Question

Which of the following complex species does not involve \(d^{2} s p^{3}\) hybridisation ? (1) \(\left[\mathrm{CoF}_{6}\right]^{3-}\) (2) \(\left[\mathrm{Co}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}\) (3) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{3-}\) (4) \(\left[\mathrm{Cr}\left(\mathrm{NH}_{3}\right)_{6}\right]^{3+}\) (5) \(\left[\mathrm{Fe}(\mathrm{CN})_{6}\right]^{4-}\)

Short answer

Complex 2 \([Co(NH_3)_6]^{3+}\) does not involve \[d^2 s p^3\] hybridization.

Step-by-step solution

- Determine central metal ion configurations

Identify the electronic configurations of the central metal ions in the given complexes. For this, note the oxidation states:

- Identify oxidation states

Calculate the oxidation states of the metal ions in each complex: (1) \(\text{Co}^{3+}\) in \(\text{[CoF}_{6}]\text{^{3-}}\), (2) \(\text{Co}^{3+}\) in \(\text{[Co(NH}_{3})_{6}]^{3+}\), (3) \(\text{Fe}^{3+}\) in \(\text{[Fe(CN}_{6})^{3-}}\), (4) \(\text{Cr}^{3+}\) in \(\text{[Cr(NH}_{3})_{6}]^{3+}\), (5) \(\text{Fe}^{2+}\) in \(\text{[Fe(CN}_{6})^{4-}}\)

- Determine possible hybridizations

Identify possible hybridizations for each oxidation state: \[Co^{3+} \rightarrow [Ar] 3d^{6};\quad Fe^{3+} \rightarrow [Ar] 3d^{5};\quad Cr^{3+} \rightarrow [Ar] 3d^{3};\quad Fe^{2+} \rightarrow [Ar] 3d^{6}\]

- Analyze each complex

Check the electronic configurations and determine the hybridization types: (1) \(\text{[CoF}_{6}]\text{^{3-}}\) uses \[d^2s p^3\] hybridization. (2) \(\text{[Co(NH}_{3})_{6}]^{3+}\) uses \[d^2s p^3\] hybridization. (3) \(\text{[Fe(CN}_{6})^{3-}}\) uses \[d^2s p^3\] hybridization. (4) \(\text{[Cr(NH}_{3})_{6}]^{3+}\) uses \[d^2s p^3\] hybridization. (5) \(\text{[Fe(CN}_{6})^{4-}}\) uses \[d^2s p^3\] hybridization.

- Identify the exception

Since all given complexes use \[d^2s p^3\] hybridization, we need to find the exception. Upon reevaluation, complex (2) \([Co(NH_3)_6]^{3+}\) actually uses \[sp^3d^2\] hybridization (inner orbital complex).

Key concepts

Coordination Chemistry

Coordination chemistry is the study of metal complexes formed between metal ions and surrounding molecules or ions known as ligands. These ligands donate electron pairs to the central metal ion, creating coordinate covalent bonds. This type of chemistry is crucial for understanding various biochemical processes, industrial catalysts, and materials science. The structure and properties of these complexes depend largely on the type of ligands, the geometry of the complex, and the oxidation state of the metal ion. In this specific exercise, we examined different metal complexes and determined the type of hybridization involved in their formation. Knowing the configuration and geometry of these complexes helps predict their reactivity, stability, and interactions with other chemical species.

Hybridization in Metal Complexes

Hybridization involves the mixing of atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds. In coordination chemistry, the type of hybridization determines the geometry of the metal complex. For instance, \[d^2sp^3\]] hybridization results in octahedral geometry, common in complexes like \[CoF_6^{3-}\]], \[Fe(CN)_6^{3-}\]], and \[Cr(NH_3)_6^{3+}\]]. However, not all complexes use the same type of hybridization. Differences in hybridization, like \[sp^3d^2\]], can change the arrangement of ligands around the metal ion, leading to different properties and behaviors. In our exercise, \[Co(NH_3)_6^{3+}\]] is an example of a complex exhibiting \[sp^3d^2\]] hybridization, differing from others that use \[d^2sp^3\]]. Thus, understanding hybridization helps predict the shapes and properties of metal complexes.

Understanding Metal Complexes

Metal complexes consist of a central metal ion bonded to a number of ligands. The nature and strength of these interactions depend on various factors like the metal ion's oxidation state, the type of ligands, and their arrangement around the metal. Ligands can be monodentate, binding through a single site, or polydentate, binding through multiple sites. These complexes play a vital role in various applications, from catalysis and medicine to environmental chemistry. For example, the complex \[Fe(CN)_6^{4-}\]] involves \[d^2sp^3\]] hybridization and forms a stable, low-spin complex typical of strong field ligands like cyanide. On the other hand, \[Co(NH_3)_6^{3+}\]], using \[sp^3d^2\]], forms an inner orbital complex. Such differences affect the complexes' electronic properties and the metal-ligand bond strength. By studying these aspects, chemists can design complexes with specific properties for targeted industrial and biological applications.