Pyrazole Ligands Research Articles

Noncovalently‐bonded 2D‐3D Metal‐organic Frameworks via Assembly of Zn(Ac)2 with 3, 5‐Dimethylpyrazole and Carboxylate Ligands

AbstractFour zinc(II) complexes, namely, Zn(Hdmpz)2(L1)2 (1) (Hdmpz = 3, 5‐dimethylpyrazole, HL1 = trichloroacetic acid), Zn(Hdmpz)2(L2)2 (2) (HL2 = 2, 4‐dichlorophenoxyacetic acid), [Zn2(μ‐dmpz)2(Hdmpz)2(L3)2] (3) (HL3 = 1‐naphthylacetic acid), and [Zn(Hdmpz)2(L4)2]·H2O (4) (HL4 = indole‐3‐acetic acid) were prepared and structurally characterized by different techniques including elemental analysis, IR spectroscopy, TG, and single‐crystal X‐ray diffraction analysis. The complexes display 2D to 3D structures with tetrahedral to pentagonal coordination around the central zinc atom. The X‐ray studies suggested that 1, 2, and 4 are mononuclear complexes, whereas 3 is a centrosymmetric dinuclear complex. The pyrazole ligand is coordinated in both terminal as well as a bridging fashion in the dinuclear moiety but the pyrazole ligand in the mononuclear complexes is coordinated only in monodentate terminal fashion with its neutral N group. The carboxylate groups behave as monodentate ligands in 1–3, whereas the carboxylate in 4 functioned as both monodentate and chelating bidentate ligand. On the basis of X‐ray crystallographic study the rich intra‐ and intermolecular weak interactions such as classical hydrogen bonds, C–H···O, CH3···O, CH–Cl, Cl–Cl, C–H···π, CH2–π, CH3–π, O–π, and π–π are analyzed. All these noncovalent interactions help to assemble the discrete complexes into high‐dimensional ordered superamolecular structures.

Bimetallic thiocyanate bridged Co(II)–Hg(II) polymers with pyrazole and imidazole ligands

In the case of two simple Co(II)–Hg(II) thiocyanate bridged polymers, synthesized in self-assembly processes, we report an interesting example of the magnetic properties of Co(II) complexes. The magnetic susceptibility measurements revealed paramagnetic behavior with negative values of the Curie–Weiss temperature. The larger values of the effective magnetic moment of 4.92μB/f.u. compared to the spin-only value of 3.87μB/f.u. for high-spin Co2+ indicate a significant orbital contribution in the compounds under study.

Crowning of Coinage Metal Pyrazolates: Double-Decker Homo- and Heteronuclear Complexes with Synergic Emissive Properties

A new pyrazole ligand with flexible thioether chelate arms was synthesized and was used to obtain an unprecedented class of hexanuclear coinage metal complexes of general formula [MM'L]3Y3 (M, M' = Cu, Ag, Au; Y = OTf, BF4). Three of them were characterized by X-ray crystallography, namely, homometallic [Ag2L]3(OTf)3 and [Ag2L]3(BF4)3 as well as heterometallic [CuAgL]3(OTf)3, revealing that the classical [M(μ-pz)]3 core is crowned by a second deck of S-bound M' ions. Depending on the solvent, these oligonuclear systems undergo rapid dynamics and show cation-anion aggregation in solution, which has been investigated by DOSY and temperature dependent NMR spectroscopy. Preliminary luminescence data for selected hexametallic [MM'L]3Y3 complexes show that the combination of ligand-directed intramolecular and supramolecular d(10) metal ion interactions in the solid state gives rise to synergic emissive properties that allow for a selective addressing of different emission wavelengths.

Cobalt Complexes with Pyrazole Ligands as Catalyst Precursors for the Peroxidative Oxidation of Cyclohexane: X‐ray Absorption Spectroscopy Studies and Biological Applications

[CoCl(μ-Cl)(Hpz(Ph))3]2 (1) and [CoCl2(Hpz(Ph))4] (2) were obtained by reaction of CoCl2 with HC(pz(Ph))3 and Hpz(Ph), respectively (Hpz(Ph)=3-phenylpyrazole). The compounds were isolated as air-stable solids and fully characterized by IR and far-IR spectroscopy, MS(ESI+/-), elemental analysis, cyclic voltammetry (CV), controlled potential electrolysis, and single-crystal X-ray diffraction. Electrochemical studies showed that 1 and 2 undergo single-electron irreversible Co(II)→Co(III) oxidations and Co(II)→Co(I) reductions at potentials measured by CV, which also allowed, in the case of dinuclear complex 1, the detection of electronic communication between the Co centers through the chloride bridging ligands. The electrochemical behavior of models of 1 and 2 were also investigated by density functional theory (DFT) methods, which indicated that the vertical oxidation of 1 and 2 (that before structural relaxation) affects mostly the chloride and pyrazolyl ligands, whereas adiabatic oxidation (that after the geometry relaxation) and reduction are mostly metal centered. Compounds 1 and 2 and, for comparative purposes, other related scorpionate and pyrazole cobalt complexes, exhibit catalytic activity for the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone under mild conditions (room temperature, aqueous H2O2). In situ X-ray absorption spectroscopy studies indicated that the species derived from complexes 1 and 2 during the oxidation of cyclohexane (i.e., Ox-1 and Ox-2, respectively) are analogous and contain a Co(III) site. Complex 2 showed low in vitro cytotoxicity toward the HCT116 colorectal carcinoma and MCF7 breast adenocarcinoma cell lines.

Well‐Defined, Nanometer‐Sized LiH Cluster Compounds Stabilized by Pyrazolate Ligands

AbstractThe assembly of well‐defined large cluster compounds of ionic light metal hydrides is a synthetic challenge and of importance for synthesis, catalysis, and hydrogen storage. The synthesis and characterization of a series of neutral and anionic pyrazolate‐stabilized lithium hydride clusters with inorganic cores in the nanometer region is now reported. These complexes were prepared in a bottom‐up approach using alkyl lithium and lithium pyrazolate mixtures with silanes in hydrocarbon solutions. Structural characterization using synchrotron radiation revealed isolated cubic clusters that contain up to 37 Li+ cations and 26 H− ions. Substituted pyrazolate ligands were found to occupy all corners and some edges for the anionic positions.

Polycatenar pyrazole and pyrazolate ligands as building blocks of new columnar Pd(II) metallomesogens.

Dicatenar pyridine-functionalised pyrazole ligands [Hpz(R(n,n)py)] (R(n,n) = C6H3(OCnH2n+1)2, n = 4, 6, 8, 10, 12, 14, 16, 18) have been strategically synthesised to be used as new building blocks for designing discotic liquid crystalline materials. Their coordination to Pd(II) fragments has allowed to achieve two novel families of metallomesogens, [Pd(pz(R(n,n)py))2] () and [PdCl2(Hpz(R(n,n)py))] (), in which the ligand is coordinated in the anionic form as pyrazolate or in the neutral form as pyrazole, respectively. Thermal studies showed that the ligands with n = 14 and 16 carbon atoms, as well as all the palladium complexes, display discotic mesophases in the temperature range of 68-141 °C. The results indicate that the coordination environment around the metal is a determining factor which allows control of the supramolecular arrangement of the mesophase. Disc-like molecules from complexes pack themselves into cylindrical structures that result in hexagonal columnar phases (Colh), while the half-disc shaped molecules from self-assemble into a layer with an antiparallel dimeric disposition which generates lamellar columnar phases (ColL). Schematic models based on X-ray powder diffraction (XRD) experiments are proposed to illustrate the molecular organisation of these Pd metallomesogens in the columnar mesophases.

Synthesis, Characterization, and Crystal Structures of Scorpionate Complexes with the Hydrotris[3‐(2′‐thienyl)pyrazol‐1‐yl]borate Ligand

AbstractSix scorpionate complexes of group 10–12 metal elements (CuI, CuII, ZnII, and CdII) containing the anionic hydrotris[3‐(2′‐thienyl)pyrazol‐1‐yl]borate (TpTn) ligand were prepared from the reaction of the thallium(I) salt of TpTn with the corresponding metal acceptors in chloroform solution. The air‐ and heat‐stable complexes were characterized by analytical and spectroscopic methods (IR, conductivity, ESI‐MS, 1H NMR and 13C NMR solution data) and structurally characterized by single‐crystal X‐ray studies. The ZnII complexes [Zn(TpTn)X] (X = Cl or Br) contain a tripodal tridentate TpTn ligand, in which the tetrahedral metal environment is completed by a halide; in [Cd(TpTn)2], cadmium is found in an octahedral environment coordinated by two TpTn ligands. In [Cu(TpTn)(PPh3)]·CHCl3 and [Cu(TpTn)(OC(O)CH3)], TpTn is also coordinated in the tripodal fashion, in which the copper environment is completed by a triphenylphosphine ligand in the former complex and by a symmetrically coordinated bidentate acetate ligand occupying trans‐coordinated sites in the latter complex. The reaction of [Zn(TpTn)X] with an excess amount of [Tl(TpTn)] in MeOH yielded [Zn(TpTn)2] and TlX, whereas the reaction of [Zn(TpTn)X] with Na(Tp) gave [Zn(TpTn)2] and [Zn(Tp)2] in a 1:1 molar ratio but not [Zn(TpTn)(Tp)]. By contrast, the reaction of [Tl(TpTn)] with copper(II) sulfate monohydrate in chloroform gave a green powder, which was identified as the [(Hpz3Tn)4CuSO4](∞|∞) coordination polymer containing OSO2O bridging sulfate groups and four coordinated pyrazole ligands on each metal center, the latter of which arises from the decomposition of the TpTn ligand through B–N bond breaking. Similarly, the interaction between [Tl(TpTn)] and platinum(II) diiodide in chloroform/DMSO proceeded through TpTn decomposition to afford a monomeric trans‐[(Hpz3Tn)2PtI2]·2(CH3)2SO complex, wherein two neutral pyrazole ligands are coordinated to the PtII center.

Tetrahedral and octahedral metallomesogenic Zn(ii) complexes supported by pyridine-functionalised pyrazole ligands

Pyridylpyrazoles with long-chained alkyloxyphenyl substituents [HpzR(n)py] (R(n) = C6H4OCnH2n+1, n = 12, 14, 16, 18) are versatile ligands for designing new zinc metallomesogens [Zn(HpzR(n)py)m][X]2 (m = 2, X = NO3−; m = 3, X = BF4−) with tetrahedral and octahedral coordination geometry, respectively. Molar conductivity measurements reveal the non-bonding character of the nitrate and tetrafluoroborate anions to Zn(II) and confirm the ionic nature of the complexes in solution. Polarised optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD) studies show that all of them are enantiotropic liquid crystals, exhibiting SmA mesophases. A layered packing with interdigitation of the alkyl chains is proposed on the basis of XRD results to explain the organisation in the SmA mesophase. TG experiments indicate that the zinc complexes are stable up to ca. 175 °C, the temperature at which mass loss is observed. On the basis of computational models using hyperchem-7 program the molecular geometry has been examined. The semi-empirical calculations suggest that, in the solid state, the counteranions could be involved in hydrogen bonds, which would contribute to obtaining the stable electronic structure.

Well‐Defined, Nanometer‐Sized LiH Cluster Compounds Stabilized by Pyrazolate Ligands

The assembly of well-defined large cluster compounds of ionic light metal hydrides is a synthetic challenge and of importance for synthesis, catalysis, and hydrogen storage. The synthesis and characterization of a series of neutral and anionic pyrazolate-stabilized lithium hydride clusters with inorganic cores in the nanometer region is now reported. These complexes were prepared in a bottom-up approach using alkyl lithium and lithium pyrazolate mixtures with silanes in hydrocarbon solutions. Structural characterization using synchrotron radiation revealed isolated cubic clusters that contain up to 37 Li(+) cations and 26 H(-) ions. Substituted pyrazolate ligands were found to occupy all corners and some edges for the anionic positions.

New nitrogen-donor pyrazole ligands for excellent liquid–liquid extraction of Fe2+ ions from aqueous solution, with theoretical study

New N-donor pyrazole derivatives L 1 –L 6 were prepared by monoalkylation, by simple and easy condensation of one equivalent of 1-(hydroxymethyl)-3,5-dimethylpyrazole and one equivalent of an appropriate primary amine. The compounds were used to extract different metal ions. Their capacity in extraction of Cu2+, Cd2+, Pb2+, Co2+, Ni2+, Zn2+, and Fe2+ was determined by measurement, by atomic absorption, of percentage extraction of the cation at pH 7. All the ligands tested extract these metals with different efficiency: efficiency of L 2 was 99 % for Fe2+ and 29 % for Zn; efficiency of L 4 was 24 % for Cu2+ and Cd2+ and 19 % for Pb2+. The geometries were optimized, the energies, spatial distributions, energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), the difference between these (E LUMO − E HOMO), known as energy band gap (ΔE), bond lengths, charges on the atoms, and electrostatic potential were then calculated. The molecule with smallest value of ΔE is the most reactive (least stable) and correlation proves that the efficiency of extraction of Fe2+ increases as molecular stability decreases.

Bis[μ-3,5-bis(pyridin-2-yl)-1H-pyrazole]bis[dibromidoiron(III)

The title dinuclear complex, [Fe2Br4(C13H9N4)2], which lies on an inversion center, features two approximately planar bis­(pyridin-2-yl)pyrazole (bpypz−) ligands [maximum deviation = 0.082 (3) Å] and four bromide ions. Each FeIII ion is octa­hedrally coordinated by four N atoms of two bpypz− ligands and two Br ions. π–π stacking inter­actions [centroid–centroid distances = 3.7004 (17)–4.0123 (18) Å] are observed between pyridyl and pyrazole rings, and between pyridyl and pyridyl rings of adjacent complex mol­ecules.

Anion effect on the coordination behavior of N,O-hybrid pyrazole ligand towards Pd(II): synthesis, characterization, and supramolecular properties

Four new Pd(II) coordination complexes using 2-(3-methyl-5-phenyl-1H-pyrazol-1-yl)ethanol (L) with different counter-anions have been prepared to examine their effect on the coordination mode of the ligand as well as on the self-assembly of the supramolecular structure. Reaction of trans-[PdCl2(L)2] (R) with AgCF3SO3 gives the ionic complex [Pd(L)2](CF3SO3)2 (1). When AgNO3 is used, [Pd(NO3)(L)2](NO3) (2) and [Pd(L)2](NO3)2 (3) are obtained in the ratio 70 : 30, respectively, where the nitrate ion is present in- and/or outside the coordination sphere. Reaction of R with Ag2SO4 in the presence of (NH4)2C2O4 yields [Pd(C2O4)(L)2] (4). These new complexes have been characterized by elemental analyzes, conductivity measurements, mass spectrometry, IR, 1H and 13C{1H} NMR spectroscopies, and X-ray diffraction, whenever possible. The denticity varies from N-monodentate to NO-bidentate, depending on the conditions, showing the versatility of L. Finally, the results of X-ray diffraction analyzes of 1 reveal that CF3SO3− plays a fundamental role in self-assembly, generating a 2-D supramolecular layer with different inter- and intra-molecular interactions. The easy preparation and the high efficiency of this ligand make it a promising alternative to improve established systems.

D→f energy transfer in Ir(III)/Eu(III) dyads: use of a naphthyl spacer as a spatial and energetic "stepping stone".

A series of luminescent complexes based on {Ir(phpy)2} (phpy = cyclometallating anion of 2-phenylpyridine) or {Ir(F2phpy)2} [F2phpy = cyclometallating anion of 2-(2′,4′-difluorophenyl)pyridine] units, with an additional 3-(2-pyridyl)-pyrazole (pypz) ligand, have been prepared; fluorination of the phenylpyridine ligands results in a blue-shift of the usual 3MLCT/3LC luminescence of the Ir unit from 477 to 455 nm. These complexes have pendant from the coordinated pyrazolyl ring an additional chelating 3-(2-pyridyl)-pyrazole unit, separated via a flexible chain containing a naphthalene-1,4-diyl or naphthalene-1,5-diyl spacer. Crystal structures show that the flexibility of the pendant chain allows the naphthyl group to lie close to the Ir core and participate in a π-stacking interaction with a coordinated phpy or F2phpy ligand. Luminescence spectra show that, whereas the {Ir(phpy)2(pypz)} complexes show typical Ir-based emission—albeit with lengthened lifetimes because of interaction with the stacked naphthyl group—the {Ir(F2phpy)2(pypz)} complexes are nearly quenched. This is because the higher energy of the Ir-based 3MLCT/3LC excited state can now be quenched by the adjacent naphthyl group to form a long-lived naphthyl-centered triplet (3nap) state which is detectable by transient absorption. Coordination of an {Eu(hfac)3} unit (hfac = 1,1,1,5,5,5-hexafluoro-pentane-2,4-dionate) to the pendant pypz binding site affords Ir–naphthyl–Eu triads. For the triads containing a {Ir(phpy)2} core, the unavailability of the 3nap state (not populated by the Ir-based excited state which is too low in energy) means that direct Ir→Eu energy-transfer occurs in the same way as in other flexible Ir/Eu complexes. However for the triads based on the{Ir(F2phpy)2} core, the initial Ir→3nap energy-transfer step is followed by a second, slower, 3nap→Eu energy-transfer step: transient absorption measurements clearly show the 3nap state being sensitized by the Ir center (synchronous Ir-based decay and 3nap rise-time) and then transferring its energy to the Eu center (synchronous 3nap decay and Eu-based emission rise time). Thus the 3nap state, which is energetically intermediate in the {Ir(F2phpy)2}–naphthyl–Eu systems, can act as a “stepping stone” for two-step d→f energy-transfer.

Synthesis and structural characterization of a mononuclear CuIIcomplex with pyrazole ligands

Synthesis and structural characterization of a mononuclear Cu^IIcomplex with pyrazole ligands

Monomeric Pd(II) complexes with trans-chelated pyrazole ligands as effective pre-catalysts for Heck cross-coupling reaction under mild aerobic conditions

A new family of mononuclear palladium(II) complexes with bidentate trans-chelating pyrazole ligands [PdCl2(LR)] (R = H, 1; Et, 2; Ph, 3; CHPh2, 4), where new ligand LEt = 2-ethyl-1,3-bis-(3,5-dimethyl-pyrazol-1-ylmethyl)-2,3-dihydro-1H-perimidine, and a new mononuclear palladium(II) complex with monodentate trans-chelated pyrazole ligand [PdCl2(Ph-pz′)2] (5), where Ph-pz′ = 3,5-dimethyl-1-phenyl-1H-pyrazole, have been synthesized and characterized. Complexes 2–5 were also structurally confirmed by single crystal X-ray diffraction analysis. Remarkably, under very mild conditions (65–70 °C), complex 4 appeared to be an active pre-catalyst for the Heck coupling reactions of iodobenzene and t-butyl acrylate in MeOH. In the presence of co-catalyst [nNBu4]Br, however, complex 5 displayed the highest catalytic activity for the Heck reactions of activated bromobenzene and t-butyl acrylate.

Insights into the coordination sphere of copper ion in polymers containing carboxylic acid and azole groups

In this work, we describe the Cu2+ ion uptake from recently developed hydrogel with polyampholyte and polyelectrolyte behavior at different concentrations of the metal ion. Solid-state NMR and EPR were used as complementary techniques to understand the coordination role of carboxylic acid and azole groups (imidazole, triazole and pyrazole) involved in the copper ion coordination. In polymers containing imidazole and triazole, the uptake took place preferentially through the azole groups, with less participation of the carboxylate groups at low concentrations of Cu2+. However, as the concentration of Cu2+ increased, these azole ligands became less active in the new sites for copper. In polymers containing pyrazole, coordination of Cu2+ was through both carboxylate and pyrazole ligands, regardless of the concentration of Cu2+.Interactions of the different ligands in the networks and the structural changes produced by copper ions (Cu1+, Cu2+) were characterized by thermal and NMR measurements.

Charge-Transfer and Ligand-Localized Photophysics in Luminescent Cyclometalated Pyrazolate-Bridged Dinuclear Platinum(II) Complexes

We present the synthesis, photophysical characterization, and electrochemistry of three series of cyclometalated binuclear platinum(II) complexes, each bridged by two 3,5-disubstituted pyrazolate ligands (μ-R2pz). These neutral compounds have the general formula [C∧NPt(μ-R2pz)]2, where C∧N is a cyclometalating ligand corresponding to 2-(2′-thienyl)pyridine (thpy), 1-phenylisoquinoline (piq), or 7,8-benzoquinoline (bzq) with R = H, Me, iPr, Ph, corresponding to series I–III dimers, respectively. Systematic variation of the cyclometalating ligands in addition to the bridging pyrazolates renders colorful structures exhibiting a range of electrochemical and spectroscopic behavior with absorption and photoluminescence properties tuned over a wide portion of the visible spectrum. Steric bulk introduced into the 3,5-positions on the pz bridges readily modulates intramolecular d8–d8 metal–metal σ interactions strongly affecting the frontier orbitals’ electronic structure, manifested by changes in absorption and emission energy, excited-state lifetime, and photoluminescence quantum yield. Cyclic voltammetry revealed the presence of two very closely spaced reversible C∧N ligand-based reductions ranging between −1.97 and −2.56 V vs Fc+/Fc, and the first metal–metal-centered oxidation wave was found to be reversible in dichloromethane and irreversible in coordinating THF in most instances. All the complexes of series I displayed triplet ligand-localized excited states at all temperatures, while an increase of steric bulk in the pz bridge in the two other molecular series resulted in a variation of photophysical behavior ranging from charge transfer to ligand localized, including admixture behavior.

Non-covalently bonded 2D–3D metal–organic frameworks from the reactions of Cd(II) and Zn(II) with 3,5-dimethylpyrazole and carboxylate ligands

Seven new complexes, namely Cd(Hdmpz)2(L1)2 (1) (Hdmpz=3,5-dimethylpyrazole, L1=N-phenylmaleamate), Cd(Hdmpz)4(L2)2 (2) (L2=1,3-benzodioxole-5-carboxylate), Zn2(μ-dmpz)2(Hdmpz)2(L3)2 (3) (L3=2-chloronicotinate), Zn(Hdmpz)2(L4)2 (4) (L4=3,5-dinitrobenzoate), Zn(Hdmpz)2(HL5)2 (5) (HL5=5-chlorosalicylate), Cd(Hdmpz)2(HL6) (6) (HL6=5-sulfosalicylate) and Cd2(Hdmpz)4(L7)2 (7) (L7=maleate), have been synthesized from the self-assembly of the Zn/Cd ions, 3,5-dimethylpyrazole and carboxylate ligands at room temperature. All the complexes were structurally characterized by different techniques, including elemental analysis, IR spectra, TG and single crystal X-ray diffraction analysis. The X-ray studies suggest that these complexes display mononuclear to dinuclear structures with a tetrahedral geometry around each zinc center, and an octahedral geometry around each cadmium center. The pyrazole ligands in all the compounds except compound 3 are coordinated only in the monodentate fashion by its neutral N group. In 2, 3, 4, 5 and 6, the carboxylate groups behave as monodentate ligands. The COO− group in 1 and the SO3- group in 6 both coordinate to the metal in a chelating bidentate fashion. The carboxylates in 7 functioned as a tetradentate bridging ligand. The uncoordinated oxygen atom of the carboxylate group in all of the compounds forms intramolecular hydrogen bonds with the N–H group of the coordinated 3,5-dimethylpyrazole ligand. On the basis of the X-ray crystallographic study, the rich intra- and intermolecular non-covalent interactions, such as classical hydrogen bonds, CH–Cl, CH3–Cl, Cl⋯Cl, Cl⋯O, C–H⋯O, CH3⋯O, C–H⋯π, CH2⋯π, CH3–π, O–π and π–π interactions, are analyzed. The various non-bonding interactions in these compounds are responsible for different structures, such as sheet, 3D network and 3D layer structures. The thermal stabilities of 1–7 were examined and the results show that the complexes seem to be good candidates for novel hybrid inorganic–organic materials with good thermal stability.

Synthesis, Crystal Structure, Spectroscopic and Magnetically Study of Two Copper(II) Complexes with Pyrazole Ligand

AbstractThe synthesis and characterization of two new CuII complexes with pyrazole ligands formulated as [Cu3(μ‐Pz)3(μ3‐OH)(Pz)2Cl2][Cu3(μ‐Pz)3(μ3‐OH)(Pz)2Cl2(DMF)]·2DMF (1) and [Cu3(μ‐DMPz)3(DMF)4(OAc)(μ3‐OH)(H2O)]+[Cu3(μ‐DMPz)3(DMF)(NCS)3(μ3‐OH)]– (2) (where Pz = 1H‐pyrazole and DMPz = 3, 5‐dimethyl‐1H‐pyrazole) are reported. The compounds were prepared by the reaction of zero valent copper metal and Pz or DMPz in the dimethylformamide solution in the presence of the different additional components (chloride or thiocyanate ligands). The crystal structures of both compounds were determined by single‐crystal X‐ray diffraction analysis. Both compounds 1 and 2 are hexanuclear clusters comprising from neutral (1) or charged (2) trinuclear triangular fragments Cu3(μ3‐OH)(μ‐Pz)3 of inverse azametallacrowns aza9‐MCCuII‐3 topology. Nevertheless, they exhibit relevant differences in their molecular structures. The magnetic measurement shows the isotropic antiferromagnetic interaction in 2 with J1 = –140 cm–1 for the cationic and J2 = –109 cm–1 (–2JSi·Sj model) for the anionic part of the molecule above 100 K and significant influence of antisymmetric exchange at lower temperatures.

N–N Bond Cleavage of Hydrazines with a Multiproton-Responsive Pincer-Type Iron Complex

N-N bond cleavage of hydrazines on transition metals is of considerable importance in understanding the mechanism of biological nitrogen fixation under ambient conditions. We found that a metal-ligand-bifunctional complex of iron with a pincer-type ligand bearing two proton-responsive pyrazole arms catalyzes the disproportionation of hydrazine into ammonia and dinitrogen. The NH groups in the pyrazole ligands and hydrazines are crucial for the reaction, which most likely occurs through multiple and bidirectional proton-coupled electron transfer between the iron complex and hydrazine. The multiproton-responsive pincer-type ligand also stabilizes the intermediate diazene complex through a hydrogen-bonding network, as revealed by structural characterization of a κ(1)N-phenylhydrazine complex.