Hexameric Silver(I) Pyrazolate: Synthesis, Structure, and Isomerization

Rhenium-Pyrazolyl-Based Figure-Eight- and Z-Shaped Metallocycles: Self-Assembly, Solid-State Structures, Dynamic Properties in Solution, and Competitive Ligand-Induced Supramolecular Transformations into Rhenium-Pyridyl/-Benzimidazolyl/-Phosphine-Based Metallocycles/Acyclic Complexes

Rhenium(I)tricarbonyl core-based heteroleptic "figure-eight"- and Z-shaped metallocycles (1a-4a) of the general formula fac-[{(CO)3Re(μ-L)Re(CO)3}2(dppz)2] were self-assembled from Re2(CO)10, H2-L (H2-L = 5,8-dihydroxy-1,4-naphthaquinone (H2-dhnq) for 1a; 1,4-dihydroxy-9,10-anthraquinone (H2-dhaq) for 2a; 6,11-dihydroxy-5,12-naphthacenedione (H2-dhnd) for 3a; 2,2'-bisbenzimidazole (H2-bbim) for 4a), and bis(4-((pyrazolyl)methyl)phenylmethane) (dppz) via one-pot coordination-driven synthetic approach. The molecular structures of 1a and 4a were unambiguously confirmed by single-crystal X-ray diffraction (SC-XRD) methods. The metallocycles in the DMSO solution exist as an acyclic dinuclear-DMSO adduct of the general formula fac-[{(CO)3Re(μ-L)Re(CO)3}(DMSO)2] (1b, L = dhnq; 2b, L = dhaq; 3b, L = dhnd; 4b, L = bbim) and dppz, which are in dynamic equilibrium. The dynamic behavior of the rhenium-pyrazolyl bond in the solution state was effectively utilized to transform metallocycles 1a-4a into pyridyl/benzimidazolyl/phosphine donor-based heteroleptic metallocycles and acyclic dinuclear complexes (4-13). These include tetranuclear rectangles fac-[{(CO)3Re(μ-L)Re(CO)3}2(4,4'-bpy)2] (4 and 11, L = dhaq for 4 and bbim for 11), dinuclear metallocycles fac-[{(CO)3Re(μ-L)Re(CO)3}(dpbim)] (5-7 and 12; L = dhnq for 5, dhaq for 6, dhnd for 7, and bbim for 12), and dinuclear acyclic complexes fac-[{(CO)3Re(μ-L)Re(CO)3}(PTA)2] (8-10 and 13; L = dhnq for 8, dhaq for 9, dhnd for 10, and bbim for 13). These transformations were achieved through component-induced supramolecular reactions while treating with competitive ligands 4,4'-bipyridine (4,4'-bpy), bis(4-((1H-benzoimidazole-1-yl)methyl)phenyl)methane (dpbim), and 1,3,5-triaza-7-phosphaadamantane (PTA). The reaction mixture in the solution was analyzed using NMR and electrospray ionization mass spectrometry (ESI-MS) analysis. Additionally, crystal structures of 4, 6, and 13, which were obtained in the mixture of the solutions, were determined, providing unequivocal evidence for the occurrence of supramolecular transformation within the system. The results reveal that the size of the chelating ligand and the pyrazolyl donor angle of the ditopic ligand play crucial roles in determining the resulting solid-state metallacyclic architecture in these synthetic combinations. The dynamic behavior of the rhenium-pyrazolyl bond in the metallocycles can be utilized to transform into other metallocycles and acyclic complexes using suitable competing ligands via ligand-induced supramolecular transformations.

Ligand-Directed Metalation of a Gold Pyrazolate Cluster

Solid "[AuL]" (HL = 3-[pyrid-2-yl]-5-tertbutyl-1H-pyrazole) can be crystallized as cyclic [Au₃(μ-L)₃] and [Au₄(μ-L)₄] clusters from different solvents. The crystalline tetramer contains a square Au₄ core with an HT:TH:TH:HT arrangement of ligand substituents, which preorganizes the cluster to chelate to additional metal ions via its pendant pyridyl groups. The addition of 0.5 equiv of AgBF₄ to [AuL] yields [Ag₂Au₄(μ₃-L)₄][BF₄]₂, where two edges of the Au₄ square are spanned by Ag⁺ ions via metallophilic Ag···Au contacts. Treatment of [AuL] with [Cu(NCMe)₄]PF₆ affords the metalloligand helicate [Cu₂Au₂(μ-L)₄][PF₆]₂, via oxidation of the copper and partial fragmentation of the cluster.

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.

Complexation of triangular silver(I) or copper(I) nitropyrazolates with dibenzothiophenes having potential use in adsorptive desulfurization

Triangular silver(i) and copper(i) 3,5-diethyl-4-nitropyrazolates (abbreviated as [Ag(denpz)]3 or Ag3pz3, and [Cu(denpz)]3 or Cu3pz3), as well as their adducts with dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (DMDBT) and benzothiophene (BT), have been prepared and characterized by a series of techniques. X-ray analyses show that these adducts are stabilized by MS, MC contacts and ππ stacking interactions. NMR measurements and theoretical calculations indicate that the intensity of interaction between the metal complexes and dibenzothiophenes follows the trend: Ag3pz3-DMDBT > Ag3pz3-DBT > Cu3pz3-DMDBT > Cu3pz3-DBT, which can be understood on the basis of a weak interaction between π-acid (Ag3pz3 or Cu3pz3) and π-base (DBT/DMDBT). Both complexes show good adsorptive ability and reusability toward the removal of DBT and DMDBT from model oil (n-octane), with the maximum adsorption capacity at room temperature being 39 mg S (DMDBT) per g Cu3pz3, 34 mg S (DMDBT) per g Ag3pz3, 40 mg S (DBT) per g Cu3pz3, 36 mg S (DBT) per g Ag3pz3, respectively. Compared to Ag3pz3, Cu3pz3 exhibits higher adsorptive capacities for DBT/DMDBT, which has been attributed to its lower molecular mass.

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 structures reported in the Cambridge Structural Database (CSD) for neutral metallacycles formed by coinage metals in their valence (I) (cations) and pyrazolate anions were examined. Depending on the metal, dimers and trimers are the most common but some larger rings have also been reported, although some of the larger structures are not devoid of ambiguity. M06-2x calculations were carried out on simplified structures (without C-substituents on the pyrazolate rings) in order to facilitate a comparison with the reported X-ray structures (geometries and energies). The problems of stability of the different ring sizes were also analyzed.

A systematic investigation of structural transformation in a copper pyrazolato system: a case study

Dissolution-recrystallization structural transformation (DRST) is a powerful tool to unravel unequivocally the mechanism of dynamic conversion processes, based on the structures of the initial reactants, final products and sometimes intermediates isolated from the reaction mixture. Herein, we illustrate the details of the conversion processes of (CuIpz)3 into [CuII(OH)pz]6 (pzH = 4-chloro-3,5-diphenylpyrazole) through DRSTs. Based on crystal structure determination and spectroscopic methods, the most encountered species, (CuIpz)3, is in equilibrium with (CuIpz)4 in solution with the tetramer becoming dominant at low temperature, indicating an entropy-controlled conversion between these two structural isomers. The CuI trimer/tetramer in solution further experiences an oxidation if exposed to the open air, resulting in the formation of a pentanuclear mixed-valence intermediate CuI3CuII2(OMe)2pz5 which can be isolated as single crystals at -20 °C and has been structurally characterized for the first time. The final product isolated from the solution is the fully oxidized hexanuclear [CuII(OMe)pz]6, which is easily transformed into [CuII(OH)pz]6 in the presence of humidity.

Mixed ligand complexes of silver(i) supported by highly fluorinated pyrazolates, and chelating and bridging N-heterocycles

A range of silver complexes featuring all nitrogen coordination environments involving pyrazolates and chelating and non-chelating bidentate N-heterocycles are reported.

Coinage metal metallacycles involving a fluorinated 3,5-diarylpyrazolate

Photoluminescent, trinuclear, coinage metal pyrazolates have been isolated using a fluorinated diaryl-pyrazolate.

The effect of solvent on one-dimensional cadmium coordination polymers

We transformed one one-dimensional coordination polymer directly to another by carrying out a dissolution–recrystallization structural transformation (DRST).