Nature of Urea−Fluoride Interaction: Incipient and Definitive Proton Transfer

1,3-bis(4-nitrophenyl)urea (1) interacts through hydrogen bonding with a variety of oxoanions in
an MeCN solution to give bright yellow 1:1 complexes, whose stability decreases with the decreasing basicity
of the anion (CH3COO- > C6H5COO- > H2PO4- > NO2- > HSO4- > NO3-). The [Bu4N][1·CH3COO]
complex salt has been isolated as a crystalline solid and its molecular structure determined, showing the
formation of a discrete adduct held together by two N−H···O hydrogen bonds of moderate strength. On
the other hand, the F- ion first establishes a hydrogen-bonding interaction with 1 to give the most stable
1:1 complex, and then on addition of a second equivalent, induces urea deprotonation, due to the formation
of HF2-. The orange-red deprotonated urea solution uptakes carbon dioxide from air to give the
tetrabutylammonium salt of the hydrogencarbonate H-bond complex, [Bu4N][1·HCO3], whose crystal and
molecular structures have been determined.

1,3-双(4-硝基苯基)脲（1）在甲基氰（MeCN）溶液中通过与多种氧酸根离子通过氢键相互作用，生成明亮的黄色1:1配合物，其稳定性随着阴离子碱性（CH3COO- > C6H5COO- > H2PO4- > NO2- > HSO4- > NO3-）的降低而降低。四丁基铵盐[Bu4N][1·CH3COO]已被分离为结晶固体，其分子结构得以确定，显示出由两个中等强度的N−H···O氢键维持的离散加合物的形成。另一方面，氟离子首先与1建立氢键相互作用，生成最稳定的1:1配合物，随后加入第二个等当量，由于HF2-的形成，诱导脲脱质子化。脱质子化的橙红色脲溶液从空气中吸收二氧化碳，生成四丁基铵盐的氢键复合物碳酸氢盐[Bu4N][1·HCO3]，其晶体和分子结构已得到确定。