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Thermal latent coordination compounds

The thermal degradation of imidazole and pyrazole adducts of metal acetates

Journal of Thermal Analysis and Calorimetry
Authors: M. Döring, W. Ludwig and H. Görls

Abstract  

The thermal behaviour of complexes of the type M(HIm)2ac2 (HIm=imidazole,ac=acetate,M=Co, Ni, Cu) is different. Comparable to the thermal degradation of Ni(acac)2(HIm)2 [10] the Ni(HIm)2ac2 loss acetic acid by formation of Ni(Im)2. All nitrogen ligands are splitt off from the copper complex by formation of stable basic copper acetate. The cobalt compound eliminated acetic acid partially while acetate and imidazolate bridging species are obtained. The thermal behaviour of the acetate complexes of pyrazole and the bulky 3,5-dimethylpyrazole is quite similar. In a first step pyrazoliumacetate is removed. The crystal structure of Ni(HPz)4ac2 is determined by X-ray diffraction: monocline, space group C 2/c. The water molecule represents the centre of two N−H...O−H...O-bridges. The system of H-bridges in the compound relieves the proton transfer, indicated by the elimination of pyrazolium acetate.

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Thermal latent coordination compounds

II. The thermal degradation of imidazole and pyrazole adducts of metal(II) picolinate and quinaldinate

Journal of Thermal Analysis and Calorimetry
Authors: M. Döring, J. Wuckelt, W. Ludwig and H. Görls

Abstract  

Complexes of the type M(Pa)2(HAz)2 and M(QA)2(HAz)2 (M=cobalt(II) and nickel(II); HPa=picolinic acid, HQa=quinaldic acid; HAz=azoles like imidazole (Him), pyrazole (HPz), benzimidazole (HBzIm) etc.) show a similar thermal behaviour. In the first step of decomposition the corresponding azolinium picolinates or quinaldinates (H2AzPa, H2AzQa) are split off with formation of polymeric mixed ligand complexes M(Pa)(Az) or M(Qa)(Az). X-ray analysis of Co(Qa)2(HBzIm)2 XIIIa illustrates a proton transfer and a subsequent thermal removal of benzimidazolinium quinaldinate (H2BzImQa): Hydrogen bridges from pyrrole nitrogen of the benzimidazole to the non-coordinated oxygen of the quinaldinate predetermine the thermal initiated proton transfer. The high volatility of the heterocyclic acids and the nitrogen coordination are responsible for the formation of the mixed ligand complex Co(Qa)(BzIm) XIVa. Exceptions are the complexes M(Pa)2(HPz)2 XIa-b and M(Qa)2(HIm)2 XVIIa-b. Pyrazole is eliminated from the complexes XIa-b with formation of the solvent-free inner complex M(Pa)2 XIIa-b. From compounds XVIIIa-b quinaldic acid or their decomposition products are split off and a high temperature modification of M(Im)2 XVIIIa-b is formed at elevated temperature. XVIIIa-b are decomposed to the cyanides M(CN)2 similarly to the thermal behaviour of Cu(Im). In the first step the thermal degradation of imidazole and pyrazole adducts of copper(II) picolinates and quinaldinates is characterized by the elimination of azoles. The reason for this thermal behaviour is the weaker coordination of the azole heterocycles in copper chelate compounds.

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Journal of Thermal Analysis and Calorimetry
Authors: W. Ludwig, M. Döring, R. Fischer, A. Friedrich, W. Seidel, E. Uhlig and D. Walther
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Abstract  

Co-authorship analyses are both difficult to perform and interpret. We have devised a new way of calculating and representing hierarchical author networks that depict relationships among authors in a more exhaustive and less equivocal manner than most available automatic analyses. Any structure, however complex, can be broken down into independent subclusters of authors that can be represented as individual interconnected networks. We illustrate our approach by analysing the authors of publications giving the European Molecular Biology Laboratory (EMBL) as an affiliation in 1994 (from the ISI 1994 CD-ROM). The networks can be interpreted by referring to the official EMBL staff list (Annual Report 1993) and, in terms of research topics, by consulting the article titles and abstracts. In this respect, correspondence analyses of the author-publication matrices—that are the counterparts of the author-author matrices—prove extremely useful in structuring the thematic information. In fact, both methods—the hierarchical author networks and the correspondence analysis biplots—mutually enrich each other and provide a global picture of the inherent structure and interests of the EMBL as given by their 1994 publications.

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