Quininium Hydrogen (S,S)-Tartrate Hemihydrate, a Salt with a Unique Conformation of the Hydrogen Tartrate Ion

Two independent ion pairs [(6-methoxy-4-quinolyl)(5-vinyl-1-azoniabicyclo[2.2.2]octan-2-yl)methanol hydrogen 2,3-dihydroxybutanedioate] and a water molecule are found in the asymmetric unit of 2C₂₀H₂₅N₂O₂⁺.2C₄H₅O₆^-.H₂O. The two cations are virtually identical, but the two anions have markedly different stereochemistry. One of these anions adopts a unique conformation not observed previously for hydrogen tartrate ions. The packing resembles the arrangement in cinchonidinium (S)-mandelate, with hydrogen-bonded chains of alternating cations and anions. The herring-bone stacking of the quinoline ring systems of the cations resembles the pattern seen in other cinchona structures.

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