16-Electron square-planar compounds
المؤلف:
Peter Atkins, Tina Overton, Jonathan Rourke, Mark Weller, and Fraser Armstrong
المصدر:
Shriver and Atkins Inorganic Chemistry ,5th E
الجزء والصفحة:
636
2025-09-30
333
16-Electron square-planar compounds
Key point: With strong-field ligands, a square-planar complex has only eight bonding MOs, thus a 16-electron configuration is the most energetically favourable configuration. One other geometry already discussed in the context of coordination chemistry is the square-planar arrangement of four ligands (Section 20.1), where we noted that it occurred only for strong-field ligands and a d8 metal ion. Because organometallic ligands often produce a strong field, many square-planar organometallic compounds exist. Stable square planar complexes are normally found with a total of 16 valence electrons, which results in the population of all the bonding and none of the antibonding MOs (Fig. 22.2). The ligands in square-planar complexes can normally provide only two electrons each, for a total of eight electrons. Therefore, to reach 16 electrons, the metal ion must provide an additional eight electrons. As a result, organometallic compounds with 16 valence electrons are common only on the right of the d block, particularly in Groups 9 and 10 (Table 22.1). Examples of such complexes include [Ir(CO)Cl (PPh3 )2] (6) and the anion of Zeise’s salt, [Pt(C2H4) Cl3]- (1). Square-planar 16-electron complexes are particularly common for the heavier elements in Groups 9 and 10, especially for Rh(I), Ir(I), Pd (II), and Pt (II), because the ligand-field splitting is large and the ligand-field stabilization energy of these complexes favours the square-planar configuration.
Figure 22.2 The energy levels of the molecular orbitals of a square-planar complex with strong-field ligands. The eight lowest MOs correspond to bonding interactions, with the higher MOs corresponding to antibonding interactions; the MOs are labelled with the d orbitals from which they are derived.
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