Cu(II)-Based Pyridyl Bridging Coordination Polymer and Its Fe Composite: Structure, Sensing, Schottky Device, and Hydrogen Evolution Reaction.

[Cu(3-bph)(PABA)2(H2O)] (CP1) (3-bph = N,N'-bis(3-pyridylmethylene)hydrazine and PABA- = p-amino benzoate) is a pyridyl-N bridging CuII coordination polymer, and PABA- acts as a carboxylate-O donor forming a square pyramidal CuN2O3 motif following a zigzag one-dimensional (1D) lattice. The CP1 shows weak antiferromagnetic coupling (J = -0.196(1) cm-1), and emission appears at 352 nm (λex = 293 nm), which is selectively quenched by Fe3+ via the FRET mechanism. The limit of detection (LOD) is 0.081 μM, and the Stern-Volmer constant (Ksv) is 1.52 × 105 M-1. The CP1 shows electrocatalytic HER activity with an overpotential of 628 mV at a current density of 10 mA cm-2 (η10) in 0.5 M H2SO4 with a Tafel slope of 129.8 mV dec-1. Because of the selectivity of CP1 to Fe3+, a composite, Fe(III)@CP1, is used to examine the current density, but it is not impressive. Fe(II)@CP1 shows better HER activity. The composite Fe(II)-n@CP1 (mole ratio of Fe(II)/CP1; 1:1, 1:2, 1:3) shows better HER activity, and Fe(II)-2@CP1 shows the lowest overpotential (η10 = 430 mV) at a current density of 10 mA cm-2 with a Tafel slope of 92.4 mV dec-1. The optical band gap of CP1 (3.72 eV; theoretical, 3.47 eV) suggests a semiconducting behavior and forms an ITO/CP1/Al electrode for the Schottky diode with an electrical conductivity of 7.47 × 10-5 S cm-1.