10.1021/cm0350434.s001
Gareth R. Williams
Gareth R.
Williams
Alexander J. Norquist
Alexander J.
Norquist
Dermot O'Hare
Dermot
O'Hare
Time-Resolved, In Situ X-ray Diffraction Studies of
Staging during Phosphonic Acid Intercalation into
[LiAl<sub>2</sub>(OH)<sub>6</sub>]Cl·H<sub>2</sub>O
American Chemical Society
2004
BPA anions intercalate
MePO 3 H
LiAl 2
OH
dianionic guest anions
LDH
EPA
MPA
methylphosphonic acid
31 P chemical shift
NMR
Cl
PPA
dianionic species
2004-03-23 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Time_Resolved_In_Situ_X_ray_Diffraction_Studies_of_Staging_during_Phosphonic_Acid_Intercalation_into_LiAl_sub_2_sub_OH_sub_6_sub_Cl_H_sub_2_sub_O/3345460
Intercalation of a range of phosphonic acids into [LiAl<sub>2</sub>(OH)<sub>6</sub>]Cl·H<sub>2</sub>O at pH 8 leads to co-intercalation of both mono- and dianionic guest anions. Solid-state <sup>31</sup>P NMR data can be
used to show that these materials exhibit a <sup>31</sup>P chemical shift that is intermediate between
the values for the monoanionic and dianionic forms of the respective acids, suggesting that
rapid proton exchange occurs between the intercalated anions. It is possible to calculate the
relative amounts of mono- and dianionic species present using the observed averaged
chemical shift of the intercalate phase. In the case of methylphosphonic acid, the ratio of
mono- and dianionic species (MePO<sub>3</sub>H<sup>-</sup>/MePO<sub>3</sub><sup>2-</sup>) is estimated to be 2.1. The intercalation
of methyl-, ethyl-, phenyl-, and benzylphosphonic acids into [LiAl<sub>2</sub>(OH)<sub>6</sub>]Cl·H<sub>2</sub>O was studied
using time-resolved, in situ energy-dispersive synchrotron X-ray diffraction. The rates of
intercalation are significantly greater for methylphosphonic acid (MPA), ethylphosphonic
acid (EPA), and benzylphosphonic acid (BPA) than for phenylphosphonic acid (PPA). The
large BPA anions intercalate the most quickly, and MPA reacts more rapidly than EPA.
Kinetic analyses of the rate data suggest that these are diffusion-controlled reactions. In
situ X-ray diffraction experiments performed with slow addition of the guest have allowed
observation of intermediate crystalline phases during the reactions with MPA and BPA.
The intermediate phases can be indexed assuming a second-stage intercalation compound
in which alternate interlayer regions are occupied by phosphonic acid and Cl<sup>-</sup> anions,
respectively (Williams et al. <i>Chem. Commun.</i> <b>2003</b>, 1816). The observation of these second-stage intermediates is very surprising, because staging in rigid layer lattices such as layered
double hydroxides (LDHs) is highly unusual.