Observation of staging during intercalation in layered α-cobalt hydroxides: A synthetic and kinetic study

Article abstract of DOI:10.1021/ic801639e

The anion-exchange reaction of the layered α-cobalt hydroxides Co(OH)_1.75(DDS)_0.25·0.6H₂O (1) and Co(OH)_1.7Cl_0.3·0.4H₂O (3) with carbonate has been investigated. For 3 the reaction proceeds by complete displacement of the interlayer Cl^- anions by CO₃^2- to give Co(OH)_1.7(CO₃)_0.15·0.6H₂O (4). Remarkably for 1 we only observe ion-exchange of the DDS^- from every other layer to give the second stage intercalate Co(OH)_1.75 (DDS)_0.07(CO₃)_0.09·0.5H₂O (2). The kinetics of these processes have been investigated using time-resolved in situ energy dispersive XRD and small/wide-angle X-ray scattering. In both cases the reaction order (n) was found to be consistent with a two-dimensional diffusion controlled model. Both 3 and 4 are magnetically ordered, and dc and ac magnetic susceptibility measurements have been used to explore their 3D ferrimagnetically ordered ground states.

Full text of DOI:10.1021/ic801639e

Inorg. Chem. 2008, 47, 11839-11846
Observation of Staging during Intercalation in Layered r-Cobalt
Hydroxides: A Synthetic and Kinetic Study
Yi Du and Dermot O’Hare*
Chemistry Research Laboratory, Department of Chemistry, UniVersity of Oxford, Mansfield Road,
Oxford, United Kingdom OX1 3TA
Received August 27, 2008
The anion-exchange reaction of the layered R-cobalt hydroxides Co(OH)1.75(DDS)0.25 · 0.6H2O (1) and
Co(OH)1.7Cl0.3 · 0.4H2O (3) with carbonate has been investigated. For 3 the reaction proceeds by complete
displacement of the interlayer Cl- anions by CO32- to give Co(OH)1.7(CO3)0.15 · 0.6H2O (4). Remarkably for 1 we
only observe ion-exchange of the DDS- from every other layer to give the second stage intercalate Co(OH)1.75
(DDS)0.07(CO3)0.09 · 0.5H2O (2). The kinetics of these processes have been investigated using time-resolved in situ
energy dispersive XRD and small/wide-angle X-ray scattering. In both cases the reaction order (n) was found to
be consistent with a two-dimensional diffusion controlled model. Both 3 and 4 are magnetically ordered, and dc
and ac magnetic susceptibility measurements have been used to explore their 3D ferrimagnetically ordered ground
states.
Introduction
stage intercalation compounds.3,4,9-13 Staging during the
intercalation of guest in a layered material describes a
phenomenon in which the interlayer galleries fill in a regular
periodicity.1,14 For example, combining the hydrophobic and
hydrophilic properties of organic and inorganic LDH inter-
calates in a single heterostructured phase will produce
amphiphilic materials,14 which may have novel ion-exchange
properties.5,7,9,15,16 For multiatom thick rigid layered hosts
such as metal oxides and hydroxides the observation of
staging is very rare, and so it is both noteworthy and
informative to discover new examples of staging for other
layered materials.
The development of novel syntheses of heterostructured
hybrid materials which combine both organic and inorganic
components offers the possibility of preparing new tunable
multifunctional materials.1,2 In this context, the preparation
of hybrid nanostructures based on hydrotalcite-like layered
hydroxides (LHs) has attracted much interest.1,3-10
Recently several groups have reported the synthesis of
ordered hybrid LHs nanostructures by the isolation of second
* To whom correspondence should be addressed. E-mail: dermot.ohare@
chem.ox.ac.uk. Fax: +44 1865 285131. Tel: +44 1865 285130.
(1) Taviot-Gueho, C.; Feng, Y. J.; Williams, G. R.; Leroux, F.; O’Hare,
D. Chem. Mater. 2006, 18 (18), 4312.
(2) Demessence, A.; Rogez, G.; Rabu, P. Chem. Mater. 2006, 18 (13),
3005.
(3) Iyi, N.; Fujii, K.; Okamoto, K.; Sasaki, T. Appl. Clay Sci. 2007, 35
(3-4), 218.
(4) Zhang, W.; He, J.; Guo, C. Appl. Clay Sci. 2008, 39 (3-4), 166.
(5) Williams, G. R.; O’Hare, D. J. Phys. Chem. B 2006, 110 (22), 10619.
(6) Liu, Z.; Ma, R.; Osada, M.; Iyi, N.; Ebina, Y.; Takada, K.; Sasaki, T.
J. Am. Chem. Soc. 2008, 128 (14), 4872.
Layered cobalt hydroxides are of major interest to both
chemists and physicists due primarily to the rich intercalation
chemistry combined with the unusual 3D magnetic ordering
exhibited by these materials.17-21 The complex and highly
(13) Taviot-Gue´hoa, C.; Leroux, F.; Payenb, C.; Bessea, J. P. Appl. Clay
Sci. 2005, 28 (1-4), 111.
(14) Ijdo, W. L.; Pinnavaia, T. J. Chem. Mater. 1999, 11 (11), 3227.
(15) Williams, G. R.; O’Hare, D. J. Mater. Chem. 2006, 16 (30), 3065.
(16) Williams, G. R.; Norquist, A. J.; O’Hare, D. Chem. Commun. 2003,
(15), 1816.
(7) Duan, X.; Evans, D. G. In Layered double Hydroxides. Structure &
Bonding; Mingos, D. M. P., Ed.; Springer: Berlin, 2005; Vol. 119.
(8) Carpani, I.; Berrettoni, M.; Giorgetti, M.; Tonelli, D. J. Phys. Chem.
B 2006, 110 (14), 7265.
(17) Ma, R.; Liu, Z.; Takada, K.; Fukuda, K.; Ebina, Y.; Bando, Y.; Sasaki,
T. Inorg. Chem. 2006, 45 (10), 3964.
(9) Williams, G. R.; O’Hare, D. Chem. Mater. 2005, 17 (10), 2632–2640.
(10) Iyi, N.; Kurashima, K.; Fujita, T. Chem. Mater. 2002, 14 (2), 583.
(11) Williams, G. R.; Norquist, A. J.; O’Hare, D. Chem. Mater. 2004, 16
(6), 975.
(12) Fogg, A. M.; Dunn, J. S.; O’Hare, D. Chem. Mater. 1998, 10 (1),
356.
(18) Liu, Z.; Ma, R.; Osada, M.; Takada, K.; Sasaki, T. J. Am. Chem. Soc.
2005, 127 (40), 13869.
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2003, 42 (21), 6709.
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10.1021/ic801639e CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 24, 2008 11839
Published on Web 11/14/2008

Du and O’Hare
Scheme 1. Schematic Representation of the Reaction of 1 with Carbonate
anisotropic magnetic exchange interactions that exist in these
materials can be tuned by the introduction of organic or
inorganic interlayer anions, and so this offers a possible route
to design, or electronic materials.19,21 However, very few
studies describing the intercalation chemistry of cobalt
hydroxides have been reported;18 furthermore, there have
been no previous kinetic studies of intercalation in these
materials. To date, only first stage intercalation compounds
of layered cobalt hydroxides have been reported.18 Consider-
ing the versatility of cobalt hydroxides as functional materi-
als, it is interesting to examine the kinetics of intercalation
of anions in cobalt hydroxides and where possible to identify
unusual staging intermediates.
In this paper we have investigated the anion-exchange
intercalation chemistry of the R-cobalt hydroxides,
Co(OH)1.75(DDS)0.25 ·0.6H2O (1) and Co(OH)1.7Cl0.3 ·0.4H2O
(3) with carbonate. To the best of our knowledge, it is the
first kinetic study of intercalation in R-cobalt hydroxides.
Both first and second staged products of R-cobalt hydroxides
have been characterized by elemental analysis (EA), FT-IR,
TGA, HRTEM, and SQUID magnetometry. The kinetics and
mechanism of the process have been investigated by means
of time-resolved, in situ energy dispersive X-ray diffraction
(EDXRD) experiments and small-angle X-ray scatter-
ing.5,15,22
Figure 1. TEM (left), HRTEM (top right), and SAED (left inset) images
of (A) 1 and (B) 2. Inset in (A, B) (bottom right) shows lattice fringes and
the corresponding scale bar.
Na2C12H25O4S (sodium dodecyl sulfate; NaDDS) (2.0 g)/NaCl (1.0
g), and HMT (2.0 g) under an ambient atmosphere as described by
the Sasaki group.17,18
Synthesis of Co(OH)1.75(DDS)0.07(CO3)0.09 ·0.5H2O; (2). A total
of 150 mg of 1 was suspended in 4 mL of 0.4 M sodium carbonate
solution and heated to between 60 and 120 °C.
Synthesis of Co(OH)1.7(CO3)0.15 ·0.6H2O (4). A total of 150 mg
of 3 was suspended in 4 mL of 2 M sodium carbonate solution
and heated to between 80 and 120 °C.
Experimental Section
Synthesis of Co(OH)1.75(DDS)0.25 ·0.6H2O (1) and Co(OH)1.7
Cl0.3 ·0.4H2O (3). Green R-cobalt hydroxides, Co(OH)1.75
(DDS)0.25 ·0.6H2O (1) and Co(OH)1.7Cl0.3 ·0.4H2O (3) were prepared
via homogeneous precipitation using hexamethylenetetramine (HMT)
as the hydrolysis agent.17,18,23 Typically, the synthesis was
performed from a dilute aqueous solution of CoCl2 ·6H2O (0.6 g),
Time-Resolved in Situ Energy-Dispersive X-ray Diffr-
action (EDXRD) Experiments. Experiments were carried out on
Station 16.4 of the U.K. Synchrotron Radiation Source at the
Daresbury Laboratory using an experimental setup reported else-
(21) Rabu, P.; Angelov, S.; Legoll, P.; Belaiche, M.; Drillon, M. Inorg.
Chem. 1993, 32, 2463.
(22) Khan, A. I.; O’Hare, D. J. Mater. Chem. 2002, 12 (11), 3191.
(23) Du, Y.; O’Hare, D. J. Phys. Chem. Solids 2008, 69 (5-6), 1040.
11840 Inorganic Chemistry, Vol. 47, No. 24, 2008

Staging during Intercalation in Layered r-Cobalt Hydroxides
Results
Intercalation of CO32- in Co(OH)1.75(DDS)0.25 ·0.6H2O
(1). Addition of an excess of Na2CO3 to the R-cobalt
hydroxide Co(OH)1.75(DDS)0.25 · 0.6H2O (1) in water at 100
°C leads to the isolation of a phase pure carbonate ion-
exchanged product. However, rather than forming the
expected first stage carbonate intercalation compound in
which all the DDS- anions had been displaced, a mixed
carbonate/DDS product was isolated. All the analytical data
indicate that the product contains equal amounts of both
DDS- and CO32-, and these ions are ordered to give a stable
second stage compound Co(OH)1.75(DDS)0.07(CO3)0.09
·
0.5H2O (2; Scheme 1).
Figure 2. FT-IR patterns for (a) 1; (b) 2; and (c) 4. *Absorptions around
2050 cm-1 should be assigned to the substrate absorptions from diamond
ATR.
The in situ small angle and wide-angle X-ray scattering
(SAXS/WAXS) data for 1 and 2 are shown in Figure S1
(Supporting Information). The Bragg reflections for 1 may
be indexed using a rhombohedral unit cell with a ) b )
3.14 Å, c ) 83.4 Å. For 2 we observe new Bragg reflections
at d ≈ 36.0 Å, 18.0 Å, and 12.1 Å, respectively. These
reflections can be assigned to the 003, 006, and 009
reflections of the second staging layered product 2 (Figure
S1b, Supporting Information), which corresponds to the
alternate interlayer occupied by DDS- and CO32-. The new
cell for 2 is a ) b ) 3.06 Å, c ) 108 Å. This corresponds
to an interlayer repeat distance of 36 Å which is equal to
the sum of 27.8 Å (from 1) and 8.2 Å which is the calculated
where.15,22 Aqueous solutions of the guests (saturated CO32-) were
injected into an ampule 1 or 3. Individual spectra were collected
with acquisition times of 20 s and a fixed detector angle (2θ )
1.58°). Depending on the chosen angle for the three-angle energy
discriminating detector a large range of d-spacings can be observed
between 10 and 60 keV (d ) 50 to 1.2 Å).
Time-Resolved Small-Angle and Wide-Angle X-ray Scat-
tering (SAXS/WAXS) Experiments. SAXS/WAXS measurements
were carried out on beamline 6.2m of the Synchrotron Radiation
Source (SRS) at Daresbury Laboratory, Warrington, U.K.24-26 The
beam energy was set at 18.0 keV, corresponding to a wavelength
of 0.69 Å. The scattered intensity was recorded using a 200 mm
radius quadrant detector located 1.25 m from the sample. The
accessible q range was thus from 0.013 to 0.45 Å-1 (d ) 2π/q).
The detector response was calibrated using the scattering from
water. The angular scales were calibrated using the scattering peaks
of silver behenate (AgC22H43O2) for SAXS and silica for WAXS.
Material Characterization. Fourier transform infrared spec-
troscopy (FT-IR) spectra of the samples were recorded over a Bio-
Rad FTS 6000 spectrometer, spectra recorded within the range of
400-4000 cm-1 with 50 scans at 4 cm-1 resolution. Elemental
analysis (EA) was performed by the analytical services department
of the Inorganic Chemistry Laboratory, Oxford University. Ther-
mogravimetric analyses (TGA) were carried out on a Rheometric
STA-1500H machine. The sample (ca. 50 mg) was mounted in a
corundum crucible and heated at a rate of 5 °C min-1 between 25
and 800 °C under a flow of argon. HRTEM was performed on a
4000EX at 400 kV. JEOL Samples were dispersed in ethanol and
loaded onto copper grids supporting Formvar film. Magnetic
measurements were made using a Quantum Design MPMS-5
SQUID magnetometer. The susceptibility was determined in an
applied field of 1 kG after cooling of the sample in both zero applied
field (ZFC) and the measuring field (FC). The saturated moment
and hysteresis loop were measured at 2 K for ZFC in fields up to
50 kG. AC measurement was performed under 3.5 Oe oscillating
field with a frequency of 500 Hz from 2 to 50 K.
2-
size required for an intercalated CO3 ion. Unfortunately
the XRD data on 2 was of poor quality. It appears that on
isolation of the sample from the reaction mixture the material
becomes highly disordered and poorly crystalline especially
along the [001] direction. The XRD data for both 1 and 2
are shown in Figure S2 (Supporting Information). The 003
and 006 Bragg reflections of 1 are very sharp and symmetric.
However, a broad feature due to the 003 Bragg reflection
was observed for 2. On the other hand, the relative intensity
of the 110 Bragg reflections for both 1 and 2 are very similar.
Both 1 and 2 were studied by high-resolution transmis-
sion electron microscopy (HRTEM) and selected area
electron diffraction (SAED) with a view to probe the
symmetry of the crystalline domains and the interlayer
stacking arrangements. Figure 1a,b shows TEM images
of 1 and 2, respectively. Both the corresponding selected
area electron diffraction (SAED) patterns (inset in Figure
1) can be indexed as a two-dimensional in-plane hexagonal
lattice. This implies that the platelets are lying on their
{001} zone axis direction.27 The HRTEM images for 1
show lattice fringes separated by 2.6 nm. The HRTEM
images for 2 show a series of lattice fringes composed of
a thinner layer of 0.8 nm thickness and a thicker layer of
2.8 nm, which is consistent with the above-mentioned
second staging structure model. Furthermore, this alternat-
ing thickness interlayer arrangement extends over long
length scales. In agreement with the XRD data, a
disordered stacking arrangement was observed when the
solvent was removed for 2. The SAXS, XRD, and HRTEM
data all support a second stage anion ordering arrangement
(24) Fan, W.; Ogura, M.; Sankar, G.; Okubo, T. Chem. Mater. 2007, 19
(8), 1906.
(25) Panzarella, B.; Tompsett, G.; Conner, W. C.; Jones, K. Chem. Phys.
Chem. 2007, 8 (3), 357.
(26) Cernik, R. J.; Barnes, P.; Bushnell-Wye, G.; Dent, A. J.; Diakun, G. P.;
Flaherty, J. V.; Greaves, G. N.; Heeley, E. L.; Helsby, W.; Jacques,
S. D. M.; Kay, J.; Rayment, T.; Ryan, A.; Tang, C.; Terrilla, N. J. J.
Synchrotron Rad. 2004, 11, 163.
(27) Du, Y.; O’Hare, D. Inorg. Chem. 2008, 47 (8), 3234.
Inorganic Chemistry, Vol. 47, No. 24, 2008 11841

Du and O’Hare
Table 1. Summary of the Elemental Microanalysis Data for 1-4
elemental composition obsd (calcd), %
compound
N
C
H
formula
1
2
3
4
0.06 (-)
0.04 (-)
21.65 (21.71)
9.1 (9.17)
0.04 (-)
5.64 (5.59)
3.66 (3.72)
2.44 (2.36)
2.74 (2.71)
Co(OH)1.75(DDS)0.25 ·0.6H2O
Co(OH)1.75(C12H25O4 S)0.07(CO3)0.09 ·0.5H2O
Co(OH)1.7Cl0.3 ·0.4H2O
1.62 (1.65)
Co(OH)1.7(CO3)0.15 ·0.6H2O
Table 2. Summary of the Kinetic Data Summary for the Conversion of
1 to 2
are characteristic of the aliphatic and sulfate groups of DDS
anions, respectively.18,29
T, °C
na
ka, 10-3 s-1
kb, 10-3 s-1
t0.5c, s
Thermogravimetric analysis (TGA) was performed to
investigate the chemical composition and to gain insight into
the thermal decomposition processes. All these results are
consistent with the formula we proposed for 2 and the
elemental microanalysis data (Table 1). TGA data of 1 and
2 were shown in Figure 3 with 4 as reference. Both 1 and 2
exhibit a three-step weight loss separated in the range <100
°C, 150-250 °C, and 300-500 °C. The first weight loss
(∼7% in both cases) is classically attributed to the evolution
of absorbed and intercalated water.28 The subsequent weigh
losses are consistent with the substitution of significant
amounts of DDS- by CO32-. In the case of both 1 and 2,
the product remained after heating to 800 °C is confirmed
to be crystalline CoO and amorphous carbon by XRD and
EA.
Time-resolved, in situ EDXRD data was collected fol-
lowing the addition of 1 to 4 mL of 0.4 M Na2CO3 at 120
°C. A three-dimensional stack plot of the in situ EDXRD
data is shown in Figure 4. The data clearly indicates the one-
step nature of the formation of second stage product 2. The
extent of reaction (R), where R(t) ) Ihkl(t)/Ihkl(max), vs time
curve was observed to cross close to R ) 0.4 indicating that
no intermediates are involved, and the contour plot clearly
shows the growth of a Bragg reflection at higher d-spacing
(36 Å, 19.5 keV) which is assigned as the 003 Bragg
reflection in 2.
120
100
80
1.20 ( 0.04
1.00 ( 0.03
1.06 ( 0.02
1.14 ( 0.05
4.59 ( 0.08
2.95 ( 0.06
1.95 ( 0.03
1.30 ( 0.04
4.57 ( 0.09
2.96 ( 0.05
1.97 ( 0.03
1.30 ( 0.04
165
223
371
555
60
a Least squares fit to the Avrami-Erofe’ev model: R ) 1 - exp{-[k(t
- tind)]n}. b Least squares fit to model: R ) 1 - exp{-[k(t - tind)]1}. c t0.5
is defined as the time when R(t)/R(t ) ∞) ) 0.5.
Table 3. Summary of the Kinetic Data Summary for the Conversion of
3 to 4
T, °C
na
ka, 10-3 s-1
kb, 10-3 s-1
t0.5c, s
120
110
100
90
1.18( 0.05
1.34 ( 0.03
1.22 ( 0.07
1.00 ( 0.07
1.20 ( 0.06
3.92 ( 0.08
2.26 ( 0.03
1.98 (0.06
1.44 ( 0.06
1.12 ( 0.02
3.88 (0.11
2.19 ( 0.08
2.02 ( 0.08
1.44 ( 0.06
1.13 ( 0.03
192
332
363
503
725
80
a Least squares fit to the Avrami-Erofe’ev model: R ) 1 - exp{-[k(t
- tind)]n}. b Least squares fit to model: R ) 1 - exp{-[k(t - tind)]1}. c t0.5
is defined as the time when R(t)/R(t ) ∞) ) 0.5.
Time-resolved, in situ EDXRD data was collected at lower
concentrations of Na2CO3 (0.2 M) reveals the existence of a
crystalline intermediate phase with a slightly enhanced
interlayer repeat. The best explanation we have for this
observation is the transient formation of a hydration form
of the sulfate group within the layers which expands the
Figure 3. TGA traces for (a) 1; (b) 2; and (c) 4.
for 2. The coexistence of both DDS- and CO3 was
2-
2-
interlayer distance and/or partial diffusion of CO3 anions
further confirmed by FT-IR and TGA experiments.
Vibrational spectroscopy has proved to be the principal
method for studying the existence and bonding mode of
into the interlayer region as indicated in Scheme 1.29 If the
reaction was performed at even lower carbonate concentra-
tions, then the reaction did not go to completion, while at
higher concentrations it became too fast to monitor. Using
an intermediate concentration, we were able to carry out a
kinetic analysis of the reaction.
CO3 and DDS- in metal complexes. The IR spectrum of
2-
2 is shown in Figure 2 with 4 as the reference. A broad
absorption ca. 3400 cm-1 can be assigned to the O-H
stretching modes of interlayer water molecules while the
other broad absorption at low-frequency region (∼700 cm-1)
is ascribed to Co-O stretching and Co-OH bending
vibrations in the brucite-like octahedral sheet.18 The two
bands at 1350 and 1469 cm-1 are characteristic of the
presence of carbonate ions indicating a low site symmetry
(C2ν) for the CO32- ions.18,28 The absorption bands at around
2857-2925 cm-1 and 1197 cm-1 displayed in Figure 2a,b
The temperature dependence of this reaction was inves-
tigated over the range 60-120 °C. In each case, the Avrami-
Erofe’ev model, [-ln(1 - R)]1/n ) k(t - tind), where R(t) )
Ihkl(t)/Ihkl(max),5,9,11,15 was fitted to the experimental data
(Figure 5) to calculate the value of the reaction exponent n
and the rate constant k. A linear Sharp-Hancock plot
{ln(-ln(1 - R)) vs ln(t)}7,12,22 indicates that the Avrami-
Erofe’ev formalism could be used to quantify the kinetic data
as shown in Figure S3 (Supporting Information). The kinetic
data are summarized in Table 2. As is intuitively anticipated,
(28) Tessier, C.; Guerlou-Demourgues, L.; Faure, C.; Demourgues, A.;
Delmas, C. J. Mater. Chem. 2000, 10 (5), 1185.
11842 Inorganic Chemistry, Vol. 47, No. 24, 2008

Staging during Intercalation in Layered r-Cobalt Hydroxides
Figure 4. In situ EDXRD data during the course of the reaction between 120 mg of 1 and 4 mL of 0.5 M Na2CO3 at 120 °C: (a) 3D stack plot showing
the evolution of the 003 Bragg reflection for 1 and the 003 Bragg reflection for 2; (b) contour plot; (c) the corresponding plot of extent of reaction (R) vs
time (t).
data is observed because of the lower crystallinity of product
with respect to the ones generated at elevated tempera-
tures.7,12,22 The activation energy is calculated to be ∼22.77(6)
kJ mol-1 from a plot of ln k vs 1/T as inset in Figure 5 on
the basis of Arrhenius equation, k ) Ae-E /RT.
a
2-
Intercalation of CO3 in Co(OH)1.7Cl0.3 · 0.4H2O (3).
Addition of an excess of Na2CO3 to the layered R-cobalt
hydroxide Co(OH)1.7Cl0.3 · 0.4H2O (3) leads to the facile
exchange of Cl- for CO3 and the formation to a stable
2-
first stage compound Co(OH)1.7(CO3)0.15 · 0.6H2O (4).
The XRD data for 3 and 4 are shown in Figure S4
(Supporting Information). The Bragg reflections for 3 may
be indexed using the rhombohedral unit cell with a ) b )
3.14 Å, c ) 24.0 Å. A full characterization on 3 has been
made by the Sasaki group.12,13 For 4 we observe new Bragg
reflections at d ≈ 8.7 Å and 4.3 Å. These reflections can be
assigned to the 003 and 006 reflections from a new unit cell
with a ) b ) 3.12 Å, c ) 26.1 Å. The interlayer repeat
distance is 8.7 Å which is the calculated size required for
an intercalate CO3 ion. FT-IR and TGA data for 4 are
shown in Figures 2 and 3 with elemental analysis data in
Table 1.
Time-resolved, in situ EDXRD data was collected fol-
lowing the addition of 3 to 4 mL of 2 M Na2CO3 at100 °C.
The EDXRD shows that 3 transforms directly to the first
staging compound 4 without the observation of any inter-
mediate phases (Figure 6). The temperature dependence of
this reaction was investigated over the range 80-120 °C with
Figure 5. Temperature dependence of extension of reaction (R) plotted
against time (t). The data have been fitted with Avrami-Erofe’ev equation
at 60 °C (pink triangles), 80 °C (blue triangles), 100 °C (red circles), and
120 °C (black squares), respectively. Inset: Arrhenius plot for the phase
conversion from 1 to 2.
the reaction rate increased with temperature and no induction
time is observed in all cases.
The Avrami exponent (n) was found to be close to 1 over
all the temperature studied. n is then fixed to be 1, and the
subsequent rate constant k was found to be consistent as
shown in Table 2. Plots of R vs reduced time (t/t0.5) were
found to be superimposable, confirming that the same
mechanism is operational in each case.7,9 The value of the
exponent (n) is consistent with a two-dimensional diffusion
controlled kinetic model, which means the rate-limiting step
is likely to be the diffusion of CO32- anions into the crystal.
At lower temperatures, a greater amount of scatter in the
2-
Inorganic Chemistry, Vol. 47, No. 24, 2008 11843

Du and O’Hare
Figure 6. In situ EDXRD data during the course of the reaction between 120 mg of 3 and 4 mL 0.5 M Na2CO3 at 100 °C: (a) 3D stack plot showing the
evolution of the 003 Bragg reflections for 3 and the 003 Bragg reflections of 4; (b) contour plot; (c) the corresponding plot of extent of reaction (R) vs time
(t).
to expand the interlayer in order to accommodate the bigger
anion CO32-. In addition, the intercalated anions become
covalent bonded to the cobalt centers so the magnitude of
the activation energy of this type of R-cobalt hydroxide based
anion exchange reaction is bigger than the common anion
exchange reaction for layered double hydroxides.7,11,12,16
Figure 8 shows the temperature-dependent dc molar
magnetic susceptibility of 1, 2, and 4 (Figure 8c) in an
applied field of 1000 Oe after zero-field-cooling (ZFC) and
field-cooling (FC) measurements. A very clear and sharp
bifurcation point is evident in all three samples, at 8.2, 6.3,
and 16.5 K, respectively. The plot of ꢀmol-1 vs T shows that
all three materials obey the Curie-Weiss law above ca. 125
Figure 7. Temperature dependence of extension of reaction (R) vs time
(t). The data have been fitted with Avrami-Erofe’ev equation at 120 °C
(dark yellow diamonds), 110 °C (pink triangles), 100 °C (blue triangles),
90 °C (red circles), and 80 °C (black squares), respectively. Inset: Arrhenius
plot for the phase conversion from 3 to 4.
K giving effective magnetic moment (µeff) of 5.0 µB, 5.2 µB,
and 4.6 µB for 1, 2, and 4, respectively. These are all slightly
higher than the spin-only value for S ) 3/2 ions but are
within the range of high-spin mixed octahedral/tetrahedral
cobalt(II) compounds.19,21
4 mL of 2 M Na2CO3. At each temperature, the Avrami-
Erofe’ev model was fitted to the experimental data (Figure
7) to calculate the value of the reaction exponent n and the
rate constant k. The data give a linear Sharp-Hancock plot.
The kinetic data are summarized in Table 3. Plots of R vs
reduced time (t/t0.5) were found to be superimposable,
confirming that the same mechanism is operational in each
case.7,9 The value of the exponent (n) is consistent with a
two-dimensional diffusion controlled model following a
much higher activation energy ∼112.8(11) kJ mol-1 calcu-
lated from Arrhenius equation (inset in Figure 7). It is
consistent with the fact that the diffusion of CO32- into 3 is
more difficult compared to 1 because 3 needs extra energy
The isothermal magnetization M(H) at 2 K for 1, 2, and 4
(Figure 9) shows hysteresis loops consistent with a 3D magneti-
cally ordered ground state, which is further confirmed by ac
susceptibility measurement as shown in Figure 10. The satura-
tion magnetizations are 1.28 µB, 1.37 µB, and 1.16 µB, for 1, 2,
and 4, respectively, which could be explained by a model based
on two antiferromagnetically coupled sublattices. For 2 this
could be formulated as [Co(oct)0.75Co(tet)0.25(OH)1.75 0.25+(CO3)0.09
]
(DDS)0.07 ·0.6H2O. Therefore, the saturation magnetization can
be calculated as (goct × Co(oct) - gtet × Co(tet)) × S ) (2 ×
0.75 - 2 × 0.25) × 1.5 ) 1.5 µB, which is consistent with the
experimental value 1.37 µB. Calculations using a similar
11844 Inorganic Chemistry, Vol. 47, No. 24, 2008

Staging during Intercalation in Layered r-Cobalt Hydroxides
Figure 9. Field dependence of the molar magnetization for (a) 4; (b) 2;
and (c) 1 at 2 K from -5 to 5 T.
Figure 10. Real component of the magnetic susceptibility (ꢀ′) as a function
of temperature for (a) 4; (b) 2; and (c) 1 under 3.5 Oe ac field and at a
frequency of 500 Hz.
groups to explain the magnetic properties of related layered
cobalt hydroxides.17,21,30-34
The temperature dependence of ac magnetic susceptibility
for 1, 2, and 4 was measured in the temperature range 2-50
K under an oscillating magnetic field of 3.5 Oe (under a
near zero dc field of 5 Oe) (Figure 10). Spontaneous magnetic
ordering for 3D magnets is characterized by a discontinuous
jump in dc magnetization which coincides with the peak in
the in-phase ac magnetization (Figure 10) and to the nonzero
out of phase (not shown) ac magnetization. The peaks in
both real (in phase) and imaginary (out of phase) components
of the ac susceptibilities are taken to be indicative of a
ferrimagnetic 3D ordering transition. The Curie temperature,
TC, of the samples, was determined to be 31, 9, and 22 K
(center peak) for 1, 2, and 4, respectively. The broad peak
for 1 could be attributed to its highly crystalline nature. The
low value of TC for 2 must be largely due to the much poorer
crystallinity.
Figure 8. (a) Plot of ꢀM and ꢀM-1 vs T for 4; data following cooling in 1
-1
kG field (0; FC) and zero applied field (O; ZFC). (b) Plot of ꢀM and ꢀM
vs T for 2; data following cooling in 1 kG field (0; FC) and zero applied
field (O; ZFC). (c) Plot of ꢀM and ꢀM-1 vs T for 1; data following cooling
in 1 kG field (0; FC) and zero applied field (O; ZFC).
magnetic model for 1 and 4 give predicted saturation moments
of 1.5 µB and 1.2 µB, which is in good agreement with the
experimental values 1.28 µB and 1.16 µB. The existence of the
long-range magnetic order has been described by several other
(29) Bubniak, G. A.; Schreiner, W. H.; Mattoso, N.; Wypych, F. Langmuir
2002, 18 (16), 5967.
Conclusions
(30) Ben Salah, M.; Vilminot, S.; Andre, G.; Richard-Plouet, M.; Mhiri,
T.; Takagi, S.; Kurmoo, M. J. Am. Chem. Soc. 2006, 128 (24), 7972.
(31) Ben Salah, M.; Vilminot, S.; Andre, G.; Bouree-Vigneron, F.; Richard-
Plouet, M.; Mhiri, T.; Kurmoo, M. Chem. Mater. 2005, 17 (10), 2612.
(32) Mohsen, B. S.; Vilminot, S.; Richard-Plouet, M.; Andre, G.; Mhiri,
T.; Kurmoo, M. Chem. Commun. 2004, (22), 2548.
The second stage intercalation compound Co(OH)1.75
(DDS)0.07(CO3)0.09 · 0.5H2O (2) has been characterized. In
order to form this material half of the DDS- anions in
Co(OH)1.75(DDS)0.25 · 0.6H2O (1) has resisted ion-exchange
(33) Forster, P. M.; Tafoya, M. M.; Cheetham, A. K. J. Phy. Chem. Solids
2004, 65 (1), 11.
(34) Kurmoo, M. J. Mater. Chem. 1999, 9, 2595.
Inorganic Chemistry, Vol. 47, No. 24, 2008 11845

Du and O’Hare
by an excess of carbonate. We have found only one other
example of second stage intermediates involving carbonate
anions.4 The activation energy for the intercalation of 1 with
carbonate is much lower than that for 3 which may be a
factor in the observation of staging. However, it is still not
clear why treatment of 1 with carbonate gives only a second
stage product, while the same reaction with 3 gives a first
stage product. The temperature dependence of the kinetics
suggest that the reactions follow a two-dimensional diffusion
controlled model. Magnetic measurements show that all the
materials behave as 3D ferrimagnets at low temperature.
Acknowledgment. The authors thank Clarendon Scholar-
ship and Balliol College, Oxford University, for funding, and
the CCLRC for access to the UK SRS. Also, thanks to Dr.
Dave Taylor and Dr. Tony Bell at Station 16.4 and Dr. Chris
Marin at Station 6.2m, on the SRS Daresbury Laboratory,
UK, for experimental set up and data processing.
Supporting Information Available: In situ SAXS and WAXs,
XRD, Sharp-Hancock plot, and FESEM. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC801639E
11846 Inorganic Chemistry, Vol. 47, No. 24, 2008