Crystal field theory (CFT) explains how the energies of a transition metal ion’s d orbitals change when ligands surround the ion. This splitting helps explain properties such as the colors and magnetic behavior of many coordination compounds.
CFT treats ligands as sources of negative charge surrounding a positively charged metal ion. The five d orbitals of an isolated metal ion have the same energy, so they are described as degenerate. When ligands approach, their electron density repels the metal’s d electrons.
All flashcards
What is crystal-field splitting?
The separation of originally degenerate metal d-orbital energies caused by the electrostatic field of surrounding ligands.
What is pairing energy in a coordination complex?
The energy cost of placing two electrons in the same orbital.
What does the spectrochemical series rank?
Ligands by the size of the d-orbital splitting they generally produce, from weaker-field to stronger-field.
What is crystal-field stabilization energy (CFSE)?
The net change in d-electron energy relative to the unsplit orbital barycenter, accounting for occupancy of lower and higher levels.
What is a charge-transfer excitation?
An electronic excitation in which electron density moves between metal and ligand orbitals.
Quiz questions
How many unpaired electrons are present in an octahedral high-spin d5 ion?Answer: Five, with one electron in each d orbital.
What magnetic behavior does a complex with one or more unpaired electrons show?Answer: Paramagnetism; it is attracted to a magnetic field.
For a given metal and ligand set, what generally happens to $$ as the metal oxidation state increases?Answer: The splitting energy generally increases.
By orbital-energy accounting, what is the CFSE of a high-spin octahedral d5 configuration relative to the barycenter?Answer: 0
Which limitation applies to crystal field theory (CFT)?Answer: It does not fully describe chemical bonding or every spectroscopic feature.