Gram-Scale Synthesis and Multifunctional Properties of a Two-Dimensional Layered Copper(II) Coordination Polymer

Accomplishing an inexpensive and industrially scalable, robust multifunctional material exhibiting a range of technologically significant phenomena is apparently essential for its projected use in a wide range of device applications. Herein we report on the extremely simple, gram-scale synthesis, electrical conductivity, redox behavior, thermoelectric properties, and magnetism of a two-dimensional (2D) layered copper(II) coordination polymer (COP) formed by treating the ligand 3,3′-diaminobenzidine (DAB) with copper(II) acetate monohydrate, Cu(OAc)2·H2O. The experimental observations show that the COP synthesized, hereafter termed Cu(DAB), and stored under ambient conditions remains intact, exhibiting resistance to air, light, heat, water, and alkaline aqueous solution. FTIR spectroscopy, Raman spectral analyses, microanalytical data, SEM-EDX imaging, surface analysis by XPS/AFM, powder X-ray diffraction, and HRTEM suggest a neutral 2D COP with Cu(DAB) repeating units. While the AC experiments completely rule out ionic conductivity, two-probe DC electrical conductivity measurements on a pellet (bulk sample) as a function of temperature (150–320 K) evidence the electrical conductivity of the COP. Notably, at room temperature (298 K) the conductivity was found to be 0.01 S/m. The inherent p-type conduction was revealed by Hall effect experiments. Apart from being redox-active, it shows thermoelectric behavior, and magnetic susceptibility vs temperature measurements reveal the spin crossover from diamagnetic to the paramagnetic state upon cooling the bulk sample.