Platinum complexes excited-stated geometry

It is the 4-coordinate square-planar geometry that makes Pt(II) complexes very different from those of most of the other metal ions familiar to the inorganic photochemist, including Cr(III), Ru(II), Os(II), Rh(III), Ir(III) (almost always 6-coordinate octahedral), copper(I) (4-coordinate tetrahedral), and lanthanides (8 or 9 coordinate). The square planar conformation is responsible for many of the key features that characterize the absorption, luminescence and other excited state properties of platinum(II) complexes. 

Apart from phosphine ligands, polypyridine ligands have been incorporated into platinum(II) alkynyl moieties to give luminescent complexes. The use of polypyridine ligands is interesting because their planar structure and the square-planar coordination geometry of the d platinum(II) center could modify the excited state of these luminescent complexes by tt tt and/or Pt- Pt interactions. The complex... 

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