Multinuclear solid-state nuclear magnetic resonance study of 2-aminoethylferrocene and its intercalation compounds with the layered host lattices MoO3 and α-Zr(HPO4)2H2O

Abstract

The isotopically labelled amino-functionalised ferrocene derivatives FcCH₂CH₂¹⁵NH₂ and Fc′CH₂CH₂NH₂[Fc = Fe(η-C₅H₅)(η-C₅H₄); Fc′= Fe(η-C₅D₅)(η-C₅D₄)] have been synthesized. Their hydrochloride salts and the lamellar intercalation compounds MoO₃(Fc′CH₂CH₂¹⁵NH₂)_0.36, and Zr(HPO₄)₂(Fc′CH₂CH₂¹⁵NH₂)_0.5(H₂O)_x(x= 0.1–0.5), have been studied by ²H, ¹⁵N and, in the last case, ³¹P solid-state NMR spectroscopy. ²H NMR lineshape analysis has probed aspects of molecular dynamical behaviour. The ²H NMR studies are consistent with rapid reorientation of the η-C₅D₅ ring about the Fe-ring centroid axis. The deuterons of the η-C₅D₄CH₂CH₂NH₂ moiety appear to be static on the ²H NMR timescale. Increased averaging of the lineshapes at higher temperatures is interpreted in terms of a rapid wobbling motion of the molecular pseudo-fivefold axis with near axial symmetry, and of progressively increasing amplitude with increase in temperature. Additionally, in the case of the hydrochloride salt and the MoO₃ intercalate, but not the Zr(HPO₄)₂H₂O intercalate, a vibration of the molecule in a plane perpendicular to the ferrocene molecular axis, in a manner whereby the molecules are ‘anchored’ at the substituent, is suggested.

The ¹⁵N CP/MAS NMR spectra reveal features of the host–guest bonding. The spectra of the intercalates are significantly different from those for FcCH₂CH₂¹⁵NH₂ and [FcCH₂CH₂¹⁵NH₃]⁺Cl^–. For MoO₃(FcCH₂CH₂¹⁵NH₂)_0.36 the ¹⁵N NMR shows two distinct environments for ¹⁵N within the layers. The major resonance is apparently intermediate between that for [FcCH₂CH₂¹⁵NH₃]⁺Cl^– and FcCH₂CH₂¹⁵NH₂, whilst the other minor resonance has been tentatively assigned to a species resulting from oxidation of the guest molecules during the intercalation reaction. The ¹⁵N and ³¹P CP/MAS NMR spectra of Zr(HPO₄)₂(FcCH₂CH₂^l5NH₂)_0.5(H₂O)_x(x= 0.1–0.5) support the hypothesis that the amine is interacting with the acidic layers through P-O ⋯ H-N hydrogen bonds.