Two polymolybdate-directed Zn(ii) complexes tuned by a new bis-pyridine-bis-amide ligand with a diphenylketone spacer for efficient ampere sensing and dye adsorption

Abstract

By introducing a new semi-rigid bis-pyridine-bis-amide ligand with diphenylketone as a spacer, 4,4′-bis(4-pyridinecarboxamide)phenylketone(L), two polymolybdate-based metal–organic complexes (MOCs), namely, [ZnL(MoO₄)] (1) and (H₂L)₄[Zn(CrMo₆(OH)₆O₁₈)₂(H₂O)₄][ZnL₂(CrMo₆(OH)₆O₁₈)₂(H₂O)₂]·8H₂O (2), were successfully assembled via a solvothermal method. Complexes 1 and 2 show different structures by introducing different Anderson-type [TeMo₆O₂₄]⁶⁻/[CrMo₆(OH)₆O₁₈]³⁻ polyoxoanions in the H₂O–EtOH mixture solvent, including the 3D network of 1 and the 0D supramolecular structure of 2. An interesting structural feature in 1 is that an inorganic {ZnMoO₄}_n layer could be formed, although an A-type [TeMo₆O₂₄]⁶⁻ polyoxoanion was utilized as the raw material. Noteworthily, complexes 1 and 2 can be employed as dual-function electrocatalysts for the electroreduction of Cr(VI), KBrO₃, and H₂O₂ and the electrooxidation of ascorbic acid (AA). They can also be used as electrochemical sensors for the quantitative detection of Cr(VI), KBrO₃, H₂O₂, and AA; in particular, low detection limits (0.033 μM for 1 and 0.037 μM for 2) were observed for Cr(VI) ions. Complex 2 shows a rapid and highly selective adsorption activity for the organic dyes crystal violet and methylene blue.