Synthesis of Cu1.8S and CuS from Copper-Thiourea Containing Precursors; Anionic (Cl-, NO3-, SO42-) Influence on the Product Stoichiometry

A novel and unique understanding pertaining to the synthesis of Cu1.8S and CuS in bulk was achieved from the analysis of the products of the Cu-Tu precursors, with Cl-, NO3-, and SO42- as the counteranions, in ethylene glycol. [Cu-4(tu)(9)] (NO3)(4) center dot 4H(2)O always yielded CuS whether the dissociation was carried out in ethylene glycol in the presence of air or argon or under solvothermal conditions. Cu1.8S was the only product when [Cu(tu)(3)]Cl was dissociated in air as well as in flowing argon in ethylene glycol. A mixture of Cu1.8S and CuS was formed from the chloride ion containing precursor when dissociated solvothermally. [Cu-2(tu)(6)]SO4 center dot H2O yielded a mixture of CuS and, Cu1.8S on dissociation in the presence of air and argon, as well as under solvothermal conditions. The oxidizing power of the anions Cl-, SO4, and NO3, present. in the precursor, greatly determined the extent of formation of Cu1.8S and CuS. While Cu1.8S showed hexagonal plate like morphology, flower like morphology was observed for CuS in the SEM images. In the mixed phase, Cu1.8S + CuS, both these morphologies were present. Cu1.8S and CuS showed scattering resonances at 470 cm(-1) and 474 cm(-1), respectively, in the Raman spectrum. Magnetization measurements at room temperature revealed diamagnetic behavior for Cu1.8S, indicating the presence of +1 oxidation state for copper. Weak paramagnetic behavior was observed for CuS with chi(M) value of 1.198 x 10(-3) emu/mol at 300 K Both Cu1.8S and CuS showed similar emission behavior in the photoluminescence spectrum with band positions centered at around 387, 390, 401, 423, and 440 nm. The origin of photoluminescence in these to copper sulfides remains elusive.