Substitution Reactions|Transition Metals
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Why does ammonia produce a deeper blue solution than water in copper (II) complexes?
Ammonia causes greater d - orbital splitting than water, so higher frequency light is absorbed
What is a ligand substitution reaction? (rctn. at lst. 1lgnd. - cmplx. ion rep. anthr. lgnd.)
A reaction in which at least one ligand in a complex ion is replaced by another ligand
Can ligand substitution reactions be reversible/complete or incomplete?
Yes
Write the equation for the reaction between hexaaquacobalt (II) and chloride ions
[Co(H2O)6]2+ + 4Cl− ⇌ [CoCl4]2− + 6H2O
How does the ligand type, coordination number and overall charge of the hexaaquacobalt (II) complex change? Refer to this equation: [Co(H2O)6]2+ + 4Cl− ⇌ [CoCl4]2− + 6H2O
There is change in ligands from water to chloride ions, there is a change in the coordination number from 6 to 4 and the overall charge changes from +2 to -2
What three factors can change during a ligand substitution reaction?
The type of ligands surrounding the transition metal ion, the coordination number and the overall charge
Why can bidentate ligands form two bonds? (lng. + flxble. engh. bnd. thru. 2l.p)
They are long and flexible enough to bond through two lone pairs
What is a bidentate ligand?
A ligand that forms two dative covalent bonds to a metal ion
What is the coordination number of complexes which have three bidentate ligands?
6
Give an example of a bidentate ligand required by AQA, draw it too
Ethane-1,2-diamine (abbreviated to en)
Write the balanced equation for hexaaquacopper (II) reacting with excess ethane-1,2-diamine (en)
[Cu(H2O)6]2+ + 3en ⇌ [Cu(en)3]2+ + 6H2O
Why does ethane-1,2-diamine not change the overall change of the complex?
It is a neutral ligand
What is the charge and structure of ethanedioate ions?
2-
How does using a negatively charged ligand affect the charge of a complex ion? (mkes. cmplx. >neg.)
It makes the overall complex ion more negative
What is meant by the chelate effect? (inc. stblty. cmplxs. frmd. w/ mltidnte. lgnds. cmprd. mndnte. lgnds.)
The increased stability of complexes formed with multidentate ligands compared to monodentate ligands
Why does entropy increase when multidentate ligands replace monodentate ligands?
The number of particles in solution increases
Why do bidentate ligands replace monodentate ligands more readily? (entrpy. inc. >prtcles. frmd. prod.)
Entropy increases as more particles are formed in the products
Explain the chelate effect in terms of entropy (whn. mono. lgnds. rplce. mltdnte. lgnd. - >prtcls. frmd. sltn. - inc. entrpy. + mke. cmplx >stble.)
When monodentate ligands are replaced multidentate ligands, so more particles are formed in solution, increasing entropy increase and making the complex more stable
How does entropy affect whether a reaction occurs?
Reactions with an increase in entropy are more likely to occur
What is a multidentate ligand? (lgnd. frms. >2 DCB - mtl. ion)
A ligand that forms more than two dative covalent bonds to a metal ion
Charge on EDTA?
4-
How many dative covalent bonds can EDTA form?
Six dative covalent bonds (hexadentate)
What type of bonding occurs between oxygen and the Fe2+ ion in haemogobin?
A dative covalent bond
Why can carbon monoxide be dangerous when it binds to haemoglobin? (frms. stble. cmplx. /esly. sub. - prvnt. O2 trnspt.)
It forms a stable complex that is not easily substituted, preventing oxygen transport