Search Results (7)

The synthesis and structural characterization of a new triangular Cu₃–μ₃OH pyrazolato complex of formula, [Cu₃(μ₃−OH)(pz)₃(Hpz)₃][BF₄]₂ (1−Cu₃), Hpz = pyrazole, is presented. The triangular unit forms a quasi-isosceles triangle with Cu–Cu distances of 3.3739(9), 3.3571(9), and 3.370(1) Å. This complex is isostructural to the hexanuclear complex [Cu₃(μ₃−OH)(pz)₃(Hpz)₃](ClO₄)₂]₂ (QOPJIP). A comparative structural analysis with other reported triangular Cu₃–μ₃OH pyrazolato complexes has been carried out, showing that, depending on the pyrazolato derivative, an auxiliary ligand or counter-anion can affect the nuclearity and/or the dimensionality of the system. The magnetic properties of 1−Cu₃ are analyzed using experimental data and DFT calculation. A detailed analysis was performed on the magnetic properties, comparing experimental and theoretical data of other molecular triangular Cu₃–μ₃OH complexes, showing that the displacement of the μ₃−OH⁻ from the Cu₃ plane, together with the type of organic ligands, influences the nature of the magnetic exchange interaction between the spin-carrier centers, since it affects the overlap of the magnetic orbitals involved in the exchange pathways. Finally, a detailed comparison of the magnetic properties of 1−Cu₃ and QOPJIP was carried out, which allowed us to understand the differences in their magnetic properties. Full article

Protic pyrazoles (N-unsubstituted pyrazoles) have been versatile ligands in various fields, such as materials chemistry and homogeneous catalysis, owing to their proton-responsive nature. This review provides an overview of the reactivities of protic pyrazole complexes. The coordination chemistry of pincer-type 2,6-bis(1H-pyrazol-3-yl)pyridines is first surveyed as a class of compounds for which significant advances have made in the last decade. The stoichiometric reactivities of protic pyrazole complexes with inorganic nitrogenous compounds are then described, which possibly relates to the inorganic nitrogen cycle in nature. The last part of this article is devoted to outlining the catalytic application of protic pyrazole complexes, emphasizing the mechanistic aspect. The role of the NH group in the protic pyrazole ligand and resulting metal–ligand cooperation in these transformations are discussed. Full article

Two differently substituted pyrazole ligands have been investigated with regard to the topology of their Pt complexes: upon deprotonation, two mononuclear 1:2 Pt^II-pyrazole complexes—one of the sterically unhindered 4-Me-pzH and one of the bulky 3,5-^tBu-pzH (pzH = pyrazole)—yield the corresponding 1:2 Pt^II-pyrazolato species; the former a triangular, trinuclear metallacycle (1), and the latter a dinuclear, half-lantern species (2) formed via the unprecedented cyclometallation of a butyl group. Stoichiometric oxidation of the colorless Pt^II₂ complex produces the deep-blue, metal–metal bonded Pt^III₂ analog (3) with a rarely encountered unsymmetrical coordination across the Pt-Pt bond. All three complexes have been characterized by single crystal X-ray structure determination, ¹H-NMR, IR, and UV-vis-NIR spectroscopic methods. The XPS spectra of the Pt^II₂ and Pt^III₂ species are also reported. Density functional theory calculations were carried out to investigate the electronic structure, spectroscopic properties, and chemical bonding of the new complexes. The calculated natural population analysis charges and Wiberg bonding indices indicate a weak σ-interaction in the case of 2 and a formal Pt-Pt single bond in 3. Full article

The crystal structure of the ferromagnetically-coupled Cu^II₃−pyrazolato complex, (Bu₄N)₂[Cu₃(μ₃-Cl)₂(μ-4-NO₂-pz)₃Cl₃] (1a, pz = pyrazolato anion), was originally determined in the triclinic P-1 space group. By varying the recrystallization solvent and temperature, two additional true polymorphs were crystallized in the monoclinic P2₁/n (1b) and orthorhombic Pbca (1c) space groups. Comparison of the metric parameters of the three polymorphs revealed only minor variations in their bond lengths and angles but clearly distinguishable packing patterns. The DFT calculations showed that, in vacuum, 1a had the lowest energetic minimum (also the densest of three polymorphs), whereas 1b and 1c lay at 6.9 kcal/mol and 7.8 kcal/mol higher energies. The existence of isolable 1b and 1c is, therefore, attributed to the intermolecular interactions analyzed by the Hirshfeld methods. Full article

Homoleptic ceric pyrazolates (pz) Ce(RR’pz)₄ (R = R’ = tBu; R = R’ = Ph; R = tBu, R’ = Me) were synthesized by the protonolysis reaction of Ce[N(SiHMe₂)₂]₄ with the corresponding pyrazole derivative. The resulting complexes were investigated in their reactivity toward CO₂, revealing a significant influence of the bulkiness of the substituents on the pyrazolato ligands. The efficiency of the CO₂ insertion was found to increase in the order of tBu₂pz < Ph₂pz < tBuMepz < Me₂pz. For comparison, the pyrrole-based ate complexes [Ce₂(pyr)₆(µ-pyr)₂(thf)₂][Li(thf)₄]₂ (pyr = pyrrolato) and [Ce(cbz)₄(thf)₂][Li(thf)₄] (cbz = carbazolato) were obtained via protonolysis of the cerous ate complex Ce[N(SiHMe₂)₂]₄Li(thf) with pyrrole and carbazole, respectively. Treatment of the pyrrolate/carbazolate complexes with CO₂ seemed promising, but any reversibility could not be observed. Full article

We present a series of pyrazolato-bridged copper complexes with interesting structures that can be considered prototypic patterns for tri-, hexa- and hepta- nuclear systems. The trinuclear shows an almost regular triangle with a μ₃-OH central group. The hexanuclear has identical monomer units, the Cu₆ system forming a regular hexagon. The heptanuclear can be described as two trinuclear moieties sandwiching a central copper ion via carboxylate bridges. In the heptanuclear system, the pyrazolate bridges are consolidating the triangular faces, which are sketching an elongated trigonal antiprism. The magnetic properties of these systems, dominated by the strong antiferromagnetism along the pyrazolate bridges, were described transparently, outlining the energy levels formulas in terms of Heisenberg exchange parameters J, within the specific topologies. We succeeded in finding a simple Kambe-type resolution of the Heisenberg spin Hamiltonian for the rather complex case of the heptanuclear. In a similar manner, the weak intermolecular coupling of two trimer units (aside from the strong exchange inside triangles) was resolved by closed energy formulas. The hexanuclear can be legitimately proposed as a case of coordination-based aromaticity, since the phenomenology of the six-spins problem resembles the bonding in benzene. The Broken-Symmetry Density Functional Theory (BS-DFT) calculations are non-trivial results, being intrinsically difficult at high nuclearities. Full article

Two anionic complexes, {[Cu₃(µ₃-OH)(µ-4-Ph-pz)₃Cl₃]₂[Cu(4-Ph-pzH)₄](µ-Cl)₂}²⁻ (1) and [Cu₃(µ₃-OH)(µ-pz)₃(µ_1,1-N₃)₂(N₃)]⁻ (2), crystallize as one-dimensional polymers, held together by weak Cu-(µ-Cl) and Cu-(µ-N₃) interactions, respectively. Variable temperature magnetic susceptibility analyses determined the dominant antiferromagnetic intra-Cu₃ exchange parameters in the solid state for both complexes, whereas the weak ferromagnetic inter-Cu₃ interactions manifested also in the solid state EPR spectra, are absent in the corresponding frozen solution spectra. DFT calculations were employed to support the results of the magnetic susceptibility analyses. Full article