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Hydrothermal Synthesis of Microporous Transition Metal Squarates Preparation and Structure of [CO3(3-OH)2(C4O4)2]╖3H2O.

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Hydrothermal Synthesis of Microporous
Transition Metal Squarates: Preparation and
- 3H,O**
Structure of [Co3(~3-OH)2(C404)2]
Siegfried 0. H. Gutschke, Michel Molinier,
Annie K. Powell, and Paul T. Wood*
+/cm-'Figure 5. Comparison of the OH regions of the IR spectra ofactivated cloverite (a)
and Y zeolite (b. Linde LZY62, Si/Al = 2.4). The spectra were normalized to 10 mg
solid, and based on the structures of the solids the ratio between the area of OH
bands in cloverite and Y zeolite should be at least approximately 1:3; however, the
observed value is only 1 :40. I = Absorbance.
In conclusion, this study reveals that the postulated terminal
OH groups in the framework of cloverite are not detectable by
IR spectroscopy. Free OH groups, in particular those due to
POH groups that vibrate at 3676 cm- are observed before and
after activation of cloverite at 573 K under ozone. Their number
increases upon activation but remains quite low, about 3.5 % of
the expected number, indicating that they correspond to defect
sites. This study does not cast doubt on the results of the X-ray
structure analysis, but rather on whether the terminal oxygen
atoms in the structure really belong to hydroxyl groups.
Received: October 31, 1996
Revised version: December 30, 1996 [Z9711 IE]
German version: Angew. Chem. 1997, 109, 1017-1019
Keywords: acidity
- cloverite
IR spectroscopy
[l] M. Estermann, L. B. McCusker, C . Baerlocher, A. Merrouche, H. Kessler,
Nature 1991, 352, 320-323.
(21 T. L. Barr, J. Klinowski, H. He, K. Alberti, G. Miiller, J. A. Lercher, Nature
1993, 365.429-431.
[3] R. L. Bedard, C. L. Bowes, N. Coombs, A. J. Holmes, T. Jiang, S . J. Kirkby,
P. M. Macdonald, A.M. Malek, G. A. Ozin, S . Petrov, N. Plavac, R. A.
Ramik, M. R. Steele, D. Young, 1 Am. Chem. Sac. 1993,115, 2300-2313.
[4] B. Zibrowius, M. W. Anderson, W. Schmidt, F.-F. Schiith, A. Aliev, K. D. M.
Harris, Zeolites 1993, 13, 607-610.
[5] G. Miiller, G. Eder-Mirth, H. Kessler, J. A. Lercher, J Phys. Chem. 1995, 99,
12327- 12331.
[6] A. Janin, J. C. Lavalley, E. Benazzr, C. Schott-Daries, H. Kessler, Stud. Sur$
Sci. Cutul. 1995, 94. 124-130.
[7] W. Schmidt, F Schiith. S . Kallus, Stud. Surf- Sci. Coral. 1997, IOJiA, 771 -778.
[S] T. B. Beebe. P. Gelin, J. T. Yates, Jr., SurJ Sci. 1984, 148, 526-550.
[9] L. Kubelkova, S . Beran, J. Lercher, Zeolites 1989, 9, 539-543.
[lo] C. Morterrd. E.Garrone, V. Bolis, B. Fubini, Spectrochim. Acta A 1987, 43,
[ll] 0 . Cairon, These de Doctorat d'universitt, Caen 1996.
[12] S . Khabt0u.T. Chevreau, J. C. Lavalley, MicroporousMuter. 1994,3,133- 148.
Many microporous main group oxides have been prepared by
hydrothermal synthesis"] but it has long been a goal to produce
lacunary materials with modulated catalytic activity by constructing frameworks with d-block metals in close proximity to
the voids. Haushalter et al. have shown how this can be achieved
for vanadium and molybdenum phosphates.['] The usefulness
of superheated fluids for preparing extended frameworks based
on metal-ligand interactions has recently been demonstrated
both by ourselvesL3]and
and we now wish to report the
extension of this technique to the preparation of a cobalt
squarate with a microporous structure. The cobalt -squaric acid
system has been extensively investigated under ambient condit i o n ~ 'and
~ ] gives compounds based on the framework found in
1 in most cases; analogous structures are also formed by the
corresponding compounds of manganese, iron, nickel, and zinc.
We report herein on compound 2, which has a structure unlike
those previously observed.
/[CO,(~l,-OH),(C,O,)21 . 3 H2O)" 2
The hydrothermal reaction of CoCl, .xH,O with squaric acid
and KOH in the ratio 2:3:8 in water at 200°C produces wellformed dark maroon crystals of 2. Small quantities ( < 5 %) of
pink crystals that we tentatively assign as the known com1 are also sometimes produced. The structurec6]of 2
is based on a backbone of Co,(OH), strips that run parallel to
the crystallographic c axis. The strips are formed from ,u3-OH
bridged equilateral triangles of cobalt atoms, which share alternating edges and vertices with the hydroxide groups lying above
and below alternate triangles (Figure 1). There are two different
Figure 1. ORTEP view of part of the cobalt chain in 2 showing the bridging of
squarate Iigands.
Dr. P. T. Wood, S . 0. H. Gutschke, Dr. M. Molinier, Dr. A. K. Powell
School of Chemical Sciences, University of East Anglia
Norwich, NR4 7TJ (UK)
Fax: Int. code +(1603)592710
e-mail: p.
[**I This work was supported by the Royal Society and the Nuffield Foundation
(P. T. W), the BBSRC (M. M.), the Wellcome Trust (A. K. P.), and through a
UEA studentship ( S . 0. H. G.). We wish to thank Dr. Gavin Whittaker of
Edinburgh University for performing the TGA measurments.
Angew. Chem. Int. Ed Engl 1997, 36, No. 9
Verlugsgesellschuft mbH. 0.69451 Wernheim, 1997
0570-0833/97/3609-0991$17.50+ .SO/O
cobalt environments, both of which have octahedral geometry.
The cobalt center Col, which lies at the shared vertex, is coordinated to two bridging hydroxide groups (Col-03 2.017(3) A)
and to four oxygen atoms from squarate ligands (Col-02
2.118(2) A), which bridge the two unshared edges of each
triangle. The cobalt center C02 and its symmetry equivalent
Co2B form the shared edge of two triangles and are bonded to
two bridging (Co2-02 2.171(2) A) and two terminal (Co2-01
2.049(2) A) squarate oxygen atoms and to two hydroxide
groups (Co2-03 2.060(2) A). The triangles formed by the
cobalt atoms are close to equilateral; the Col -C02 distance is
3.160(1) A and the Co2-Co2B distance 3.102(1) A.
The squarate ligands lie about an inversion center, have C-C
distances of 1.460(4) and 1.461(4) A, and bridge a total of six
cobalt atoms in two adjacent chains. The metal-ligand interactions result in infinite channels parallel to the c axis, with cobalt
hydroxide chains along the edges and squarate anions forming
the faces (Figure 2). The channels have lozenge-shaped cross-
[CU,(OH),(C,O,),]~~H,O has a similar open framework
structure with even larger channels, whereas Mn" and Zn" form
[M,(OH),(C,O,)], which contains a different morphology of
brucite-like strip that allows tighter stacking of squarate anions
and consequently less free space within the lattice. r91
In conclusion, we have shown that hydrothermal synthesis is
a powerful technique for preparing new coordination solids
containing transition metals. The use of templates to modify
recognized mineral forms to produce materials tailored for
specific functions is common in Nature in the form of biomineralization. The parallels between this process and our approach
are clear and indicate that this methodology is a promising route
for engineering tailored materials.
Experimental Sect ion
Hydrated cobalt(i1) chloride (0.250 g, 1.93 mmol), squaric acid (H,C,O,) (0.329 g,
2.88 mmol), and KOH (0.433 g, 7.72 mmol) were placed along with water (7 mL) in
a 23 mL-Teflon-lined autoclave and heated at 200°C for 112 h. The autoclave was
allowed to cool to room temperature over 4 h. The product was filtered and washed
with water to give the product as well-formed dark maroon crystals. Yield 0.15 g,
48% based on Co. Elemental analysis: Calcd. for C,H,O,,Co,: C 19.65,; H 1.65;
found: C 19.91, H 1.27%.
Received: April 25, 1996
Revised version: January 3, 1997 [29068IE]
German version: Angew. Chem. 1997,109,1028-1029
Keywords: cobalt crystal engineering * hydrothermal synthesis
microporosity squaric acid
Figure 2. Packing diagram of 2 parallel to [OOl]. The cobalt centers are drawn as
solid spheres.
sections; the distances of approximately 9.3 and 12.9 8, between
opposite vertices correspond to the lengths of the a and b axes,
respectively. Allowing for the van der Waals' radii of the atoms
this leaves approximately 7.5 8, of free space between opposite
vertices. The bridging hydroxide group points directly into the
void and is hydrogen-bonded to one of the water molecules
(03-04 2.847(7) A), whilst the second water molecule has only
a weak interaction with the framework ( 0 5 - 0 2 3.162(15) A).
The cobalt hydroxide strips are based on the Mg(OH), (brucite)
structure, the same as for CO(OH),,[~]with a portion of the
p3-bridging hydroxide groups replaced by oxygen atoms from
the squarate ligands. Thus, the structure can be viewed as
Co(OH), which has been modified by inclusion of squarate
anions. Modification of mineral structures by organic templates
has peviously been observed by us for polyhomometallic Fe3
and A13 hydroxo(oxo) clusters.18]
Thermal gravimetric analysis performed under an inert atmosphere shows that the compound loses 9 % of its mass smoothly
between 100 and 300 "C, corresponding to loss of the included
water. No further changes occur until 405°C where there is a
sharp loss of a further 41 % of the original mass corresponding
to decomposition to one of the oxides of cobalt. Single crystals
of 2 have been dehydrated but readily reabsorb most of the
water to regenerate a variant of the original structure that contains slightly less water. Hence the totally dehydrated form must
retain the same framework topology, and we are currently investigating its ability to absorb small molecules.
8 VCH Verlugsgesellschafr mbH, 0-69451 Weinheim. 1997
[l] R M. Barrer, The Hydrorhermai Chemistry of Zeolites, Academic Press, London, 1982.
(21 M. 1. Khan, L. M. Meyer, R. C. Haushalter. A. L. Schweitzer, J. Zubieta, J. L.
Dye. Chem. Muter. 1996.8, 43-53, and references therein.
[31 a) S. 0. H Gutschke, A. M. Z. Slawin, P. T, Wood. J. Chem. Soc Chem. Commun. 1995, 2197-2198; b) S. 0. H. Gutschke, M. Molinier, A. K. Powell.
R. E. P. Winpenny. P. T. Wood, Chem. Commun. 1996, 823-824.
[4] 0. M. Yaghi, H. Li, .
IAm. Chem. Soc. 1995, 117,10401-10402.
[5] a) R. West, H. Y Niu. .I Am. Chem. Soc. 1963,85,2589-2590; b) A. Ludi, P.
Schindler, Angew. Chem. 1968, 80. 664; Angew. Chem. Int. Ed. Engl. 1968, 7,
638; c) A. Weiss, E. Riegler. I. Alt, H. Bohme, C. Robl, Z. Nururforsch. B 1986,
41,18-24;d)O. S. Headley, L. A. Hall,Pol~hrdron1986,5,1829-1831;e)D. I.
Mahdraj, L. A Hall, ihid. 1988. 7. 2155-2157; f) I. Brach, J. Roziere, B. Anselment, K. Peters, Acta Crj,stallogr. C 1987, 43, 458-460.
[6] Crystal data of 2: C,H,O,,Co,, red parallelapiped, 0.08 x0.08 xO.19 mm,
monoclinic, C2/m, a = 9.330(1), h = 12.865(1), c = 5.506(1)& = 90.38(2)',
V = 660.9(1) A', Z = 2 . pc.(cd= 2.46gcrn-',
i(MoKJ =
0.71073 A, o scans, T = 293 K, 71 refined parameters, 615 unique reflections of
which 541 had F>4u(F). data were corrected for Lorentz and polarization
factors and an empirical absorption correction applied by using TEXSAN software, ~(Mo,,) = 3.80 mm-', min./max. transmission factors 0.7475-0.9991.
The structure was solved by direct methods (SHELXTL-PLUS), the hydrogen
atoms of the water molecules could not be located, the hydroxyl hydrogen atom
was located in a difference map and refined isotropically, all other atoms were
refined anisotropically using full-matrix least-squares on I F 2 I to give
R1 = 0.0241 (for 40 data), wR2 = 0.0692, S = 1.066, maximum residual electron density (largest electron hole) = 0.71( - 0.50) e k 3 . Crystallographicdata
(excluding structure factors) for the structure reported in this paper have been
deposited with the Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-179.167 Copies of the data can be obtained free of
charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2
lEZ, U K (fax: Int. code +(1223) 336-033; e-mail: deposit&
[7] A. F. Wells, Structurd Inorganic Chemistrv, Clarendon Press, Oxford, 1984.
[S] a) S. L. Heath, A K. Powell, Angew. Chem. 1992,104, 191-192; Angew. Chem.
In!. Ed. Engl. 1992.31, 191-193; b) S. L. Heath, P. A. Jordan, I D. Johnson,
G R. Moore, A. K. Powell, .
Inorg. Biochem. 1995.59, 785-794.
[9] S. 0. H. Gutschke. P. T. Wood, unpublished results.
0570-0833/97/3609-09923 17.50f .SO/O
Angew Chem. Int. Ed. Engl. 1997,36,No. 9
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preparation, microporous, structure, synthesis, c4o4, metali, hydrothermal, 3h2o, co3, transitional, squarate
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