Question

What is the formula of tetraammineaquachlorocobalt(III) chloride?
A.$\left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}{{\text{H}}_2}{\text{OBr}}} \right]{\text{C}}{{\text{l}}_2}$
B.$\left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_2}} \right)}_4}{{\text{H}}_2}{\text{OBr}}} \right]{\text{Cl}}$
C.$\left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_4}} \right)}_4}{{\text{H}}_2}{\text{OBr}}} \right]{\text{Cl}}$
D.$\left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}{{\text{H}}_2}{\text{OBr}}} \right]{\text{Cl}}$

Answer 1

A complex is a compound in which a metal atom or ion is joined to a ligand, which is a collection of neutral molecules or anions. Coordination compounds are uncharged neutral substances with at least one ion present as a complex. The following is a list of coordination compounds and their names.
A. Always identify the cation before the anion when naming a coordination molecule, regardless of whether the complex ion is the cation or the anion. (It's the same as naming an ionic compound.)
B. When it comes to naming the complicated ion.

Complete answer: 1. Name the ligands first, then the metal atom or ion, in alphabetical order. In the chemical formula, the metal atom or ion is written before the ligands.
2. A list of some commonly used ligands is provided.
Change the ends of anionic ligands that finish in "-ide" (e.g. chloride), "-ate" (e.g. sulphate, nitrate), and "-ite" (e.g. nirite) as follows: -ide -o; -eat -ato; -ite -itto
For neutral ligands, the molecule's common name is given, such as ${H_2}NC{H_2}C{H_2}N{H_2}$(ethylenediamine). Water is referred to as ‘aqua,' ammonia is referred to as ‘ammine,' carbon monoxide is referred to as ‘carbonyl,' and ${N_2}$ and ${O_2}$are referred to as ‘dinitrogen' and ‘dioxygen,' respectively.
Now coming to tetraammineaquachlorocobalt(III)
Ammine refers to ammonia hence option b and c are not the correct answers.
Considering$\left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}{{\text{H}}_2}{\text{OBr}}} \right]{\text{C}}{{\text{l}}_2}$
The oxidation state of Co here is 3
Whereas in $\left[ {{\text{Co}}{{\left( {{\text{N}}{{\text{H}}_3}} \right)}_4}{{\text{H}}_2}{\text{OBr}}} \right]{\text{Cl}}$
The oxidation state of Co here is 2
Hence option A is correct.

Note:
The number of each kind of ligand in the complex ion is designated by Greek prefixes, such as di-, tri-, and tetra-. The prefixes bis-, tris-, tetrakis-, and pentakis- are used instead if the ligand already has a Greek prefix (e.g. ethylenediamine) or if the ligand is polydentate (i.e. may connect to more than one binding site). The oxidation state of the metal in the complex is indicated as a Roman numeral in parentheses after the name of the metal.