When does or in which complex water act as strong field ligands and when weak field ligand..
When does or in which complex water act as strong field ligands and when weak field ligand..
Case for metals in +2 oxidation state :
Ligands are classified as weak , intermediate and strong depending upon whether they are sigma and pi donor, sigma donor only and sigma donor and pi acceptor respectively. H2O comes under the category of intermediate field ligand because it can donate only through sigma bonding. The reason it is not weak ligand is it cannot donate electron through pi bonding i.e only sigma donor, because after donating one electron pair oxygen attains positive charge which makes it difficult to donate another pair of electron. Also there is no vacant orbital to accommodate electron from metal ( pi back Bonding) is the reason it is not strong ligand.
Case of metal in +3 oxidation state:
However it acts as strong ligand when metal ion is in +3 oxidation for metals like cobalt , nickel and copper and weak ligand for metals like Sc , Ti, V, Cr, Mn and Fe in +3 Oxidation state.
And for 4d bad 5d series metals in any oxidation state it acts as strong ligand without any exceptions.
Case for metals in +2 oxidation state :
Ligands are classified as weak , intermediate and strong depending upon whether they are sigma and pi donor, sigma donor only and sigma donor and pi acceptor respectively. H2O comes under the category of intermediate field ligand because it can donate only through sigma bonding. The reason it is not weak ligand is it cannot donate electron through pi bonding i.e only sigma donor, because after donating one electron pair oxygen attains positive charge which makes it difficult to donate another pair of electron. Also there is no vacant orbital to accommodate electron from metal ( pi back Bonding) is the reason it is not strong ligand.
Case of metal in +3 oxidation state:
However it acts as strong ligand when metal ion is in +3 oxidation for metals like cobalt , nickel and copper and weak ligand for metals like Sc , Ti, V, Cr, Mn and Fe in +3 Oxidation state.
And for 4d bad 5d series metals in any oxidation state it acts as strong ligand without any exceptions.
