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Halogen and hydrogen bonds architectures in switchable chains of di- and trihaloimidazoles Micha# Andrzejewski, Jedrzej Marciniak, Kacper W. Rajewski, and Andrzej Katrusiak Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/cg501561w • Publication Date (Web): 20 Feb 2015 Downloaded from http://pubs.acs.org on March 5, 2015
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Crystal Growth & Design
Halogen and hydrogen bonds architectures in switchable chains of di- and trihaloimidazoles Michał Andrzejewski, Jędrzej Marciniak, Kacper W. Rajewski, Andrzej Katrusiak* *Corresponding author:
[email protected], Tel.: +48(61)8291590 Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznań, Poland Keywords: hydrogen bonds, halogen interactions, imidazole, ferroelectric relaxors
Abstract:
Halogen bonds have been employed for controlling the structure of NH···N hydrogen-bonded chains in halogenated imidazoles; the CH···halogen contacts stabilize the coplanar arrangement of molecules whereas the halogen···halogen contacts twist the molecules around the NH···N bonds and stretch their N···N distances. The interplay of halogen-halogen and NH···N hydrogen bonds lead to isostructural relations of 4,5-dihaloimidazoles as well as between trichloro- and tribromoimidazole. However the increasing steric hindrances excludes the triiodoimidazole from this isostructural series and the triiodo-derivative forms an unusual structure with three symmetry-independent molecules. All symmetrically substituted 4,5dichloro-, dibromo- and diiodoimidazoles, as well as trichloro-, tribromo- and triiodoimidazoles have been synthesized, crystallized and their structures determined. The derived rules also apply to the co-crystal structures of 4,5-diiodoimidazole:2,4,51 ACS Paragon Plus Environment
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triiodoimidazole, as well as of 4-iodoimidazole:2,4-diiodoimidazole. The halogen interactions prove an efficient means for engineering and tuning new materials with desired dielectric properties relying on highly polarizable NH···N hydrogen bonds.
Introduction: Materials with high dielectric permittivity, hysteresis, piezoelectric, piroelectric and ferroelectric properties are sought because of their possible applications in electronic, optoelectronic, detectors and electromechanic devices1. Crystals with NH···N hydrogen bonds were shown to exhibit ferroelectric properties due to the switchable bond polarization depending on the proton site2,3. Recently, ferroelectric properties of NH···N hydrogen-bonded molecular crystals of 2-methylbenzimidazole and 5,6-dichloro-2-methyl-benzimidazole were reported4. Also pyrazole, 1,2-diazole, was shown to undergo pressure-induced phase transition analogous to those in KH2PO4 (KDP) type ferroelectrics5. Imidazole, 1,3-diazole, centrosymmetric at ambient conditions, space group P21/c, at high-pressure crystallizes in a noncentrosymmetric form of polar space group Aba26. In the ambient-pressure phase α, the chains of NH···N bonded mutually twisted imidazole molecules are arranged antiparallel, whereas in high-pressure phase β the NH···N bonded planar chains run along diagonal directions [011] and [0-11] and, consequently, all chains contribute to the polarity of the crystal along [001]. This suggested that imidazole derivatives can exhibit ferroelectric properties associated with the bistable NH···N bonds in polar crystals. In our present study we have synthesized a series of new imidazole derivatives by substituting the H-atoms with halogen atoms. It was our intension to employ the interactions between halogen atoms for generating new arrangements and architectures of chains. The unsubstituted imidazole and benzimidazole form chains with molecules twisted around the NH···N bonds, however moderate pressure changes this preference to chains with coplanar or nearly coplanar 2 ACS Paragon Plus Environment
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Crystal Growth & Design
molecules6,7,8. It appears that parallel chains may be more favorable for ferroelectric structures, as it was observed in 2-methylbenzimidazole4. Halogen bonds (X···X bonds, X=Cl, Br, I) are generally defined as electrostatic interaction between a halogen atom, acting as a Lewis acid, and a neutral or anionic Lewis base9. The X···X bonds are classified into two types, according to the C-X···X angles10,11, and they also form supramolecular X3 synthons12. The X···X bonds are selective, directional and their energy can be comparable to that of hydrogen bonds13. Therefore X···X bonds have been used for designing molecular systems of desired properties14, such as molecular conductors, optoelectronic materials15 and other functional materials16. Presently we have used the X···X bonds in conjunction with bistable NH···N bonds for designing the crystals of halogenated imidazoles. The energy of X···X bonds between positive polar and negative equatorial regions of halogen atoms depends on their electronegativity and polarizability in the F
