Solid state 2H NMR study of the orientation and dynamics of cobaltocenium intercalated in the layered silicate LaponiteRD

Abstract

Ion-exchange intercalation of [Co(η-C ₅ D ₅ ) ₂ ] ⁺ ions in the smectite clay LaponiteRD [Na _0.46 Mg _5.42 Li _0.46 Si ₈ (OH) ₄ O ₂₀ ] yields [Mg _5.42 Li _0.46 Si ₈ (OH) ₄ O ₂₀ {Co(η-C ₅ D ₅ ) ₂ } _0.4 Na _0.1 ]. Structural and dynamic information about the material was obtained with the benefit of ² H NMR spectroscopic measurements, performed on powder and specially prepared oriented samples, combined with comparisons to ² H NMR lineshape simulations. The cobaltocenium cations adopt an ordered arrangement in the host lattice with their principal molecular axes parallel to the silicate layers. In addition to rotation about the principal molecular axis, previously observed for similar cobaltocenium layered intercalates, the emergence of an inner component with a splitting of 22.3 kHz over the temperature range 220-300 K strongly suggests the molecule is undergoing n-fold reorientations about the C ₂ axis of symmetry. Concurrent to this dynamic motion is an additional vibrational motion in and out of the plane parallel to the silicate layers. Coupled with rotation about the C ₂ axis, this gives rise to a gyratory motion in the slow-intermediate regime which increases with temperature until the fast regime is reached at 330 K.