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  • 1
    ISSN: 0044-2313
    Keywords: Bis(1, 3-diketonato)cobalt-bisimidazoles ; crystal structure ; thermal degradation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Structure and Thermal Degradation of Bis(1,3-diketonato)cobaltbisimidazolesThe crystal structure of Co(bzac)2(HIm)2. 2MeOH (I) and Co(acac)2(HIm)2 (II) were determined by x-ray diffraction. II: triclinic, space group P1, Z = 2, a = 746.3(1), b = 948.2(1), c = 1396.7(2)pm, α = 85.18(1)°, β = 88.96(1)°, γ = 80.72(1)°, R = 3.0% for a total of 2194 observed reflections. I: monoclinic, P21/c, Z = 2, a = 964.2(3), b = 864.5(2), c = 1769.8(4)pm, β = 98.87(2)°, R = 4.7% for a total of 967 observed reflections. In both compounds centrosymmetric molecules with two bidentate diketonato groups and two imidazole ligands in trans-position are present. The molecules of II are linked by N—H…O-bridges within layers, while in the lattice of I by the interaction with methanol molecules N-H…O-H…O-bridges are formed.The nature of the H-bridges is the deciding factor for the first step of the thermal degradation of the complexes. The N-H…O-bridges of II relieves the change of the acidic protons of the imidazole to the acetylacetonato ligands. Therefore in the first step acetylacetone is eliminated. No such bridges are present in the complex I. Therefore, in the first step, imidazole and methanol are removed. On heating in O-donor solvents the reaction of I is quite analogous, and this is the reason for the application of this complex as a latent initiator of the epoxide polymerisation.
    Notes: Die Kristallstrukturen von Co(bzac)2(HIm)2 · 2MeOH (I) und Co(acac)2(HIm)2 (II) wurden durch Röntgenbeugung bestimmt. II: triklin, Raumgruppe P1, Z = 2, a = 746,3(1), b = 948,2(1) c = 1396,7(2)pm, α = 85,18(1)°, β = 88,96(1)°, γ = 80, 72(1)°, R = 3,0% fur 2194 beobachtete Reflexe; I: monoklin, P21/c, Z = 2, a = 964,2(3), b = 864,5(2), c = 1769,8(4)pm, β = 98,87(2)°, R = 4,7% für 967 Reflexe. In beiden Verbindungen liegen zentrosymmetrische Moleküle vor mit jeweils zwei chelatartig gebundenen Diketonatgruppen und zwei transständigen Imidazol-Liganden. Bei II sind die Moleküle über N—H…O-Brücken zu Schichten miteinander verknüpft, während bei I eine Verkettung über die Methanol-Moleküle mit N—H…O…H…O-Brücken vorliegt. Die Art der H-Brücken ist maßgebend für den ersten Schritt des thermischen Abbaus der Komplexe. Die N—H…O-Brücken von II erleichtern den Übergang der aciden Protonen der Imidazol- auf die Acetylacetonatoliganden. Im ersten Schritt wird daher Acetylaceton abgespalten. Dem Komplex I fehlen solche Brücken, deshalb werden im ersten Schritt Imidazol und Methanol eliminiert. Ganz analog verhält sich I beim Erhitzen in O-Donatorlösungsmitteln (Alkohole, Epoxide). I ist daher als latenter Initiator fur die Polymerisierung von Epoxiden geeignet.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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