Co-ordination Compounds MCQs for NEET — Chemistry Questions with Answers

Potassium ferrocyanide, K4[Fe(CN)6], has an octahedral geometry around the Fe2+ ion. The six cyanide (CN-) ligands are arranged in an octahedral fashion around the central iron ion.

In an octahedral structure, the pair of d-orbitals involved in $d^2sp^3$ hybridization are $d_{x^2-y^2}$ and $d_{z^2}$. These orbitals point directly along the axes and are capable of forming strong directional bonds with the surrounding ligands.

$[Fe(CN)_6]^{4-}$ is diamagnetic because the Fe2+ ion in this complex has a low-spin configuration due to the strong field ligand (cyanide, CN-). This results in paired electrons in all the d-orbitals, leading to no unpaired electrons and hence diamagnetic behavior.

The magnitude of \( \\Delta_0 \\) (crystal field splitting energy) depends on the field strength of the ligands. In the given complexes, the ligands are CN^-, C_2O_4^{2-}, H_2O, and NH_3. Among these, CN^- is a strong field ligand and causes the maximum splitting. Therefore, \( [Co(CN)_6]^{3-} \\) will have the highest \( \\Delta_0 \\).

For the complex \( [Co(NH_3)_6]^{3+} \\), Co is in the +3 oxidation state (d^6 configuration). NH_3 is a strong field ligand causing pairing of electrons, resulting in 0 unpaired electrons. For \( [CoF_6]^{3-} \\), Co is also in the +3 oxidation state (d^6 configuration) but F^- is a weak field ligand, so it does not cause pairing of electrons, resulting in 4 unpaired electrons.

An outer orbital complex involves the use of the outer d orbitals in bonding. Among the given options, $ [Ni(NH_3)_6]^{2+} $ is an outer orbital complex. This is because Nickel in this complex uses its 4s and 4p orbitals for bonding, rather than the inner 3d orbitals.

$ [Co(NH_3)_6]Cl_3 $ is a low-spin complex due to the presence of strong field ligand NH3. In this case, all electrons are paired up, leading to a magnetic moment of zero. Therefore, the correct answer is zero.

In $Fe(CO)_5$, the bonding involves both sigma ($ ext{σ}$) and pi ($ ext{π}$) characters. The carbon monoxide ligand donates a pair of electrons to form a sigma bond with the iron atom. Additionally, the filled d-orbitals of iron back-donate electrons into the empty π*-orbitals of the CO ligand, forming a pi bond. This synergic bonding results in a bond that has both sigma and pi characters.

According to Werner’s theory, coordination compounds have two types of valencies: primary and secondary. The primary valency corresponds to the oxidation state of the metal and can be ionized. The secondary valency corresponds to the coordination number of the metal and involves coordinate bonds with ligands, which typically cannot be ionized.

Ligands in a complex salt can be either ions or molecules linked by coordinate (dative covalent) bonds to a central metal atom or ion. This means that ligands can be anions, cations, or neutral molecules, as long as they donate a pair of electrons to the metal center to form a coordinate bond.