Use of symmetrical and pendant pyrazole derivatives for the construction of two polyoxometalate-based complexes as electrochemical sensors

Through the use of two pyrazole derivatives, one symmetrical, namely 1,1′-bis(3,5-dimethyl-1H-pyrazol-4-yl)methane (H2bdpm), and one asymmetrical, namely 4-propyl-4,5-dihydro-1H-pyrazole (pdp), two polyoxometalate (POM)-based complexes constructed from saturated Wells–Dawson and mono-Cu(II)-substituted Keggin anions, respectively, were hydrothermally synthesized and structurally characterized as [(Cu2(H2bdpm)2)[H2P2W18O62]0.5]·2H2O (1) and [(Cu3(pdp)6Cl2)(H5PMo11CuO39)2]·12H2O (2). In complex 1, the bidentate H2bdpm ligands link CuI centers to form a 1D wave-like metal–organic chain. Adjacent chains are parallel with each other, with Wells–Dawson anions occupying the gaps. In complex 2, six pdp ligands are coordinated to three CuII centers to form a trinuclear cluster. Two Cl− anions are also coordinated to the copper centers. The mono-Cu(II)-substituted Keggin anions connect the trinuclear clusters to construct a 2D grid-like structure. Both 1 and 2 are semiconducting in nature, with Eg valves of 2.61 and 2.81, respectively. The electrochemical behavior of both complexes has been studied. Carbon paste electrodes of both can be used as electrochemical sensors for the detection of hydrogen peroxide, bromate and nitrite.