hexadentate to a transition metal salt solution? (1)
The hexadentate such as EDTA will replace all six water ligands in the aqua ion.
what is the chelate effect? (1)
when there is a significant increase in the entropy which drives the reaction right, for this reason chelate complexes with polydentate ligands are favoured over complexes with monodentate ligands
What is haemoglobin? (1)
haemoglobin is the red pigment in blood, its is responsible for carrying oxygen from the lungs to the cells of the body
what is the structure of haemoglobin? (1)
the molecule consists of an Fe2+ ion with a co-ordination number of 6. Four of the co-ordination sites are taken up by a ring system called a porphyrin which acts as a tetradentate ligand, this complex is called haem. Below the plane of this ring is a fifth nitrogen acting as a ligand, this complex is called globin.
How does a haemoglobin molecule accept an oxygen molecule? (1)
The sixth site can accept an oxygen molecule as a ligand, the Fe2+ to O2 bond is weak as 02 is not a very good ligand allowing the molecule to be easily given up to cells.
Why is it an advantage that O2 is a bad ligand? (1)
better ligands than oxygen can bond irreversibly to the iron and so destroy haemoglobins oxygen-carrying capacity, this explains the poisonous effects of carbon monoxide.
why do complex ions differ in shape? (1)
because some complex ions have different ligands, in the case of chlorine, it is a larger ligand than other molecules and so fewer ligands can be around the central atom.
What kind of isomerism can occur in transition metals? (1)
transition metal complexes can form both geometrical isomers and optical isomers.
Descrive geometrical isomerism in the case of transition metal complexes. (1)
here ligands differ in their position in space relative to one another. This isomerism occurs in octahedral and square planar complexes.
describe geometrical isomerism in terms of octahedral complexes. (1)
the ligands may be on opposite sides of the molecule (the trans- or E-form) or next to each other (the cis- or Z-form)
describe geometrical isomerism in terms of square planar complexes. (1)
the ligands may be on opposite sides of the molecule (the trans- or E-form) or next to each other (the cis- or Z-form)
describe optical isomerism in transition metal complexes. (1)
here the two isomers are non-superimposable mirror images of each other, in transition metal complexes this occurs when there are two or more bidentate ligands in a complex.
