Molecular structure of tetrapropylammonium-2,3-dichloro-5,6-dicyano-p-benzoquinone compared toM ⁺ TCNQ⁻ (M ⁺=Rb⁺, K⁺, Cs⁺, or organic cations; TCNQ⁻=tetracyanoquinomethane) charge-transfer complexes

Abstract

The crystal and molecular structure of tetrapropylammonium-2,3-dichloro-5,6-dicyano-p-benzoquinone (TPA⁺ DDQ⁻) has been determined from single-crystal X-ray diffraction analysis. The crystals are monoclinic, space groupP2₁/n, witha=13.297(5),b=12.851(4),c=13.099(5) Å,β=101.34(2)°, andZ=4. The compound consists of discrete (DDQ) ²⁻₂ anion dimers and two TPA⁺ cations inserted between the (DDQ) ²⁻₂ dimers, with an infinite stack running along b of the type ⋯(DDQ) ²⁻₂ [(C₃H₇)₄N⁺] (DDQ) ²⁻₂ 2[(C₃H₇)₄N⁺]⋯

The (DDQ) ²⁻₂ anion is formed by two DDQ⁻ anions dimerized through a crystallographic center of symmetry; each DDQ⁻ moiety is nearly planar and exhibits molecular dimensions similar to those found in analogous compounds. The comparison between the (DDQ) ²⁻₂ anion and a neutral DDQ molecule clearly shows that bond lengths are markedly influenced by the 2-anionic charge. Tetrapropylammomum cation assumes a distorted tetrahedral configuration as observed in TEA⁺ DDQ⁻ (TEA⁺=tetraethylammonium cation). The data are discussed in connection with the electrical conductivity of “organic metals”.