A Computational Study of Metallacycles Formed by Pyrazolate Ligands and the Coinage Metals M = Cu(I), Ag(I) and Au(I): (pzM)n for n = 2, 3, 4, 5 and 6. Comparison with Structures Reported in the Cambridge Crystallographic Data Center (CCDC)

The use of DOSY experiments to determine the solution structures of coinage metal pyrazolates: The case of {[3,5-(CF3 )2 Pz]Ag}3

A series of DOSY experiments have been carried out to determine the solution stoichiometry of silver(I) 3,5-bis (trifluoromethyl)pyrazolate species. This compound exists as a trimer in the solid state (n = 3) but in solutions of chlorinated solvents, the DOSY data suggest the presence of a mixture of solvent stabilized monomer (n = 1) and dimer (n = 2) in equilibrium. Different approximations have been used including the Stokes-Einstein and the Stokes-Einstein-Gierer-Wirtz equations. Some methodological problems are discussed.

Tetranuclear and trinuclear copper(I) pyrazolates as catalysts in copper mediated azide-alkyne cycloadditions (CuAAC)

Homoleptic, tetranuclear copper(I) pyrazolates {[3,5-(t-Bu)₂Pz]Cu}₄, {[3-(CF₃)-5-(t-Bu)Pz]Cu}₄, and {[4-Br-3,5-(i-Pr)₂Pz]Cu}₄ are excellent stand-alone catalysts for azide-alkyne cycloaddition reactions (CuAAC). This work demonstrates that a range of pyrazolates, including those with electron donating and electron-withdrawing groups to sterically demanding substituents on the pyrazolyl backbones, can serve as effective ligand supports on tetranuclear copper catalysts. However, in contrast to the tetramers and also highly fluorinated {[3,5-(CF₃)₂Pz]Cu}₃, trinuclear copper(I) complexes such as {[3,5-(i-Pr)₂Pz]Cu}₃ and {[3-(CF₃)-5-(CH₃)Pz]Cu}₃ supported by relatively electron rich pyrazolates display poor catalytic activity in CuAAC. The behavior and degree of aggregation of several of these copper(I) pyrazolates in solution were examined using vapor pressure osmometry. Copper(I) complexes such as {[3,5-(CF₃)₂Pz]Cu}₃ and {[3-(CF₃)-5-(t-Bu)Pz]Cu}₄ with electron withdrawing pyrazolates were found to break up in solution to different degrees producing smaller aggregates while those such as {[3,5-(i-Pr)₂Pz]Cu}₃ and {[3,5-(t-Bu)₂Pz]Cu}₄ with electron rich pyrazolates remain intact. In addition, kinetic experiments were performed to understand the unusual activity of tetranuclear copper(I) pyrazolate systems.

The Influence of Aryl Substituents on the Supramolecular Structures and Photoluminescence of Cyclic Trinuclear Pyrazolato Copper(I) Complexes

Cyclic trinuclear complexes with group 11 metal(I) ions are fascinating and important to coordination chemistry. One of the ligands known to form these cyclic trinuclear complexes is pyrazolate, which is a bridging ligand that coordinates many transition metal ions in a Npz–M–Npz linear mode (Npz = pyrazolyl nitrogen atom). In these group 11 metal(I) ions, copper is the most abundant metal. Therefore, polynuclear copper(I) complexes are very important in this field. The cyclic trinuclear copper(I) complex [Cu(3,5-Ph₂pz)]₃ (3,5-Ph₂pz^– = 3,5-diphenyl-1-pyrazolate anion) was reported in 1988 as a landmark complex, but its photoluminescence properties have hitherto not been described. In this study, we report the photoluminescence and two different polymorphs of [Cu(3,5-Ph₂pz)]₃ and its derivative [Cu(3-Me-5-Phpz)]₃ (3-Me-5-Phpz^– = 3-metyl-5-phenyl-1-pyrazale anion). The substituents in [Cu(3-Me-5-Phpz)]₃ cause smaller distortions in the solid-state structure and a red-shift in photoluminescence due to the presence of intermolecular cuprophilic interactions.

Synthesis and Structural Characterization of a Silver(I) Pyrazolato Coordination Polymer

Coinage metal(I)···metal(I) interactions are widely of interest in fields such as supramolecular assembly and unique luminescent properties, etc. Only two types of polynuclear silver(I) pyrazolato complexes have been reported, however, and no detailed spectroscopic characterizations have been reported. An unexpected synthetic method yielded a polynuclear silver(I) complex [Ag(μ-L1Clpz)]_n (L1Clpz⁻ = 4-chloride-3,5-diisopropyl-1-pyrazolate anion) by the reaction of {[Ag(μ-L1Clpz)]₃}₂ with (ⁿBu₄N)[Ag(CN)₂]. The obtained structure was compared with the known hexanuclear silver(I) complex {[Ag(μ-L1Clpz)]₃}₂. The Ag···Ag distances in [Ag(μ-L1Clpz)]_n are slightly shorter than twice Bondi’s van der Waals radius, indicating some Ag···Ag argentophilic interactions. Two Ag–N distances in [Ag(μ-L1Clpz)]_n were found: 2.0760(13) and 2.0716(13) Å, and their N–Ag–N bond angles of 180.00(7)° and 179.83(5)° indicate that each silver(I) ion is coordinated by two pyrazolyl nitrogen atoms with an almost linear coordination. Every five pyrazoles point in the same direction to form a 1-D zig-zag structure. Some spectroscopic properties of [Ag(μ-L1Clpz)]_n in the solid-state are different from those of {[Ag(μ-L1Clpz)]₃}₂ (especially in the absorption and emission spectra), presumably attributable to this zig-zag structure having longer but differently arranged intramolecular Ag···Ag interactions of 3.39171(17) Å. This result clearly demonstrates the different physicochemical properties in the solid-state between 1-D coordination polymer and metalacyclic trinuclear (hexanuclear) or tetranuclear silver(I) pyrazolate complexes.