Structural transference and regulation of bimodal assembly of charge-assisted hydrogen-bonded networks

Sang Ok Lee, Danielle M. Shacklady, Matthew J. Horner, Sylvie Ferlay, Mir W. Hosseini, Michael D. Ward

Research output: Contribution to journalArticlepeer-review


The salt [2,2′-(1,4-phenylene)pyrimidine2+] [hexacyanocyclopropanediide2-] ([PBA2+][C 6(CN)62-]) (1) crystallized from organic solvents as two polymorphic forms through charge-assisted N-H⋯NC hydrogen bonding between the oppositely charged ions. The red polymorph (1R) crystallized in the Fdd2 space group, forming ribbons in which the pair of N-H groups on the same side of the PBA2+ ion entered two modes of hydrogen bonding, one that can be described as a R22(15) motif involving a pair of geminal cyano groups (i.e., on the same methylidene carbon atom) of the C6(CN)62- ion and the other a R22(18) motif involving a pair of nongeminal cyano groups (i.e., on different methylidene carbon atoms). The green polymorph (1G) crystallized in the P1 space group and adopted a "staircase" ribbon motif with "risers" comprising two PBA2+ ions that bridged C6(CN)62- ions through N-H⋯NC hydrogen bonds. This form also exhibited two modes of hydrogen bonding, the R 22(15) motif and a more complex one involving multiple molecules. The different colors of the polymorphs were assignable to π-π charge-transfer interactions between the weak C6(CN)6 2- electron donor and the weak PBA2+ electron acceptor in the solid state, a feature suggested by single-crystal X-ray diffraction and confirmed by infrared spectroscopy. Heating 1G above 275 °C produced a crystalline white polymorph (1W). The 1R form, however, exhibited thermal stability up to at least 300°C. The related salt [2,2′-(1,2- ethanediyl)pyrimidine2+]-[hexacyanocyclopropanediide2-] ([EBA2+][C6(CN)62-]) (2Y) crystallized in the P2lc space group as yellow bipyramidal plates, forming infinite zigzag hydrogen-bonding ribbons. Unlike 1R and 1G, however, 2Y only exhibits the R22(18) motif because the shorter span of the EBA2+ molecule, as defined by the intramolecular separation between N-H groups, did not allow formation of the R22(15) motif. These structures reveal that the hydrogen-bonding modes of a bimodal system can be regulated through adjustment of key molecular structure parameters, which in the case of EBA2+ produces a single hydrogen-bonding mode that is required for a hypothetical cyclic motif. Furthermore, the structural parameters of the ribbon motifs provide guidance for the choice of guest molecules capable of promoting formation of a cyclic motif through templating.

Original languageEnglish (US)
Pages (from-to)995-1003
Number of pages9
JournalCrystal Growth and Design
Issue number3
StatePublished - May 2005

ASJC Scopus subject areas

  • General Chemistry
  • General Materials Science
  • Condensed Matter Physics


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