Classical and Weak Hydrogen Bonding Interactions between 4,4′-Bipyridine and Organic Acids: From Co-Crystal to Organic Complex

Reaction of 4,4′-bipyridine (4,4′-bipy) with barbituric (BAH), orotic (ORH), and uracil-5-carboxylic acids (U5CAH) yielded three new products, which have been characterized by single-crystal X-ray diffraction. The products include a co-crystal of neutral species with Z′ = 2 (4,4′-bipy/BAH), an organic complex ion pair (4,4′-bipy/ORH) and a compound containing both ionic and hydrogen-bonded neutral species (4,4′-bipy/U5CAH). Partial proton transfer is observed in both of the ionic cases, and in all three structures the crystal packing arrangement is such that weak hydrogen bonding, π···π and molecular dipole interactions are optimized.

4,4′-联吡啶（4,4′-bipy）与巴比妥酸（BAH）、乳清酸（ORH）以及尿嘧啶-5-羧酸（U5CAH）的反应生成了三种新型产物，这些产物通过单晶X射线衍射进行了表征。产物包括中性物种与Z′ = 2的共晶体（4,4′-bipy/BAH）、一种有机复合离子对（4,4′-bipy/ORH）以及一种含有离子和氢键中性物种的化合物（4,4′-bipy/U5CAH）。在两种离子情况下观察到部分质子转移，且在这三种结构中，晶体堆积排列使得弱氢键、π···π和分子偶极相互作用得到优化。