Effect of the Nature of Haloacetic Acids on the Type of Morpholine Complexes Formed. Crystal Structure of the First Palladium Tetracarboxylate with Monocarboxylic Acid: Morpholinium Tetrakis(trifluoroacetato)palladate(II), (O(CH2CH2)2NH2)2[Pd(CF3COO)4]

Abstract

The effect of the nature of halogen-substituted carboxylic acids RCOOH, where R is ClCH₂, Cl₂CH, Cl₃C, or F₃C, on the complexation of palladium halocarboxylates with morpholine C₄H₉NO was investigated. Reactions with ClCH₂COOH and Cl₂CHCOOH gave binuclear complexes [(C₄H₉NO)₂Pd₂(μ-OOCR)₂(OOCR)₂] with palladium-coordinated morpholine, whereas reactions with Cl₃CCOOH and F₃CCOOH afforded the first tetra(halocarboxylate) palladium complexes with protonated morpholine as the cation, (C₄H₁₀NO)₂[Pd(RCOO)₄]. The acid–base balance of morpholine and halocarboxylic acid was the key factor determining the composition of the resulting complexes. For the formation of palladium tetra(halocarboxylates) with morpholine, the difference between the morpholine and acid pK_a values should be not lower than 7.63. X-ray diffraction studies were carried out for the first tetra(halocarboxylate) palladium complex with a monocarboxylic acid (C₄H₁₀NO)₂[Pd(OOCCF₃)₄ ∙ 2H₂O] (I) and for trans-[(C₄H₉NO)₂Pd(OOCCH₂Cl)₂ ∙ 2H₂O] (II), trans-[(C₄H₉NO)₂Pd(OOCCHCl₂)₂] (III), and trans-[(C₄H₉NO)₂Pd(OOCCF₃)₂ ∙ 2H₂O] (IV) (CIF files CCDC nos. 1008564, 1894300, 1008566, and 1894299, respectively).