Four different octahedral chromium coordination compounds...

Four different octahedral chromium coordination compounds exist that all have the same oxidation state for chromium and have $\mathrm{H}_{2} \mathrm{O}$ and $\mathrm{Cl}^{-}$ as the ligands and counterions. When $1 \mathrm{~mol}$ of each of the four compounds is dissolved in water, how many mol of silver chloride will precipitate upon addition of excess $\mathrm{AgNO}_{3} ?$

Key Concepts

Coordination Compounds

Composition and structure in coordination compounds are defined by a central metal ion bound to surrounding ligands. Their properties—including reactivity and types of isomerism—depend on the number, type, and arrangement of these ligand bonds, which is particularly significant in octahedral complexes where six sites surround the metal ion.

Inner-sphere vs Outer-sphere Ligands

In coordination chemistry, ligands directly bonded to the metal center are called inner-sphere ligands, whereas ions that balance the charge but are not coordinated are termed outer-sphere or counterions. This distinction is crucial because only the outer-sphere ions typically participate in reactions such as precipitation when interacting with other species.

Ionization Isomerism

Ionization isomerism occurs when there is an interchange of a ligand in the coordination sphere with an ion in the counterion sphere, resulting in isomers with identical formulas that release a different number of ions in solution. This is particularly important when predicting reactivity such as the number of precipitate forming ions available upon a chemical reaction.

Precipitation Reactions in Coordination Chemistry

Precipitation reactions involve the formation of an insoluble compound from soluble reactants. In coordination chemistry, these reactions are used to probe the presence of specific ions (like chloride) released into solution. The interaction of silver ions with free chloride ions to form silver chloride provides a practical method to quantify the number of non-coordinated chloride ions in different isomers.

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