Showing papers by "Milan Melnik published in 2009"

Determination of intermolecular copper–copper distances from the EPR half-field transitions and their comparison with distances from X-ray structures: applications to copper(II) complexes with biologically important ligands

Abstract: An EPR method involving measurement of half-field transitions was applied to determine the intermolecular Cu–Cu distances in copper(II)-carboxylate complexes with biologically important ligands. The experimental powder EPR spectra are composed of allowed (ΔM S = ±1) transitions centered at ~3,200 Gauss and of weak intensity, nominally forbidden, half-field (ΔM S = ±2) peaks observable at ~1,600 Gauss. Values of the average interspin distance for each complex were determined from the ratios of integrated allowed and forbidden peak areas using each of several methods. The calculated interspin distances were correlated with the copper–copper distances experimentally obtained by X-ray crystallography. The distances determined from the EPR spectra agree well with the X-ray determined values when the crystallographic value for one member of a series is used to calibrate the series. Less satisfactory agreement is found when methods based on Cu-spin-label systems are used.

Structural and spectroscopic characterization of copper(II) tolfenamate complexes

Abstract: The synthesis and characterization of four new solid complexes, Cu(tolf)2L2 (tolf = tolfenamate, L = 2-pyridylmethanol (2-pyme), 3-pyridylmethanol (3-pyme), nicotinamide (na)) and Cu(tolf)2(dena)2(H2O)2 (dena = N,N-diethylnicotinamide) is reported. The composition and stereochemistry as well as the mode for ligand coordination have been determined by elemental analysis, IR, electronic and EPR spectra. The carboxyl group of the tolfenamate anion coordinates to the Cu(II) atom as an unidentate or as a chelating ligand. The EPR spectra of the powdered solids are consistent with spin S = ½. The crystal structure of Cu(tolf)2(dena)2(H2O)2 has been determined at 293 K. The Cu(II) atom has a tetragonal–bipyramidal arrangement (CuO4N2). The spectroscopic data indicate that each copper(II) atom in Cu(tolf)2L2 has a tetragonal–bipyramidal environment built up by bidentate unsymmetrically coordinate tolfenamates and unidentate N-donor atom ligands.

Distortion isomerism and plasticity of the coordination sphere of binuclear Cu(II) complexes: Crystal structure of the monoclinic isomer of [Cu2(2-bromopropionato)4(caffeine)2]

Abstract: The crystal and molecular structure of monoclinic [di(caffeine)tetrakis(2-bromopropionato)dicopper(II)] · 0.8 water was determined using direct methods and Fourier techniques. The complex crystallizes in space group C2/c and is dimeric with square pyramidal geometry at each copper(II) center. The Cu ··· Cu distance is 2.674(1) A. Experimental data are compared with those found in a similar triclinic [Cu2(2-bromopropionato)4(caffeine)2] complex. The isomers differ in the geometry of copper(II) and the inter-aromatic interaction of caffeine molecules. The correlation of Cu ··· Cu distances vs. apical Cu–O bond length for dimeric copper(II) carboxylate complexes were interpreted by the bond-valence model. Minimum lengths of apical Cu–O bond and Cu ··· Cu separation were predicted.

Synthesis, spectroscopic properties, crystal structure and biological activities of copper(II) 2-methylthionicotinate complexes with furopyridines

Abstract: The synthesis and characterization of six new 2-methylthionicotinate (2-MeSnic) copper(II) monomeric complexes [Cu(2-MeSnic)2L2] (L is furo[3,2-c]pyridine—fpy, 2-methylfuro[3,2-c]pyridine—Mefpy, 2,3-dimethylfuro[3,2-c]pyridine—Me2fpy or benzo[4,5]furo[3,2-c]pyridine—Bfp), [Cu(2-MeSnic)2(fpy)2(H2O)], as well as [Cu(2-MeSnic)2(CF3Phfpy)2(H2O)2] (CF3Phfpy is 2-(3-trifluoromethylphenyl)furo[3,2-c]pyridine) are reported. The characterizations were based on elemental analysis, infrared, electronic and EPR spectra. The crystal structure of one of the complexes has been determined. The CuII atoms of [Cu(2-MeSnic)2(fpy)2(H2O)] are six-coordinated in a highly distorted tetragonal–bipyramidal arrangement by two nitrogen atoms, one from each fpy, in trans-positions, by three oxygen atoms of the carboxyl groups of 2-MeSnic ligands (one monodentate, one asymmetrically bidentate), one axial position being occupied by the oxygen of a water molecule. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi. A comparison of the IC50 and MIC values has shown a decrease of inhibition activities of tested compounds in the order: [Cu(2-MeSnic)2(Bfp)2] > Bfp > [Cu(2-MeSnic)2(CF3Phfpy)2(H2O)2] > [Cu(2-MeSnic)2(Me2fpy)2] > CF3Phfpy > [Cu(2-MeSnic)2(Mefpy)2] > Me2fpy > [Cu(2-MeSnic)2(fpy)2(H2O)] > [Cu(2-MeSnic)2(H2O)]2 > Mefpy > fpy = 2-MeSnicH = CuSO4.

Structural Aspects of Cadmium(II) Complexes - Isomers

Abstract: The coordination chemistry of cadmium(II) covers wide fields, as shown by a survey covering the crystallographic and structural data of over 600 examples. About 8 % of those complexes exist as isomers and are summarised. Included are distortion (91.5 %), ligand isomerism (6.5 %), mixed isomerism (distortion and cis trans) (1 %) and polymerisation isomerism (1 %). These are discussed in terms of the coordination about the cadmium atom, and correlations are drawn between donor atom, bond lengths and interbond angles. Distortion isomers, differing only by degree of distortion in Cd L and L Cd L angles, are the most common. There are four (tetrahedrally), five (trigonal bipyramidally), six (pse.udo octahedrally), seven (pentagonal bipyramidally) and eight (dodecahedrally, hexagonal bipyramidally) coordinate cadmium(Il) atoms. Most common are pseudo octahedral. Noticeably, in the chemistry of zinc(II) only two types of isomerism were formed, namely distortion (96 %) and ligand isomerism (4 %).

Isomers of Organotin Compounds II. Di - to Polymeric Compounds

Abstract: The dito polymeric organotin compounds cover a wide field, as shown by a recent survey covering the crystallographic and structure data of almost six hundred examples. About 10 % of these compounds exist as isomers and are summarised in this review. Included are distortion (92 %), ligand, cis trans, and η mer isomerism. These are discussed in terms of the coordination about the tin atom, and correlations are drawn between donor atom, bond length and bond angles. Distortion isomers, differing only by degree of distortion in Sn L distances and L Sn L angles, are the most common. The tin atoms are found in the oxidation states, Sn, Sn2 and Sn.

Isomerism in the Chemistry of Organogermanium Compounds (Part II)

Abstract: The organogermanium chemistry covers huge fields, as shown by a survey covering the crystallographic and structural data of over four hundred and fifty examples. Over 10 percent of those compounds exist as distortion isomers (around 97 %) and ligand isomers (around 3 %). These are discussed in term of coordination around the Ge(II), Ge(IV) and Ge2 +3 atoms, and correlations are drawn between donor atoms, bond lengths and bond angles. Distortion isomers dif- fer by degree of distortion in Ge - L distances and L-Ge-L angles. Interestingly, in the chemistry germanium coordination complexes besides configuration isomers, also distortion isomers dominate.

Stereochemistry of Platinum Organometallics

Abstract: The organometallic chemistry of platinum covers a huge field, as shown by a recent survey covering the crys- tallographic and structural data of almost one thousand organometallic derivatives. About nine percent of those deriva- tives exist as isomers and are summarized in this review and include distortion (90 %), cis - trans (6%) and ligand isomer- ism (4%). These are discussed in terms of the coordination about the platinum atom, and correlations are drawn between donor atom, bond length and interbond angles, with attention to any trans - effect. Distortion isomers, differing only by degree of distortion in Pt-L bond lengths and L- Pt -L bond angles, are the most nu- merous. They are also spread over a wider range of oxidation states of platinum, (zero, +1, +2, +4, mixed valence +1 plus +2 and +2 plus +4), compared to cis-trans and ligand isomerism in which only +2 is found.

Distortion Isomerism in the Chemistry of Heterometallic Tin Clusters

Abstract: The heterometallic tin clusters cover a huge field, as shown by a recent survey covering the crystallographic and structural data of over six hundred examples. About 8 % of these clusters exist as isomers and are summarised in this review. The isomers are examples of distortion isomerism. These are discussed in terms of the coordination about the tin as well as heterometal atoms, and correlations are drawn between the donor atom, bond length and bond angles, with attention to distortion of the respective geometry. Distortion isomers, differing only by degree of distortion in M L and L M L angles, are the most common.