Organoimido-Derivatized Hexamolybdates with a Remote Carboxyl Group: Syntheses and Structural Characterizations

Four
novel organoimido derivatives of hexamolybdate containing
a remote carboxyl group have been synthesized: [Bu4N]2[Mo6O18(N-C6H4-3-COOH)] (1), [Bu4N]2[Mo6O18(N-C6H4-2-CH3-4-COOH)] (2), [Bu4N]2[Mo6O18(N-C6H4-2-CH3-5-COOH)] (3), and [Bu4N]2[Mo6O18(N-C6H4-2-CH3-3-COOH)] (4) with 3-aminobenzoic acid, 4-amino-3-methylbenzoic
acid, 3-amino-4-methylbenzoic acid, and 3-amino-2-methylbenzoic acid
as the imido-releasing agents, respectively. Their structures have
been characterized by IR, UV–vis, 1H NMR, ESI–MS,
and single-crystal X-ray diffraction techniques. Hydrogen bonding
interactions play an important role in the supramolecular assemblies
of these compounds in the solid state. Although the incorporated organic
ligands are similar to each other, their supramolecular assembly behaviors
are quite different. For compound 1, the dimer structure
is formed via hydrogen bonding between the carboxyl group and the
POM cluster of two neighboring cluster anions. For compound 2, the 1D chain structure is formed via hydrogen bonding between
the carboxyl groups and the POM clusters of the cluster anions. For
compound 3, the 2D plane structure is formed via two
types of hydrogen bonding between the aromatic rings and the POM clusters
of the cluster anions. For compound 4, the 1D plus 2D
structures are formed via three types of hydrogen bonding between
the aromatic rings and the POM clusters of the two types of cluster
anions with different orientations.

本研究合成了四种带有远端羧基的六钼酸根有机亚胺衍生物：[Bu₄N]₂[Mo₆O₁₈(N-C₆H₄-3-COOH)]（1）、[Bu₄N]₂[Mo₆O₁₈(N-C₆H₄-2-CH₃-4-COOH)]（2）、[Bu₄N]₂[Mo₆O₁₈(N-C₆H₄-2-CH₃-5-COOH)]（3）以及[Bu₄N]₂[Mo₆O₁₈(N-C₆H₄-2-CH₃-3-COOH)]（4），分别以3-氨基苯甲酸、4-氨基-3-甲基苯甲酸、3-氨基-4-甲基苯甲酸和3-氨基-2-甲基苯甲酸作为亚胺释放试剂。采用红外光谱（IR）、紫外-可见光谱（UV-vis）、核磁共振氢谱（¹H NMR）、电喷雾质谱（ESI-MS）以及单晶X射线衍射技术对其结构进行了表征。氢键相互作用在该类化合物的固态超分子组装过程中发挥着重要作用。尽管所引入的有机配体结构相似，但其超分子组装行为却存在显著差异。对于化合物1，两个相邻簇阴离子的羧基与多金属氧酸盐（Polyoxometalate, POM）簇之间通过氢键作用形成二聚体结构；对于化合物2，簇阴离子的羧基与多金属氧酸盐簇之间通过氢键作用形成一维链状结构；对于化合物3，簇阴离子的芳环与多金属氧酸盐簇之间通过两种氢键作用形成二维平面结构；对于化合物4，两种不同取向的簇阴离子的芳环与多金属氧酸盐簇之间通过三种氢键作用形成一维与二维共存的组装结构。