Synthesis and structural characterization of copper–cuprizone complexes

Abstract

Copper(II) coordination by bis(cyclohexanone)oxalyldihydrazone (also known as cuprizone), resulting in the formation of an intensely coloured blue complex, was first reported over 70 years ago. The cuprizone reaction has been...

Informing our understanding of the copper–cuprizone reaction with computational chemistry

“…While our experimental characterizations have clarified a number of the unresolved questions in the copper–cuprizone field, 9 several questions remain which have not been addressed elsewhere in the literature: (i) the apparent asymmetric hydrolysis of 1 in the blue product demands an explanation, (ii) the mechanism of copper–cuprizone complex formation that leads to two very different structures must be resolved, and (iii) the observed formation of Cu( iii ) from a reaction mixture that contained only Cu( ii ) requires plausible justification. We employ density functional structure calculations to explicitly model copper–cuprizone complex formation as well as characterize the thermodynamics of key structures and reactions involved.…”

“…In so doing we identify how copper induces hydrolysis of 1 , drives deprotonation of the oxalyldihydrazone backbone (a vital step necessary for stable copper chelation), stabilizes either Cu( ii ) or Cu( iii ), depending on the mechanism of complex formation, as well as identify a plausible route for the generation of Cu( iii ). It is recommended that the interested reader refer to our experimental work on this topic first, 9 as results therein inform the choice of computational models we employ and define the structure and oxidation states of the target end-products.…”

“…Experimental characterization supports structures for the green and blue products, where both amide N-atoms from each ligand are deprotonated and bound to a metal centre. 9 Taking all possible routes to complex formation into account for one or more Cu( ii ) atoms and one or more CPZ or CPZmh ligands is not feasible. Moreover, the final products (the green or blue coloured complexes described in Pushie et al 9 ) are insoluble and appear to correspond to high molecular weight species with ill-defined long-range structure at present.…”

“…9 Taking all possible routes to complex formation into account for one or more Cu( ii ) atoms and one or more CPZ or CPZmh ligands is not feasible. Moreover, the final products (the green or blue coloured complexes described in Pushie et al 9 ) are insoluble and appear to correspond to high molecular weight species with ill-defined long-range structure at present. It must be pointed out that our computational approach employs a “stabilizing” correction for the presence of aqueous solvation, however, the coloured products are not soluble, therefore making calculation of their associated Δ G calc (aq) problematic with the inclusion of Δ G (solv) .…”

“…It must be pointed out that our computational approach employs a “stabilizing” correction for the presence of aqueous solvation, however, the coloured products are not soluble, therefore making calculation of their associated Δ G calc (aq) problematic with the inclusion of Δ G (solv) . We therefore focus only on key steps in the copper coordination process which lead to formation of products characterized in Pushie et al 9…”