Question

Dimethyl sulfoxide (DMSO) reacts with cobalt(II) perchlorate in EtOH to give a pink compound A which is a 1: 2 electrolyte and has a magnetic moment of \(4.9 \mu_{\mathrm{B}}\) Cobalt(II) chloride also reacts with DMSO, but in this case the dark blue product, \(\mathbf{B}\), is a 1: 1 electrolyte, and the magnetic moment of \(\mathbf{B}\) is \(4.6 \mu_{\mathrm{B}}\) per Co centre. Suggest a formula and structure for A and B.

Short answer

A: [Co(DMSO)_6](ClO_4)_2; B: [CoCl_2(DMSO)_4].

Step-by-step solution

Identify the Details of Compound A

Compound A is a pink product with a 1:2 electrolyte nature. The magnetic moment is given as \(4.9 \mu_{\mathrm{B}}\). A 1:2 electrolyte typically signifies that it dissociates into three ions (one ion of one type and two ions of another type) in solution.

Determine Possible Structure for Compound A

Given the 1:2 electrolyte behavior, Compound A likely dissociates into one cobalt ion and two perchlorate ions. The magnetic moment of \(4.9 \mu_{\mathrm{B}}\) is close to that expected for high-spin Co(II), which typically has unpaired electrons. Therefore, a viable formula for A can be \([\text{Co(DMSO)}_6](\text{ClO}_4)_2\). In this structure, cobalt is octahedrally coordinated by six DMSO ligands.

Identify the Details of Compound B

Compound B is a dark blue product with a 1:1 electrolyte nature. The magnetic moment is \(4.6 \mu_{\mathrm{B}}\). A 1:1 electrolyte signifies dissociation into two ions in solution.

Determine Possible Structure for Compound B

The 1:1 electrolyte suggests that Compound B dissociates into a cobalt complex ion and a single chloride ion. The magnetic moment of \(4.6 \mu_{\mathrm{B}}\) also points towards high-spin Co(II). A plausible structure for B is \([\text{CoCl}_2(\text{DMSO})_4]\). This allows for four DMSO ligands and two chloride ions around cobalt, resulting in five possible coordination sites taken by ligands and leaving one free.

Key concepts

Coordination Chemistry

Coordination chemistry explores the intricate world of compounds formed between metal ions and ligands. A ligand is typically a molecule or ion that can donate a pair of electrons to a metal, forming a coordination bond. This leads to the formation of a coordination complex. In the case of compounds A and B from our exercise, cobalt acts as the central metal ion while dimethyl sulfoxide (DMSO) acts as the coordinating ligand. In a coordination complex, metal ions exhibit various coordination numbers, which in simplest terms is the number of ligand donor atoms bonded to the central metal ion. For compound A, cobalt is surrounded by six DMSO molecules, exhibiting octahedral coordination. Compound B, on the other hand, features four DMSO molecules, illustrating a different coordination arrangement. Understanding coordination chemistry allows us to predict the properties and reactivity of complexes, such as their color and magnetic traits, which are evident in the distinct appearances and magnetism of compounds A and B.

Electrolyte Dissociation

Electrolyte dissociation refers to the process by which an ionic compound dissociates into ions when dissolved in a solvent, typically water or ethanol as in this problem. Electrolytes are essential in determining the nature of solution chemistry and are characterized by their ability to conduct electricity in solution due to the free movement of ions.In coordination chemistry, understanding how complex compounds dissociate in solution provides insights into their structure. For example, compound A behaves as a 1:2 electrolyte, meaning it dissociates into three ions: one cobalt ion and two perchlorate ions. This behavior supports the suggestion of its formula as \([Co(DMSO)_6](ClO_4)_2\), indicating that the entire cobalt-DMSO complex remains as one species, with perchlorate ions dissociating separately. Similarly, compound B is a 1:1 electrolyte, dissociating into two ions when dissolved. This guides the identification of its structure as being \([CoCl_2(DMSO)_4]\), indicating one cobalt-DMSO complex ion and one chloride ion dissociating separately.

Magnetic Properties

Magnetic properties of coordination complexes are heavily influenced by their electron configurations and the arrangement of electrons in the metal ion's d-orbitals. The terms high-spin and low-spin complexes describe how electrons are distributed among these orbitals.For both compounds A and B, the observed magnetic moments fall within the range typical for high-spin cobalt(II) complexes. High-spin means that the energy difference between the d orbitals is low, and electrons spread out to occupy all available orbitals, increasing the number of unpaired electrons and thereby the magnetic moment. Compound A exhibits a magnetic moment of \(4.9 \mu_B\), close to the expected value for high-spin Co(II), which results from several unpaired electrons. For compound B, the magnetic moment of \(4.6 \mu_B\) also indicates a high-spin state with a slightly different arrangement of ligands and electrons compared to compound A. Understanding these magnetic properties helps confirm the proposed structures and the electronic environments within these coordination complexes.

Cobalt Complexes

Cobalt complexes are fascinating due to their variable color and magnetic properties, which are directly linked to their electronic configurations and the ligands involved. Cobalt can exist in several oxidation states, but in these exercises, we focus on cobalt(II) complexes, known for their distinct magnetic properties. The exploration of DMSO as a ligand demonstrates cobalt’s tendency to form stable, colorful complexes. In compound A, the pink hue and distinct electrolyte nature are a result of cobalt being octahedrally coordinated by DMSO, interacting to create specific electron arrangements that absorb and reflect particular wavelengths of light. For compound B, the dark blue color indicates a different, perhaps more condensed, electronic interaction with the cobalt ion, influenced by its coordination which includes chloride ions as part of the ligand framework. Understanding these properties not only enlightens us on the nature of cobalt in these chemical matrices but also aids in designing complexes with specific desired properties in industrial and research applications.