Željko K. Jaćimović

Reaction of copper(II) with 1-carboxamide-3,5-dimethylpyrazole, 1-carboxamidine-3,5-dimethylpyrazole, 4-acetyl-3-amino-5-methylpyrazole and 5-amino-4-carboxamide-1-phenylpyrazole ☆

Abstract Complex formation of copper(II) bromide and acetate with 1-carboxamide-3,5-dimethylpyrazole (HL3) and copper(II) bromide with 5-amino-4-carboxamide-1-phenylpyrazole (L2), 4-acetyl-3-amino-5-methylpyrazole (HL4) and 1-carboxamidine-3,5-dimethylpyrazole (HL5), was studied. The obtained compounds, CuBr2(L2)2, Cu(L3)2, CuBr2(HL4)2, CuBr2(HL5)2 and [CuBr(HL1)(L3)]2 (HL1 denotes the 3,5-dimethylpyrazole), are characterized by elemental analysis, FT-IR spectrometry, molar conductivity, TG-MS and DSC. The X-ray structure of [CuBr(HL1)(L3)]2 and Cu(L3)2 is discussed. For [CuBr(HL1)(L3)]2 a dimeric penta-co-ordinated structure has been found; the co-ordination around the metal in Cu(L3)2 is trans-square planar. To CuBr2(L2)2 and CuBr2(HL4)2 a nearly tetrahedral, while for CuBr2(HL5)2 an octahedral geometry may be assumed. It means that the geometry of the compounds in the first place depends on the ligand substituents. The course of the complex formation reaction is anion-dependent and may be explained on the basis of Pearsons theory, taking into account the steric factors. A low stability intermediate formation was observed in the thermal decomposition of Cu(L3)2.

Structural, spectroscopic and computational studies of the HgL2Cl2 complex (L = 3,5-dimethyl-1-thiocarboxamide pyrazole) and the crystal structure of L

In the present paper we report the synthesis as well as the structural and vibrational characterisation of the HgL2Cl2 complex (L = 3,5-dimethyl-1-thiocarboxamide). The crystal and molecular structures of both L and the HgL2Cl2 complex were determined by single-crystal X-ray diffraction. The coordination propensity of L to HgCl2 was explored by quantum chemical calculations. We found the preference of the monodentate coordination of L to HgCl2 through the sulfur atom (instead of the “pyridine” nitrogen) to be in agreement with Pearson’s acid–base character of the atoms involved and the steric effects. The vibrational properties of HgL2Cl2 were evaluated by a joint FT-IR and quantum chemical analysis. In addition, the thermal decomposition of the complex and ligand is reported.

Transition Metal Complexes with Pyrazole-Based Ligands 7. Zn(II), Co(II), Mn(II) and Cu(II) complexes with 3-amino-5-methylpyrazole

Complexes represented by the general formula [MCl2L2] (M(II)=Zn, Mn, Co) and complexes of [Cu3Cl6L4] and CuSO4L2·4H2O, CoSO4L2·3H2O, [ZnSO4L3] where L stands for 3-amino-5-methylpyrazole were prepared. The complexes were characterized by elemental analysis, FT-IR spectroscopy, thermal (TG, DTG, DSC and EGA) methods and molar conductivity measurements. Except for the Zn-complexes, the magnetic susceptibilities were also determined.Thermal decomposition of the sulphato complexes of copper(II) and cobalt(II) and the chloro complexes of cobalt(II) and manganese(II) resulted in well-defined intermediates. On the basis of the IR spectra and elemental analysis data of the intermediates a decomposition scheme is proposed.

TRANSITION METAL COMPLEXES WITH PYRAZOLE-BASED LIGANDS Part 21. Thermal decomposition of copper and cobalt halide complexes with 3,5-dimethyl-1-thiocarboxamidepyrazole

The thermal decomposition of Cu2L2Cl4 ,C u 2L2Cl2 ,C u 2L2Br2 and Co2L2Cl4 complexes (L=3,5-dimethyl-1-thiocarboxamidepyrazole) is described. The influence of the central ion to ligand mole ratio on the course of complex formation is examined in reaction of L with copper(II) chloride. In Cu(II):L mole ratio of 1:1, in methanolic solution the reaction yields to yellow-green Cu2L2Cl4 crystals. In the filtrate a thermodynamically more stable orange Cu2L2Cl2 copper(I) complex is forming. With a Cu(II):L mole ratio of 1:2 only the latter compound is obtained. The composition and the structure of the compounds have been determined on the basis of customary methods. On the basis of FTIR spectrum of the intermediate which is forming during the thermal decomposition of Cu2L2Cl2 a decomposition mechanism is proposed.

Environmental status and geochemical assessment sediments of Lake Skadar, Montenegro

The environmental mobility and geochemical partitioning of ten metals were examined in sediments collected from the six locations around Lake Skadar in Montenegro. A three-step sequential extraction procedure was used to determine the distribution of the metals in various substrates of lacustrine sediments, and the concentrations were measured in the liquid extract by ICP-OES. The largest portion of the total amount of cadmium, strontium and manganese can be found in sediment bound to the hydrated iron and manganese oxides; cobalt, lead, copper and nickel in the oxidizable fraction and the highest portion of chromium, vanadium and zinc are in the residual fraction. The most mobilized and potentially mobile metals are strontium, cadmium and cobalt while the most immobilized metals are chromium, vanadium and zinc. Based on geochemical parameters, an assessment of sediment contamination by the investigated metals was performed and the results showed potential risks ranging from “no risk” to “low risk” to the environment.

Kinetics and mechanism of the substitution reactions of some monofunctional Pd(II) complexes with different nitrogen-donor heterocycles

Substitution reactions of five monofunctional Pd(II) complexes, [Pd(terpy)Cl]+ (terpy = 2,2′;6′,2″-terpyridine), [Pd(bpma)Cl]+ (bpma = bis(2-pyridylmethyl)amine), [Pd(dien)Cl]+ (dien = diethylenetriamine or 1,5-diamino-3-azapentane), [Pd(Me4dien)Cl]+ (Me4dien = 1,1,7,7-tetramethyldiethylenetriamine), and [Pd(Et4dien)Cl]+ (Et4dien = 1,1,7,7-tetraethyldiethylenetriamine), with unsaturated N-heterocycles such as 3-amino-4-iodo-pyrazole (pzI), 5-amino-4-bromo-3-methyl-pyrazole (pzBr), 1,2,4-triazole, pyrazole, pyrazine, and imidazole were investigated in aqueous 0.10 M NaClO4 in the presence of 10 mM NaCl using variable-temperature stopped-flow spectrophotometry. The second-order rate constants k2 indicate that the reactivity of the Pd(II) complexes decrease in the order [Pd(terpy)Cl]+ > [Pd(bpma)Cl]+ > [Pd(dien)Cl]+ > [Pd(Me4dien)Cl]+ > [Pd(Et4dien)Cl]+. The most reactive nucleophile of the heterocycles is pyrazine, while the slowest reactivity is with pyrazole. Activation parameters were determined for all reactions and negative entropies of activation, ΔS≠, supporting an associative mode of substitution. The reactions between [Pd(bpma)Cl]+ and 1,2,4-triazole, pzI, and pzBr were also investigated by 1H NMR to define the manner of coordination. These results could be useful for better explanation of structure-reactivity relationships of Pd(II) complexes as well as for the prediction of potential targets of Pd(II) complexes toward common N-heterocycles, constituents of biomolecules and different N-bonding pharmaceutical agents. Substitution reactions of five monofunctional Pd(II) complexes with unsaturated N-heterocycles were investigated using variable-temperature stopped-flow spectrophotometry and 1H NMR. The results are useful for better explanation of structure-reactivity relationship of Pd(II) complexes as well as for prediction of potential targets of Pd(II) complexes toward common N-heterocycles, constituents of biomolecules and different N-bonding pharmaceutical agents.

Kinetics and mechanism of the substitution reactions of some monofunctional Pt(II) complexes with heterocyclic nitrogen donor molecules. Crystal structure of [Pt(bpma)(pzBr)]Cl2·2H2O

Abstract Substitution reactions of [Pt(terpy)Cl]+ (terpy = 2,2′;6′,2′′-terpyridine), [Pt(bpma)Cl]+ (bpma = bis(2-pyridylmethyl)amine), [Pt(dien)Cl]+ (dien = diethylenetriamine or 1,5-diamino-3-azapentane) and [Pt(tpdm)Cl]+ (tpdm = tripyridinedimethane) with nitrogen donor heterocyclic molecules, such as 3-amino-4-iodo-pyrazole (pzI), 5-amino-4-bromo-3-methyl-pyrazole (pzBr) and imidazole (Im), were studied in aqueous 0.10 M NaClO4 in the presence of 10 mM NaCl using variable-temperature UV–vis spectrophotometry. The second-order rate constants k2 indicate decrease in reactivity in the order [Pt(terpy)Cl]+ > [Pt(bpma)Cl]+ > [Pt(tpdm)Cl]+ > [Pt(dien)Cl]+. The most reactive nucleophile among the heterocyclic compounds is imidazole, while pzI shows slightly higher reactivity than pzBr. Activation parameters were also determined and the negative values for entropies of activation, ΔS≠, support an associative mode of substitution for all substitution processes. Crystal structure of [Pt(bpma)(pzBr)]Cl2·2H2O was determined by single-crystal X-ray analysis. The coordination geometry of the complex is distorted square-planar while the bond distance Pt–N2(pzBr) is longer than the other three Pt–N distances.

Functionalization of plasmonic metamaterials utilizing metal–organic framework thin films

We considered theoretically and experimentally a strategy to functionalize plasmonic metamaterials utilizing either a metal–organic framework (MOF) or inorganic–organic hybrids for application in adsorption-based gas sensing. MOFs are one-dimensional (1D), 2D or 3D crystalline compounds that simultaneously contain metal ions or ion clusters and organic moieties, forming thus porous networks ensuring an increased effective surface for adsorption. Metamaterials can enhance plasmonic sensor performance through metal–dielectric nanocompositing that simultaneously tailors the electromagnetic response and boosts adsorption of the targeted analyte through the use of nanopores. To perform functionalization, it is necessary to integrate one or several layers of MOF nanocrystals with the metamaterial scaffold. The simplest approach is to use dip or drop coating or the layer-by-layer technique. The scaffolds that we considered included freestanding, ultrathin membranes and sandwich structures with nanoaperture arrays. For this investigation, we used a non-aqueous sol–gel route to synthesize vanadium oxyanthracene carboxylate, a novel material with 1D crystal structure. Our results suggest that preferential concentration of analyte within the MOF pores may ensure improved adsorption and thus sensor sensitivity enhancement. Also, one may increase selectivity by introducing nanoparticle fillers or by utilizing other functionalizing materials such as catalysts or ligands.

Synthesis and characterization of copper, nickel, cobalt, zinc complexes with 4-nitro-3-pyrazolecarboxylic acid ligand

In the continuation of our systematic research of pyrazole coordination compounds, complexes of Cu(II), Ni(II), Co(II) and Zn(II) with 4-nitro-3-pyrazolecarboxylic acid ligand (L) were synthesized in the reaction of warm ethanolic solutions of the ligand and CuCl2·2H2O, Ni(CH3COO)2, CoCl2·6H2O and Zn(CH3COO)2, mixed in the metal-to-ligand ratio of 1:2. As the compounds could not be obtained in the form suitable for single-crystal structure analysis, their bis(ligand) structures, ML2 (M = CuII, NiII, CoII and ZnII) were proposed on the basis of elemental analysis, IR spectrometry, conductometric and TG–MS measurements. The low conductivity of the compounds additionally supports the deprotonation of the ligand and the formation of neutral complexes. The solvent content was calculated using the thermogravimetric (TG) data. According to TG data, the copper(II) compound crystallizes with 8 while nickel(II) complex with 4 water molecules, CuL2·8H2O, NiL2·4H2O. Complexes of Co(II) and Zn(II) contain 1 and 1.5 water molecules. Despite the differences in solvation properties, the high similarity in the course of the decomposition refers to the similar coordination mode of the organic ligand. The crystal and molecular structures of HL·H2O and NH4[LHL] were determined by single-crystal X-ray structure analysis. Biological research based on determining the inhibition effect of commercial fungicide Cabrio top, ligand, and all newly synthesized complexes on Ph. viticola has been carried out using the phytosanitary method.

Crystal structure of 4-bromo-2-(1H-pyrazol-3-yl)phenol, C9H7BrN2O

Abstract C9H7BrN2O, triclinic, C2/c (no. 15), a = 16.255(3) Å, b = 4.4119(9) Å, c = 25.923(5) Å, β = 107.99(3)°, V = 1768.2(7) Å3, Z = 8, Rgt(F) = 0.0450, wRref(F2) = 0.0960, T = 150 K.