From mono to polydentate azole and benzazole derivatives, versatile ligands for main group and transition metal atoms

A new approach to study semi-coordination using two 2-methyl-5-nitroimidazole copper(ii) complexes of biological interest as a model system

Two novel copper(ii) complexes [Cu(2mni)2(H2O)2](NO3)2·2H2O (1) and [Cu(2mni)2(NO3)2] (2), where 2mni is 2-methyl-5-nitroimidazole, were prepared and characterized in the solid state using single-crystal and powder X-ray diffraction analyses, EPR, electronic and vibrational spectroscopies (FTIR and Raman), and thermogravimetric methods. Both products present an elongated distorted octahedral geometry with axial Cu-O bond lengths of 2.606(14) and 2.593(15) Å, indicating semi-coordination. Density functional theory (DFT) calculations at the B3LYP/LANL2DZ theory level were used to study the electronic properties of 1 and 2. The Independent Gradient Model (IGM) was employed to determine the Intrinsic Bond Strength Index (IBSI) of the semi-coordination and to plot δg isosurfaces for the electronic sharing between the metal center and ligands. A moderate to weak antibacterial activity against Escherichia coli cultures was found for 1 with a 50% growth inhibition (GI50) value of 0.25 mmol L-1. To the best of our knowledge, this is the first time that the semi-coordination analysis using IGM was carried out for a copper(ii) complex with axial elongation, finding a good correlation between the bond length and the IBSI, and the study was extended for a series of analogous complexes described in the literature.

Tuning the metal-ligand bond in the σ-complexes of stannylenes and azabenzenes

The metal-ligand bond in a set of 60 σ-complexes has been investigated by electronic structure computations. These σ-complexes originate from the unique combination of 12 stannylenes (SnX₂ ) with five azabenzene ligands (pyridine, pyrazine, pyrimidine, pyridazine, and s-triazine), where the nitrogen center of the ligand acts as σ-donor and the tin(II) center as σ-acceptor in a 1:1 fashion. The Sn ← N bond and the total interaction between the stannylene and azabenzene moieties of the σ-complexes are characterized in depth to relate the Sn ← N strength to the substitution pattern at SnX₂ and to the number and the positioning of N atoms in the azabenzenes. Such X substituents as (iso)cyano and trifluoromethyl groups enhance the interaction strength, while the presence of alkyl, phenyl, and silyl substituents in SnX₂ diminishes the stability of σ-complexes. A gradual weakening of the total interaction is associated with the growing number of N atoms in the azabenzenes, while the N-atom positioning in pyridazine is particularly effective in strengthening the interaction with stannylenes. Variations in the Sn ← N bond strength usually follow those in the total interaction between the moieties but the interacting quantum atoms picture of Sn ← N reveals certain intriguing exceptions.

Crystal structure of {tris((1H-benzo[d]imidazol-2- yl)methyl)amine-κ 4 N,N′,N′′,N′′′}-(succinato-κ 2 O,O′)nickel(II) – methanol (1/4), C32H41N7NiO8

C32H41N7NiO8, monoclinic, P21/c (no. 14), a = 10.0076(5) Å, b = 18.6561(10) Å, c = 19.0893(18) Å, β = 108.532(6)°, V = 3378.4(4) Å3, Z = 4, Rgt (F) = 0.0607, wRref (F 2) = 0.1340, T = 111.9(1) K.

The Role of Zinc(II) Ion in Fluorescence Tuning of Tridentate Pincers: A Review

Tridentate ligands are simple low-cost pincers, easy to synthetize, and able to guarantee stability to the derived complexes. On the other hand, due to its unique mix of structural and optical properties, zinc(II) ion is an excellent candidate to modulate the emission pattern as desired. The present work is an overview of selected articles about zinc(II) complexes showing a tuned fluorescence response with respect to their tridentate ligands. A classification of the tridentate pincers was carried out according to the binding donor atom groups, specifically nitrogen, oxygen, and sulfur donor atoms, and depending on the structure obtained upon coordination. Fluorescence properties of the ligands and the related complexes were compared and discussed both in solution and in the solid state, keeping an eye on possible applications.

Crystal structure of {tris((1H-benzo[d]imidazol-2-yl)methyl)amine-κ4 N,N′,N′′,N′′′}-(nitrito-κ2 O,O′)nickel(II) perchlorate – ethanol (1/1), C26H27ClN8NiO7

C26H27ClN8NiO7, triclinic, P1̄ (no. 2), a = 9.893(2) Å, b = 11.503(2) Å, c = 13.295(3) Å, α = 78.77(3)°, β = 70.52(3)°, γ = 83.40(3)°, V = 1397.0(6) Å3, Z = 2, R gt(F) = 0.0423, wR ref(F 2) = 0.1032, T = 153.15 K.

Crystal structure of (pyridine-2-carboxamide-κ2 N,O)-[tris((1H-benzo[d]imidazol-2-yl)methyl)amine-κ4 N,N′,N′′,N′′′]nickel(II) diperchlorate — methanol (1/3), C33H39Cl2N9NiO12

C33H39Cl2N9NiO12, monoclinic, P21/c (no. 14), a = 9.7478(4) Å, b = 20.6247(7) Å, c = 19.0897(11) Å, β = 92.767(5)°, V = 3833.4(3) Å3, Z = 4, R gt(F) = 0.0527, wR ref(F 2) = 0.1143, T = 108.4(2) K.

trans-Di-chlorido-bis-(dimethyl sulfoxide-κO)bis-(4-fluoro-benzyl-κC1)tin(IV): crystal structure and Hirshfeld surface analysis

The SnIV atom in the title diorganotin compound, [Sn(C7H6F)2Cl2(C2H6OS)2], is located on a centre of inversion, resulting in the C2Cl2O2 donor set having an all-trans disposition of like atoms. The coordination geometry approximates an octa-hedron. The crystal features C-H⋯F, C-H⋯Cl and C-H⋯π inter-actions, giving rise to a three-dimensional network. The respective influences of the Cl⋯H/H⋯Cl and F⋯H/H⋯F contacts to the mol-ecular packing are clearly evident from the analysis of the Hirshfeld surface.

A palladium-catalyzed synthesis of (hetero)aryl-substituted imidazoles from aryl halides, imines and carbon monoxide

We describe here a tandem catalytic route to prepare imidazoles in a single operation from aryl iodides, imines and CO. The reaction involves a catalytic carbonylation of aryl halides with imines to form 1,3-dipoles, which undergo spontaneous 1,3-dipolar cycloaddition. Overall, this offers an alternative to coupling reactions to construct the (hetero)aryl-imidazole motif, where variation of the building blocks can allow the synthesis of broad families of imidazoles with independent control of all substituents.

Crystal structure of metronidazolium tetra-chlorido-aurate(III)

Metronidazole (MET) [systematic names: 1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazole and 2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethanol] is a medication that is used to treat infections from a variety of anaerobic organisms. As with other imidazole derivatives, metronidazole is also susceptible to protonation. However, there are few reports of the structures of metronidazolium derivatives. In the title compound, (C6H10N3O3)[AuCl4] [systematic name: 1-(2-hy-droxy-eth-yl)-2-methyl-5-nitro-1H-imidazol-3-ium tetra-chlorido-aur-ate(III)], the asymmetric unit consists of a metronidazolium cation, [H(MET)](+), and a tetra-chlorido-aurate(III) anion, [AuCl4](-), in which the Au(III) ion is in a slightly distorted square-planar coordination environment. In the cation, the nitro group is essentially coplanar with the imidazole ring, as indicated by an O N-C=C torsion angle of -0.2 (4)°, while the hy-droxy-ethyl group is in a coiled conformation, with an O(H)-C-C-N torsion angle of 62.3 (3)°. In the crystal, the anion and cation are linked by an inter-molecular O-H⋯Cl hydrogen bond. In addition, the N-H group of the metronidazolium ion serves as a hydrogen-bond donor to the O atom of the hy-droxy-ethyl group of a symmetry-related mol-ecule, leading to the formation of chains along [010].

Copper(II) complexes as catalyst for the aerobic oxidation of o-phenylenediamine to 2,3-diaminophenazine

Two new mononuclear copper(II) complexes [Cu (L) (NO3)2] (1) and [Cu (L) Br2] (2) where (L=bis(1-(pyridin-2-ylmethyl)-benzimidazol-2-ylmethyl)ether) are synthesized and characterized by single-crystal X-ray diffraction analysis, elemental analysis, UV-Visible, IR spectroscopy, EPR and cyclic voltammetry. The complexes exhibit different coordination structures; the E1/2 value of the complex (1) is found to be relatively more cathodic than that of complex (2). X-band EPR spectra at low temperature in DMF supports a tetragonally distorted complex (1) while complex (2) shows three different g values suggesting a rhombic geometry. These complexes were utilized as a catalyst for the aerobic oxidation of o-phenylenediamine to 2,3-diaminophenazine assisted by molecular oxygen. The initial rate of reaction is dependent on the concentration of Cu(II) complex as well as substrate, and was found to be higher for the nitrate bound complex, while presence of acetate anion acts as a mild inhibitor of the reaction, as it is likely to pick up protons generated during the course of reaction. The inhibition suggests that the generated protons are further required in another important catalytic step.

Development of a regioselective N-methylation of (benz)imidazoles providing the more sterically hindered isomer

An efficient and highly regioselective N-methylation of (NH)-(benz)imidazoles furnishing the sterically more hindered, less stable, and usually minor regioisomer has been developed. The methodology involves very mild reaction conditions and tolerates a wide range of functional groups.

Cytotoxic copper(II), cobalt(II), zinc(II), and nickel(II) coordination compounds of clotrimazole

Sixteen novel mononuclear Cu(II), Co(II), Zn(II), and Ni(II) complexes of the biologically active ligand clotrimazole (clotri) of the forms [M(clotri)(2)Cl(2)]·nH(2)O (1-4), [M(clotri)(2)Br(2)]·nH(2)O (5-7), [M(clotri)(3)Br(2)] (8), [M(clotri)(3)NO(3)]NO(3)·nH(2)O (9, 11), [M(clotri)(3)(NO(3))(2)]·nH(2)O (10), and [M(clotri)(3)(OH(2))(2)NO(3)]NO(3)·nH(2)O (12) were synthesized and fully characterized. Dinuclear [Cu(2)(clotri)(4)μ(2)-Cl(4)]·2H(2)O (1a) and [Cu(2)(clotri)(4)μ(2)-Br(2)]·2H(2)O (5b) as well as tetranuclear [Cu(4)(clotri)(4)μ(4)-Br(6)μ(4)-O] (5a) complexes were also isolated. Complexes 1-7, 9, and 11 present a tetrahedral geometry; complex 8 exhibits a pentacoordinated structure; complexes 1a, 10 and 12 an octahedral geometry. X-ray crystal structures of [Cu(clotri)(2)Cl(2)](1), [Cu(clotri)(2)(EtOH)Cl(2)](1·EtOH), [Zn(clotri)(2)Cl(2)] (3), [Zn(clotri)(2)Br(2)] (7), and [Cu(4)(clotri)(4)μ(4)-Br(6)μ(4)-O] (5a) were obtained. Complexes 1-12 were tested for cytotoxic activity against the human carcinoma cell lines HeLa (cervix-uterine), PC3 (prostate), and HCT-15 (colon) displaying IC(50) values <30 μM. Confocal microscopy and nuclear dying (DAPI) for complex 1 showed condensation of cromatin and nuclear membrane fragmentation. Immunocytochemical detection/expression of biomarkers suggests that complexes 1 and 9 induce cell death via apoptosis. TUNEL assay detected DNA fragmentation in HeLa cells, resulting from apoptotic signaling cascades induced by Cu(II) complexes 1 and 9. (1)H NMR studies of the Zn(II) complexes showed that they can bind to nucleotides.

Metronidazolium perchlorate

In the crystal structure of the title compound [systematic name: 1-(2-hy­droxy­eth­yl)-2-methyl-5-nitro-1H-imidazol-3-ium perchlorate], C₆H₁₀N₃O₃⁺·ClO₄⁻, the cations are linked by inter­molecular N—H⋯O hydrogen bonds into zigzag chains along the c axis. The cations and anions are connected by O—H⋯O and C—H⋯O hydrogen bonds. A weak intra­molecular C—H⋯O hydrogen bond is also observed.