Chloride Encapsulation by a Tripodal Tris(4-pyridylurea) Ligand and Effects of Countercations on the Secondary Coordination Sphere

A series of anion complexes of the
4-pyridyl-functionalized tripodal
tris­(urea) receptor (L) have been synthesized. Ligand L forms the 1:1 anion complex [Cl⊂L]− with various metal chloride salts, MClx (M = Na, K, Mg, Ca, Mn, Co, x =
1 or 2). When M = Na, K, Mg, and Ca, the metal ions are not coordinated
by the pyridyl groups of L but are involved in second-sphere
coordination to form three-dimensional structures. However, in the
complex of Co2+, the transition metal ions are directly
coordinated by the pyridyl groups. Interestingly, the Mn2+ ion forms two complexes with both of the above two types of structure.
In all complexes, one chloride ion is “half” encapsulated
in the cleft of one ligand by N–H···Cl hydrogen
bonds to form the [Cl⊂L] units, which are further
linked via intermolecular interactions into three-dimensional structures.
Moreover, the fluoride and carbonate complexes of L have
also been obtained. The solution anion binding properties of L have been studied by 1H NMR spectroscopy and
electrospray ionization mass spectrometry.

本研究合成了一系列由4-吡啶基功能化的三脚架型三脲受体（L）构筑的阴离子配合物。配体L可与多种金属氯化物盐MClₓ（M=Na、K、Mg、Ca、Mn、Co，x=1或2）形成1:1型阴离子配合物[Cl⊂L]⁻。当M为Na、K、Mg和Ca时，金属离子未与配体L的吡啶基配位，而是通过第二配位球作用形成三维结构；而当M为Co²⁺时，过渡金属离子则直接与吡啶基配位。值得注意的是，Mn²⁺离子可形成上述两种结构类型的配合物。
在所有配合物中，一个氯离子通过N–H···Cl氢键被半包裹于一个配体的裂隙中，形成[Cl⊂L]结构单元，该单元进一步通过分子间相互作用连接为三维结构。
此外，配体L的氟离子与碳酸根离子配合物也已成功制备。本研究采用氢核磁共振（¹H NMR）波谱法与电喷雾电离质谱法，对配体L在溶液中的阴离子结合性能进行了研究。