Three-dimensional crystal orbital calculations on mononucleotide crystallohydrates. II. Diprotonated mononucleotides

1997

Int. J. Quant. Chem.

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whereas such chains are present in the latter crystal. In such a way, the effect of the polyiodide chain formation on the electronic structure of crystalline organic iodides was studied. The present calculations show that crystalline organic iodides with polyiodide chains could, in principle, be quasi-one-dimensional semiconductors. A polyiodide chain could be a carrier of semiconductivity only when it is formed by fully charged iodide Ž . anions no charge transfer from the chain .

Polyiodide chains in crystalline organic iodides: Ab initio Hartree-Fock crystal orbital study

1997

Int. J. Quant. Chem.

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A comparative three‐dimensional Hartree–Fock crystal orbital study of double‐stack organic charge‐transfer (semi)conductors: TTF–TCNQ, TTF–DCNQI, and TTF–2,5‐Me ₂ ‐DCNQI

1998

Int. J. Quantum Chem.

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Three-dimensional X dicyanbenzoquinondiimine DCNQI , and N, N -dicyan-2,5-dimethyl-1,4-Ž . benzoquinondiimine 2,5-Me -DCNQI were studied within the ab initio Hartree᎐Fock 2 crystal orbital approximation using the CRYSTAL92 routine package. A qualitative agreement with the experimental data was achieved, and a definite border between one-electron and many-electron effects in the specific physical properties of the crystals under study was drawn. The calculations led to the tentative conclusion that the true chemical reaction corresponding to the charge transfer in such systems is a two-step transfer of two electrons from the donor's HOMO to the acceptor's LUMO and not only single-electron transfer, as usually believed. Then, whether the system is conductive or Ž semiconductive depends upon the degree of the charge transfer one, two, or no . electrons, respectively . But the final degree of the charge transfer and the density of states on the Fermi level should be determined by many-electron effects. The theoretical approach used in this work seems to be of crucial importance in designing organic crystals with specific physical properties.

Ab initio Hartree-Fock crystal orbital studies on charge-transfer complexes: Different crystal modifications of the same compounds

1998

Int. J. Quant. Chem.

Ab initio Hartree᎐Fock crystal-orbital calculations of dimorph Ž. tetramethyltetraselenafulvalene᎐tetracyanoquinodimethane TMTSF᎐TCNQ and Ž . dibenzotetrathiafulvalene᎐tetracyanoquinodimethane DBTTF᎐TCNQ , both as red and black crystals, were carried out. The crystal structures of the red and black TMTSF᎐TCNQ are essentially different from each other, whereas the red and black DBTTF᎐TCNQ are Ž . qualitatively very similar although not completely isomorphous . The results of the present calculations definitely show that even subtle differences in the crystal structures are crucial for the electronic properties of the systems under study.