Final answer:
The student's question relates to the classification of ligands in crystal field theory. Weak-field ligands like iodide cause small crystal field splittings, whereas strong-field ligands like cyanide cause larger splittings, affecting the Δoct values and spin states of complexes.
Step-by-step explanation:
The question pertains to crystal field theory, which is a model that describes the breaking of degeneracies of electronic orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution, such as the arrangement of ligands around a central atom in a complex or coordination compound. In the context of crystal field splitting, ligands can be classified into two categories based on their ability to split the d orbital energy levels of the central metal ion. Weak-field ligands, such as iodide (I⁻), cause smaller splittings, while strong-field ligands, like cyanide (CN⁻), cause larger splittings. This splitting is quantified by the parameter Δoct, the crystal field splitting energy for an octahedral complex.
Ligands that cause smaller Δoct values do not pair electrons in the d orbitals unless necessary and are associated with high-spin complexes. Conversely, ligands that result in larger Δoct values tend to pair electrons within the d orbitals, leading to low-spin complexes. For example, an octahedral complex with iodide ligands will have a lower Δoct value compared to the same metal complex with cyanide ligands, indicating that iodide is a weak-field ligand and cyanide is a strong-field ligand.