The Crystal and Molecular Structure of Pelargonindin Bromide Monohydrate

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Abstract
The structure of pelargonidin, 3,5,7,4''-tetrahydroxyflavylium, bromide monohydrate, obtained by the hydrolysis of pelargonin, the major pigment of Dahlia variabilis has been determined by the X-ray method. The crystals are triclinic space group .hivin.1 with a = 8.929(2), b = 11.360(3), c = 7.299(2).ANG., .alpha. = 95.00(5), .beta. = 93.61(5), .gamma. = 93.35(5).ANG. and Z = 2. The structure was solved by the heavy atom method and refined by least-squares to a final R-value of 0.057 for 2351 observed reflexions. The molecule is nearly planar. The phenyl ring makes a dihedral angle of only 3.8.ANG. with the benzopyrylium plane. The sp2-sp2 single bond connecting the benzopyrylium portion and phenyl ring is 1.458.ANG.. The bond lengths in the benzopyrylium portion show a characteristic feature of resonance structure. The hydroxyl groups at the 7- and 4''-positions of pelargonidin cation form hydrogen bond with Br ions. The pelargonidin moelcules related by the center of symmetries are stacked along the c axis. The hydrogen bonding schemes and stacking modes of anthocyanidins so far determined are summarized.
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