Question

The IUPAC name of the complex $\left[ {CrC{l_2}{{\left( {{H_2}O} \right)}_4}} \right]N{O_3}$ is:
A. Dichlorotetraaquachromium(III) nitrate
B. Tetraaquadichlorochromium(III) nitrate
C. Chromiumtetraaquadichloro nitrate
D. Dichlorotetraaquadnromium nitrate

Answer 1

Hint: We must know how a coordination compound is written and accordingly name it. The basic formula for writing a coordination compound is ${\left[ {M{{\left( {Ligand} \right)}_x}} \right]^{ch\arg e}}$ ion-. The formula of a coordination complex is written in a different order than its name. The chemical symbol of the metal center is written first. The ligands are written next, with anion ligands coming before neutral ligands. If there is more than one anion or neutral ligand, they are written in alphabetical order according to the first letter in their chemical formula.

Complete step by step answer:
The number of ligands that attach to a metal depends on whether the ligand is monodentate or polydentate.
Some rules for naming coordination numbers are:
1. Ligands that act as anions which end in "-ide" are replaced with an ending "-o" (e.g., Chloride → Chloro). Anions ending with "-ite" and "-ate" are replaced with endings "-ito" and "-ato" respectively (e.g., Nitrite → Nitrito, Nitrate → Nitrato).
2. Most neutral molecules that are ligands carry their normal name. The few exceptions are the first four on the chart: ammine, aqua, carbonyl, and nitrosyl.
3. The number of ligands present in the complex is indicated with the prefixes di, tri, etc. The exceptions are polydentates that have a prefix already in their name. When indicating how many of these are present in a coordination complex, put the ligand's name in parentheses and use bis (for two ligands), tris (for three ligands), and tetrakis (for four ligands).
 In addition, the first rules to follow are:
1.Ligands are named first in alphabetical order.
2.The name of the metal comes next.
3.The oxidation state of the metal follows, noted by a Roman numeral (II, IV).
For the coordination compound $\left[ {CrC{l_2}{{\left( {{H_2}O} \right)}_4}} \right]N{O_3}$ the ligands are Chlorine and water. Therefore, we will use the polydentate ligand names of "chloro" and a neutral ligand name “aqua”. Since four atoms of chlorine are present,we the prefix –tetraaqua and two atoms of chlorine are present so we use “-dichloro” .The oxidation state of the central metal atom Cr is calculated to be +3. Nitrate ion is present outside the sphere so it will be named after naming the complex. Thus,going alphabetically, the name of the coordination compound is Tetraaquadichlorochromium(III) nitrate

So, the correct answer is Option C.

Note: In order to name any coordination compound,the concept of ligands must be clear.Identifying the ligands,naming them and placing them alphabetically is important before proceeding further. In addition to the mentioned rules,identifying the metal atom and calculating its oxidation state must also be known. Also for the above compound, it may seem that Dichlorotetraaquachromium(III) nitrate is the name but adding -tetraaqua before -chromium is not possible since the water molecules are not attached to the chromium.