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

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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”.