Chemistry - Complete d-block Question with Solution | TestHub

Explain Question :

Match the given inorganic compounds with their properties, including color, magnetic behavior, and electronic transitions.

Concept :

This question is based on the properties of coordination and transition metal compounds:

Colour: Caused by d-d transitions or charge transfer (LMCT/MLCT).

Magnetic behavior: Paramagnetic (unpaired electrons) or Diamagnetic (all electrons paired).

Electronic transitions: d-d transitions are common in transition metal ions. Charge transfer transitions can also occur, where an electron is transferred from a ligand to a metal (LMCT) or vice versa (MLCT).

Solution:

(A) K₂Cr₂O₇: This compound is potassium dichromate. It is bright orange-red in color. The central metal, Cr, is in a +6 oxidation state ($3d^0$ configuration), so there are no d-electrons available for d-d transitions. The color is due to a Ligand to Metal Charge Transfer (LMCT) transition, where an electron from an oxygen ligand is excited to an empty d-orbital of chromium. It has no unpaired electrons, so it is diamagnetic.

Matches: (P) Coloured, (S) Diamagnetic, (T) LMCT

(B) KMnO₄: This is potassium permanganate. It is an intense purple color. The central metal, Mn, is in a +7 oxidation state ($3d^0$ configuration). Like dichromate, its intense color is due to an LMCT transition. It has no unpaired electrons, so it is diamagnetic.

Matches: (P) Coloured, (S) Diamagnetic, (T) LMCT

(C) [Cu(CH₃CN)₄]BF₄: This is tetrakis(acetonitrile)copper(I) tetrafluoroborate. In this complex, the copper is in the +1 oxidation state ($3d^{10}$ configuration). Since the d-orbital is completely filled, there are no unpaired electrons, and d-d transitions are not possible. Thus, the complex is colorless and diamagnetic.

Matches: (Q) Colourless, (S) Diamagnetic

(D) [Ti(H₂O)₆]Cl₃: The complex ion is $[Ti(H_{2}O{)}_6{]}^{3+}$. Titanium is in the +3 oxidation state. The electronic configuration of Ti³⁺ is $[Ar]3d^1$. It has one unpaired electron, making it paramagnetic. The presence of the single d-electron allows for a d-d transition, where the electron is excited from the $t_{2g}$ to the $e_g$ orbital. This transition is responsible for its characteristic purple color.

Matches: (P) Coloured, (R) Paramagnetic

Final answer:

(A) - (P), (S), (T)

(B) - (P), (S), (T)

(C) - (Q), (S)

(D) - (P), (R)