Hydrogen Bond Patterns of Dipyridone and Bis(Hydroxypyridinium) Cations

Dipyridonyl-substituted
derivatives 2–4 of
benzene, pyridine, and pyrazine, respectively, were synthesized to
examine the ability of 2-pyridone and its protonated species to direct
the self-assembly by hydrogen bonding. Structural analysis by single-crystal
X-ray diffraction (SCXRD) of 2 and 4 in
trifluoroacetic acid demonstrated that salts are formed as a result
of the transfer of protons from the acid to the base (organic species)
to generate a bis­(hydroxypyridinium) dication. However, if no proton
transfer takes place like in the case of crystals of 3 grown from DMSO/H2O, the self-assembly is mainly directed
by the typical R22(8) hydrogen bond motif of 2-pyridone. These
results indicate that the process of converting a neutral 2-pyridonyl
group into a hydroxypyridinium cation makes structure prediction difficult.
Consequently, examination of proton transfer and assembly of dipyridone
and its protonated species are of interest. In combination with SCXRD,
Hirshfeld surface analysis (HSA) was also used to have a better understanding
on the nature of intermolecular interactions within crystal structures
of 2–4. The large number of F···H/H···F,
H···O/O···H, H···H, and
H···C/C···H contacts revealed by HSA
indicates that hydrogen bonding and van der Waals interactions mainly
contribute to crystal packing.

分别以苯、吡啶、吡嗪为母核的二吡啶酮基取代衍生物2~4被合成，用于探究2-吡啶酮及其质子化物种通过氢键引导自组装的能力。对在三氟乙酸中培养的衍生物2与4的单晶X射线衍射（single-crystal X-ray diffraction, SCXRD）结构分析显示，质子从酸转移至有机碱物种后，会形成双（羟基吡啶鎓）二价阳离子盐。但若未发生质子转移——例如从DMSO/H₂O混合溶剂中生长得到的衍生物3的晶体——其自组装主要由2-吡啶酮典型的R₂²(8)型氢键基序介导。上述结果表明，将中性2-吡啶酮基团转化为羟基吡啶鎓阳离子会大幅增加晶体结构预测的难度。因此，对二吡啶酮及其质子化物种的质子转移与组装过程开展研究具有重要学术价值。本研究结合单晶X射线衍射技术，同时采用赫希菲尔德表面分析（Hirshfeld surface analysis, HSA）以更深入地解析衍生物2~4晶体结构内的分子间相互作用本质。赫希菲尔德表面分析揭示了大量F···H/H···F、H···O/O···H、H···H及H···C/C···H接触相互作用，证实氢键与范德华相互作用是晶体堆积的主要贡献因素。