Question

The statements that are incorrect about the nickel(II) complex of dimethylglyoxime are :
A. It is red in colour.
B. It has a high solubility in water at pH = 9.
C. The Ni ion has two unpaired d-electrons.
D. The N – Ni – N bond angle is almost close to 90°.
E. The complex contains four five-membered metallacycles (metal containing rings).
Choose the correct answer from the options given below :

• A. C and E Only
• B. B, C and E Only
• C. A, D and B Only
• D. C and D Only

Hint:

Work out the hybridization and geometry of the nickel complex first. That single structure, square planar, diamagnetic, two chelate rings per ligand, settles most of the statements at once, rather than checking each one from memory.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
$Ni(DMG)_2$ is a square planar, neutral complex. Its stability and distinct color are due to its unique structure involving intramolecular hydrogen bonding.
Step 2: Detailed Explanation:
- Statement A: Correct. The complex is a rosy-red precipitate. - Statement B: Incorrect. It is highly insoluble in water, which is why it's used for the gravimetric estimation of Nickel. - Statement C: Incorrect. As a square planar $d^8$ complex with strong field behavior (from $N$ donors), it is diamagnetic (0 unpaired electrons). - Statement D: Correct. Square planar geometry implies angles close to 90°. - Statement E: Incorrect. It contains two five-membered chelate rings (Ni-N-C-C-N) and two six-membered rings formed by hydrogen bonding (O-H...O).
Step 3: Final Answer:
The incorrect statements are B, C, and E.

Answer 2

Concept:

• Build the structure of the complex first, then check every statement against that one structure instead of recalling each fact separately.
• $Ni^{2+}$ is a $d^8$ ion. With the strong-field $N$ donor atoms of dimethylglyoxime, it adopts $dsp^2$ hybridization and a square planar geometry.
• Each dimethylglyoxime ligand binds through two nitrogen atoms to form one chelate ring, and two O-H...O hydrogen bonds link the two ligand units together.

Step 1: Fix the hybridization and geometry of the complex.
$Ni^{2+}$ has the configuration $3d^8$. Strong-field $N$-donor ligands pair up all the electrons, leaving the $d_{x^2-y^2}$ orbital empty for bonding.
This gives $dsp^2$ hybridization, a square planar shape, and zero unpaired electrons, so the complex is diamagnetic.
This directly settles Statement C: it claims two unpaired electrons, which is false.

Step 2: Use the square planar geometry to settle Statement D.
In a square planar arrangement, all bond angles around the central atom are $90$ or $180$ degrees.
The $N-Ni-N$ angle between adjacent nitrogen atoms is therefore close to $90$ degrees, so Statement D is true.

Step 3: Use the bonding pattern to settle Statement E.
Each dimethylglyoxime ligand attaches through its two $N$ atoms directly to $Ni$, closing one five-membered ring ($Ni-N=C-C=N$) per ligand.
With two ligand molecules in the complex, there are only two such five-membered chelate rings, not four.
So Statement E, which claims four five-membered rings, is false.

Step 4: Use the resulting molecular packing to settle Statements A and B.
The compact, hydrogen-bonded square planar structure with the bulky methyl groups pointing outward gives the complex a characteristic rosy-red colour, confirming Statement A.
This same neutral, tightly packed, largely non-polar structure has very poor interaction with water molecules, so the complex precipitates out rather than dissolving, even at pH $= 9$. Statement B, which claims high solubility, is false.

Step 5: Collect the false statements.
False statements: B, C and E.

Final Answer: B, C and E Only