Question

A certain first-row transition metal ion forms many different colored solutions. When four coordination compounds of this metal, each having the same coordination number, are dissolved in wa ter, the colors of the solutions are red, yellow, green, and blue Further experiments reveal that two of the complex ions are para magnetic with four unpaired electrons and the other two are dia magnetic. What can be deduced from this information about th four coordination compounds?

Short answer

The metal ion in all four coordination compounds is Mn^3+ due to the presence of four unpaired electrons in two of these complexes. The compounds have different colors and magnetic behavior due to different geometries and ligands in the coordination sphere. The paramagnetic complexes have octahedral geometry, while the diamagnetic ones have tetrahedral geometry.

Step-by-step solution

Identify the possible metal ions

As the compounds are formed by a first-row transition metal ion, the possible options are from Scandium (Sc) to Zinc (Zn). Keep in mind that electronic configurations and the number of unpaired electrons in these ions will play a role in determining their magnetic behavior. Step 2:

Understand the role of unpaired electrons in magnetic behavior

Paramagnetic compounds have unpaired electrons, and the presence of a magnetic field causes them to be attracted to it. On the other hand, diamagnetic compounds, with no unpaired electrons, do not show any magnetic behavior. The following are the electronic configurations of the first-row metal ions with oxidation numbers: - Sc^3+ : \([Ar]\) - Ti^4+ : \([Ar]\) - V^5+ : \([Ar]\) - Cr^2+ : \([Ar]3d^4\) - Mn^3+ : \([Ar]3d^4\) - Fe^2+ : \([Ar]3d^6\) - Co^3+ : \([Ar]3d^6\) - Ni^4+ : \([Ar]3d^6\) - Cu^1+ : \([Ar]3d^10\) - Zn^2+ : \([Ar]3d^10\) Notice that only Cr^2+ and Mn^3+ have four unpaired electrons in their ground state electronic configurations. Therefore, the metal ion in all four complexes must be either Cr^2+ or Mn^3+. Step 3:

Analyze coordination numbers for Cr^2+ and Mn^3+

As all the coordination compounds have the same coordination number, it is important to analyze the coordination numbers that are usually found in compounds containing Cr^2+ and Mn^3+. Cr^2+ typically forms octahedral complexes (coordination number 6) with various ligands, and Mn^3+ can form octahedral (coordination number 6) and tetrahedral (coordination number 4) complexes. Since there are only four different colored solutions, it's plausible that the metal ion is Mn^3+. We can assume that the two paramagnetic complexes likely have octahedral geometry, while the two diamagnetic complexes could have tetrahedral geometry. #Conclusion#: We deduced that the metal ion in all four coordination compounds is Mn^3+ due to the presence of four unpaired electrons in two of these complexes. The compounds have different colors and magnetic behavior due to different geometries and ligands in the coordination sphere. The paramagnetic complexes have octahedral geometry, while the diamagnetic ones have tetrahedral geometry.

Key concepts

Paramagnetic and Diamagnetic Compounds

Understanding the difference between paramagnetic and diamagnetic compounds is fundamental in coordination chemistry. These properties are directly linked to the presence or absence of unpaired electrons in an atom or molecule.

Paramagnetic compounds contain at least one unpaired electron, making them attracted to external magnetic fields. This is because unpaired electrons create a magnetic moment—a vector quantity that represents the compound's tendency to align with a magnetic field.

Diamagnetic compounds, on the other hand, have all their electrons paired. Paired electrons cancel out each other's magnetic moments, resulting in no overall magnetic moment. Consequently, diamagnetic substances are not attracted to a magnetic field; in fact, they are slightly repelled.

As seen in the exercise, the color variations in coordination compounds may suggest different types of ligands or different electronic structures, but the magnetic properties allow us to narrow down the number of unpaired electrons and therefore, the identity of the metal ion.

Coordination Number in Chemistry

The coordination number of a central atom in a molecule or crystal structure is the number of ligand atoms to which the metal is directly bonded. In coordination chemistry, the coordination number is critical because it determines the geometry of the complex, which can greatly affect its reactivity and properties.

For example, a coordination number of six often leads to octahedral geometry, whereas four can lead to tetrahedral or square planar geometries. Knowing the coordination number and the probable geometries can help predict and understand the color and magnetic properties of a compound.

Moreover, the coordination number influences the strength and type of interaction between the central atom and the ligands. This interaction can lead to different energy levels for the electrons, and thus, color variations—as evidenced by the different colored solutions of the metal complexes in the exercise.

Electronic Configuration of Transition Metals

Transition metals are known for their ability to form various compounds with different properties, mainly due to their unique electronic configurations. These metals have electrons in the d subshell, which can be removed or shared during bond formation.

The electronic configuration of a transition metal ion is important because it affects the compound's overall magnetic properties and the types of bonds it can form. Transition metal ions with different numbers of unpaired d electrons will exhibit distinct magnetic behaviors, as seen with the Cr^2+ and Mn^3+ ions in the exercise solution.

Transition metals often exhibit variable oxidation states, further diversifying the possible electronic configurations and, correspondingly, the properties of their coordination compounds. In-depth understanding of these configurations is crucial when studying transition metal chemistry, both for predicting the properties of unknown compounds and for designing new materials with desired behaviors.