624wavelength (nm) H. halobium mutant (JW 5), and the Deutsche Forschungsgemeinschaft and the Fonds der Chemischene Industrie for financial support.

Reaction of bis(2,9-dimethyl-1,10-phenanthroline)copper(I) iodide [Cu(DMP)2I] with lithium tetracyanoquinodimethanide, LiTCNQ, yields the compound [Cu(DMP)2]2[TCNQ]2, which crystallizes in the triclinic system, space group PI, with lattice parameters a = 12.784 A, b = 13.400 A, c = 12.136 k, a = 113.51°, ß = 112.58°, and 7 = 62.80°. The structure of the compound was solved by Fourier methods and refined by least-squares techniques to R = 0.060 on the basis of 1957 observed reflections. The structure consists of [Cu(DMP)2]+ cations and exocyclically -bonded [TCNQ]22~d imers. The carbon-carbon bond in the dimer is 1.630 (13) A, and the [TCNQ]22_ dimeric ions are arranged in linear chains along the [110] direction. Single-crystal electron paramagnetic resonance studies have been carried out in the temperature range 300-490 K, and thermally activated triplet-state (5=1) EPR spectra as well as doublet-state (5 = */2) EPR spectra have been detected and thoroughly characterized. The data show that strongly localized triplet excitons on [TCNQ]22" anions (self-trapped Frenkel excitons) give rise to triplet-state EPR spectra with zero-field splitting parameters \D/hc\ = 0.0111 cm"1 and \E/hc\ = 0.0015 cm"1. Theoretical calculations of the dipolar splitting indicate that the electronic and molecular structure of the excited state of the [TCNQ]22" dimeric anion is best characterized by two distorted TCNQ" anions with a distorted distribution of spin densities. An EPR signal at g = 2.0025 has been attributed to isolated TCNQ" radical anions. The activation energies for the triplet excitons (which corresponds to the breaking of the -bond) and for the isolated TCNQ" radical anions are 0.55 and 0.24 eV, respectively.

No abstract

No abstract

No abstract