Electronic crystal spectra for coordination complexes of platinum(II)

The limited number of crystals of platinum(II), discussed here have provided a great deal of information both about the molecular energy levels and about crystal interactions. The spectra have provided a definitive assignment of energy states of PtCl²₄ from the vibronic selection rules in a system with a rigorous center of symmetry. With KPt(NH₃)Cl₃·H₂O the effect of a ligand field asymmetry combined with vibronic excitation has been demonstrated. With Pt(en)Cl₂, however, spectra are dominated by crystal effects, and compelling evidence for the excitation of ionic exciton has been uncovered. Each of these crystals possesses a structure in either tetragonal or orthorhombic lattices with alignment of ions or molecules which could scarcely be more favorable for interpretation. Unfortunately, such ideal structures must be rare. In addition, it is necessary to prepare exceedingly thin and fragile crystals in order to exploit even the highly forbidden d-d bands. Limitations in preparative techniques for crystals suitable for spectral work may well severely curtail the number of systems which can be studied profitably.