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Step-by-Step Solution
Step 1: Understand the Complex Formula
The given complex has the formula Co(en)2Cl3, where “en” (ethylenediamine) is a bidentate ligand, meaning each en can coordinate through two nitrogen atoms.
Step 2: Analyze the Reaction with Silver Nitrate
It is stated that 3 moles of the metal complex produce 3 moles of AgCl upon treatment with excess AgNO3. This indicates that exactly one chloride ion per complex is free (i.e., present as an ion) and thus gets precipitated as AgCl. The net ionic reaction can be represented as:
3\,\bigl[\mathrm{Co}(\mathrm{en})_{2}\mathrm{Cl}_{2}\bigr]\mathrm{Cl} + \mathrm{AgNO_{3}}\,(excess) \;\longrightarrow\; 3\,\mathrm{AgCl} + \ldots
Since there is only one chloride per formula unit that is ionic (i.e., outside the coordination sphere), the remaining two chloride ions must be bonded (inside the coordination sphere) to cobalt.
Step 3: Determine the Coordination Number (Secondary Valency)
Each en ligand occupies two coordination sites. There are two en ligands, thus:
\text{Sites from 2 en ligands} = 2 \times 2 = 4
Additionally, the complex contains two chlorides within the coordination sphere. Hence, total sites occupied around Co are:
4 \,(\text{from en}) + 2 \,(\text{from Cl}) = 6
This total, 6, is the secondary valency (coordination number) of cobalt in the complex.
Step 4: Final Answer
Therefore, the secondary valency (coordination number) of Co is 6.
