Too much water? Not enough? In situ monitoring of the mechanochemical reaction of copper salts with dicyandiamide

Abstract

In situ monitoring of mechanochemical reactions between dicyandiamide (DCD) and CuX₂ salts (X = Cl⁻, NO₃⁻), for the preparation of compounds of agrochemical interest, showed the appearance of a number of phases. It is demonstrated that milling conditions, such as the amount of water added in wet grinding and/or the milling frequency, may affect the course of the mechanochemical reactions, and drive the reaction towards the formation of different products. It has been possible to discover by in situ monitored experiments two novel crystalline forms, namely the neutral complexes [Cu(DCD)₂(OH₂)₂(NO₃)₂] (2) and [Cu(DCD)₂(OH₂)Cl₂]·H₂O (4), in addition to the previously known molecular salt [Cu(DCD)₂(OH₂)₂][NO₃]₂·2H₂O (1, DIVWAG) and neutral complex [Cu(DCD)₂(OH₂)Cl₂] (3, AQCYCU), for which no synthesis conditions were available. Compounds 2 and 4 were fully characterized via a combination of solid-state techniques, including X-ray diffraction, Raman spectroscopy and TGA.