On copper(I) fluorides, the cuprophilic interaction, the preparation of copper nitride at room temperature, and the formation mechanism at elevated temperatures

Abstract

Our attempts to synthesize the hitherto unknown binary copper(I) fluoride have led to first successes and a serendipitious result: By conproportionation of elemental copper and copper(II) fluoride in anhydrous liquid ammonia, two copper(I) fluorides were obtained as simple NH3 complexes. One of them presents an example of ligand-unsupported "cuprophilic" interactions in an infinite [Cu2 (NH3 )4 ](2+) chain with alternating Cu-Cu distances. We discovered that both copper(I) fluorides can easily be converted into Cu3 N at room temperature, just by applying a vacuum. Additionally, we investigated the formation mechanism of the classical synthesis route of Cu3 N that starts with CuF2 and flowing NH3 in the temperature range between ambient and 290 °C by means of thermal analysis and in situ neutron diffraction. The reaction proceeds at elevated temperatures through the formation of a blue and amorphous ammoniate Cu(NH3 )2 F2 , the reformation of CuF2 , and finally the redox reaction to form Cu3 N.

Keywords: copper; cuprophilic interactions; fluorides; nitrides; structure elucidation.