Hydrothermal synthesis and characterization of a layered cobalt phenylphosphonate, Co(PhPO3)(H2O)

Article abstract of DOI:10.1039/b510942f

We report the hydrothermal synthesis and characterization of a layered cobalt phenylphosphonate. Unlike most metal phosphonates reported to date, the structure was solved by single crystal X-ray diffraction (SC-XRD). Co(ii) centres are hexa-coordinated by oxygen and the octahedra corner-share into a layer. The layers are capped by phenylphosphonate groups, where the phenyl groups define a hydrophobic bilayer region. The material was also characterized by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) and SQUID (superconducting quantum interference device) magnetometry. The material undergoes an antiferromagnetic transition at a relatively low Neel temperature of 4.0 K, while the Curie-Weiss temperature of -76.5 K reflects the low-dimensionality of the magnetic structure. The effective magnetic moment of 5.01 _B per Co²⁺ verifies a high-spin configuration and an octahedral coordination of the metal centres. This layered material was correctly predicted in the literature from powder data, adds to the structural diversity of the cobalt phosphonates, and may be useful as an intercalation or exfoliation compound. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b510942f

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PAPER
www.rsc.org/dalton | Dalton Transactions
Hydrothermal synthesis and characterization of a layered cobalt
phenylphosphonate, Co(PhPO3)(H2O)
T. O. Salami,a X. Fan,a P. Y. Zavalijb and S. R. J. Oliver*a
Received 1st August 2005, Accepted 2nd December 2005
First published as an Advance Article on the web 19th December 2005
DOI: 10.1039/b510942f
We report the hydrothermal synthesis and characterization of a layered cobalt phenylphosphonate.
Unlike most metal phosphonates reported to date, the structure was solved by single crystal X-ray
diffraction (SC-XRD). Co(II) centres are hexa-coordinated by oxygen and the octahedra corner-share
into a layer. The layers are capped by phenylphosphonate groups, where the phenyl groups define a
hydrophobic bilayer region. The material was also characterized by powder X-ray diffraction (PXRD),
thermogravimetric analysis (TGA) and SQUID (superconducting quantum interference device)
magnetometry. The material undergoes an antiferromagnetic transition at a relatively low Ne´el
temperature of 4.0 K, while the Curie–Weiss temperature of −76.5 K reflects the low-dimensionality
of the magnetic structure. The effective magnetic moment of 5.01 lB per Co2+ verifies a high-spin
configuration and an octahedral coordination of the metal centres. This layered material was correctly
predicted in the literature from powder data, adds to the structural diversity of the cobalt
phosphonates, and may be useful as an intercalation or exfoliation compound.
Accordingly, our research has led to a series of layered
Introduction
phosphonate compounds. We reported several tin14 and lead15
phenylphosphonates, where the phosphonates bond to the metal
centres of the layers and the phenyl rings point towards the
interlamellar space. Of this series of compounds, one also contains
pyridine solvent molecules of crystallization, which reside between
the layers and increase the layer separation.15 A wide range of
layered metal phenylphosphonates have been reported in the
literature based on calcium,16 strontium,17 aluminium,18 uranium19
and transition metals, such as manganese,9,20 iron,8 cobalt,7,21
copper,22 zinc7,20–23 and zirconium.24,25
A large and important class of inorganic–organic hybrid com-
pounds is the extended metal phosphonates. They are related to
the inorganic metal phosphites and phosphates, where an organic
functionality replaces a hydrogen or oxo group on the phosphorus,
respectively. Metal phosphonates have been extensively studied
due to their catalytic, ion exchange, sensor and nonlinear opti-
cal properties.1–8 Magnetic properties have also been described
for transition metal phosphonates. For example, manganese
phenylphosphonate revealed a canted antiferromagnetic interac-
tion between the spin carriers.9 Iron phenylphosphonate exhibits
long-range 3D antiferromagnetic ordering, coupled with weak
ferromagnetic behaviour below its Ne´el temperature of 21.5 K.8
These materials are most frequently prepared by simple ambi-
ent crystallization1–9 or solvothermal synthesis.6,9–11 The ease of
preparing metal phosphonates is due to the strong interaction of
phosphate with metalate species and therefore the tendency to
polymerize.12 If the organic group of the phosphonate is long, a
layered structure is likely to form, with a bilayer or interdigitated
hydrophobic interlamellar region. A small methyl group, on the
other hand, tends to give rise to a framework structure, where the
methyl groups point into unidimensional, hydrophobic channels.13
The wide range of possible phosphonate organic groups has not
surprisingly led to a large variety of structure types, for many
metals of the periodic table.
Only synthesis under ambient conditions and computer sim-
ulation of the structure have been reported for many of these
transition metal phenylphosphonates,21 as the crystals were not
large enough for structure analysis. Herein we describe the
synthesis, single crystal structure and thermal and magnetic
characterization of one member of this isostructural series, the
layered transition metal phenylphosphonate, Co(PhPO3)(H2O).
Experimental
Synthetic procedure
All reagents were used as-received and added sequentially to
a 100 mL Nalgene beaker: (i) solvent (deionized water); (ii)
Co source (CoCl2·6H2O, Sigma); (iii) phenylphosphonic acid
(C6H5PO3H2, Alfa Aesar). The molar ratio of the reactants—
water, cobalt chloride hydrate and phenylphosphonic acid—was
50 : 1 : 1 (13.89 g: 2.43 g: 3.66 g), respectively. The resultant pink
solution was mechanically stirred for 5 min until the reactants
completely dissolved. The clear mixture was then placed in an
18 mL capacity Teflon-lined autoclave (home constructed) and
heated statically between 125 and 175 ◦C for 3 to 5 days. The
pink plate-like crystals were suction-filtered, rinsed with water
and allowed to air-dry.
aDepartment of Chemistry and Biochemistry, University of California, Santa
Cruz, 1156 High Street, Santa Cruz, CA 95064, USA
bInstitute for Materials Research, State University of New York at
Binghamton, Binghamton, NY 13902-6000, USA. E-mail: soliver@
chemistry.ucsc.edu; Fax: +1-(831) 459-2935; Tel: +1-(831) 459-5448
† Current address: Department of Chemistry and Biochemistry, University
of Maryland, College Park, MD 20742, USA.
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Elemental analysis (Quantitative Technologies Inc., White-
house, NJ) of the as-synthesized product (30.89% C, 2.44% H)
agrees well with the theoretical values (30.90% C, 3.03% H).
at 50 kV and 40 mA. The detector was placed at a distance of
5.17 cm from the crystal. A total of 1993 frames were collected
with a scan width of 0.3◦ in x and an exposure time of 10 s
frame−1 using SMART.26 The total data collection time was 7.47 h.
The frames were integrated with the SAINT software package
using a narrow-frame integration algorithm.26 Data were corrected
for absorption effects with the semi-empirical from equivalents
method using XPREP.27 The structure was solved and refined
using the SHELXS-9727 and SHELXL-9728 software.
Characterization methods
PXRD was performed on a Scintag XDS 2000 diffractometer with
˚
Cu Ka radiation (k = 1.5418 A), solid-state detector, scan range
◦
2◦ to 45◦ (2h), step size 0.02◦ and scan rate 4.0 C min−1. All
samples were ground thoroughly in a mortar and pestle before
mounting the resultant powder in the PXRD sample holder. TGA
was performed on a TA Instruments 2950, with a 10 ◦C min−1 scan
rate and nitrogen purge. Magnetic measurements were obtained
using a SQUID magnetometer (Quantum Design MPMS XL-5).
The dc magnetic susceptibility was measured in a magnetic field
H of 1000 Oe over the temperature range 2 to 298 K.
Results and discussion
Highly crystalline pink plates sufficiently large for SC-XRD
analysis were obtained by optimizing the hydrothermal conditions.
Detailed crystallographic data are given in Table 1. The optimum
reaction conditions in terms of percent yield were 175 ◦C and
5 days, with a yield of 76.8% (Table 2, Expt. #1). Lower heating
temperature and/or time were attempted to see if other phases
would form (Table 2, Expt. #2 to #5). Instead, the yield of the
material simply decreased, with only a trace amount of solid at
125 ◦C or 150 ◦C. The pH of the reaction mixture was ∼6 for all
experiments. Lower temperatures did not yield a solid product.
The crystal structure of SLUG-4 consists of inorganic layers of
CoO6 octahedra, which corner-share via oxygens into a continuous
sheet (view of one layer, Fig. 1a). Each of these in-plane oxygens
(four for each octahedron) also bond to one phosphorus, and are
therefore triply-bridging. Since each CoO6 octahedron connects to
four octahedra and four phosphonates (Fig. 1a), the Co : P ratio is
1 : 1 as reflected in the formula of the compound. The fifth and sixth
vertices of the CoO6 octahedra are occupied by two out-of-plane
oxygens. One is a terminal water molecule involved in an intralayer
hydrogen bond (Table 3), while the other is a doubly-bridging
oxygen that also connects to a phosphorus centre. This layout was
correctly predicted in earlier reports where the crystal structure
could not be solved due to the ambient synthesis conditions that
led to small particle size.21
The phosphonates cap the layers alternately above and below
the plane of the layer (side view of two layers, Fig. 1b). As for other
metal phenylphosphonates,8,20 the phenyl rings point into the
interlayer space, defining a hydrophobic bilayer region. The Co–O
and P–O distances are given in Table 3, and the thermal ellipsoids
at 30% probability and atom labeling scheme are shown in Fig. 2.
The C(1) and C(4) carbons of the phenyl ring are ordered, while
the beta and gamma carbons are disordered (see CIF file). The
structure has mirror plane symmetry, as can be seen from Fig. 1
and 2. The phenyl ring is disordered such that in one orientation it
lies in the plane, and the other perpendicular to the plane (Fig. 2).
The inorganic layer topology is identical to two very recently
reported pillared metal 1,4-phenylbisphosphonates of Cao et al.,
where the metal is Mn or Co.29 The layers are not surprisingly
SC-XRD structure determination
The title compound (which we denote SLUG-4, for University
of California, Santa Cruz, Structure No. 4) was determined by
manually selecting a pink plate of approximate dimensions 0.24 ×
0.17 × 0.005 mm3. The X-ray intensity data were measured at
294(2) K on a three-circle diffractometer system equipped with a
Bruker SmartApex CCD area detector, graphite monochromator
˚
and a Mo Ka fine-focus sealed tube (k = 0.71073 A) operated
Table 1 Crystal data for Co(PhPO3)(H2O)a
Empirical formula
Formula weight
Temperature
Wavelength
Crystal size
Crystal shape
Crystal system
Space group
C6 H7 Co O4 P
233.01
294(2) K
˚
0.71073 A
0.24 × 0.17 × 0.005 mm3
Pink plate
Orthorhombic
Pmn21
◦
˚
Unit cell dimensions
a = 5.6238(10) A, a = 9◦0
˚
b = 14.391(3) A, b = 90◦
˚
c = 4.8615(9) A, c = 90
3
˚
Volume
393.44(12) A
Z
2
Density, qcalc
1.967 g cm−3
2.350 mm−1
783
Absorption coefficient, l
Observed reflection, I > 2r(I)
Variation in check reflections
Refinement technique
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices:
R1, I > 2r(I)
wR2, all data
Weighting scheme
−0.46%
Full-matrix least-squares on F2
890/2/89
0.977
0.0394
0.0778
w = 1/[r2(Fo2) + (0.021P)2],
P = [max(Fo2,0) + 2Fo2]/3
a R1 = RꢀFo| − |Fcꢀ/R|Fo|, wR2 = [Rw(Fo − Fc2)2/Rw(Fo2)2]1/2
.
2
Table 2 Hydrothermal experiments conducted for the synthesis of the layered cobalt phenylphosphonate (PPA = phenylphosphonic acid)
Ref. No.
Molar ratios
Synthesis time/days
Synthesis temp./◦C
Percent yield
1
2
3
4
5
50 H2O: 1 PPA: 1 CoCl2·6H2O
50 H2O:1 PPA:1 CoCl2·6H2O
50 H2O:1 PPA:1 CoCl2·6H2O
50 H2O:1 PPA:1 CoCl2·6H2O
50 H2O:1 PPA:1 CoCl2·6H2O
5
3
5
3
175
175
150
150
125
76.8%
42.5%
Trace amount
Trace amount
Trace amount
1.5
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◦
˚
Table 3 Selected bond lengths (A), angles ( ) and hydrogen bond
information for Co(PhPO3)(H2O)
Co1–O3
Co1–O2b
Co1–O2d
P1–O3
2.056(4)
2.069(3)
2.237(3)
1.522(5)
1.546(3)
1.394(12)
1.377(19)
1.381(18)
Co1–O2a
Co1–O1
Co1–O2f
P1–O2e
2.069(3)
2.106(5)
2.237(3)
1.546(3)
1.780(8)
1.394(12)
1.377(19)
P1–O2
P1–C1
C1–C2Be
C4–C3B
C2B–C3B
C1–C2B
C4–C3Be
O3–Co1–O2a
O2a–Co1–O2b
O2a–Co1–O1
O3–Co1–O2d
O2b–Co1–O2d
O3–Co1–O2f
O2b–Co1–O2f
O2d–Co1–O2f
O3–P1–O2
90.74(12)
100.19(17)
91.92(14)
86.36(14)
96.66(7)
86.36(14)
162.94(13)
66.40(15)
113.11(17)
107.3(3)
O3–Co1–O2b
O3–Co1–O1
O2b–Co1–O1
O2a–Co1–O2d
O1–Co1–O2d
O2a–Co1–O2f
O1–Co1–O2f
90.74(12)
175.8(2)
91.92(14)
162.94(13)
90.16(16)
96.66(7)
90.16(17)
O2e–P1–O2
O2e–P1–C1
104.8(3)
109.23(18)
O3–P1–C1
O2–P1–C1
109.23(18)
D–H · · · A
d(D–H)
d(H · · · A)
d(D · · · A)
∠(DHA)
O1–H1 · · · O3b
0.77(2)
0.77(2)
2.33(5)
2.33(4)
2.844(1)
2.993(6)
125(5)
144(5)
O1–H1 · · · O2c
D = donor atom, H = hydrogen, A = acceptor. Symmetry transformation
codes:a x − 1/2, −y + 1,z + 1/2; b −x + 1/2, −y + 1, z + 1/2; c −x + 1/2,
−y + 1, z + 3/2; d x, y, z + 1; e −x, y, z; f −x, y, z + 1.
pillared, due to the bisphosphonic functionality.30 These
pillars increase the stability of the material, but also limit the
potential for intercalation and prevents exfoliation of the layers.
As for known metal phosphonates, the cobalt centres readily
coordinate to phosphorus through bridging oxygen atoms. The
majority of metal phosphate and phosphonate extended structures
are built up from MO4, MO5 and MO6 units. As previously
noted, the dimensionality and topology of the structure formed
depends considerably on the organic substituent of the phosphonic
acid (RPO3H2). Larger R groups such as phenyl or long alkyl
chains tend to give rise to layered structures, while less bulky
groups tend to result in 3D as well as 1D structures.12,13,31 One
exception is a 1D cobalt phosphonate chain recently demonstrated
by Clearfield and co-workers.32 Despite using a long chain 1,8-
octylenebisphosphonic acid, the octahedral cobalt atoms connect
to phosphonate only at the axial positions to create the chain.
Four terminal water molecules terminate the cobalt coordination
sphere and therefore the dimensionality.
Fig. 1 (a) The b-projection of one layer of SLUG-4, showing corner
sharing CoO6 octahedra (dark grey) that link to the phosphonate centres
(black circles) via bridging oxygens; (b) The projection along the c-axis
shows the capping phenylphosphonates, with an interlamellar bilayer of
partially disordered phenyl groups. All hydrogens are omitted for clarity.
The TGA of the material shows two distinct steps (Fig. 3). At
approximately 150 ◦C, there is a weight loss that corresponds
well to the loss of the covalently bound water molecule (one
per formula unit, experimental: 7.6%, theoretical: 7.7%). This
result agrees with previous reports of dehydration upon heating,
reducing the cobalt coordination number from six to five.21 The
second weight loss event occurs at approximately 500 ◦C, and
is consistent with the breakdown of the organic phenyl groups
(experimental: 33.0%, theoretical: 33.2%), also in agreement with
reported thermal data.21 The black residue after the TGA run was
poorly crystalline and the specific phase could not be elucidated
by PXRD, but is likely to be a cobalt phosphate.
Fig. 2 Thermal ellipsoids at 30% probability level and atom labeling
scheme.
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to the low dimensionality of the magnetic architecture in the
title compound. Low-dimensional magnetic compounds usually
exhibit a large suppression of their Curie–Weiss temperature due to
short-range correlations above the critical Ne´el temperature TN,33
as observed in a closely related Fe(II) phenylphosphonate system.8
The effective magnetic moment of 5.01 lB per Co(II) deduced
from the Curie constant C is in the typical range of magnetic
moments (4.7 to5.2 lB) observed for octahedral Co2+ ions.34 It is
much higher than the expected spin only value of 3.87 lB for a
free Co2+ ion with a high-spin state S = 3/2, due to the spin-
orbit coupling in Co(II) containing compounds.29 From Weiss
field theory, the estimated exchange coupling constant is J/kB =
[3h/zS(S + 1)] ∼ −15.3 K, assuming a coordination number (z)
of four with respect to magnetic nearest-neighbours. This value is
reasonable, as interlayer magnetic interaction is negligible due to
˚
the large distance of over 14 A between two cobaltate layers.
CCDC reference number 279873.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b510942f
Fig. 3 The TGA trace shows two sharp events, with weight losses that
agree well with expected values.
Conclusions
A layered cobalt phenylphosphonate was synthesized readily by
hydrothermal techniques. The optimum conditions were found to
be 175 ◦C for 5 days and pH ∼ 6. Unlike most metal phosphonates,
the crystal plates were of sufficient size and quality for structure
determination by SCXRD. The material shows a large weight
◦
loss around 500 C due to decomposition of the phenyl groups.
The magnetic properties indicate a long-range antiferromagnetic
ordering below TN = 4.0 K, with an estimated intralayer magnetic
coupling constant of −15.3 K from Curie–Weiss theory. The
effective magnetic moment of 5.01 lB was deduced from the
Curie–Weiss law above 50 K, falling well within the range
typically observed for compounds containing octahedral Co2+.
This material may show interesting intercalation properties due to
its large interlayer distance and hydrophobic interlayer space.
Fig. 4 Temperature dependence of the magnetic susceptibility at 1000 Oe.
Insets: (a) Expansion of the low temperature region; (b) Plot of the
reciprocal of susceptibility versus temperature.
Acknowledgements
Fig. 4 shows the temperature dependence of the magnetic
susceptibility v on temperature. As the temperature decreases,
the magnetic susceptibility gradually increases and attains a
well-defined peak at Tp ∼ 6.5 K (Fig. 4a), indicative of an
antiferromagnetic transition. Similar behavior was reported for
the two isostructural Mn- and Co-phenylenebisphosphonates of
Cao et al. mentioned above.29 Both of their compounds exhibit
a dominant antiferromagnetic interaction between the magnetic
centres below 50 K. For our compound, the Ne´el temperature TN,
taken as the maximum of d(vT)/dT, is around 4.0 K, just below
the peak temperature Tp.
The susceptibility obeys the Curie–Weiss law [v = v0 + C/(T −
h)] in the temperature region 50 to 298 K (Fig. 4b). Data fitting
(solid line, Fig. 4b) gives the following parameters: temperature-
independent contribution v0 = 7 × 10−5 emu g−1; Curie constant
C = 0.014 emu K g−1; Curie–Weiss temperature h = −76.5 K. The
negative sign of h indicates antiferromagnetic interaction between
the Co ions. The magnitude of h is much larger than the Ne´el
temperature TN = 4.0 K. The ratio TN/|h | = 0.05 is well below
the predicted value of 1 based solely on molecular field theory of
antiferromagnetic systems.33 This discrepancy can be attributed
This research was supported by an NSF Career Award (DMR-
0506279). We acknowledge Dr N. Chernova of the Institute for
Materials Research, State University of New York at Binghamton,
for magnetic data collection.
References
1 D. L. Cocke, in Design of New Materials, ed. A. Clearfield, Plenum,
New York, 1986, pp. 121.
2 G. Alberti, in Comprehensive Supramolecular Chemistry, ed. J. M. Lehn,
Pergamon, Elsevier Science Ltd., Oxford, UK, 1996.
3 B. Zhang and A. Clearfield, J. Am. Chem. Soc., 1997, 119, 2751–2752.
4 C. Maillet, P. Janvier, M. Pipelier, T. Praveen, Y. Andres and B. Bujoli,
Chem. Mater., 2001, 13, 2879–2884.
5 G. Cao, H. Hong and T. E. Mallouk, Acc. Chem. Res., 1992, 25, 420–
427.
6 R. Go´mez, J. L. Segura and N. Martin, J. Org. Chem., 2000, 65, 7566–
7574.
7 K. J. Frink, R. C. Wang, J. L. Colo´n and A. Clearfield, Inorg. Chem.,
1991, 30, 1438–1441.
8 C. Bellitto, F. Federici, A. Altomare, R. Rizzi and S. A. Ibrahim, Inorg.
Chem., 2000, 39, 1803–1808.
9 G. E. Fanucci, J. Krzystek, M. W. Meisel, L.-C. Brunel and D. R.
Talham, J. Am. Chem. Soc., 1998, 120, 5469–5479.
This journal is
The Royal Society of Chemistry 2006
Dalton Trans., 2006, 1574–1578 | 1577
©

View Article Online
10 M. P. Attfield, H. G. Harvey and S. J. Teat, J. Solid State Chem., 2004,
177, 2951–2960.
11 H. G. Harvey, A. C. Herve, H. C. Hailes and M. P. Attfield, Chem.
Mater., 2004, 16, 3756–3766.
12 S. Oliver, A. Kuperman and G. A. Ozin, Angew. Chem., Int. Ed., 1998,
37, 46–62.
23 F. Fredoueil, M. Evain, D. Massiot, M. Bujoli-Doeuffb and B. Bujoli,
J. Mater. Chem., 2001, 11, 1106–1116.
24 A. Clearfield, W. J. Don, Y. Tian, E. Stein and C. Bhardwaj, J. Solid
State Chem., 1995, 117, 275–289.
25 A. Clearfield and Z. J. Wang, J. Chem. Soc., Dalton Trans., 2002, 2937–
2947.
13 K. Maeda and F. Mizukami, Catal. Surv. Jpn., 1999, 3, 119–126.
14 D. E. Lansky, P. Y. Zavalij and S. R. J. Oliver, Acta Crystallogr., Sect.
C, 2001, C57, 1051–1052.
26 SMART and SAINT, Bruker AXS Inc., Madison, Wisconsin, USA,
1999.
27 G. M. Sheldrick, SHELXL-97 and XPREP, University of Go¨ttingen,
15 D. T. Tran, Y.-S. Kam, P. Y. Zavalij and S. R. J. Oliver, Inorg. Chem.,
2003, 42, 2165–2172.
Germany, 1997.
28 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, A46, 467–473.
29 D.-K. Cao, S. Gao and L.-M. Zheng, J. Solid State Chem., 2004, 177,
2311–2315.
16 A. H. Mahmoudkhani and V. Langer, Solid State Sci., 2001, 3, 519–
525.
17 A. H. Mahmoudkhani, V. Langer and L. Smrcok, Solid State Sci.,
2002, 4, 873–878.
30 1,4-Phenylbisphosphonic acid is often used as a spacer or ligand in the
synthesis of supramolecular compounds, as well as the fabrication of
multilayered thin films based on metal phosphonates.
31 (a) S. R. J. Oliver, A. Kuperman, A. Lough and G. A. Ozin, Chem.
Mater., 1996, 8, 2391–2398; (b) B. A. Adair, S. Neeraj and A. K.
Cheetham, Chem. Mater., 2003, 15, 1518–1529; (c) N. K. Mal, S.
Ichikawa and M. Fujiwara, Chem. Commun., 2002, 112–113.
32 E. V. Bakhmutova, X. Ouyang, D. G. Medvedev and A. Clearfield,
Inorg. Chem., 2003, 42, 7046–7051.
18 N. Zakowsky, G. B. Hix and R. E. Morris, J. Mater. Chem., 2000, 10,
2375–2380.
19 D. M. Poojary, D. Grohol and A. Clearfield, Angew. Chem., Int. Ed.,
1995, 34, 1508–1510.
20 (a) G. Cao, H. Lee, V. M. Lynch and T. E. Mallouk, Inorg. Chem., 1988,
27, 2781–2785; (b) J.-G. Mao, Z. Wang and A. Clearfield, Inorg. Chem.,
2002, 41, 2334–2340.
21 (a) D. Cunningham, P. J. D. Hennelly and T. Deeney, Inorg. Chim. Acta,
1979, 37, 95–102; (b) G. Cao and T. E. Mallouk, Inorg. Chem., 1991,
30, 1434–1438.
22 B. Menaa, B. M. Kariuki and I. J. Shannon, New J. Chem., 2002, 26,
906–909.
33 R. Navarro, in Magnetic Properties of Layered Transition Metal
Compounds, ed. L. J. De Jongh, Kluwer, Dordrecht, The Netherlands,
1990.
34 R. L. Carlin, Magnetochemistry, Springer-Verlag, Berlin, Germany,
1986.
1578 | Dalton Trans., 2006, 1574–1578
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The Royal Society of Chemistry 2006
©