Improved capacitive performances and electrocatalytic reduction activity by regulating the bonding interaction between Zn-bistriazole-pyrazine/pyridine units and diverse Anderson-type polyoxometalates.

Electrochemical performances can be effectively improved by introducing metal-organic units (MOUs) into polyoxometalates (POMs). However, regulating the bonding strength between POMs and MOUs at the molecular level to improve the electrochemical performance is a challenging task. Three new POM-based metal-organic complexes (MOCs), namely H{Zn 2 (Hpytty) 2 (H 2 O) 8 [CrMo 6 (OH) 6 O 18 ]}·2H 2 O (1), H{Zn 2 (Hpyttz) 2 (H 2 O) 6 [CrMo 6 (OH) 6 O 18 ]}·8H 2 O (2), and {(μ 2 -OH) 2 Zn 6 (pyttz) 2 (H 2 O) 10 [TeMo 6 O 24 ]}·2H 2 O (3) (H 2 pytty = 3-(pyrazin-2-yl)-5-(1 H -1,2,4-triazol-3-yl)-1,2,4-triazolyl, H 2 pyttz = 3-(pyrid-2-yl)-5-(1 H -1,2,4-triazol-3-yl)-1,2,4-triazolyl), were obtained. Single-crystal X-ray diffraction shows that the bonding strength (from the hydrogen bond to the coordination bond) between Zn-bistriazole-pyrazine/pyridine units and diverse Anderson-type POMs gradually increases from complexes 1 to 3. Glassy carbon electrodes modified with complex 3 (3-GCE) has the highest specific capacitance, which is 930 F g -1 at 1 A g -1 . Moreover, carbon paste electrodes (1-3-CPEs) modified with complexes 1-3 are used as electrochemical sensors for detecting Cr(VI) ions, with limits of detection well below the World Health Organization (WHO) maximum level in drinking water.