Trinuclear copper(ii) pyrazolate compounds: a long story of serendipitous discoveries and rational design

Abstract

In the past decade great effort has been put into the development of synthetic strategies to produce trinuclear triangular CuII ( TTC) arrays, which may be synthetic analogues of the trinuclear site in ascorbate oxidase and blue oxidase. A large number of scientific contributions have been dedicated to the synthesis and spectroscopic characterization of TTC arrays. In contrast, only a small number of studies deal with their possible applications. As a consequence, systematic studies describing their reactivity are very rare and the few existing models can only partially explain how structural and molecular parameters influence their reactivity and their possible uses and applications. This contribution reports a summary of all experimental results related to the Cu-3(mu(3)-OH)(mu-pz)(3) core (pz = unsubstituted pyrazolate). We describe here all species, distinguishing them according to whether they are neutral, cationic or anionic, as well as their main structural features, the synthetic procedures employed for their production, their reactivity toward nucleophiles and strong acids and, finally, their possible and perspective applications

Rivalry between Regium and Hydrogen Bonds Established within Diatomic Coinage Molecules and Lewis Acids/Bases

“…[8] Additionally, experimental evidences of the (Pyrazole-Cu) 3 with simultaneous interactions between three copper atoms and one hydroxyl group were recently studied. [9] From a theoretical perspective, most studies were focused on gold metal due to its importance as a catalyst. [10] For example, the resonance character of B•••Au regium bond (RB), in B:AuX complexes, were studied at the BP86 level.…”

“…Complexes between gold carboranes and trimethylphosphine were synthesized and study by X‐ray crystallography [8] . Additionally, experimental evidences of the (Pyrazole‐Cu) 3 with simultaneous interactions between three copper atoms and one hydroxyl group were recently studied [9] …”

Interaction between Trinuclear Regium Complexes of Pyrazolate and Anions, a Computational Study

“…A search in the Cambridge Structural Database (CSD) [112] (Version 5.41 with updates of March, May and August 2020) was carried in order to find crystal structures of (Py-M) 3 structures with halides. It should be noted that complementary studies focused on the analysis of the crystal structures that show the interaction between (Py-M) 3 molecules and the hydroxyl anion are available in the literature [68].…”

“…Pyrazolate ligands (Py) with coinage metals, forming regium bonds, are also common, in any oxidation state: Cu(I)/Cu(II), Ag(I) and Au(I)/Au(III) [56,[61][62][63][64][65][66]. Particularly, cyclic [Py-M(I)] 3 systems with M = Cu, Ag and Au were studied [67] and the experimental evidences of the (Py-Cu) 3 systems with simultaneous interactions of the three copper atoms with one hydroxyl group were recently reviewed [68]. So, these aforementioned systems present very interesting features, which make them good candidates for exhibiting regium bonds.…”

Investigation on the interconversion from DMF-solvated to unsolvated copper(ii) pyrazolate coordination polymers

“…These trinuclear complexes self-assemble in hexanuclear clusters through carboxylate bridges and form extended 1-D, 2-D or 3-D CPs or supramolecular networks, displaying intriguing catalytic activity in the cycloalkane oxidation to alcohols. [27][28][29][30][31][32][33][34][35][36][37][38][39][40]41 Completely different results were obtained when Cu(II) carboxylates were reacted with pzH in MeCN, yielding the pale-pink 1-D CP [Cu(µ-pz) 2 •H 2 O] n independently from the carboxylate employed (Scheme 1). [42][43][44] This compound reversibly loses water, yielding [Cu(µ-pz) 2 ] n .…”