Discarding metal incorporation in pyrazole macrocycles and the role of the substrate on single-layer assemblies

Pyrazole derivatives are key in crystal engineering and liquid crystal fields and thrive in agriculture, pharmaceutical, or biomedicine industries. Such versatility relies in their supramolecular bond adaptability when forming hydrogen bonds or metal-pyrazole complexes. Interestingly, the precise structure of pyrazole-based macrocycles forming widespread porous structures is still unsolved. We bring insight into such fundamental question by studying the self-assembled structures of a bis-pyrazole derivative sublimed in ultra-high-vacuum conditions (without solvents) onto the three (111) noble metal surfaces. By means of high-resolution scanning tunneling microscopy that is validated by gas phase density functional theory calculations, we find a common hexagonal nanoporous network condensed by triple hydrogen bonds at the molecule-metal interface. Such assembly is disrupted and divergent after annealing: (i) on copper, the molecular integrity is compromised leading to structural chaos, (ii) on silver, an incommensurate new oblique structure requiring molecular deprotonation is found and, (iii) on gold, metal-organic complexes are promoted yielding irregular chain structures. Our findings confirm the critical role of these metals on the different pyrazole nanoporous structure formation, discarding their preference for metal incorporation into the connecting nodes whenever there is no solvent involved.

Synthesis, Crystal Structures, Genotoxicity, and Antifungal and Antibacterial Studies of Ni(II) and Cd(II) Pyrazole Amide Coordination Complexes

In this study, we synthesized two coordination complexes based on pyrazole-based ligands, namely 1,5-dimethyl-N-phenyl-1H-pyrazole-3-carboxamide (L1) and 1,5-dimethyl-N-propyl-1H-pyrazole-3-carboxamide (L2), with the aim to investigate bio-inorganic properties. Their crystal structures revealed a mononuclear complex [Ni(L1)2](ClO4)2 (C1) and a dinuclear complex [Cd2(L2)2]Cl4 (C2). Very competitive antifungal and anti-Fusarium activities were found compared to the reference standard cycloheximide. Additionally, L1 and L2 present very weak genotoxicity in contrast to the observed increase in genotoxicity for the coordination complexes C1 and C2.

Novel family of bis-pyrazole coordination complexes as potent antibacterial and antifungal agents

A new pyrazole ligand, N,N-bis(2(1′,5,5′-trimethyl-1H,1′H-[3,3′-bipyrazol]-1-yl)ethyl)propan-1-amine (L) was synthesized and characterized by ¹H-NMR, ¹³C-NMR, FT-IR and HRMS. The coordination ability of the ligand has been employed for the construction of a new family of coordination complexes, namely: [Cu₂LCl₄] (1), [ML(CH₃OH)(H₂O)](ClO₄)₂ (M^II = Ni (2), Co (3)) and [FeL(NCS)₂] (4). The series of complexes were characterized using single-crystal X-ray diffraction, HRMS, FT-IR and UV-visible spectroscopy. Moreover, the iron(ii) analogue was investigated by ⁵⁷Fe Mössbauer spectroscopy and SQUID magnetometry. Single-crystal X-ray structures of the prepared complexes are debated within the framework of the cooperative effect of the hydrogen bonding network and counter anions on the supramolecular formations observed. Furthermore, within the context of biological activity surveys, these compounds were reviewed against different types of bacteria to validate their efficiency, including both Gram-positive as well as Gram-negative bacteria. Enhanced behaviour towards Fusarium oxysporum f. sp. albedinis fungi, were detected for 1 and 4.

A new pyrazole ligand L and four coordination complexes were synthesized and characterized by different spectroscopic methods. These were found to be promising antibacterial and antifungal agents.

Bis(pyrazol-1-yl)methane-4,4′-dicarboxylic Acid

The molecular structure of bis(pyrazol-1-yl)methane-4,4′-dicarboxylic acid (H2bpmdc) was determined by single crystal X-Ray diffraction analysis. The compound crystallizes in a monoclinic crystal system; the unit cell contains four formula units. The molecules of H2bpmdc are linked into zig-zag chains by intermolecular carboxyl–carboxyl hydrogen bonds. Other types of supramolecular interactions, namely, CH···N and CH···O short contacts, CH–π interactions and carbonyl–carbonyl interactions were detected in the crystal structure.

Approaches to the Synthesis of Dicarboxylic Derivatives of Bis(pyrazol-1-yl)alkanes

Carboxylation of bis(pyrazol-1-yl)alkanes by oxalyl chloride was studied. It was found that 4,4'-dicarboxylic derivatives of substrates with electron-donating methyl groups and short linkers (from one to three methylene groups) can be prepared using this method. Longer linkers lead to significantly lower product yields, which is probably due to instability of the intermediate acid chlorides that are initially formed in the reaction with oxalyl chloride. Thus, bis(pyrazol-1-yl)methane gave only monocarboxylic derivative even with a large excess of oxalyl chloride and prolonged reaction duration. An alternative approach involves the reaction of ethyl 4-pyrazolecarboxylates with dibromoalkanes in a superbasic medium (potassium hydroxide-dimethyl sulfoxide) and is suitable for the preparation of bis(4-carboxypyrazol-1-yl)alkanes with both short and long linkers independent of substitution in positions 3 and 5 of pyrazole rings. The obtained dicarboxylic acids are interesting as potential building blocks for metal-organic frameworks.

An experimental and theoretical exploration of supramolecular interactions and photoresponse properties of two Ni(ii) complexes

Two new nickel(ii) complexes, C₃₂H₂N₈NiClO₉ (1) and C₃₆H₂₈N₁₂NiOF₂₄P₄ (2) are reported. The noncovalent interactions witnessed in their crystal packing have been analysed using DFT calculations.

New Bis-Pyrazole-Bis-Acetate Based Coordination Complexes: Influence of Counter-Anions and Metal Ions on the Supramolecular Structures

A new flexible bis-pyrazol-bis-acetate ligand, diethyl 2,2’-(pyridine-2,6-diylbis (5-methyl-1H-pyrazole-3,1-diyl))diacetate (L), has been synthesised, and three coordination complexes, namely, [Zn(L)2](BF4)2 (1), [MnLCl2] (2) and [CdLCl2] (3) have been obtained. All ligands and complexes were characterised by IR, mass spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction. Single crystal X-ray diffraction experiment revealed that the primary supramolecular building block of 1 is a hexagonal chair shaped 0D hydrogen bonded synthon (stabilised by C–H∙∙∙O hydrogen bonding and C=O∙∙∙π interactions), which further built into a 2D corrugated sheet-like architecture having a 3-c net honeycomb topology, and finally extended to a 3D hydrogen bonded network structure having a five nodal 1,3,3,3,7-c net, through C–H∙∙∙F interactions. On the other hand, the two crystallographically independent molecules of 2 exhibited two distinct supramolecular structures such as 2D hydrogen bonded sheet structure and 1D zigzag hydrogen bonded chain, sustained by C–H∙O and C–H∙∙∙Cl interactions, which are further self-assembled into a 3,4-c network structure, and 3 showed a 2D hydrogen bonded sheet structure. The supramolecular structural diversity in these complexes is due to the different conformations adopted by the ligands, which are mainly induced by different metal ions with coordination environments controlled by different anions. Hirshfeld surface analysis was explored for the qualitative and quantitative analysis of the supramolecular interactions.

Efficient and Environmentally Friendly Adsorbent Based on β-Ketoenol-Pyrazole-Thiophene for Heavy-Metal Ion Removal from Aquatic Medium: A Combined Experimental and Theoretical Study

A new sustainable and environmentally friendly adsorbent based on a β-ketoenol-pyrazole-thiophene receptor grafted onto a silica surface was developed and applied to the removal of heavy-metal ions (Pb(II), Cu(II), Zn(II), and Cd(II)) from aquatic medium. The new material SiNPz-Th was well characterized and confirms the success of covalent binding of the receptor on the silica surface. The effect of environmental parameters on adsorption including pH, contact time, temperature, and the initial concentration were investigated. The maximum adsorption capacities of SiNPz-Th for Pb(II), Cu(II), Zn(II), and Cd(II) ions were 102.20, 76.42, 68.95, and 32.68 mg/g, respectively, at 30 min and pH = 6. The adsorption isotherms, kinetics, and thermodynamic process were investigated and showed efficiency and selectivity toward Pb(II) and good regeneration performance. Density functional theory, noncovalent-interaction, and quantum theory of atoms in molecules calculations were used to study and to gain a deeper understanding of both the adsorption mechanism and selectivity of metal ions onto the adsorbent. Accordingly, metal ions such as Pb(II), Cu(II), and Zn(II) were bidentate coordinated with the adsorbent by nitrogen and oxygen atoms of the Schiff base C=N and hydroxyl group -OH, respectively, to form stable complexes. Whereas Cd(II) was coordinated in a monodentate fashion with oxygen atom of the hydroxyl group. Furthermore, the affinity of SiNPz-Th toward the metal ions was decreased in the order of Pb(II) > Cu(II) > Zn(II) > Cd(II), in good agreement with the experimental results. All these results highlight that SiNPz-Th has good potential to be an advanced adsorbent for the removal of lead ions from real water.

Synthesis, structure and photocatalytic properties of coordination polymers based on pyrazole carboxylic acid ligands

The photocatalytic activities of two novel different 2-D coordination polymers constructed from 5-hydroxy-1H-pyrazole-3-carboxylic acid ligand have been explored.

Iron(ii) coordination pyrazole complexes with aromatic sulfonate ligands: the role of ether

Diethyl ether altered the usual homoleptic FeN₆ self-assembly of Fe(ii) mononuclear complexes to yield an FeN₄O₂ heteroleptic coordination environment.

Highly Selective Removal of Pb(II) by a Pyridylpyrazole-β-ketoenol Receptor Covalently Bonded onto the Silica Surface

Efficient materials capable of capturing toxic metals from water are widely needed. Herein, a new pyridylpyrazole-β-ketoenol receptor, X-ray diffraction analyzed, was covalently incorporated into the silica surface to produce solid and recyclable adsorbent particles. The new material, fully characterized, revealed extremely efficient removal of toxic metals from water, with a selectivity order of Pb(II) > Zn(II) > Cu(II) > Cd(II). The adsorption was exceptionally rapid at optimum pH and concentrations, showing Pb(II) removal of 93 mg g-1 within 5 min and maximum Pb(II) adsorption of 110 mg g-1 after only 20 min. Sorption isotherms agreed well with the Langmuir model suggesting a monolayer adsorption, whereas kinetics agreed with the pseudo-second-order model suggesting a chemisorption binding mechanism. Thermodynamics of adsorption were fitted with an endothermic and spontaneous process. The material, recyclable for at least five cycles, is therefore promising for the cleanup of water polluted by toxic metals, especially lead.