Structural Transference and Regulation of Bimodal Assembly of Charge-Assisted Hydrogen-Bonded Networks

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• 作者：Sang-Ok Lee ; Danielle M. Shacklady ; Matthew J. Horner ; Sylvie Ferlay ; Mir W. Hosseini ; and Michael D. Ward
• 刊名：Crystal Growth & Design
• 出版年：2005
• 出版时间：May 2005
• 年：2005
• 卷：5
• 期：3
• 页码：995 - 1003
• 全文大小：422K
• 年卷期：v.5,no.3(May 2005)
• ISSN：1528-7505

文摘

The salt [2,2'-(1,4-phenylene)pyrimidine²⁺][hexacyanocyclopropanediide^2-] ([PBA²⁺][C₆(CN)₆^2-]) (1)crystallized from organic solvents as two polymorphic forms through charge-assisted N-H···NC hydrogen bondingbetween the oppositely charged ions. The red polymorph (1R) crystallized in the Fdd2 space group, forming ribbonsin which the pair of N-H groups on the same side of the PBA²⁺ ion entered two modes of hydrogen bonding, onethat can be described as a bscribe/journals/cgdefu/5/i03/eqn/cg049660we10001.gif">(15) motif involving a pair of geminal cyano groups (i.e., on the same methylidenecarbon atom) of the C₆(CN)₆^2- ion and the other a bscribe/journals/cgdefu/5/i03/eqn/cg049660we10002.gif">(18) motif involving a pair of nongeminal cyano groups (i.e., ondifferent methylidene carbon atoms). The green polymorph (1G) crystallized in the P space group and adopted a"staircase" ribbon motif with "risers" comprising two PBA²⁺ ions that bridged C₆(CN)₆^2- ions through N-H···NChydrogen bonds. This form also exhibited two modes of hydrogen bonding, the bscribe/journals/cgdefu/5/i03/eqn/cg049660we10003.gif">(15) motif and a more complex oneinvolving multiple molecules. The different colors of the polymorphs were assignable to - charge-transferinteractions between the weak C₆(CN)₆^2- electron donor and the weak PBA²⁺ electron acceptor in the solid state, afeature suggested by single-crystal X-ray diffraction and confirmed by infrared spectroscopy. Heating 1G above 275C produced a crystalline white polymorph (1W). The 1R form, however, exhibited thermal stability up to at least300 C. The related salt [2,2'-(1,2-ethanediyl)pyrimidine²⁺]-[hexacyanocyclopropanediide^2-] ([EBA²⁺][C₆(CN)₆^2-]) (2Y)crystallized in the P2/c space group as yellow bipyramidal plates, forming infinite zigzag hydrogen-bonding ribbons.Unlike 1R and 1G, however, 2Y only exhibits the bscribe/journals/cgdefu/5/i03/eqn/cg049660we10004.gif">(18) motif because the shorter span of the EBA²⁺ molecule, asdefined by the intramolecular separation between N-H groups, did not allow formation of the bscribe/journals/cgdefu/5/i03/eqn/cg049660we10005.gif">(15) motif. Thesestructures reveal that the hydrogen-bonding modes of a bimodal system can be regulated through adjustment ofkey molecular structure parameters, which in the case of EBA²⁺ produces a single hydrogen-bonding mode that isrequired for a hypothetical cyclic motif. Furthermore, the structural parameters of the ribbon motifs provide guidancefor the choice of guest molecules capable of promoting formation of a cyclic motif through templating.