Milica Kosović

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.

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.

The crystal structure of ethyl 1-(4-nitrophenyl)-5-(trifluoromethyl)-1H-pyrazole-4-carboxylate, C13H10F3N3O4

Abstract C13H10F3N3O4, triclinic, P1̅ (no. 2), a = 7.0524(14) Å, b = 7.8044(16) Å, c = 12.954(3) Å, α = 97.93(3)°, β = 96.29(3)°, γ = 100.11(3)°, V = 688.6(3) Å3, Z = 2, Rgt(F) = 0.0478, wRref(F2) = 0.1140, T = 200 K.

In situCoIIoxidation upon coordination to the dithiocarbamate derivative

Dithiocarbamate derivatives, besides other industrial applications, are used for many years now as powerful fungicides and pesticides. [1] Complexes of Co(II) and Co(III) with our, previously reported, biologically active ligand, N,N-diacetato-N-dithiocarbamate (dadtc 3) (1) [ 2 ] were prepared and characterized by classical physico-chemical methods, with the aim of enhancing the already intriguing fungicidal activity of the ligand itself. Anionic Co(II) complex [Co2(H2dadtc)5] − (2), obtained by a simple addition of the acidic ligand solution to the aqueous solution of [Co(H2O)6]Cl2 at RT, undergoes, in presence of air, over several days, spontaneous Co(II) oxidation to the Co(III) state, followed by an overall chemical rearrangement, resulting in the formation of the molecular Co(III) complex 3. Complex 2 reveals a binuclear structure where two hexacoordinated cobalt(II) centres (CoA and CoB) are presumably doublebridged by two sulfur atoms from two ligand molecules. Remaining two sulfurs of these ligand molecules both coordinate the CoB centre. Its octahedral coordination sphere is completed by two sulfurs from the CSS group of the third ligand molecule. CoA is also bound to four sulfurs from remaining two ligand molecules. Formation of the anionic species (2) was undoubtly proven by MALDI TOFF analysis. Magnetic measurements revealed a strong antiferromagnetic coupling of two neighbouring paramagnetic Co(II) centres, suggesting the double bridged arrangement as described here and by others.[3] The elemental analysis is in a very good agreement with NH4 +