pH-Dependent Assembly of 1D to 3D Octamolybdate Hybrid Materials Based on a New Flexible Bis-[(pyridyl)-benzimidazole] Ligand

Four octamolybdate hybrid materials based on a new flexible multidentate ligand, namely, H 4 L (γ-Mo 8 O 26 )·2H 2 O ( 1 ), [Cu(H 2 L )(β-Mo 8 O 26 )(H 2 O) 2 ]·3H 2 O ( 2 ), [Cu(H 2 L )(γ-Mo 8 O 26 )]·3H 2 O ( 3 ), and Cu(H L ) 2 (β-Mo 8 O 26 ) ( 4 ), where L is 1,1′-(1,4-butanediyl)bis[2-(4-pyridyl)benzimidazole], have been synthesized at different pH values under hydrothermal conditions. Compound 1, which is hydrothermally prepared at pH ≈ 1, exhibits a rare one-dimensional (1D) molybdenum oxide chain. Compounds 2 and 3 are hydrothermally obtained at pH ≈ 2.5. In 2, Cu II cations are bridged by H 2 L 2+ ligands and (β-Mo 8 O 26 ) 4– anions to form an interesting two-dimensional (2D) layer. In 3, the H 2 L 2+ ligands and (γ-Mo 8 O 26 ) 4– clusters bridge adjacent Cu II cations to form a 3D framwork. When the pH value is adjusted to 3.5, compound 4 is obtained. Because the H L + cation acts as a monodentate ligand, compound 4 only exhibits a 1D chain structure. The structural diversities of 1 – 4 reveal that the pH value of the reaction system plays a crucial role in the assembly of POM-based metal–organic frameworks (MOFs). In addition, the electrochemical property of compound 4 has also been investigated in 1 M H 2 SO 4 aqueous solution.