Pyrazolato Anion Research Articles

Crystal Structure, Hirshfeld Analysis, and DFT Calculations of Three Trinuclear Cu(II) Polymorphs

The crystal structure of the ferromagnetically-coupled CuII3−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.

Direct Evidence for Neutral N-Pyrazolyl Radicals: Paddlewheel Dibismuthanes Bearing Pyrazolato Ligands with Very Short Bi-Bi Single Bonds.

Neutral N-pyrazolyl radicals [3,5-R2pz]• as reactive intermediates were generated by one-electron oxidization of the corresponding 3,5-disubstituted pyrazolato anions [3,5-R2pz]- (R = tBu, Ph) with BiCl3 and trapped by the use of 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap, which was confirmed by electron paramagnetic resonance spectral analysis. With dimerization of the postulated pyrazolato low-valent BiII radical species, two novel paddlewheel pyrazolatodibismuthanes [L2(Bi-Bi)L2] [L = η1,η1-3,5-R2pz; R = tBu (5α, 5β, and 5γ), Ph (6)] were isolated and structurally characterized.

Towards ionic liquids with tailored magnetic properties: bmim+ salts of ferro- and antiferromagnetic Cu triangles.

Complexes (bmim)2[Cu3(μ3-Cl)2(μ-pz)3Cl3] (1), (bmim)[Cu3(μ3-OH)(μ-pz)3Cl3] (2) and (bmim)2[Cu3(μ3-OH)(μ-Cl)(μ-pz)3Cl3] (3) were synthesized (bmim+ = 1-butyl-3-methylimidazolium, pz- = pyrazolato anion). Dianionic complexes 1 and 3 were obtained as crystalline solids, whereas the monoanionic complex 2 was obtained as a viscous paste. Magnetic susceptibility and X-band EPR studies revealed intramolecular ferromagnetic interactions for 1 with small magnetoanisotropy in its ground state (D3/2∼ 10-3 cm-1) and intramolecular antiferromagnetic interactions for 2 and 3 (-285 and -98 cm-1 average J, respectively) with important magnetic anisotropy in their ground states stemming from a combination of low magnetic symmetry and antisymmetric exchange interactions. Thermal studies revealed a clear melting point of 140 °C for 1, which is lower than that of its PPN+ and Bu4N+ analogues (1PPN and 1Bu4N, respectively, PPN+ = bis(triphenylphosphine)iminium). Upon cooling, 1 remains molten down to 70 °C. Mixtures of the salts 1, 1PPN and 1Bu4N, exhibited modified melting behaviours, with the mixtures exhibiting lower melting points than those of either of their pure components.

Substituent Effects on the Supramolecular Aggregation of AgI-Pyrazolato Trimers

The interplay of argentophilic and dipolar (π-acid···base) interactions, on one hand, and the presence or absence of interstitial solvent molecules, on the other, determines the supramolecular organization of trinuclear silver-pyrazolato complexes in the solid state. The crystal structures of one gold and six silver metallacyclic complexes of the type [MI(μ-pz*)]3, where pz* are the substituted pyrazolato anions 3,5-Ph2-pz, 3-Me-5-Ph-pz, 4-Br-3,5-Ph2-pz, 4-Br-3-tBu-pz and 3-(o-Cl-C6H4)-pz and M = Ag and Au, are discussed in the context of their supramolecular organization. Two silver complexes, for which the π-acid character of their Ag3-faces is maximized by their peripheral electron-withdrawing substituents, show crystal packing dominated by short Ag3···Br contacts, the first structural manifestation of supramolecular structure via dipolar interactions involving the tunable π-acidity of the Ag3-face.

Synthesis and Crystal Structures of Dinuclear Zinc Complexes with the 3,5‐Bis(pyridine‐2‐yl)pyrazolato Ligand

AbstractZincation of 3,5‐bis(pyridine‐2‐yl)pyrazole with Zn[E(SiMe3)2]2 in tetrahydrofuran yields dimeric 3,5‐bis(pyridine‐2‐yl)pyrazolato zinc bis(trimethylsilyl)amide (E = N, 1) and bis(trimethylsilyl)methanide (E = CH, 2). These complexes crystallize in the space groups $\rm P2_1/n$, respectively. The zinc atoms are in distorted tetrahedral environments. In the solid state the 3,5‐bis(pyridine‐2‐yl)pyrazolato anions act as bridging tridentate bases with one pyridyl group not participating in the coordination behavior. In solution, exchange processes, which are fast on the NMR time scale, lead to a single set of resonances for the pyridyl substituents.

Spin relaxation in a ferromagnetically coupled triangular Cu 3 complex

The trinuclear complex [Bu 4N 2[Cu 3(μ 3-Cl) 2(μ-pz) 3Cl 3] (pz = pyrazolato anion) ( 1) exhibits ferromagnetic interactions resulting in an S = 3/2 ground state which is characterized by a small zero field splitting tensor [17]. Herein, the S = 3/2 state is further characterized using High-Frequency and -Field Electron Paramagnetic Resonance spectroscopy. The spin relaxation properties of 1 are studied with alternating current susceptometry in the presence of external magnetic fields. In the 4.5–8.0 K temperature range, the system relaxes via an Orbach mechanism involving transitions between the S = 3/2 and the excited S = 1/2 spin manifolds.

Dinuclear gold(III) pyrazolato complexes – Synthesis, structural characterization and transformation to their trinuclear gold(I) and gold(I/III) analogues

The reaction of AuCl 3py with Na(pz∗) (pz∗ = pyrazolato, or substituted pyrazolato anion) yields stable dinuclear [ cis-Au IIICl 2(μ-pz∗)] 2 complexes. In the presence of a base, the latter undergo reduction with concomitant transformation of the dinuclear Au 2 III -structure to trinuclear Au 2 III Au I, Au III Au 2 I (containing trans Au IIICl 2-centres) and Au 3 I species.

First Structural Characterization of a Delocalized, Mixed-Valent, Triangular Cu37+ Species: Chemical and Electrochemical Oxidation of a CuII3(μ3-O) Pyrazolate and Electronic Structure of the Oxidation Product

The chemical or electrochemical one-electron oxidation of the all-CuII complex [Cu3(mu3-O)(mu-pz)3X3]2- leads to its formally CuII2CuIII analogue (pz = pyrazolato anion; X = Cl- and PhCOO-). The X-ray single-crystal structure and density functional theory analysis of the latter agree in revealing the delocalized nature of its mixed-valent Cu3(7+) core.

Effect of pyrazole-substitution on the structure and nuclearity of Cu(II)-pyrazolato complexes

Trinuclear Cu(II)-pyrazolates of the general formula (Bu4N)2[Cu3(μ3-Cl)2(μ-4-R-pz)3Cl3] (pz=pyrazolato anion, R=Cl, Br, I, Me), 1–4, have been prepared and characterized by X-ray diffraction and/or 1H NMR, IR, UV–Vis spectroscopy and elemental analysis. Their structure and spectroscopic properties match the ones of the parent unsubstituted complex (Bu4N)2[Cu3(μ3-Cl)2(μ-pz)3Cl3], indicating that 4-substitution of the pyrazole ligands with halogen or methyl groups does not induce structural variation. In contrast, dinuclear complexes (Bu4N)4[Cu2(μ-3-Me-pz)2Cl4]Cl2·4H2O, Cu2(μ-Cl)(μ-3,5-Me2-pz)(3,5-Me2-pzH)4Cl2, Cu2(μ-Cl)(μ-OH)(3-Me-5-Ph-pzH)4Cl2·3-Me-5-Ph-pzH and Cu2(μ-Cl)2(3,5-Ph2-pzH)4Cl2, 5–8, have been prepared with 3- and 3,5-substituted pyrazoles by the same or similar synthetic protocols.

Triangular, ferromagnetically-coupled CuII 3-pyrazolato complexes as possible models of particulate methane monooxygenase (pMMO).

Magnetic susceptibility and EPR studies show that trinuclear Cu(II)-pyrazolato complexes with a Cu(3)(mu3-X)2 core (X = Cl, Br) are ferromagnetically coupled: J(Cu-Cu) = +28.6 cm(-1) (X = Cl), +3.1 cm(-1) (X = Br). The orderly transition from an antiferromagnetic to a ferromagnetic exchange among the Cu centers of Cu(3)(mu3-X) complexes, X = O, OH, Cl, Br, follows the change of the Cu-X-Cu angle from 120 degrees to approximately 80 degrees. The crystal structures of [Bu4N]2"[Cu3(mu3-Br)2(mu-pz*)3Br3] (pz* = pz (1a) or 4-O2N-pz (1b), pz = pyrazolato anion, C(3)H(3)N(2)(1-)) are presented.

Synthesis, spectroscopic investigation and X-ray structure of mononuclear and binuclear oxo complexes of rhenium(V) with pyrazolato ligands

The [{Re(O)Cl(PPh3)}2(μ-O)(μ-N2C3H3)2] (1), [{Re(O)Br(PPh3)}2(μ-O)(μ-N2C3H3)2] (2), [ReOCl2{η2-N2C3H3CMe2O}(PPh3)] (3) and [ReOBr2{η2-N2C3H3CMe2O}(PPh3)] (4) complexes have been synthesized by reacting [ReOX3(PPh3)2] with an excess of pyrazole under different conditions. The rhenium(V) centers of (1) and (2) are linked through two bridging pyrazolato anions and an oxo group. The rhenium(V) atoms in mononuclear complexes (3) and (4) are six coordinated in an octahedral environment with a trans arrangement of the oxo group and oxygen atom of anionic bidentate ligand C3H3N2C(Me)2O− formed in the reaction of pyrazole and Me2CO.

Supramolecular assembly of trimeric gold(I) pyrazolates through aurophilic attractions.

The supramolecular architecture of trinuclear gold(I) pyrazolato aggregates is held together by intermolecular aurophilic attractions, sterically governed by the substituents on the pyrazole rings. A two-dimensional network of [Au(mu-pz)]3 complexes, 1 (pz = pyrazolato anion, C3H3N2-), and a large intricate aggregate of 16 [Au(mu-4-Me-pz)]3 complexes in 2 have been determined crystallographically. Under UV irradiation at ambient temperature, solid samples of 1 and 2 luminesce with lambda max = 626 and 631 cm-1, respectively, attributed to intermolecular Au...Au aurophilic contacts.

Metal derivatives of azoles, part VII. Pyrazolato-bridged dinuclear complexes containing either cyclopalladated or -platinated trimesitylphosphine or -arsine

The halogen bridges of the dimeric, cyclometallated trimesityl-arsine and -phosphine complexes of palladium(II) and platinum(II), where M=Pd or Pt and E=P or As have been replaced with pyrazolate groups to give the corresponding and less symmetric pyrazolato-bridged complexes, where M=Pd or Pt, E=P or As, Pz=pyrazolato anion, and M=Pd, E=As, Pz=3,5-dimethylpyrazolato anion. In the case of the palladium complexes,1H. n.m.r. clearly indicates the presence of only one isomer which is most likely to have thetrans configuration while the platinum complexes are mixtures of bothcis andtrans forms.

Metal derivatives of azoles. 3. The pyrazolato anion (and homologs) as a mono- or bidentate ligand: preparation and reactivity of tri-, bi-, and mononuclear gold(I) derivatives

Metal derivatives of azoles. 3. The pyrazolato anion (and homologs) as a mono- or bidentate ligand: preparation and reactivity of tri-, bi-, and mononuclear gold(I) derivatives

Pyrazolato and related anions. Part IV. Salts of 4-nitropyrazole

Abstract A number of metal salts of 4-nitropyrazole (HNO2Pz) is reported. Salts of Cd, Zn, Mn, Co, Ni and Cu are synthesized from ammonia solution, or by addition of NaOH to a NHO2Pz complex in water. The compounds are identified and characterized by chemical analyses, infrared and ligand field spectra. The pyrazolato anion coordinates as a bidentated ligand. In the salts of Cd, Mn, Co, Ni, and Cu ammonia and water molecules are participating in the coordination of the metal ion. A tentative vibrational assignment of salts and neutral ligand is given.