JEE Main · 2025 · 22 Jan 2025 · Shift 2 · Coordination Compounds

Dimethylglyoxime (dmgH2) is a bidentate ligand; on deprotonation of one oxime $-\mathrm{OH}$ per molecule it binds $\mathrm{N}{\mathrm{i}}^{2+}$ through both nitrogen atoms, and two such ligand units wrap around the nickel to give the square-planar, neutral complex $\left[\mathrm{Ni}(\mathrm{dmg}{)}_2\right]$, held rigid by two intramolecular $\mathrm{O}-\mathrm{H}\cdots \mathrm{O}$ hydrogen bonds bridging the two ligand units.

Each dmg unit in the complex, $\mathrm{C}{\mathrm{H}}_3-\mathrm{C}(=\mathrm{N}-{\mathrm{O}}^{-})-\mathrm{C}(=\mathrm{N}-\mathrm{OH})-\mathrm{C}{\mathrm{H}}_3$ (one oxime deprotonated, the other retaining its proton and hydrogen-bonded across to the deprotonated oxygen of the neighboring ligand), carries 7 hydrogen atoms: 6 from its two methyl groups plus 1 from its remaining O–H.

With two dmg units in the complex, the total hydrogen count is $2\times 7=14$.