Question

Is PPh₃ a strong ligand?

Answer 1

Hint: PPh₃ is a strong field ligand according to crystal field theory and spectrochemical series because it can produce strong splitting.

Complete Step by Step Solution:
Ligand: These are the ions or molecules attached to the primary atom/ion in the coordination entity. For example, Cl^-, NH₃, N(CH₂CH₂NH₂)₃.
There are mainly four types of ligands: Unidentate, Didentate, Polydentate, and Ambidentate.
It does not form a pure organometallic compound because the bonding between the metal and the ligand is through Phosphorus and not Carbon.
It has a lone pair on the Phosphorus atom which is basic and nucleophilic. It serves as $\sigma$ donor to the metal atom.
It has empty orbitals on the Phosphorus atom which can act as Lewis acid and overlaps with the d-orbital on the metal ion and behaves as $\pi$ acceptors.
There are basically two types of bonding:
$\sigma$ bonding between the metal and the Phosphorus atom
$\pi$ back bonding between the metal and $\sigma^*$ (lowest unoccupied molecular orbital) of the phosphorus atom.

Additional information:
Unidentate ligand: Ligand is attached to a metal ion by a single donor atom such as Cl^-, H₂O, NH₃.
Didentate ligand: A ligand is attached to the two donor atoms such as C₂O₄^-, H₂NCH₂CH₂NH₂.
Polydentate ligand: The presence of many donor atoms in a single ligand like N(CH₂CH₂NH₂)₃.
Ambidentate ligand: The ligand with two different donor atoms in the complex like NO₂^-, SCN^-.

Note: A "strong field" ligand results in a large $\Delta_{\sigma}$ and a low spin configuration, while a "weak field" ligand results in a small $\Delta_{\sigma}$ and a high spin configuration. $\Delta_{\sigma}$ is the difference between the energy required to pair two electrons and the energy required to place an electron in a high-energy state.