Question

Write the formulas for the following coordination compounds:
 Tris (ethane-1,2-diamine) chromium (III) chloride.

Answer 1

Hint: Coordination compounds are usually the compounds which have a positive central metal bonded to negatively charged ligands by coordinate bonds. The given compound name is a coordination compound, hence it will also have a positively charged metal ion attached to negatively charged ligands.

Complete Step by step answer:
-The following rules are followed while writing the nomenclature of the coordination compounds-
(i) The central metal atom is written first.
(ii) The ligands are written in alphabetical order.
(iii) Polydentate ligands are also written alphabetically. In the case of abbreviated ligand, the first letter of the abbreviation is used to determine the position of the ligand in the alphabetical order.
(iv) The formula for the entire coordination compound is enclosed in square brackets.
(v) There should be no space between the ligands and metal within a coordination sphere.
(vi) The counterion is written with the gap of the coordination sphere.
(vii) The charge is indicated outside the square brackets as a right superscript with the number before the sign.
(viii) The charge of the cation(s) is balanced by the charge of the anions.
-For writing the chemical formula from the name, we need to consider the above-written rules and following steps-
(i) As stated, we started the nomenclature from the central metal atom, hence for writing formulas we will first identify the central metal atom from the name. In the name, Tris (ethane-1,2-diamine) chromium (III) chloride, we have identified cobalt as the central metal ion.
(ii) The ligands are named and arranged alphabetically in the nomenclature, so we will now write the ligands present in the given coordination complex. We have identified two ligands in the given complex, that is ‘en’ and ‘Cl’.
(iii) We will now enclose the metal and ligands in the square bracket.
(iv) Identify the counter ion from the name and write it outside the square bracket.
(v) Balance the charge of the centre metal ion with the charge of counterion.

Following the above rules and guidelines, we have the formula for the given compound as- $[Cr{{(en)}_{3}}]C{{l}_{3}}$

Note: Chromium coordination complexes are nearly all octahedral, that has 6 ligands attached to the central metal Chromium atom which is in +3 oxidation state. The chromic centre has a ${{d}^{3}}$ electronic configuration with three unpaired electrons. Chromium ion in +3 oxidation state has a large charge to size ratio and is considered as a hard Lewis acid.