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Thermal latent coordination compounds

The thermal degradation of imidazole and pyrazole adducts of metal acetates

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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.

Zusammenfassung

Komplexverbindungen des Typs M(HIm)2ac2 (HIm=Imidazol,ac=Acetat,M=Co, Ni, Cu) zeigen ein differenziertes thermisches Verhalten. Der thermische Abbau der Nickelverbindung erfolgt analog dem Ni(acac)2(HIm)2 [10] unter Freisetzung von Essigsäure und Bildung von Ni(Im)2. Der Kupferkomplex apaltet alle stickstoffhaltigen Liganden unter Ausbildung stabiler basischer Kupferacetate ab. Die Cobaltverbindung elininiert thermisch teilweise Essigsäure, sodaß stabile acetat- bzw. imidazolatverbrückte Species entstehen.

Die Pyrazol- bzw. die sterisch anspruchsvollen 3,5-Dimethylpyrazol-komplexe zeigen ein untereinander vergleichbares Verhalten, wobei in einem ersten Schritt jeweils Pyrazoliumacetat freigesetzt wird.

Die Kristalstruktur von Ni(HPz)4ac2 wurde durch Röntgenbeugung bestimmt: monoklin, Raumgruppe C2/c.

Die Verbindung besitzt ein ausgeprägtes Wasserstoffbrückensystem mit einem Wassermolekül als Zentrum zweier N−H...O−H...O-Brücken, wodurch der leichte Protonentransfer unter Abspaltung von Pyrazoliumacetat verständlich wird.

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Authors and Affiliations

  1. Institute of Inorganic and Analytical Chemistry, University, Jena

    M. Döring & W. Ludwig

  2. Max Planck Society, Working Group on ‘CO2 Chemistry’, Jena, Germany

    H. Görls

Authors
  1. M. Döring
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  2. W. Ludwig
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  3. H. Görls
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Döring, M., Ludwig, W. & Görls, H. Thermal latent coordination compounds. Journal of Thermal Analysis 42, 443–459 (1994). https://doi.org/10.1007/BF02548527

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