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Figure 2
Part of the crystal structure of polymorph (Ib)[link], showing the hydrogen-bonding inter­actions. Adjacent inversion-related ribbons formed by cytosine mol­ecules A and B are inter­linked by N—H⋯O hydrogen bonds, forming a hexa­meric hydrogen-bonded cavity with an R66(30) motif. Hydrogen bonds are shown as dashed lines and H atoms not involved in hydrogen bonding have been omitted for clarity. Only atoms involved in hydrogen bonding are labelled. [Symmetry codes: (i) x, −y + [{1\over 2}], z − [{1\over 2}]; (ii) x, −y + [{1\over 2}], z + [{1\over 2}]; (iii) −x + [{1\over 2}], y, z − [{1\over 2}]; (iv) −x + [{1\over 2}], y, z + [{1\over 2}]; (v) x − [{1\over 2}], y + [{1\over 2}], −z + 1.]

Journal logoSTRUCTURAL
CHEMISTRY
ISSN: 2053-2296
Volume 71| Part 2| January 2015| Pages 128-135
doi:10.1107/S2053229615000492
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