Optical Properties of Linear Chain Haloamine Platinum Complexes

Coordination complexes of platinum(H) generally have the coordination number of 4 with a square-planar arrangement of bonds. Such complexes are diamagnetic and with all the electrons paired can be considered as the strong-field type. One platinum d orbital is utilized in the sigma bonds to the four ligands. Since the electronic configuration of PtII is 5d 8, the other four d orbitals are filled. With the chloro- or bromoamine complexes the lowest unoccupied orbital is the σ* orbital based on the platinum d orbital which is isolated from other orbitals. The complexes typically have a number of absorption bands in the visible and near-ultraviolet region which involve excitation of electrons from the d orbitals into this lowest σ* orbital. These ligand-field or d-d transitions are of sufficiently low intensity that the optical absorption for the complexes in the crystalline state is frequently measurable. It is therefore possible to determine differences in the energies and intensities of transitions between a free complex, usually dissolved as an aqueous solute or in some rather polar solvent, and the same complex in different situations of crystal packing.