Tetrahedral coordination electronic configurations

The next most common coordination number is 4. Two shapes are typically found for this coordination number. In a tetrahedral complex, the four ligands are found at the vertices of a tetrahedron, as in the tetrachlorocobaltate(ll) ion, [CoCl4]2 (2). An alternative arrangement, most notably for atoms and ions with ds electron configurations such as Pt2+ and Au +, is for the ligands to lie at the corners of a square, giving a square planar complex (3). 

In other instances, irradiation of the d-d transition leads to no observable reaction. Examples of this behavior are found for complexes having a variety of d electron configurations and coordinative geometries square planar Ni(II) (3d)3 in Ni(CN)42 124 and mww-Ni(gIy)2 124 square planar Pd(II) in Pd(CN)42-,124 and tra -Pd(gly)2 square planar Pt(II) in Pt(CN)42" (5d)3 124 octahedral Co(III) (3d)6 in a variety of complexes (cf. Sect. III-C and III-D). A striking example of this type of behavior is afforded by the nonreversible photoisomerization of cis-Pt(gly)2 (5d)8 to trans-Pt(g y)2 [reaction (2)].124 It has been proposed that irradiation of either of these square planar complexes leads to the same tetrahedral intermediate which decays exclusively to mwj-Pt(gly)2. This behavior may be contrasted with the reversible photoisomerization shown in reaction (3).3... 

Copper(II) has a 3d9 electronic configuration. In principle, pure octahedral and tetrahedral symmetries can never be observed because Jahn-Teller distortions (see Section 3.3.1) remove the orbital degeneracy of the ground state. The separation of the electronic energy levels depends on the coordination number and stereochemistry, as well as on the nature of the ligands. However, the ground state orbital is always well isolated from the excited states, and therefore the electronic relaxation mechanisms are relatively inefficient. Copperfll) complexes have thus relatively sharp EPR signals, and it is often possible to record these spectra at room temperature. 

Table 2.3. Electronic configurations and crystal field stabilization energies of transition metal ions in tetrahedral coordination... 

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