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NEET Chemistry Notes Coordination Compounds – Bonding in Coordination Compounds

NEET Chemistry Notes Coordination Compounds – Bonding in Coordination Compounds

Bonding in Coordination Compounds

Bonding in Coordination Compounds

The bonding formation in coordination compounds can be explained by using the two approaches as given below:

Valence Bond Theory (VBT)

According to this theory, the metal atom or ion under the influence of ligands form inner orbital and outer orbital complex. These hybridised orbitals are allowed to overlap with ligand orbitals that can donate electron pairs for bonding.

Six Ligands (Unidentate) Octahedral Entity

Generally, central atom belongs to 3d series and ligands can be monodentate or didentate but coordination number should be six. The shape of complexes will be octahedral. Such complexes are of the following two types:

  • Inner Orbital Complexes (hyperligated com- plexes) which are formed due to strong field ligands or low spin ligands, has d2 sp3 -hybridisation (where two orbitals are of 3d, one orbital of 4s and three orbitals of 4p) and shape of complex will be octahedral
  • Outer Orbital Complexes (hypoligated complexes) which are formed due to weak field ligands or high spin ligands, has sp3d2  hybridisation (where one orbital is of 4s, three orbitals of 4p and two orbitals of Ad).
  • Generally halides NEET Chemistry Notes Coordination Compounds - Bonding in Coordination Compounds 1form outer orbital complexes and other ligands form inner orbital complexes,
    e.g.
    NEET Chemistry Notes Coordination Compounds - Bonding in Coordination Compounds 2
  • All electrons are paired, therefore complex will be diamagnetic in nature.
    NEET Chemistry Notes Coordination Compounds - Bonding in Coordination Compounds 3
  • Complex has unpaired electrons, therefore it will be paramagnetic in nature.

Four-Ligands (Unidentate), Tetrahedral and Square Planar Entity

Tetrahedral complexes can also form inner orbital or outer orbital complexes, characteristics of which are shown below:
NEET Chemistry Notes Coordination Compounds - Bonding in Coordination Compounds 4
NEET Chemistry Notes Coordination Compounds - Bonding in Coordination Compounds 5
All electrons are paired, thus complex will be diamagnetic in nature.
NEET Chemistry Notes Coordination Compounds - Bonding in Coordination Compounds 6
Complex has unpaired electrons, so it will be paramagnetic in nature.

Limitations of Valence Bond Theory

Although this theory described the formation, structure and magnetic behaviour of complexes sucessfully but it suffers from the following short comings:

  •  It involves a number of assumptions.
  •  It describes bonding in coordination compounds only qualitatively. It does not offer any explanation for the optical absorption spectra of complexes.
  • It does not describe the detailed magnetic properties of coordination compounds.
  •  It does not give a quantitative interpretation of the thermodynamic or kinetic stabilities of coordination compounds.
  • It does not make exact predictions regarding the tetrahedral and square planar structures of 4-coordinate complexes.
  • It does not distinguish between weak and strong ligands

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