Transformations of Cobalt(II) Trifluoroacetates in 1,4-Dioxane: Solvent Effect on the Composition, Structure, and Crysta
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Transformations of Cobalt(II) Trifluoroacetates in 1,4-Dioxane: Solvent Effect on the Composition, Structure, and Crystal Packing of the Molecules M. A. Uvarovaa and S. E. Nefedova, * aKurnakov
Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow, 119991 Russia *е-mail: [email protected] Received February 25, 2020; revised March 26, 2020; accepted April 8, 2020
Abstract—The reaction of aqueous cobalt(II) acetate with trifluoroacetic acid in methanol affords complex [Co(OOCF3)2(OH2)4] (I). The same reaction in a methanol–benzene–dioxane mixture of solvents gives mononuclear complex [Co(OOCF3)2(OH2)6] ∙ O(CH2CH2)2O (II) in which the solvate dioxane molecule forms a single crystal by the formation of hydrogen bonds with coordinated water molecules. A similar reaction in pure dioxane affords trinuclear complex {Co3(OOСCF3)4(OH2)2(OOСCF3)2[O(CH2CH2)2O]2} ∙ 2HOOСCF3 ∙ 2O(CH2CH2)2O (III) containing both solvate and coordinated dioxane molecules. The crystallization of complex III from an isopropanol–dioxane mixture leads to complex [Co(OOСCF3)2(OH2)4] ∙ 2O(CH2CH2)2O (IV). The reaction of complex III with pyrazole (HРz) affords mononuclear complex [Co(OOСCF3)2(HРz)4] ∙ 2O(CH2CH2)2O (V). The reaction of complex I with HРz in methylene dichloride leads to mononuclear complex [Co(OOСCF3)2(HРz)4] (VI). The structures of coordination compounds I– VI are determined by X-ray diffraction analysis (СIF files CCDC nos. 1985667 (I), 1985666 (II), 1985671 (III), 1985670 (IV), 1985665 (V), and 1985669 (VI) at Т = 296(2) K and 1985668 (VI) at Т = 150(2) K). Keywords: cobalt(II) trifluoroacetates, 1,4-dioxane, isopropyl alcohol, structural phase transition, pyrazole, synthesis, X-ray diffraction analysis DOI: 10.1134/S1070328420090079
INTRODUCTION The knowledge of specific features of coordination modes and transformations of anions of the initial compounds and the solvent used for the reaction makes it possible to predict the compositions and structures of the formed coordination compounds [1, 2]. It is known that anions of strong acids (for example, trifluoromethanesulfonic or trifluoroacetic acid) can easily be displaced from the coordination sphere of the metal by solvents containing nucleophilic atoms such as acetonitrile, tetrahydrofuran, and dioxane liberating orbitals for the fixation of various donor molecules. 1,4-Dioxane used as a solvent has two oppositely lying nucleophilic centers and thus can act as a bridging ligand similarly to γ,γ'-bipyridine or pyrazine, which results in the formation of polynuclear complexes or coordination polymers [3–7]. It has recently been shown that coordination polymers [8–10] and difluorides of the corresponding metals during the thermal decomposition of Fe(OOC-
CF3)2(HOOCCF3)2, Mn2(OOCCF3)4(HOOCCF3)4, and Co(OOCCF3)2(H2O)4 [11] can be synthesized from 3d-transition metal trifluoroacetates. Note that the heterocyclic pyrazole molecule bearing the pyridinic nitrogen atom and pyrrole fragment capable
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