Unstable Complexes

Unstable complexes are those complexes that are highly reactive and easily decompose to form new compounds or ligands. The instability of a complex depends on various factors such as the size and nature of the ligands, the charge on the metal ion, and the steric hindrance around the metal ion. In this question, we have to identify the most unstable complex among Ti(C2H5)3, Ti(CH2Ph)4, Pb(CH3)4, and Pb(C2H5)4.

Comparison of Complexes

Ti(C2H5)3:

- This complex has three ethyl (C2H5) ligands attached to the titanium (Ti) metal ion.
- Ethyl ligands are small-sized, and they do not have any steric hindrance around the metal ion.
- The charge on the Ti metal ion is +3, making it highly electropositive.
- Therefore, the Ti(C2H5)3 complex is relatively stable.

Ti(CH2Ph)4:

- This complex has four benzyl (CH2Ph) ligands attached to the Ti metal ion.
- Benzyl ligands are bulkier than ethyl ligands, and they have some steric hindrance around the metal ion.
- The charge on the Ti metal ion is +4, making it less electropositive than Ti(C2H5)3.
- Therefore, the Ti(CH2Ph)4 complex is less stable than Ti(C2H5)3.

Pb(CH3)4:

- This complex has four methyl (CH3) ligands attached to the Pb metal ion.
- Methyl ligands are small-sized, and they do not have any steric hindrance around the metal ion.
- The charge on the Pb metal ion is +4, making it less electropositive than Ti(C2H5)3.
- Therefore, the Pb(CH3)4 complex is less stable than Ti(C2H5)3.

Pb(C2H5)4:

- This complex has four ethyl (C2H5) ligands attached to the Pb metal ion.
- Ethyl ligands are small-sized, and they do not have any steric hindrance around the metal ion.
- The charge on the Pb metal ion is +4, making it less electropositive than Ti(C2H5)3.
- Therefore, the Pb(C2H5)4 complex is less stable than Ti(C2H5)3.

Conclusion

Based on the above comparisons, we can conclude that Ti(C2H5)3 is the most stable complex among the given options, and the most unstable complex is Ti(CH2Ph)4. The steric hindrance around the Ti metal ion due to the bulkier benzyl ligands makes the Ti(CH2Ph)4 complex highly unstable.