Synthesis and properties of Zn-Al layered double hydroxides containing ferrocenecarboxylate anions

Zn-Al layered double hydroxides (LDHs) intercalated by ferrocenecarboxylate (FcCOO) and 1,1'-ferrocenedicarboxylate [Fc(COO)(2)] anions have been prepared by co-precipitation from aqueous solution. The Zn/Al ratio in the final materials was in the range of 1.8-1.9. Powder X-ray diffraction (XRD) indicates that the material Zn2Al-Fc(COO)(2) contains a monolayer of guest anions resulting in a basal spacing of 15.5 Angstrom. The material Zn2Al-FcCOO exhibits a basal spacing of 20.0 Angstrom, consistent with the formation of a bilayer of organometallic guest species. FTIR, FT Raman and C-13 MAS NMR spectroscopy confirm the presence of structurally intact ferrocenecarboxylate and 1,1'-ferrocenedicarboxylate anions. The nature of the Al centers in the samples was probed by 1- and 2-D (triple- quantum) Al-27 MAS NMR spectroscopy. Thermal properties were studied by thermogravimetric analysis and by measuring powder XRD patterns at increasing temperatures in the range of 25-450 degreesC. Up to 160 degreesC the materials lose interlayer water molecules. Dehydration of Zn2Al-Fc(COO)(2) prompts reorientation of the ferrocene guest anions, resulting in the formation of a collapsed phase with an interlayer separation of 12.3 Angstrom. The structural transformation is fully reversible upon hydration. Heat treatment of Zn2Al-FcCOO only resulted in a gradual contraction of the interlayer separation and not the formation of a collapsed phase. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.