What Is the Crystal Field Theory?

The crystal field theory is a theory that studies the chemical bonds of transition group elements (complexes). Based on the theory of electrostatics, it combines quantum mechanics and group theory (the theory of studying material symmetry) to explain the physical and chemical properties of transition group elements and lanthanides, and focuses on the d of the central ion of the ligand. The effect of orbits and f orbits. ^[1]

crystal field theory is referred to as CFT theory . ^[2]

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1.Magnetism of the complex

(1) When the electron symmetry energy p> , high spin, all F- complexes p> , high spin.

(2) When p <, low spin, CN-complex p <, low spin.

(3) The tetrahedral complex is generally high-spin <p.

(4) Regarding the d1, d2, d3, d8, d9, and d10 metal ion complexes, regardless of the weak field strength field, there is only one arrangement and no high or low spin. Only d4 ~ d7 can spin high and low.

(5) If the number of single electrons in the complex is zero, it is diamagnetic, and if there is a single electron, it is paramagnetic.

2. Explain the spatial configuration of ligands: judged by CFSE.

3. Explain the visible spectrum (color) of the complex: dd transition. For example, it is explained that the divalent hydrated manganese ion is very light in color because five electrons occupy five d orbitals. For example, visible light-excitation electron transition needs to overcome the electron pairing energy, which requires high energy. So the divalent manganese ion is light pink.

4. Stability of complex ion:

With CFSE, the larger the value, the more stable the complex.

5. The crystal field theory is not ideal in explaining the coordination ability of the ligand to the central ion. At this time, the coordination field theory is applied. ^[1]