Peter Segľa

Synthesis, Crystal Structure, Spectroscopic Properties and Potential Biological Activities of Salicylate-Neocuproine Ternary Copper(II) Complexes

Mixed ligand copper(II) complexes containing derivatives of salicylic acid and heterocyclic ligands with nitrogen donor atoms have been the subject of various studies and reviews. In this paper, synthesis and characterization of the ternary copper(II) complexes of neocuproine (2,9-dimethyl-1,10-phenanthroline, Neo) and salicylate ligands (Sal) are reported. In addition, the crystal structures of ([Cu(H2O)(5-Cl-Sal)(Neo)] (1), [Cu(μ-Sal)(Neo)]2 (2), Cu2(μ-5-Cl-Sal)(5-Cl-HSal)2(Neo)2]·EtOH (3)) were determined. In order to compare structural and biological properties of the prepared complexes, spectroscopic and biological studies were performed. Results of X-ray diffraction show that prepared complexes form three types of crystal structures in a given system: monomeric, dimeric and dinuclear complex. The preliminary study on the DNA cleavage activity has shown that the complexes under study behave as the chemical nucleases in the presence of added hydrogen peroxide with slight differences in the activity (1 > 2 > 3). The complexes 1 and 2 exhibited nuclease activity itself indicating the interaction of complexes with the DNA. It has been proposed that the enhanced destructive effect of the complexes 1 and 2 on the DNA is a result of two possible mechanisms of action: (i) the conversion of closed circular DNA (form I) to the nicked DNA (form II) caused by the copper complex itself and (ii) damage of DNA by Reactive Oxygen Species (ROS)—products of the interaction of copper with hydrogen peroxide by means of Fenton reaction (hydroxyl radicals). Thus the biological activity of the prepared Cu(II) complexes containing derivatives of salicylic acid and phenanthroline molecules is substantiated by two independent mechanisms. While derivatives of salicylic acids in the coordination sphere of copper complexes are responsible for radical-scavenging activity (predominantly towards superoxide radical anion), the presence of chelating ligand 2,9-dimethyl-1,10-phenanthroline significantly enhances capability of Cu(II) complexes binding to DNA via intercalation.

Copper(II) and cobalt(II) hydroxypyridinecarboxylates: Synthesis, crystal structures, spectral and magnetic properties

Synthesis and characterization of six copper(II) and cobalt(II) octahedral complexes [M(6-OHpic)2(H2O)2] (6-OHpic is 6-hydroxypicolinato), [M(2-OHnic)2(H2O)2] (2-OHnic is 2-hydroxynicotinato), [Cu(6-OHnic)2(H2O)2] (6-OHnic is 6-hydroxynicotinato) as well as [Co(H2O)6](6-OHnic)2 are reported. Their characterization was carried out using elemental analysis, infrared, and magnetic measurements. Based on IR spectra, N,O-coordination of 6-OHpic (via the oxygen atom of the carboxyl group and the nitrogen atom of the pyridine ring), O,O-asymmetrically chelating coordination of the carboxyl groups as well as ionic coordination of 6-OHnic and chelating O,O-coordination (through the oxygen atom of the carboxyl group and the oxygen atom of the amide group) of keto(amide) tautomer of 2-OHnic were supposed. Moreover, crystal structures of 2-OHnicH and the complex [Co(2-OHnic)2(H2O)2]) were determined by X-ray single crystal structure analysis. The system of hydrogen bonds predominantly stabilizes the keto(amide) tautomer of both 2-hydroxynicotinic acid and 2-OHnic anion in the cobalt(II) complex. Intermolecular hydrogen bonds (between the oxygen atom of the amide group and the hydrogen atom of the NH group) interconnect two neighbouring molecules of 2-OHnicH forming dimers. Cobalt(II) in complex [Co(2-OHnic)2(H2O)2] has nearly a regular compressed tetragonal bipyramidal arrangement.

Synthesis, spectral and electrochemical study of coordination molecules Cu4OX6L4: 3-cyanopyridine Cu4OBrnCl(6−n)(3-CNpy)4 complexes

Seven new 3-cyanopyridine Cu4OBrnCl(6−n)(3-CNpy)4 (n = 0–6) complexes were prepared and studied by infrared spectra, electronic spectra, and cyclic voltammetry. Infrared spectra revealed a distortion of the tetrahedral Cu4O core to C2ν or C3ν symmetries and a donor-acceptor vibrational coupling with the in-plane pyridine ring bending within the O-Cu-(pyridine ring)CN system involving the π-back bonding between Cu(II) atoms and 3-CNpy ligands. Bands of the electronic spectra and half-wave potentials of the complexes are consistent with the weak donor and strong acceptor behaviour of the 3-CNpy ligands. The results were compared with analogous complexes of pyridine, 3-substituted and 4-substituted pyridine ligands.

catena-Poly[[bis­[2-(2,3-dimethyl­anilino)benzoato-κO]cadmium(II)]-di-μ-3-pyridylmethanol-κ2N:O;κ2O:N]

In the crystal structure of the title compound, [Cd(C15H14NO2)2(C6H7NO)2]n, the Cd atom displays a distorted octahedral geometry, including two pyridine N atoms and two hydroxyl O from four symmetry-related 3-pyridylmethanol (3-pyme) ligands and two carboxylate O atoms from mefenamate [2-(2,3-dimethylanilino)benzoate] anions. The Cd atoms are connected via the bridging 3-pyme ligands into chains, that extend in the a-axis direction. The Cd atom is located on a center of inversion, whereas the 3-pyme ligands and the mefenamate anions occupy general positions.

Different structural types of copper(II) furan- and thiophencarboxylates: X-ray structural, EPR, spectral and magnetic analyses

Synthesis and characterization of eight new complexes of various structural types are reported. With 5-nitro-2-furancarboxylic acid (5-NO2-2-fucH), two monomeric complexes, [Cu(5-NO2-2-fuc)2(H2O)2] (II) and [Cu(5-NO2-2-fuc)2(H2O)4] (III), as well as a dimeric complex with ethylnicotinate (Etnic), [Cu(5-NO2-2-fuc)2(Etnic)2]2 (V), were prepared. With other acids: 2,5-dimethyl-3-furancarboxylic acid (2,5-Me2-3-fucH), 2-thiophencarboxylic acid (2-tpcH), 3-methyl-2-thiophencarboxylic acid (3-Me-2-tpcH) or 5-methyl-2-thiophencarboxylic acid (5-Me-2-tpcH), only dimeric complexes [Cu(2,5-Me2-3-fuc)2(H2O)]2 (I), [Cu(2,5-Me2-3-fuc)2(Etnic)]2 (IV), [Cu(2-tpc)2(Etnic)]2 (VI), [Cu(3-Me-2-tpc)2(Etnic)]2 (VII) and Cu(5-Me-2-tpc)2(Etnic)]2 (VIII) have been synthesised. Characterizations of the complexes were based on elemental analysis and infrared, electronic, EPR and magnetic measurements. Moreover, complexes III, V, VII and VIII were also studied by X-ray structural analysis. Two structural types of dimeric complexes were observed differing in the number of carboxylate bridges. Most of the dinuclear complexes exhibit the common “paddle-wheel” structural motif while the molecular structure of V contains two pentacoordinated copper(II) ions bridged by two carboxylate groups of two 5-nitro-2-furancarboxylate ligands resulting in the intramolecular copper-copper distance of 4.4960(8) Å. Magnetic properties (monomeric EPR signal and isotropic exhchange constant (J of approximately 0 cm−1) of V confirmed a very weak magnetic interaction between copper centres.

trans-Diaqua­bis(ethyl­enediamine-κ2 N,N′)copper(II) bis[3-(3-pyrid­yl)propionate] dihydrate

The asymmetric unit of the title complex, [Cu(C2H8N2)2(H2O)2](C8H8NO2)2·2H2O, contains one anion, one half-cation and one water molecule. The CuII atom in the [Cu(en)2(H2O)2]2+ cation (en is ethylenediamine) lies on an inversion centre. The four N atoms of the en ligands in the equatorial plane around the CuII atom form a slightly distorted square-planar arrangement, while the slightly distorted Jahn–Teller octahedral coordination is completed by two water O atoms in axial positions. In the crystal structure, intra- and intermolecular N—H⋯O and O—H⋯O hydrogen bonds form a three-dimensional network.

trans-Tetra­aqua­bis[3-(3-pyrid­yl)acrylato-κN]cobalt(II)

The asymmetric unit of the title compound, [Co(C8H6NO2)2(H2O)4], contains one half-molecule. The CoII atom lies on an inversion centre and is coordinated by two N atoms of the pyridine rings of 3-(3-pyridyl)acrylate anions and four O atoms of water molecules in a distorted octahedral coordination geometry. In the crystal structure, intermolecular O—H⋯O hydrogen bonds link the molecules, forming a three-dimensional network.

Bis(chloro­acetato)-κ2O,O′;κO-methanol-κO-bis­(2-methyl­furo[3,2-c]pyridine-κN)copper(II)

In the title compound, [Cu(C2H2ClO2)2(C8H7NO)2(CH4O)], the Cu2+ ion has a highly distorted square-bipyramidal (4 + 1 + 1) coordination environment and is bonded to three carboxylate O atoms of two chloroacetate anions (monodentate and asymmetrically bidentate), two pyridine N atoms of 2-methylfuro[3,2-c]pyridine and one methanol O atom. There is an intramolecular O—H⋯O hydrogen bond. Intermolecular C—H⋯O hydrogen bonds result in the formation of a three-dimensional network and π–π stacking interactions [3.44–3.83 Å] are observed between symmetry-related rings of 2-methylfuro[3,2-c]pyridine. Further interactions in the crystal structure are a short Cl⋯Cl interaction [3.384 (2)Å] and C—H⋯π interactions between 2-methylfuro[3,2-c]pyridine rings.

Structural study and magnetic properties of copper(II) thiophene-2-carboxylate with 4-pyridinemethanol and isonicotinamide

The synthesis and characterization of [Cu(5-Me-2-tpc)2(4-pyme)2] (I), [Cu(3-Me-2-tpc)2(4-pyme)2] (II), [Cu(2-tpc)2(4-pyme)2] (III), [Cu(2-tpc)2(isonia)2(2-tpcH)] (IV), [Cu(5-Me-2-tpc)2(isonia)2(5-Me-2-tpcH)] (V), [Cu2(2-tpc)4(4-pyme)2] (VI), [Cu2(3-Me-2-tpc)4(isonia)2] (VII) (where 2-tpc is 2-thiophenecarboxylate, 3-Me-2-tpc is 3-methyl-2-thiophenecarboxylate, 5-Me-2-tpc is 5-methyl-2-thiophenecarboxylate and 4-pyme is 4-pyridinemethanol and isonia is isonicotinamide) are reported. The complexes under study were characterized by electronic, IR and EPR spectroscopy, magnetic susceptibility over the temperature range and X-ray structure analysis. Structural studies revealed a distorted tetragonal-bipyramidal environment around the copper ion for monomeric complexes I–V. The structure of dimeric complexes VI and VII consists of units of the known paddle-wheel dicopper(II) tetracarboxylates, which are made up of four thiophene-2-carboxylate ions thus bridging the two copper atoms. The complex molecules of all compounds are connected through H-bonds into supramolecular chains or frameworks. The spectral and magnetic properties are discussed with regard to X-ray data.

XXVI. International Conference on Coordination Chemistry (26th ICCBiC), June 2017, Slovakia

The XXVI. International Conference on Coordination and Bioinorganic Chemistry (ICCBiC) was held from June 4 to June 9, 2017, in the Smolenice Castle, Slovakia. The conference was organized by the Slovak Chemical Society, the Slovak Academy of Sciences, and Slovak University of Technology in Bratislava. The founder of the traditional ICCBIC conferences in 1964 was Prof. Ing. Ján Gažo, DrSc. (1929–1983) and in his honour the organizing committee of the ICCBIC suggested and the Slovak Chemical Society established the “Ján Gažo Award”, consisting of the “Ján Gažo Medal” and the certificate of the Slovak Chemical Society in the form of a diploma. The first medal was awarded to Prof. Ing. Gregor Ondrejovič, DrSc. at the official opening ceremony of the conference, on June 4, 2017. After the sudden death of Prof. Gažo in 1983, Prof. Ondrejovič continued to organize regular conferences with his colleagues from the Department of Inorganic Chemistry, STU, in 1983–2000. This year, 72 scientists from abroad and 38 scientists from Slovakia participated in the conference; geographically, 22 countries from four continents were represented. Active participation of 43 colleagues younger than 35 years is a clear sign of the challenging future of both coordination chemistry and the series of ICCBiC. The participants have