Coordination Chemistry

Mn (CO) has a structure with a direct Mn-Mn single bond, ten terminal CO groups, and no bridging CO groups. Each Mn is in a zero oxidation state.
Co (CO) has a more complex structure. It can exist in different isomeric forms. The most common structure involves bridging CO groups and a Co-Co bond. In another form, there are only terminal CO ligands and a Co-Co bond. In either isomeric form, Co (CO) features a metal-metal bond, terminal CO groups, and can have bridging CO groups. Each Co atom is also in the zero oxidation state.
So, the common features are Metal-Metal linkage (A), Terminal CO groups (B), and Metal in zero oxidation state (D).

An ambidentate ligand is a ligand that can bind to a central metal ion through two different donor atoms.

(Oxalate): Oxalate is a bidentate ligand, meaning it binds through two oxygen atoms. However, both oxygen atoms are equivalent, so it is not ambidentate. It always binds through its two oxygen atoms.

(Thiocyanate): Thiocyanate can bind through either the sulphur atom (thiocyanate-S) or the nitrogen atom (thiocyanate-N), making it ambidentate.

(Nitrite): Nitrite can bind through either the nitrogen atom (nitro) or the oxygen atom (nitrate), making it ambidentate.

(Cyanide): Cyanide can bind through either the carbon atom (cyano) or the nitrogen atom (isocyanate), making it ambidentate. Although cyanide preferentially binds through carbon, the possibility of N-bonding makes it technically ambidentate.

The order of absorption of light (wavelength) is determined by the ligand field strength, where stronger field ligands tend to absorb light at shorter wavelengths, while weaker field ligands absorb light at longer wavelengths.
1. A. : Ammonia (NH₃) is a moderate field ligand.
Thus, this complex absorbs light at a medium wavelength.
2. B. : Cyanide (CN⁻) is a strong field ligand, leading to a large splitting of d-orbitals and absorption of light at a shorter wavelength (higher energy).
3. C. : Water (H₂O) is a weak field ligand, resulting in small d-orbital splitting and absorption at longer wavelengths (lower energy).
4. D. : Titanium in the +3 oxidation state (with water ligands) is a relatively weak field complex, leading to light absorption at longer wavelengths compared to ammonia and cyanide complexes.

Thus, the correct order of the wavelength of light absorbed is:
Therefore, the correct answer is (3) C A D B.