Which of the following coordination complexes has a coordination number of $6$?

• A. $\left[\mathrm{Co}\right({\mathrm{NH}}_3\left)6\right]{\mathrm{Cl}}_3$
• B. $\left[\mathrm{Ag}\right(\mathrm{CN}\left)2\right]{\mathrm{Na}}_2$
• C. $\left[\mathrm{Cu}\right({\mathrm{NH}}_3\left)4\right]{\mathrm{SO}}_4$
• D. ${\mathrm{Fe}}_2\left({\mathrm{SO}}_4\right)3$

Answer: (A)

Verified step by step guidance

1. Understand that the coordination number of a complex is the total number of ligand donor atoms bonded directly to the central metal ion.
2. Examine each complex and count the number of ligands attached to the metal center, considering the subscript numbers indicating how many of each ligand are present.
3. For the complex \([Co(NH_3)_6]Cl_3\), note that there are 6 ammonia (\(NH_3\)) ligands coordinated to cobalt, so the coordination number is 6.
4. For \([Ag(CN)_2]Na_2\), there are 2 cyanide (\(CN\)) ligands attached to silver, so the coordination number is 2.
5. For \([Cu(NH_3)_4]SO_4\), there are 4 ammonia ligands coordinated to copper, so the coordination number is 4; and for \(Fe_2(SO_4)_3\), this is an ionic compound, not a coordination complex, so coordination number is not defined in the same way.