The tetrahedral crystal field

  So far we have restricted the discussion to octahedral complexes; we now turn to the tetrahedral crystal field. Figure 1.1 shows a convenient way of relating a tetrahedron to a Cartesian axis set. With the complex in this orientation, none of the metal d orbitals points exactly at the ligands, but the d_xy, d_yz and _dxz orbitals come nearer to doing so than the d_z² and d_x²_-y² orbitals. For a regular tetrahedron, the splitting of the d orbitals is inverted compared with that for a regular octahedral structure, and the energy difference (Δ_tet) is smaller.

Fig. 1.1 The relationship between a tetrahedral ML₄ complex and a cube; the cube is readily related to a Cartesian axis set. The ligands lie between the x, y and z axes; compare this with an octahedral complex, where the ligands lie on the axes.

   If all other things are equal (and of course, they never are), the relative splittings Δ_oct and Δ_tet are related by equation 1.1.

                          (1.1)

   Figure 1.2 compares crystal field splitting for octahedral and tetrahedral fields; remember, the subscript g in the symmetry labels  is not needed in the tetrahedral case.

   Since Δ_tet is significantly smaller than Δ_oct , tetrahedral complexes are high-spin. Also, since smaller amounts of energy are needed for an t₂←e transition (tetrahedral) than for an eg←t₂g transition (octahedral), corresponding octahedral and tetrahedral complexes often have different colours. Jahn–Teller effects in tetrahedral complexes are illustrated by distortions in d⁹ (e.g. [CuCl₄]^2-) and high-spin d⁴ complexes. A particularly strong structural distortion is observed in [FeO₄]^4-.

Fig. 1.2 Crystal field splitting diagrams for octahedral (left-hand side) and tetrahedral (right-hand side) fields.

مواضيع ذات صلة

ايجاد الصيغة التركيبية للمعقدات

معقدات الخارصين

معقدات النحاس

كيمياء ومعقدات بعض عناصر السلسلة الانتقالية الاولى

تعريف المركبات المعقدة

Crystal Field Stabilization Energies

Colors of Transition-Metal Complexes

The Nature of the Ligands

Principal Quantum Number of the Metal

Charge on the Metal Ion

Factors That Affect the Magnitude of Δo

Electronic Structures of Metal Complexes