Determine IUPAC Name of Tetraaqua Diammine Cobalt Complex

To determine the systematic IUPAC name for the coordination complex $[\text{Co}(\text{H}_2\text{O})_4(\text{NH}_3)_2]\text{Cl}_3$, we follow the standard IUPAC nomenclature rules for coordination compounds:

1. Identification of Cation and Anion:

   • The complex sphere $[\text{Co}(\text{H}_2\text{O})_4(\text{NH}_3)_2]^{3+}$ is the cationic species and is named first.
   • The ion outside the coordination sphere, $\text{Cl}^-$, is the anionic counter-ion and is named second as "chloride".

2. Determination of Oxidation State of Central Metal Atom:

   • Let the oxidation state of Cobalt ($\text{Co}$) be $x$.
   • Neutral ligands: $\text{H}_2\text{O}$ has a charge of $0$, and $\text{NH}_3$ has a charge of $0$.
   • Chloride ion ($\text{Cl}^-$) has a charge of $-1$. $\text{Oxidation equation: } x + 4(0) + 2(0) + 3(-1) = 0 \implies x = +3$
   • Thus, Cobalt is in the $+3$ oxidation state, denoted as cobalt (III).

3. Naming the Ligands in Alphabetical Order:

   • Neutral ligand $\text{NH}_3$ is named ammine (spelled with double 'm'). Since there are 2 ammine molecules, the prefix is di-, giving diammine.
   • Neutral ligand $\text{H}_2\text{O}$ is named aqua. Since there are 4 aqua molecules, the prefix is tetra-, giving tetraaqua.
   • Ligands are listed in alphabetical order according to their name (ignoring prefixes):
     • ammine comes before aqua ($m$ precedes $q$ in the alphabet).
     • Therefore, "diammine" is placed before "tetraaqua".

4. Combining the Name:

   • Combining the ligands, central metal, oxidation state, and counter-ion gives: $\text{Diamminetetraaquacobalt (III) chloride}$

Hence, the correct option is D.