Transition Elements - 2 (ligands, and sub reactions, isomers...) Flashcards
Colour of Co2+ complex hydroxide precipitate and equation
Blue which turns beige in the presence of air
+ 2OH- -> (H2O)4(OH)2 + 2H2O
Colour of Fe2+ hydroxide precipitate and equation
Green, then turns brick red in presence of O2
Colour of Fe3+ hydroxide precipitate and equation
Brick red/ rusty brown
Colour of Cu2+ hydroxide precipitate and equation
Blue
What is a bidentate ligand?
A ligand which can donate two lone pairs of electrons to the central metal ion to form coordinate bonds
Ligand substitution in complexes:
Cu 2+ and ammonia, first a small amount then in excess
A small amount: pale blue precip. of Cu(OH)2
Excess: precip. dissolves, deep blue solution + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
Cu 2+ and hydrochloric acid
Initially turns green then yellow solution
+ 4Cl- equil. [CuCl4]2- + 6H2O
Co 2+ and conc. hydrochloric acid
Dark blue solution
+ 4Cl- equil. [CoCl4]2- + 6H2O
Co 2+ and ammonia
Small amount: = 2NH3 -> (H2O)4(OH)2 + 2NH4+ green precip
Excess: start from same complex ion, + 6NH3 -> []6NH3 2+ + 6H2O beige then black on standing
What is a coordinate bond?
Bond in which both electrons in shared pair are donated by the same bonding atom
What is a ligand?
A molecule or ion which donates a pair of electrons to the central metal ion to form a coordinate bond
What is coordination number?
The total number of coordinate bonds formed between a central metal ion and its ligands
Why do transition metal ions form complex ions?
They are relatively small and have two or more charges, therefore their high charge density makes them strongly polarizing and able to attract lone pairs of electrons or ions on molecules
Requirement to act as a ligand
At least one lone pair of electrons
Formula and charges of following ligands:
- Water
- Ammonia
- Thiocyanate
- Cyanide
- Chloride
- Hydroxide
- :OH2 & neutral
- :NH3 & neutral
- :SCN- & -1
- :CN- & -1
- :Cl- & -1
- :OH- & -1
What is a monodentate ligand?
A ligand that donates just one pair of electrons to the central metal ion to form one coordinate bond
Using VSEPR, describe how coordination number influences the shape of complex ions
Electron pairs repel each other, coordinate bonds are bonding electron pairs which will repel each other equally and as far apart as possible to minimize repulsion. Thus, number of coordinate bonds will influence the shape of the complex ion
What type of complex ions does cis/trans isomerism occur in?
Octahedral complex ions that contain four of one type of ligand and two of another
Square planar complex ions
Difference between cis and trans complex ion isomers
In the cis, the two ligands which are the same are at adjacent corners and 90~ to one another
In the trans, the two ligands which are the same are at opposite corners and 180~ to one another
What is a bidentate ligand?
A ligand that can donate two lone pairs of electrons to the central metal ion to form two coordinate bonds.
What is a hexadentate ligand?
A ligand with 6 lone pairs of electrons, each forming a coordinate bond to a metal ion in a complex ion
Which complex ions form optical isomers?
Octahedral complexes that contain multidentate ligands
Requirements for optical isomers
(No plane of symmetry)
- A complex with three molecules or ions of a bidentate ligand
- A complex with two molecules or ions of a bidentate ligand, and two molecules or ions of a monodentate ligand
- A complex with one hexadentate ligand
What is a ligand substitution?
A reaction in which one ligand in a complex ion is replaced by another ligand
Reaction between copper (II) ions and ammonia
Small amount of ammonia: ammonia acts as base and blue precipitate of Cu(OH)2 is formed (from blue solution)
When excess ammonia is added, the pale blue precip dissolves and a deep blue solution is formed. Four of water ligands are replaced by ammonias.
[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
Reaction between copper (II) ions and conc. HCl
Blue solution turns green then yellow. When green, both the blue and yellow, aqua and the chloro complexes are present.
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2O
Cobalt (II) ions and conc. HCl
Pale pink solution turns dark blue.
[Co(H2O)6]2+ 4Cl- CoCl4 2- + 6H2O
Cobalt (II) ions and ammonia
Small amount: Green precip of hydroxide
Excess: Straw coloured solution is formed
[Co(H2O)6]2+ + 6NH3 [Co(NH3)6]2+ + H2O
What is the equation for Kstab?
[new complex]/[aqua complex][new ligands]^no. of moles of ligand in eqn.
What does large Kstab value show about equilibrium?
The position of equilibrium lies to the right
What does a large Kstab value show about stability and formation of ion?
Complex ions with larger Kstab values are more stable than those with lower ones, large stability shows that the ion is easily formed
