Structure and assignment of the luminescence of a new mixed-ligand copper(I) polymer

The synthesis and crystal structure of a new copper(I) polymer, [{(Ph(3)P)(2)Cu-2(mu-Cl)(2)(mu-pyrazine)}(infinity)], are reported. The polymer is photoluminescent with its emission maximum at 16 340 cm(-1) at a temperature of 20 K. The emitting state is assigned with the assistance of excited state distortions determined by using resonance Raman intensities. The polymer consists of (PPh(3))(pyz)Cu(mu-Cl-2)Cu(pyz)(PPh(3)) units in which pyrazine ligands bridge copper pairs to form a chain of dimers. The packing arrangement contains two inversion centers. Each dimer has an inversion center between the two coppers and the bridging chlorine atoms. A second inversion center is located in the center of the pyrazine ligand, which links the dimers in an infinite linear chain. The nitrogen atom of the pyrazine, the phosphorus atom of one triphenylphosphine, and the two chlorine atoms form a slightly distorted tetrahedron about the copper. The largest distortions in the lowest excited electronic state, determined from the resonance Raman intensities, occur along totally symmetric modes of the pyrazine ligand. The emission is assigned to copper(I) to pyrazine charge transfer.