Showing papers by "Milan Melnik published in 1997"

Copper(ii) coordination compounds: classification and analysis of crystallographic and structural data ii. mononuclear-, hexa-, hepta-and octacoordinate compounds

Abstract: This review summarizes the data for over five hundred and fifty six-, seven- and eight-coordinate Cu(II) coordination compounds. The six-coordinate derivatives are mostly distorted tetragonal (elongation along a single C 4 axis). The seven-coordinate derivatives are only penta-gonal-bipyramidal with different degrees of distortion and the eight-coordinate complexes are dodecahedral. The most common ligands are O- and N-donors. There is a trend for the Cu-L distance to increase with covalent radius of the coordinated atom and also increasing coordination number. In general, Cu(II) compounds “prefer” a monoclinic class and are blue or green. Several relationships were found and discussed. The data are compared and discussed with those of four- and five-coordinate Cu(II) compounds.

Lead coordination and organometallic compounds: classification and analysis of crystallographic and structural data

Abstract: This review covers over three hundred and sixty coordination and organometallic complexes of lead. About 20% of these contain lead in its +4 oxidation state, of which one fifth are dilead(+6) units, and two are anionic clusters. The Pb(IV) derivatives are predominantly organometallic, many stabilized by sandwich ligation. The majority of the Pb(ll) compounds are typical coordination complexes. Monto polynuclear derivatives are found, with coordinations numbers from 2 to 12. The effect of the non bonded pair of valence electrons is observed in lower coordination number Pb(ll) complexes. Examples of distortion, geometric and coordination isomerism are observed. Factors affecting bond lengths and bond angles are discussed, and some ambiguities in coordination polyhedra are outlined.

Structural aspects of iron coordination compounds: i. monomeric derivatives

Abstract: This review summarises almost nine hundred crystallographic structures of monomelic iron coordination compounds. The number of examples per given oxidation state for the iron increases in the order: Fe(-II) (tetrahedral) < Fe(-I) (tetrahedral) < Fe(IV) (six coordinated and square pyramidal) < Fe(0) (five coordinated ) < Fe(I) (square pyramidal and square planar) < Fe(III) (three to seven coordinated) < Fe(II) (two to eight and ten coordinated). Variations and trends in bond lengths and angles are discussed.

1H NMR Ganglioside Ceramide Resonance Region on the Differential Diagnosis of Low and High Malignancy of Brain Gliomas

Abstract: 1. The high-resolution 1H NMR (MRS) spectra of human brain tumor homogenates revealed a broad resonance at 5.3-5.4 ppm in glioblastoma multiforme (N = 16) and brain metastases (N = 3). The broad resonance was identified as ceramide, a sphingosine-fatty acid combination portion of ganglioside, indicating an elevated abundance of monounsaturated fatty acids. GLC analysis of gangliosides in the highly malignant glioblastoma multiforme revealed that the elevated monounsaturated fatty acid is oleic acid (C18:1). The resonance at 5.3-5.4 ppm region was not detectable in normal human brain (N = 2), in meningiomas (N = 2), or in low-grade astrocytomas (N = 12). In normal human brain the abundance of monounsaturated fatty acid is minimal. 2. This investigation was made possible because the method of producing homogenate resulted in (i) no loss of lipids during the process and (ii) a well-homogenised sample, with (iii) no loss in chemical integrity. 3. The properties of tumor gangliosides include antigenic specificity and immunosuppressive activity and the ceramide, a sphingosine-fatty acid combination, noticeably influences the ganglioside immunosuppressive activity. 4. The observation of 1H NMR ceramide resonance in high-malignant brain tumors emphasizes the dramatic role of aberant gangliosides and ceramide precursors on the grade of malignancy and invasiveness. 5. Further insight into the specific nature of the ceramide portion of gangliosides in grading the malignancy of brain tumors should be investigated further.

Heterometallic lead coordination and organometallic compounds: classification and analysis of crystallographic and structural data

Abstract: This review covers the heterometallic complexes of lead, and is the first of three reviews. The other two are surveys of about two hundred oxo-acids and halides and nearly four hundred coordination complexes of lead. There are over sixty of heterometallic derivatives in which the heterometal atoms include both transition and non-transition metals, both hard (class A) and soft (class B). The bi-, triand pentanuclear derivatives exhibit the most examples, with tetra-, decaand polynuclear examples also occuring. Both Pb(ll) and Pb(IV) oxidation states are represented, and one decanuclear example with lead in an anionic cluster. The compounds include both organometallic and coordination complexation around the lead and heterometal atoms.

Lead oxyacids and halide compounds: classification and analysis of crystallographic and structural data

Abstract: This review is the last of three reviews covering the structures of lead compounds, and covers over two hundred lead oxoacids and halides, only fourteen of which have the lead atom in its +4 oxidation state. Only octahedral coordination is found for Pb(IV), but the coordination around Pb(ll) varies from trigonal to dodecahedral. Bond distances and interbond angles are correlated with covalent radii of the ligand atoms, and the effect of the non-bonded pair of valence electrons on Pb(ll) is discussed. There are examples of distortion and structural isomerism in these derivatives.

Organometallic and Carbonyl Compounds of Cadmium: Analysis of Crystallographic and Structural Data

Abstract: This review draws together the structural information presently available for almost 40 organocadmium and carbonyl derivatives. The cadmium oxidation state varies from 0 to +2. There is only one example of Cd(I), which is in a distorted tetrahedral environment. The oxidation state of +2 is most abundant, with Cd(II)found in digonal, trigonal planar, tetrahedral and five-coordinate (mostly trigonal-pyramidal) environments. The nuclearity ranges from one to seven, and one example each of nine and 13 metal atoms. Correlations are drawn between bond lengths and bond angles, and comparisons made with the corresponding zinc and mercury analogues.