Crystal Structures for the Electron Donor Dibenzotetrathiafulavalene, DBTTF, and Its Mixed-stack Charge-transfer Salts with the Electron Acceptors 7,7,8,8-tetracyano-p-quinodimethane, TCNQ, and 2,5-difluoro-7,7,8,8-tetracyano-p-quinodimethane, 2,5-TCNQF2

Abstract

Crystal structures for the electron donor DBTTF and its charge-transfer salts with the acceptors TCNQ and 2,5-TCNQF2 are reported. Crystal data for the three systems are as follows: (a) neutral DBTTF; monoclinic, space group P2₁/c, a=12.082(2) Å, b=3.955(1) Å, c=14.553(2) Å, β=114.36(1)⁰, V=633.6 ų; (b) DBTTF-TCNQ; triclinic, space group P1, a=9.215(3) Å, b=10.644(4) Å, c=7.734(2) Å, α=113.32(3)⁰, β=122.28(2)⁰, γ=67.66(3)⁰, V=574.6 ų; (c) DBTTF-2,5-TCNQF2; triclinic, space group P1, a=8.838(2) Å, b=9.276(2) Å, c=7.794(1) Å, α=101.29(2)⁰, β=100.89(1)⁰, γ =107.42(2)⁰, V=576.6 ų. The crystal structure of the neutral DBTTF donor is dominated by columns of DBTTF molecules as found in the similar structure of the donor TTF. The crystalline motifs adopted by the TCNQ and 2,5-TCNQF2 salts of DBTTF are composed of columns in which the donor and acceptor molecules alternate. These … DADADA … stacked columns are tied into sheets through weaker donor-donor overlapping. While the structures of the TCNQ and 2,5-TCNQF2 salts are very similar, they differ in the way sheets of donor-coupled … DADADA … stacks are arranged relative to each other. Madelung energies for both salts have been computed from charge distributions obtained from LCAO-MO calculations. Degrees of charge transfer are evaluated from the molecular geometries of both the donor and acceptor molecules and from the cyano stretching frequencies of the acceptors.