Co-ordination compounds

  • 0_1546537724848_IMG_20190103_231753.jpg
    Answer given is 2
    Shouldn't the answer be Option 3? As nh3 is a string field ligand

  • @kalpita
    A really important thing you have to understand here is that;

    The strength of a ligand actually depends upon the metal atom to which it is coordinated to.
    For eg; Cl- is considered as a weak ligand generally. But if you consider the complex [PtCl4]2- here Cl acts as a strong field ligand and causes e- pairing in Pt2+. This is mainly because of the large size of Pt atom.And for this reason,this complex is square planar and not tetrahedral.
    But to an extent,the strength of a ligand can be found out relating to its electronegativity.If a species is highly electronegative it has less tendency to donate e-s and thus is a weak field ligand.But still it is not completely acceptable as seen in the above anomaly.
    Being lewis bases(those who donate electrons) the ligands with less electronegativity will be stronger.

    Therefore, in general halogen or oxygen donors (eg-F-,Cl-,Br-,H2O)are weak field ligands and the ones in which carbon or nitrogen atom is the donor (eg-CN-,CO,NH3) are strong field ligands.

    After knowing this i highly recommend you read an article on crystal field theory, after which you will be able to determine whether the the ligands will form high spin or low spin complexes.
    Strong field and weak field ligands are semi-empirical concepts from crystal field theory.In short, weak field ligands (e.g. F-, Cl-, OH-, H2O) will result in lower splitting of the d-orbitals of the metal in the center of a complex, while strong field ligands (e.g. NH3, CN-, NO+, CO) will result in larger splitting.

    Wether a ligand produces a "strong" or a "weak" field was initially determined experimentally, which resulted in the so-called spectrochemical series, which lists ligands according to their field strengths.
    0_1546538952063_2016-11-25_08-38-41_chem 110.jpg

  • @kalpita
    this is a drawback of vb theory
    Cl- is a weak ligand but acts as **strong field ligand **in this particular case0_1546516309699_IMG_20190103_115009.jpg

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