A structurally diverse series of aluminum chloride alkoxides [Cl xAl(μ-OR)y]n (R = nBu, cHex, Ph, 2,4-tBu2C6H3)

Article abstract of DOI:10.1021/ic802251g

A diverse series of aluminum chloride alkoxides, [Cl_xAl(μ-OR) _y]_n(R=ⁿBu, ^cHex, Ph, 2,4- ^tBu₂C₆H₃), was synthesized using the reactions of dichlorethylalane

Full text of DOI:10.1021/ic802251g

8106 Inorg. Chem. 2009, 48, 8106–8114
DOI: 10.1021/ic802251g
A Structurally Diverse Series of Aluminum Chloride Alkoxides [ClxAl(μ-OR)y]n
(R = nBu, cHex, Ph, 2,4-tBu2C6H3)
Zdenek Moravec,† Radek Sluka,† Marek Necas,† Vojtech Jancik,‡ and Jiri Pinkas*,†
†Department of Chemistry, Masaryk University, Kotlarska 2, CZ-61137 Brno, Czech Republic, and ‡Instituto de
´
ꢀ
ꢀ
Quımica, Universidad Nacional Autonoma de Mexico, Circuito Exterior, Ciudad Universitaria, 04510,
ꢀ
ꢀ
Mexico D.F., Mexico
Received November 22, 2008
A diverse series of aluminum chloride alkoxides, [ClxAl(μ-OR)y]n (R = nBu, cHex, Ph, 2,4-tBu2C6H3), was synthesized using
the reactions of dichlorethylalane (EtAlCl2) with cyclohexanol (cHexOH), n-butanol (nBuOH), and phenols (PhOH and
2,4-tBu2C6H3OH). Eight molecular products were isolated and structurally characterized. The dimeric [Cl2Al(μ-
OcHex)2AlCl2] (1) was the smallest oligomer isolated among the cyclohexanolate derivatives. The adduct of 1 with
cyclohexanol is a dinuclear molecule [Cl2(HOcHex)Al(μ-OcHex)2AlCl2] (2) which represents a possible intermediate in the
conversion reaction leading to the formation of a trinuclear bicyclic [ClAl{(μ-OcHex)2AlCl2}2] (3). Two polymorphic forms of
3 were isolated. Further coordination of cyclohexanol to the Lewis acidic five-coordinate aluminum atom in 3 provided
[Cl(HOcHex)Al{(μ-OcHex)2AlCl2}2] (4) with octahedrally coordinated central aluminum. Compound 4 could be regarded
as a precursor to the well-known Mitsubishi (tridiamond) tetranuclear species. The reactions of EtAlCl2 with less sterically
demanding nBuOH yielded a cyclic trimer, [Cl2Al(μ-OnBu)]3 (5), and a unique trinuclear ionic species, [Cl2Al{(μ-OH)(μ-
OnBu)AlCl(HOnBu)3}2]Cl (6) with a linear Al(μ-O)2Al(μ-O)2Al core. In the reactions with phenols, the aromatic groups
preferentially stabilized dimeric structures of [Cl2Al(μ-OR)2AlCl2] (R = Ph, 7; 2,4-tBu2C6H3, 8). Since these compounds
could be considered as intermediates in the nonhydrolytic condensation reactions of metal halides with metal alkoxides, a
mixture of EtAlCl2 with cHexOH was used as a precursor for the nonaqueous synthesis of alumina by alkylhalide elimination.
Introduction
the preparation of alumina materials by nonhydrolytic sol-
gel,2 thermolytic,3 and atomic layer deposition4 methods.
There are only two structurally characterized examples of
monomeric aluminum chloride alkoxides, ROAlCl2(OEt2)
(Chart 1; A, R = 2,6-tBu2-4-MeC6H25a and 2,4,6-tBu3C6H25b),
that were sterically protected by bulky aryloxide groups and
electronically stabilized by the coordination of Et2O. Alumi-
num chloride alkoxides with smaller substituents undergo
intermolecular coordination of alkoxide oxygens to the Lewis
acidic Al atoms and are thus stabilized by the formation of
oligomers. Dimeric6 and trimeric7 aluminum chloride alkox-
ides [ROAlCl2]n (Chart 1; n = 2 (B), 3 (C)) are more common
than monomers, and they were in some cases proposed to exist
simultaneously in solution.6,8 ROAlCl2 oligomers undergo
Aluminum chloride alkoxides [ClxAl(μ-OR)y]n (R=alkyl,
aryl) are molecules that possess reaction centers of a high Lewis
acidity and therefore were studied as species important to
catalysis in organic reactions of carbonyl compounds and also
in ring-opening polymerizations.1 The presence of both Al-Cl
and Al-OR bonds that are capable of alkylhalide elimination
and condensation to Al-O-Al makes aluminum chloride
alkoxides promising precursors for the nonaqueous synthesis
of aluminum oxide. They were considered as intermediates in
*To whom correspondence should be addressed. Phone: þ420549496493.
Fax: þ420549492443. E-mail: jpinkas@chemi.muni.cz.
(1) (a) Antelmann, B.; Chisholm, M. H.; Iyer, S. S.; Huffman, J. C.;
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cules 2001, 34, 3159–3175. (b) Chisholm, M. H.; Navarro-Llobet, D.; Simonsick,
W. J. Macromolecules 2001, 34, 8851–8857. (c) Chisholm, M. H.; Gallucci, J.;
Navarro-Llobet, D.; Zhen, H. Polyhedron 2003, 22, 557–561.
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r
pubs.acs.org/IC
Published on Web 08/06/2009
2009 American Chemical Society

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8107
Chart 1
Tetranuclear tricyclic molecules of a specific structure
resembling the Mitsubishi logo (Chart 1; F)15 were observed
in several classes of aluminum compounds, such as homo-
leptic alkoxide tetramers [Al(OR)3]4,15 alkyl alkoxides [Al-
{(μ-OR)2MR2}3], and heterometallic alkoxides [M{(μ-OR)2
Al(OR)2}3].16 These molecules proved to be attractive stoi-
chiometric precursors to oxide materials, such as Al2O3 or
mixed metal oxides.17 The thermolysis reactions of aluminum
chloride alkoxides with aluminum alkyl alkoxides could also
lead to the formation of Al-O-Al moieties and alumoxane
materials.18
Interestingly, also several aluminum chloride alkoxides
[Al{(μ-OR)2AlCl2}3] (Chart 1; F, R = Et, nBu,6,19) were
shown to possess the Mitsubishi structure. They were formed
by different routes, such as alcoholysis of RAlCl2 followed by
a conversion reaction of an unknown mechanism, or by
ligand-scrambling reactions between EtAlCl2 and Al(OR)3.
We are interested in the synthesis of molecular precursors
for aluminum oxide and phosphate materials.20 Aluminum
chloride alkoxides emerge as suitable starting reagents for the
fabrication of alumina and aluminophosphates by nonhy-
drolytic condensation routes. However, their structural di-
versity and complex reactivity is not completely understood.
Here, we report on the synthesis and structural characteriza-
tion of a series of aluminum chloride alkoxides and alumi-
num chloride aryloxides [ClxAl(μ-OR)y]n (R=nBu, cHex, Ph,
2,4-tBu2C6H3) with substituents of a different steric demand.
Molecular structures and metric parameters of these mole-
cules involving dimeric and trimeric species and the products
of their conversion to trinuclear bicyclic molecules are dis-
cussed. The Lewis acidity of the Al centers is demonstratedby
the coordination of alcohol molecules and an increase of the
coordination number of aluminum from 4 to 5 and also from
5 to 6. These alcohol-coordinated species are proposed as
precursors to the molecules of high nuclearity. Finally, the
solution thermolysis of a mixture of EtAlCl2 with cHexOH is
shown to provide alumina by a nonhydrolytic condensation
reaction.
redistribution reactions in solution9 and on crystallization
provide neutral or ionic polynuclear complexes with Al/OR/
Cl stoichiometry different from the starting ratio 1:1:2. One type
of these oligomers is the trinuclear bicyclic molecules [ClAl-
{(μ-OR)2AlCl2}2] (Chart 1; D, R=Et,6 nBu,6 sBu,6 iBu,6 iPr,6,10
t
CH2 Bu6) with one five- and two four-coordinate Al atoms. The
transformation of ROAlCl2 to [ClAl{(μ-OR)2AlCl2}2] prob-
ably involves a Cl/OR ligand redistribution or replacement of
Cl in the reaction with ROH since a third of the ROAlCl2
molecules must be converted to (RO)2AlCl to finally form
[ClAl{(μ-OR)2AlCl2}2]. The mechanism of this reaction has not
been completely elucidated. The compounds of this type were
also prepared by the scrambling reactions of AlCl3 and Al-
Experimental Section
10
(OR)3 or by the reactions of the stoichiometry-optimized
General. All reactions were carried out under dry N2 using
vacuum line techniques or in an M. Braun drybox with both
H2O and O2 levels below 1 ppm. EtAlCl2 was purchased from
Aldrich (0.9 M solution in heptane) or from Witco. Cyclohex-
anol and n-butanol were distilled and kept over a molecular
sieve. Phenol and 2,4-t-Bu2C6H3OH (Fluka) were used as
mixtures of MeOAlCl2 and (MeO)2AlCl with bifunctional
alcohols.11 The structural motif D is also known in other
families of compounds, such as homoleptic trimeric aluminum
alkoxide [cHexOAl{(μ-OcHex)2Al(OcHex)2}2]12 and alkyl alk-
oxides [RAl{(μ-OR)2AlR2}2].13
A molecule that can be regarded as being derived from
these [ClAl{(μ-OR)2AlCl2}2] trinuclear species by the coor-
dination of an alcohol to the central Al atom was structurally
(15) (a) Folting, K.; Streib, W. E.; Caulton, K. G.; Poncelet, O.; Hubert-
Pfalzgraf, L. G. Polyhedron 1991, 10, 1639–1646. (b) Shiner, V. J., Jr.;
Whittaker, D.; Fernandez, V. P. J. Am. Chem. Soc. 1963, 85, 2318–2322. (c)
Turova, N. Ya.; Kozunov, V. A.; Yanovsky, A. I.; Boky, N. G.; Struchkov, Yu. T.;
Tarnopolsky, B. L. J. Inorg. Nucl. Chem. 1979, 41, 5–11.
i
characterized for PrOH and features a six-coordinate Al
center (Chart 1; E, R = iPr).14 It was obtained from the
reaction of MeAlCl2 with iPrOH in a 1:2 stoichiometric ratio.
(16) (a) Atwood, D. A.; Jegier, J. A.; Liu, S.; Rutherford, D.; Wie, P.;
Tucker, R. C. Organometallics 1999, 18, 976–981. (b) Munoz-Hernandez, M.-
A.; Wie, P.; Liu, S.; Atwood, D. A. Coord. Chem. Rev. 2000, 210, 1–10. (c)
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Neumuller, B. Chem. Soc. Rev. 2003, 32, 50–55.
(9) Belanger-Gariepy, F.; Hoogsteen, K.; Sharma, V.; Wuest, J. D. Inorg.
Chem. 1991, 30, 4140–4145.
(10) Yanovsky, A. I.; Kozunov, V. A.; Turova, N. Ya.; Furmanova, N.
G.; Struchkov, Yu. T. Dokl. Akad. Nauk SSSR (Russ.) 1979, 244, 119–122.
(11) Ziemkowska, W.; Pasynkiewicz, S.; Anulewicz-Ostrowska, R.; Frac-
(17) Wang, Y.; Bhandari, S.; Mitra, A.; Parkin, S.; Moore, J.; Atwood, D.
A. Z. Anorg. Allg. Chem. 2005, 631, 2937–2941.
(18) (a) Kosinska, W.; Zardecka, K.; Kunicki, A.; Boleslawski, M.;
Pasynkiewicz, S. J. Organomet. Chem. 1978, 153, 281–288. (b) Kosinska,
W.; Kunicki, A.; Boleslawski, M.; Pasynkiewicz, S. J. Organomet. Chem. 1978,
161, 289–297.
zak, M. Main Group Met. Chem. 2000, 23, 169–177.
::
(12) Pauls, J.; Neumuller, B. Z. Anorg. Allg. Chem. 2000, 626, 270–279.
(13) (a) Martınez, G.; Pedrosa, S.; Tabernero, V.; Mosquera, M. E. G.;
Cuenca, T. Organometallics 2008, 27, 2300–2305. (b) Uhl, W.; Gerding, R.;
Vester, A. J. Organomet. Chem. 1996, 513, 163–172. (c) Ziemkowska, W.;
(19) (a) Kunicki, A. R.; Orechin, A.; Zachara, J. Main Group Met. Chem.
1998, 21, 365–370. (b) Mitra, A.; Wang, Y.; Parkin, S.; Atwood, D. Dalton Trans.
2008, 1037–1042.
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45, 6562–6564.
Pasynkiewicz, S.; Glowiak, T. J. Organomet. Chem. 1998, 562, 3–10.
::
(14) Jorchel, P.; Sieler, J. Z. Kristallogr. 1997, 212, 884–889.

8108 Inorganic Chemistry, Vol. 48, No. 17, 2009
Moravec et al.
received. All hydrocarbon solvents were freshly distilled from
Na/benzophenone under N2. Tetraglyme was vacuum-distilled
(93-105 °C/ 3 Pa) and stored under dry N2. Benzene-d6 was
dried over and distilled from Na/K alloy and degassed prior to
use. Solution NMR spectra (1H, 13C) were recorded at 300 K on
Bruker Avance DRX 300 and DRX 500 MHz spectrome-
SADI) together with the restraints for the Uij values (SIMU,
DELU). Compound 4 crystallized as a racemic twin in the space
group P212121 with the Flack parameter refined to 0.50(4). The
completeness of the data set for compound 7 is only 88% due to
a defect in a low-temperature device during the data collection.
Unfortunately, we were not able to grow other crystals of this
compound; thus, the incomplete data set is used for the discus-
sion, as the data-to-parameter ratio is 12:9. Compound 6
crystallizes in a monoclinic space group C2/c with half of a
molecule in the asymmetric unit (a = 18.491, b = 17.032, c =
16.429 A, β = 114.44°) and is presented only as a model due to
the poor quality of the crystals. The programs included in the
SHELXTL, version 5.1 program package have been used to
solve22 and refine23 the structures and to prepare the tables
(XCIF). The drawings were rendered using the Gretep and
POV-Ray programs.24,25
Synthesis of [Cl2Al(μ-OcHex)2AlCl2] (1). A solution of cyclo-
hexanol (140 mg, 1.4 mmol) in heptane (5 cm3) was added
dropwise to a stirred solution of EtAlCl2 (178 mg, 1.4 mmol)
in heptane (5 cm3). A white solid precipitated and was subse-
quently dissolved to a clear colorless solution by heating to 45 °C
in a water bath. A slow cooling to ambient temperature afforded
a small crop of colorless crystals of X-ray quality that were used
for the X-ray diffraction analysis.
Synthesis of [Cl2(HOcHex)Al(μ-OcHex)2AlCl2] (2) and
[ClAl{(μ-OcHex)2AlCl2}2] (3). To a stirred solution of EtAlCl2
(3 mmol) in isohexane (6 cm3) at 0 °C was added dropwise a
solution of cyclohexanol (3 mmol) in hexane (10 cm3). A white
solid was formed, and the suspension was subsequently heated
to 50 °C. Upon heating, the solid was observed to dissolve over a
1 h period. The solution was cooled to 0 °C, yielding colorless
crystals of 2. The crystals were separated by decantation and
washed by a small volume of cold hexane at -50 °C. The
solution was further concentrated by solvent evaporation. A
batch of single crystals of 3 was obtained after cooling to 0 °C.
The crystals were separated by decantation and washed by a
small volume of cold hexane at -50 °C. The crystals of 2 and 3
were unstable at room temperature and darkened in a few days
on storage in the drybox.
1
ters with deuterated solvents as the internal lock. The H and
13C{1H} NMR spectra were referenced to the residual proton
signals or carbon resonances of benzene-d6 (7.15 and 128.0 ppm,
respectively). Thermal analyses (thermogravimetric/differential
thermal analysis, TG/DTA) were carried out on a MOM
Derivatograph-C instrument under static air with a heating rate
of 5 °C min-1 from 25 to 1100 °C. Samples (10-20 mg) were
contained in corundum crucibles. Gas chromatography/mass
spectrometry (GC/MS) spectra were obtained on a Shimadzu
GCMS-QP2010 mass spectrometer. A DB-XLB column (30 m,
diameter 0.25 mm, 150 kPa) was heated at 20 °C min-1 to 250 °C.
The ionization energy was set to 70 eV, and the spectra were
scanned from 35 to 400 m/z. A Stoe-Cie STADI P transmission
diffractometer operating with Ge monochromatized Co (λ =
1.788965 A) radiation (40 kV, 30 mA) and equipped with a
position sensitive detector was used for the powder X-ray
diffraction (XRD) data acquisition at ambient temperature.
IR spectra (4000-400 cm-1) were collected on an EQUINOX
55/S/NIR FTIR spectrometer. Samples were prepared as KBr
pellets. The FT Raman spectral measurements with FT-RA
module FRA 106/S were performed with a resolution of 1.5 cm-1
.
An air-cooled Nd:YAG laser (1064 μm, max output 500 mW)
was used for spectra excitation. The chloride content was
determined by potentiometric titrations with AgNO3. A Jobin
Yvon 170 Ultrace (lateral observation, generator 40 MHz, out-
put 1.0 kW, plasma gas flow 12 L min-1, monochromator 1 m)
inductively coupled plasma spectrometer was used for the
determination of aluminum content. The measurements were
performed at the Al lines at 309.271 and 396.152 nm. A Haake
Phoenix P1 Circulator cryostat with controlled cooling at 10°
day-1 was used for growing single crystals suitable for the X-ray
diffraction analysis. Scanning electron microscopy (SEM) mi-
crographs were taken on a Jeol 6700 Field emission microscope.
Dried powder was suspended in isopropanol and a drop was
placed on a cleaned silicon (100) slide. Surface areas and pore
volumes were determined by nitrogen adsorption at 77.4 K using
a volumetric technique21 on a Quantachrome Autosorb-1MP
instrument. Prior to the measurements, the samples were de-
gassed at 25 °C for at least 24 h until the outgas rate was less than
0.4 Pa min-1. The adsorption-desorption isotherm was mea-
sured for each sample at least three times. The specific surface
area was determined by the multipoint Brunauer-Emmett-
Teller (BET) method with at least five data points with relative
pressures between 0.05 and 0.23. Analysis was performed with
the instrument software package.
Yield of 2: 0.283 g, 38%. 1H NMR (2, CDCl3, ppm): δ 1.18-
1.35 (m), 1.55-1.65 (m), 1.84-1.87 (m), 2.22-2.31 (m), 4.10 (tt,
11.3, 3.8 Hz, OCH), 4.29 (tt, 10.8, 4.0 Hz, OCH), 5.8 (br s, OH).
13C-APT NMR (2, CDCl3, ppm): δ 24.32, 24.50 (C-3/5), 24.76,
25.26 (C-4), 34.59, 35.52 (C-2/6), 78.46, 79.00 (OCH). 27Al
NMR: δ 44 (ν1/2=470 Hz, Al[5]), 93 (ν1/2=390 Hz, Al[4]). Anal.
Calcd for Al2Cl4O3C18H34: Al, 10.9; Cl, 28.7. Found: Al, 12.4;
Cl, 28.7. For IR and Raman spectra of 2, see the Supporting
Information.
Yield of 3: 0.200 g, 30%. 1H NMR (3, C6D6, ppm): δ 0.58-
0.85 (m), 0.91-1.07(m), 1.27-1.53 (m), 1.74 (dq, 2 Hz, 11 Hz),
2.07 (d, 10 Hz), 2.40 (d, 10 Hz), 4.01 (tt, 10 Hz, 4 Hz), 4.20 (tt, 11 Hz,
3.5 Hz). 13C-APT NMR (3, C6D6, ppm): δ 24.10, 24.20 (C-3/5),
24.85, 25.35 (C-4), 35.07, 35.95 (C-2/6), 78.86, 79.67 (OCH).
27Al NMR: δ 45 (ν1/2 = 780 Hz, Al[5]), 91 (ν1/2 = 900 Hz, Al[4]).
For IR spectra of 3, see the Supporting Information.
Synthesis of [Cl(HOcHex)Al{(μ-OcHex)2AlCl2}2] (4). A solu-
tion of EtAlCl2 in isohexane (3 mmol, 6 cm3) was added
dropwise to a stirred solution of cyclohexanol (3 mmol) in
hexane (20 cm3) at 25 °C. A small amount of white solid was
formed. It was filtered out, and the colorless solution was put
into a cryostat. A small crop of crystals was formed at -10 °C.
X-Ray Structure Analysis. The intensity data of compounds
1-8 were collected on a KUMA KM-4 CCD κ-axis diffract-
ometer using graphite monochromatized Mo KR radiation (λ =
0.71073 A) equipped with an Oxford Cryosystem LT device at
120 K and corrected for absorption effects using ψ scan. The
structures were solved by direct methods. Non-hydrogen atoms
were refined anisotropically, while hydrogen atoms were in-
serted in calculated positions and isotropically refined assuming
a riding model. Where possible, the CH hydrogens were loca-
lized from the electron density map and refined isotropically
c
with Uij tied to the parent atom. The disordered Hex (in the
crystal of 4), nBu (in the crystal of 5), and tBu (in the crystal of 8)
were refined using geometry and distance restraints (SAME,
(22) SHELXS-97, Program for Structure Solution: Sheldrick, G. M. Acta
Crystallogr. 1990, A46, 467–473.
::
::
::
(23) SHELXL-97: Sheldrick, G. M. Universitat Gottingen: Gottingen,
Germany, 1997.
(21) (a) Rouquerol, F.; Rouquerol, J.; Sing, K. Adsorption by Powders and
Porous Solids; Academic Press: London, 1999. (b) Lowell, S.; Shields, J. E.;
Thomas, M. A.; Thommes, M. Characterization of Porous Solids: Surface
Area, Pore Size and Density; Kluwer Academic Publishers: Dordrecht, The
Netherlands, 2004.
(24) Laugier, J.; Bochu, B. GRETEP, version 2; Domaine Universitaire: St
Martin d'Heres, France, 2003.
(25) The POV-Ray Team. POV-Ray 3.6 - the Persistence of Vison
Raytracer. http://www.povray.org (accessed Aug 2009).

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8109
Table 1. Crystallographic Data and Refinement Parameters for Compounds 1-5, 7, and 8
compound number
empirical formula
1
2
3
4
5
7
8
C12H22
Al2Cl4O2
394.06
triclinic
P1
120(2)
0.71073
6.566(1)
8.509(2)
8.828(2)
97.73(3)
111.79(3)
99.25(2)
442(1)
C18H34
Al2Cl4O3
494.21
triclinic
P1
120(2)
0.71073
10.349(2)
11.416(2)
11.892(3)
74.84(3)
85.43(2)
67.18(3)
1250(1)
2
C24H44
Al3Cl5O4
654.78
monoclinic
P21/c
120(2)
0.71073
13.271(3)
13.056(3)
19.726(4)
90
109.50(3)
90
3222(1)
4
0.560
C30H56
Al3Cl5O5
754.94
orthorhombic triclinic
P212121
120(2)
0.71073
10.652(2)
15.056(3)
24.167(3)
90
C12H27
Al3Cl6O3
512.98
C12H10
Al2Cl4O
381.96
triclinic
P1
120(2)
0.71073
7.442(2)
7.867(2)
8.384(3)
115.09(2)
113.93(3)
94.14(3)
388.2(2)
1
C
28H42
Al2Cl4O2
606.38
monoclinic
C2/c
fw
cryst syst
space group
temp, K
λ, A
a, A
b, A
c, A
P1
120(2)
120(2)
0.71073
8.345(2)
16.094(3)
18.646(4)
101.23(2)
98.90(3)
98.48(3)
2386(1)
4
0.71073
12.524(1)
16.450(2)
15.921(1)
90
100.26(1)
90
3228(1)
4
0.444
R, deg
β, deg
90
90
γ, deg
V, A3
3876(1)
4
0.477
Ζ
1
0.767
μ, mm-1
no. of reflns collected
0.560
12479
0.840
15550
0.870
2434
2617
1505 (0.0364)
25158
50185
18760
no. of indep. reflns (Rint
)
no. of data/restraints/params 1505/0/91
4379 (0.0482)
4379/0/247
0.866
5651 (0.0363)
5651/0/325
1.045
6812 (0.0479)
6812/480/448
0.935
8149 (0.0457)
8149/95/461
0.984
1199 (0.0634)
1199/0/91
1.004
2838 (0.0239)
2838/63/197
1.079
GoF on F2
0.976
R1,a wR2b (I > 2σ(I))
R1,a wR2b (all data)
0.0311, 0.0720 0.0356, 0.0599 0.0287, 0.0681 0.0302, 0.0548 0.0378, 0.0893 0.0425, 0.1021 0.0351, 0.0871
0.0391, 0.0756 0.0707, 0.0682 0.0385, 0.0727 0.0463, 0.0578 0.0481, 0.0941 0.0553, 0.1113 0.0373, 0.0887
P
P
P
P
a R1 = ||Fo| - | Fc||/ |Fo|. b wR2 = [ w(Fo2 - Fc2)2/ (Fo2)2]1/2
.
Synthesis of [Cl2Al(μ-OnBu)]3 (5). To a stirred solution
of EtAlCl2 (178 mg, 1.4 mmol) in heptane (5 cm3) was added
dropwise a solution of n-butanol (104 mg, 1.4 mmol) in heptane
(5 cm3). The reaction mixture was stirred for 1 h and then
concentrated by solvent evaporation. As no solid precipita-
ted, the solvent was removed completely. The resulting color-
less viscous liquid was frozen in liquid N2 and then left to
warm to ambient temperature. This treatment led to the forma-
1200 (m), 1261 (m), 1302 (w), 1351 (w), 1466 (m), 2893 (s), 2927 (s),
3404 (m). Anal. Found: C, 12.9; H, 5.4%.
Results and Discussion
The syntheses of moisture-sensitive compounds 1-8 were
all carried out under anhydrous conditions by employing the
reactions between a particular alcohol or phenol and dichlor-
ethylalane in an equimolar ratio in hydrocarbon solvents at a
room temperature or with ice-bath cooling. In all cases, the
ethyl group of EtAlCl2 reacted completely with the acidic
hydrogen of the alcohol or phenol, and the ethane release
served as a driving force in these reactions. Aluminum
chloride alkoxides are known to produce mixtures of oligo-
mers and also undergo ligand scrambling and dynamic
exchange in solution.6,8,9 The distribution of species depends
on the reaction conditions, stoichiometry, time, and the
nature of substituents. Therefore, it is difficult to relate the
solution data, such as NMR spectra or cryoscopic molecular
weight, of these reaction mixtures to the solid state structures
of isolated products. The resulting stoichiometries of some of
the reported products (3, 4, and 6) differ from the starting
1:1:2 ratio for Al/OR/Cl, which may indicate that other
unidentified species were present in the mother liquor. In
our case, the X-ray-quality crystals were selected from a small
crop of crystalline products, and the molecular structures
were established by single-crystal X-ray diffraction experi-
ments. Crystal data and refinement parameters for com-
pounds 1-5, 7, and 8 are given in Table 1. A limited
stability of the solid products at room temperature even
under a drybox atmosphere prevented us from obtaining
meaningful CHN elemental analysis data. The content of Al
and Cl was established for 2 and agrees with the observed
structure.
1
tion of crystals suitable for the X-ray diffraction analysis. H
NMR (5, CD2Cl2, ppm): δ 1.00 (m, CH3), 1.42 (qn, 7.3 Hz,
CH2), 1.94-1.97 (m, CH2), 3.86 (m, OCH2), 4.11 (m, OCH2),
4.58 (t, 6 Hz, OCH2). 13C-APT NMR (5, CD2Cl2, ppm): δ 13.84,
13.95 (CH3), 18.72, 19.34, 33.78, 34.73 (CH2), 67.05, 73.20
(CH2O).
Synthesis of [Cl2Al{(μ-OH)(μ-OnBu)AlCl(HOnBu)3}2]Cl (6).
To a solution of EtAlCl2 (5.6 mmol) in isohexane (10 cm3) at
0 °C was added dropwise a solution of n-butanol (5.6 mmol) in
hexane (20 cm3). A small amount of a white solid was formed,
from which a clear solution was decanted. The solution was
concentrated by removing the solvent under reduced pressure.
Colorless crystals of 6 were formed after storing the solution for
several months at -15 °C.
Synthesis of [Cl2Al(μ-OPh)2AlCl2] (7). To a stirred solution of
EtAlCl2 (178 mg, 1.4 mmol) in heptane (5 cm3) was added
dropwise a solution of phenol (132 mg, 1.4 mmol) in heptane
(5 cm3). After a short period of stirring, a white solid precipi-
tated. It was dissolved by heating to 65 °C, and a clear colorless
solution was left to cool down slowly to room temperature.
Colorless crystals of 7 were formed.
Synthesis of [Cl2Al(μ-O-2,4-tBu2C6H3)2AlCl2] (8). A solution
of 2,4-di-tertbutylphenol (1.6 mmol) in toluene (10 cm3) was
added dropwise to a stirred solution of EtAlCl2 (1.5 mmol) in
toluene (10 cm3) at 0 °C. A light yellow solution was concen-
trated under reduced pressure and then was cooled to -15 °C.
Crystals of 8 were formed.
Reaction of EtAlCl2 with Cyclohexanol at a High Tempera-
ture. To a stirred solution of EtAlCl2 (3.0 mmol) in tetraglyme
(20 cm3) at room temperature was added dropwise a solution of
cyclohexanol (4.5 mmol) in tetraglyme (20 cm3). A clear solution
was heated to 150 °C for 14 h. A white precipitate was formed.
The solid product was isolated by centrifugation and washed
twice with toluene and dried under vacuum conditions. IR (KBr,
cm-1): ν 591 (s), 682 (s), 809 (s), 851 (s), 1033 (m), 1106 (vs),
The reactions provided three products of a general formula
[ROAlCl2]2 that crystallized from the solution as dimeric
cyclic species (Chart 1, B) in the case of compounds 1 (cHex),
7 (Ph), and 8 (2,4-tBu2C6H3). A dimer with four-coordinate
aluminum and three-coordinate oxygen atoms was pre-
viously structurally authenticated only in one aluminum

8110 Inorganic Chemistry, Vol. 48, No. 17, 2009
Moravec et al.
relatively high yield, which implied a partial conversion of
nBuOAlCl2 to (nBuO)3Al.6 We then isolated compound 5 by
crystallization of an oily product from the reaction mixture of
n
EtAlCl2 with BuOH and characterized it structurally as a
cyclic trimer (Figure 2). A comparison of corresponding
bond distances and angles in 5 with two structural data sets7
for trimeric [MeOAlCl2]3 is given in Table 4. Although the
coordination environment around O atoms is nearly planar
(Σ° 358.6-359.2), the Al3O3 central ring in 5 is highly
n
puckered (skewed boat) due to the packing of the Bu and
Cl groups.
So far, we have shown that, in the isolated compounds 1, 2,
5, 7, and 8, both chlorine atoms remained attached to Al.
However, further concentration of the reaction solutions or
different crystallization conditions in both cHexOH and
nBuOH systems led to the formation of trinuclear molecules
3, 4, and 6. The RO/Cl group exchange or HCl release must
have taken place to replace one Cl by an alkoxide.
Figure 1. Molecular structures of 1, 7, and 8 with numbering schemes.
All H atoms were omitted for clarity. Thermal ellipsoids are drawn at the
50% probability level.
dichloride alkoxide with monofunctionalbulky CH2C(CH3)3
substituents.6 Dimeric structures are displayed by a number
of aluminum chloride alkoxides with substituents possessing
additional oxygen or nitrogen donor atoms, which increase
the coordination number of aluminum to five (Chart 1, G).26
Molecules 1 and 7 form centrosymmetric dimeric structures
with four-membered Al2O2 planar cores (Figure 1). In con-
trast, the molecule of 8 displays a C2 molecular symmetry
with a puckered central Al2O2 ring (Figure 1). Selected bond
lengths and angles are compared for dimeric molecules in
Table 2. Their Al-Cl and Al-O bond lengths are shorter
than the corresponding distances in the five-coordinate
dimeric aluminum alkoxyalkoxide chlorides.26
The bicyclic trinuclear molecules 3 and 4 were obtained
from the cHexOH reaction. Compound 4 is derived from 3
by the coordination of one cyclohexanol molecule. Simi-
lar derivatives were reported for iPrOH (Chart 1, D, E; R =
iPr).10,14 The molecular structures of 3 and 4 are presented in
Figure 2, and a comparison of their bond distances and
angles with the analogous OiPr derivatives is shown in
Table 5. Compound 3 was obtained in two polymorphic
forms crystallizing in the same monoclinic space group but
with different cell parameters. It features a pseudo-C2 mo-
lecular symmetry, implying the presence of two enantiomers.
The two four-membered rings are fused at the central Al
atom, which is found in a near perfect trigonal-bipyramidal
coordination with the value of the geometric parameter τ =
98.0%.27 The peripheral Al atoms in 3 are four-coordinate
with a distorted tetrahedral geometry. The expected differ-
ences in the Al-Cl and Al-O bond lengths to four- and five-
coordinate Al centers were observed, as well as longer axial
Al-O bonds in comparison to the equatorial ones at the
trigonal-bipyramidal Al center. The 27Al NMR spectrum of 3
revealed two signals at 45 and 91 ppm that suggest the
presence of four- and five-coordinate Al atoms in solution.
The molecule of 4 lacks any symmetry elements and thus
has to provide two enantiomers. The central octahedrally
coordinated Al atom is bound to one Cl, four alkoxide, and
one alcohol O atom. The Cl ligand exerts a strong trans
influence that elongates the Al-O bond to the trans alkoxide
(Table 5). The preferential cyclohexanol binding to the five-
coordinate Al center instead of the four-coordinate one,
which would be expected on Lewis acidity grounds, may be
caused by additional stabilization by intramolecular hydro-
gen bonding of the cyclohexanol hydrogen to a bridging alko-
A novel compound, 2, formed in the reaction of EtAlCl2
c
with HexOH was obtained by crystallization at 0 °C in
contrast to 1, where the crystals grew at room temperature.
The molecule of 2 is derived from 1 by the coordination of
cyclohexanol oxygen to one Al center. The presence of excess
cHexOH over the starting 1:1 stoichiometry may stem from
an incomplete reaction. The alcohol coordination reveals
that four-coordinate Al atoms in dimeric 1 are still suffi-
ciently Lewis acidic. The molecule of 2 features one tetra-
hedrally coordinated Al and one trigonal-bipyramidal Al
atom (Figure 2). Relevant bond distances and angles are
gathered in Table 3. The five-coordinate Al atom displays
longer Al-OcHex and Al-Cl bonds than the four-coordi-
nate one. In the crystal lattice, two molecules of 2 are
connected by pairs of O-H
Cl hydrogen bonds to form
supramolecular dimeric aggregates.
3 3 3 3
To observe the steric influence of the alkoxide R-carbon
branching on the structure of ROAlCl2, we also carried out
n
the reactions of EtAlCl2 with BuOH. A similar system of
MeAlCl2 and nBuOH was previously studied with the aim of
xide O atom (O HO = 2.29 A).
3 3 3
n
1
preparing BuOAlCl2.6 The reported results of H NMR
spectroscopy suggested the presence of dimeric and trimeric
forms of nBuOAlCl2 (Chart 1, B, C) and a small amount of
the tetranuclear Mitsubishi-type molecule (Chart 1, F). This
tetranuclear species crystallized out on cooling to -15 °C in a
A low temperature crystallization of the EtAlCl2/nBuOH
system provided, besides the monocyclic trimer 5, a novel
trinuclear molecule, 6. Because of the small size of crystals of
6, only a structural model was obtained from the analysis of
X-ray diffraction data. As can be gathered from Figure 3, 6 is
an ionic compound with a trinuclear cation and chloride
anion. This result corresponds with a low temperature of
crystallization, which in the XAlCl2-THF systems (X=Me,
Cl) favored the ionic forms [Al(THF)4][XAlCl3] over the
(26) (a) Pietrzykowski, A.; Skrok, T.; Pasynkiewicz, S.; Brzoska-Mizgals-
ki, M.; Zachara, J.; Anulewicz-Ostrowska, R.; Suwinska, K.; Jerzykiewicz,
L. B. Inorg. Chim. Acta 2002, 334, 385–394. (b) Lin, C.-H.; Ko, B.-T.; Wang, F.-
C.; Lin, C.-C.; Kuo, C.-Y. J. Organomet. Chem. 1999, 575, 67–75. (c) Sobota, P.;
Utko, J.; Brusilovets, A. I.; Jerzykiewicz, L. B. J. Organomet. Chem. 1998, 553,
379–385. (d) Schumann, H.; Kaufmann, J.; Decherta, S.; Schmalz, H.-G.
Tetrahedron Lett. 2002, 43, 3507–3511.
(27) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.; Verschoor, G.
C. J. Chem. Soc., Dalton Trans. 1984, 1349–1356.

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8111
Table 2. Selected Bond Distances (A) and Angles (deg) of Dimeric [ROAlCl2]2
CH2 Bu6
7
8
t
bond
1
Al(1)-Cl(1)
Al(1)-Cl(2)
Al(1)-O(1)
Al(1)-O(1)#1a
2.089(1)
2.094(1)
1.796(2)
1.808(2)
2.056(2)
2.049(2)
1.772(3)
1.776(3)
2.083(2)
2.064(2)
1.814(2)
1.776(2)
2.094(1)
2.086(1)
1.833(1)
1.827(1)
CH2 Bu6
7
8
t
angle
1
O(1)-Al(1)-O(1)#1
Cl(1)-Al(1)-Cl(2)
Al(1)-O(1)-Al(1)#1
81.4(1)
114.0(1)
98.6(1)
82.5(1)
117.0(1)
97.5(1)
83.0(1)
117.8(1)
97.0(1)
80.8(1)
114.1(1)
98.0(1)
a #1: x þ 1, -y þ 1, -z þ 1 (1); -x, -y þ 1, -z (7); -x þ 1, y, -z þ 1/2 (8).
Figure 2. Molecular structure of 2 withC-H hydrogens omittedfor clarity and atomthe numberingscheme. A pair of2 molecules is connected bytwo O-
Cl bridges to form a dimer. Molecular structures of 3, 4, and 5 with all H atoms omitted for clarity are also shown. Thermal ellipsoids are drawn at the
50% probability level.
H
3 3 3 3
Table 3. Selected Bond Distances (A) and Angles (deg) of 2
compound 2
Table 4. Selected Bond Distances (A) and Angles (deg) of Trimeric [ROAlCl2]3
5, nBu
Mea,7b
Me7a
Bond
Bond
Al-Cl
Al-O
2.094-2.107(1)
1.796-1.815(2)
2.075-2.117(1)
1.788-1.803(1)
2.088-2.102(1)
1.801-1.810(2)
Cl(1)-Al(1)
Cl(2)-Al(1)
Cl(3)-Al(2)
Cl(4)-Al(2)
Al(1)-O(1)
2.097(1)
2.107(1)
2.194(1)
2.142(1)
1.764(2)
Al(1)-O(2)
Al(2)-O(1)
Al(2)-O(2)
Al(2)-O(3)
1.811(2)
1.897(2)
1.849(2)
1.931(2)
Angle
Cl-Al-Cl
O-Al-O
Al-O-Al
113.6-114.9
95.1-101.4
121.1-123.9
113.2-117.7
100.6-101.2
124.0-133.3
112.5-116.5
95.4-100.4
121.9-122.8
Angle
Al(1)-O(1)-Al(2)
Al(1)-O(2)-Al(2)
O(1)-Al(1)-O(2)
O(1)-Al(2)-O(3)
O(1)-Al(2)-O(2)
O(2)-Al(2)-O(3)
Cl(1)-Al(1)-Cl(2)
Cl(3)-Al(2)-Cl(4)
O(1)-Al(1)-Cl(1)
100.2(1)
100.3(1)
81.9(1)
167.2(1)
77.5(1)
89.7(1)
111.7(1)
117.4(1)
115.8(1)
O(2)-Al(1)-Cl(1)
O(1)-Al(1)-Cl(2)
O(2)-Al(1)-Cl(2)
O(1)-Al(2)-Cl(3)
O(2)-Al(2)-Cl(3)
O(3)-Al(2)-Cl(3)
O(1)-Al(2)-Cl(4)
O(2)-Al(2)-Cl(4)
O(3)-Al(2)-Cl(4)
113.9(1)
a Only data for the [MeOAlCl2]3 molecule are compared.
115.2(1)
115.6(1)
93.6(1)
118.4(1)
91.5(1)
95.1(1)
124.1(1)
93.1(1)
longed crystallization. The total charge balance is maintained
by one chloride ion equally distributed in two positions and
bound by hydrogen bonds to the bridging OH and one
alcohol. These Cl ions bind in the same way also to the
neighboring molecules, thus forming supramolecular chains
(Figure 3). The structure of 6 is related to the previously
reported compound [Cl2Al(μ-OAlCl3)(μ-OiPr)AlCl(iPrOH)3]14
(Chart 2, H) that can be thought of as 6 devoid of one
[AlCl(OH)(OR)(ROH)3] moiety and its bridging oxide atom
coordinated by Lewis acid AlCl3 instead of Brønsted acid
HCl.
We also examined the effect of aromatic substituents
on the structure of ROAlCl2. Previous studies on PhOAlCl2
by cryoscopy and IR spectroscopy8a reported the predomi-
nance of a trimer after vacuum distillation and dissolu-
tion in benzene. The presence of mixed oxygen-chloride
bridges in the trimeric molecule was proposed based on the
observed Al-O-C vibrations. In contrast, we found that the
neutral adducts [XAlCl2(THF)2].28 The molecule of 6 fea-
tures a centrosymmetric trinuclear Al(μ-O)2Al(μ-O)2Al core
with two fused four-membered rings and all three Al atoms
octahedrally coordinated. The central aluminum possesses
two trans-oriented Cl ligands and four oxygens. Each of the
two equivalent outer Al atoms is coordinated to one Cl,
bridging OH and alkoxide oxygens, and the octahedron is
completed by three n-butanol molecules. Their presence may
suggest an influence of adventitious moisture during pro-
(28) (a) Means, N. C.; Means, C. M.; Bott, S. G.; Atwood, J. L. Inorg.
Chem. 1987, 26, 1466–1468. (b) Sluka, R.; Necas, M.; Sindelar, P. Acta
Crystallogr. 2004, E60, m447–m448.

8112 Inorganic Chemistry, Vol. 48, No. 17, 2009
Moravec et al.
Figure 3. Model of structure 6. C-H hydrogens were omitted for clarity. (a) Molecule of 6 with intramolecular OH
Cl hydrogen bonds shown. (b) A
3 3 3 3
supramolecular chain connected by intermolecular OH
Cl hydrogen bonds.
3 3 3 3
Table 5. Selected Bond Distances (A) and Angles (deg) of Trinuclear [ClAl{(μ-
Chart 2
i
OR)2AlCl2}2] (R = cHex (3), Pr (D)) and [Cl(HOR)Al{(μ-OR)2AlCl2}2] (R =
cHex (4), iPr (E))
3
D, iPr10
Bond
AlV-Cl
2.129(1)
2.141(5)
av. 2.095
1.917(7)
1.840(7)
av. 1.794
AlIV-Cl
AlV-Oaxial
AlV-Oequat
AlIV-O
2.094-2.108(1)
1.898-1.904(1)
1.833-1.838(1)
1.772-1.793(1)
nuclear 3 by the coordination to one-half of dimeric 1. The
second coordination of cyclohexanol provides the hexa-
coordinate Al center in 4. We can speculate that 4 may
release HCl and form a putative K possessing a terminal
alkoxide group, which by reacting with monomeric ROAlCl2
could finally yield the tetranuclear F. In light of the presented
structural findings, the previously suggested system of ligand
scrambling reactions in ROAlCl2 with AlCl3 as one of the
products6 seems less plausible because the solubility of AlCl3
in hydrocarbon solvents is low.
Angle
Oaxial-AlV-Oaxial
O equat-AlV-Oequat
O-AlIV-O
167.5
108.7
av. 82.2
112.9-114.6
98.6
170.6
110.8
82.8
112.1
98.2
100.6
Cl-AlIV-Cl
Al-Oaxial-Al
Al-Oequat-Al
100.4-100.7
4
E, iPr14
AlVI-Cl
2.211(1)
2.287(2)
AlIV-Cl
2.112-2.131(1)
1.967(2)
1.982(2)
1.936(2)
1.929, 1.933(2)
1.767-1.783(2)
2.101-2.110(2)
1.961(3)
1.943(3)
1.922(3)
1.906, 1,913(3)
1.770-1.783(3)
To test the effectiveness of the aluminum cyclohexylalk-
oxide chlorides in nonhydrolytic sol-gel synthesis of alumi-
na, we used the mixture of EtAlCl2 and cyclohexanol as a
precursor for the solution thermolysis, which is expected to
induce condensation by alkylhalide elimination. The molar
ratio of EtAlCl2 to cyclohexanol was chosen to be 3:4.5 to
AlVI-O(H)
AlVI-O(trans to Cl)
AlVI-O(trans ROH)
AlVI-O(cis Cl/ROH)
AlIV-O
c
molecular structure of [Cl2Al(μ-OPh)2AlCl2] (7) is dimeric
with phenoxide bridges (Figure 1) when 7 is directly crystal-
lized from the reaction mixture. The substitution of the
phenyl ring at one of the ortho positions with the tBu group
did not change the oligomerization degree, and we isolated
compound 8, which is also dimeric (Figure 1) with the
aryloxide bridging groups. A similar ortho-disubstituted
ensure a complete elimination of HexCl. A high boiling
solvent, tetraglyme (bp 276 °C), was used to heat the mixture
to 150 °C for 14 h. During the reaction, a white solid
precipitated and was isolated by centrifugation. It consisted
of uniform spherical particles with a diameter of about 1 μm
(Figure 4). The as-prepared material contained 12.9% C and
5.4% H, which shows an incomplete condensation and
8b
c
2,6-Me2C6H3OAlCl2 was proposed to be dimeric with Cl
partial retention of the Hex groups; however, the GC/MS
bridges based on molecular weight determination and IR
spectra.
analysis of the volatile components of the reaction solution
revealed the presence of cHexCl, the expected condensation
byproduct. Thermal behavior of the solid powder was
studied by TG/DTA, which showed a continuous mass loss
(55%) from an ambient temperature to 550 °C. This weight
decrease was accompanied by two exothermic effects at 268
and 449 °C that correspond to oxidation of organic groups.
The solid residue after the TG/DTA analysis at 1100 °C
featured broad lines in the XRD diffractogram that were
The above-discussed series of structurally characterized
aluminum cyclohexylalkoxide chlorides 1-4 suggests a pos-
sible pathway for the transformation reactions that could
lead from ROAlCl2 to trinuclear and to tetranuclear deriva-
tives (Scheme 1). The dimeric 1 is coordinated by an alcohol
molecule to form 2, and this adduct can convert by splitting
off HCl through an unidentified intermediate J to the tri-

Article
Inorganic Chemistry, Vol. 48, No. 17, 2009 8113
assigned to poorly crystalline γ-Al2O3 (JCPDS card 10-425).
The surface area of the nonhydrolytic alumina powder was
measured by the BET method. The as-prepared product had
a surface area of 3.9 m2 g-1 when mild degassing conditions
(25 °C) were applied. However, the surface rose to 150 m2 g-1
after degassing at 350 °C under a vacuum for 10 h. This was
probably caused by the removal of residual organic groups
from the surface that decreased the size of alumina particles
and consequently increased the surface area.
Conclusions
The reactions of EtAlCl2 with alcohols yielded a wealth of
aluminum alkoxide chloride derivatives. This series shows
enormous variability of products that are present in the
reaction solution and undergo interconversion reactions
upon a slight change of the reaction and crystallization
conditions or in correspondence to the character of their
substituents.
Three new dimeric [Cl2Al(μ-OR)2AlCl2] molecules (1, 7,
c
and 8) were structurally authenticated. The Hex, Ph, and
2,4-tBu2C6H3 groups stabilize these dimers with the alkoxide
n
bridges. Less branched Bu substituents allowed the isolation
and structural characterization of trimeric [Cl2Al(μ-OnBu)]3 (5)
possessing a puckered central six-membered ring. A novel
structure of the alcohol-coordinated dimer [Cl2(HOcHex)-
Al(μ-OcHex)2AlCl2] (2) was established for the first time. It
proves that the AlO2Cl2 centers in dimeric [ROAlCl2]2 are still
sufficiently Lewis acidic to accept the coordination of cyclohex-
anol oxygen. This species may be an intermediate in the
conversion of ROAlCl2 to trinuclear aluminum alkoxide-chlor-
ides, such as [ClAl{(μ-OcHex)2AlCl2}2] (3), which was obtained
in two polymorphic forms. An increase in the coordination
Figure 4. SEM of the alumina particles from a nonhydrolytic condensa-
tion of EtAlCl2 with cyclohexanol.
Scheme 1

8114 Inorganic Chemistry, Vol. 48, No. 17, 2009
Moravec et al.
number of the central Al atom in 3 was effected by the
coordination of one alcohol molecule to form 4, which is only
the second example of the hexa-coordinate [Cl(HOR)Al{(μ-
OR)2AlCl2}2] species. This case shows a coordinatively unsa-
tisfied AlO4Cl center which is saturated by alcohol bonding.
The stability of 4 is augmented by intramolecular hydrogen
bonding of cyclohexanol OH to a bridging alkoxide oxygen.
A unique ionic trinuclear molecule, [Cl2Al{(μ-OH)(μ-On-
Bu)AlCl(HOnBu)3}2]Cl (6), with a linear Al(μ-O)2Al(μ-O)2-
Al array and all three Al atoms in an octahedral environment
represents a novel structural type among aluminum alkoxide
chlorides and attests to the known chemical and structural
variability in this class of compounds. A low crystallization
temperature suggests the entropic preference for its ionic
character.
Aluminum chloride alkoxides can serve as precursors to
alumina, as was shown by the thermolysis of the mixture of
EtAlCl2 and cyclohexanol in a high boiling solvent tetra-
glyme that provided HexCl and alumina particles by non-
hydrolytic condensation reactions.
c
Acknowledgment. Financial support for this work
through the grants MSM0021622410 and GACR 203/
08/1111 is gratefully acknowledged. The authors thank
J. Matejkova for the SEM measurements.
Supporting Information Available: Complete X-ray data for
compounds 1-5, 7, and 8 in CIF format; IR and Raman spectral
data of 2 and 3. This material is available free of charge via the
Internet at http://pubs.acs.org.