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Bis-(S-Benzylthiuronium) Chloranilate Supramolecular Crystal Structure:  Preparation and Characterization

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posted on 22.03.2005, 00:00 by Dimitrios V. Stergiou, Stavroula Skoulika, Nicholaos P. Evmiridis, Panayotis G. Veltsistas
A novel supramolecular structure, [C8H11N2S]2·(C6Cl2O4), based on hydrogen bonding of the organic S-benzylthiuronium (SBT) cation and the chloranilate dianion, is presented. Chloranilic acid or 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone, is a strong quinoidal diphenic acid (pK1 = 1.09 and pK2 = 2.42), with molecular formula C6Cl2O4H2 (H2CA). The CA-dianions and the aromatic rings of the SBT-cations form columns along the c-axis giving an ordered pattern of dianions surrounded by densely populated areas of SBT-cations. Each CA-dianion forms eight hydrogen bonds with the amine protons of six SBT-cations, through its oxygen atoms. In this way, an extended H-bond network, containing infinite chains of alternative R42(8) and R22(9) cyclic patterns, is obtained. The whole arrangement leads to a C2/c space group crystal structure, with unit cell dimensions a = 15.109 Å, b = 11.606 Å, and c = 14.390 Å and with unit cell angles of α = γ = 90°, and β = 97.01°, and average density of 1.43 g/cm3. Dissolution of the crystalline material in DMSO leads to the formation of associated organic ions or charge-transfer complexes as evidenced from the bathochromic shift of the absorption band of chloranilic acid from 420 to 520 nm.