Solid-State Structure Dependence of the Molecular Distortion and Spectroscopic Properties of the Cu(I) Bis(2,9-dimethyl-1,10-phenanthroline) Ion

The relation between the geometry and spectroscopic properties of a series of salts of the Cu(I) bis(2,9-dimethyl-1,10-phenanthroline) ion, (Cu ^(I)(dmp)₂)⁺, is explored. The distortions from the idealized D_2d geometry, which include flattening, rocking of the dmp ligands, and displacement of the Cu atoms out of the dmp planes, show considerable variation, indicating the importance of packing forces in the crystalline environment. The change in the absorption spectra upon flattening of the complex, expressed as the variation of the angle between the dmp planes, which varies from 88° in the BF₄ and tosylate salts to 73° in the picrate, agrees qualitatively with parallel DFT calculations. No correlation is found between ground state geometry and luminescence lifetimes, recorded both at room temperature and at 16 K. The low temperature lifetimes vary by a factor of 8 among the (Cu^(I)(dmp)₂)⁺ salts examined, the longest lifetime (2.4 μs at 16 K) being observed for the tosylate salt.