Extended coordination frameworks incorporating heterobimetallic squares

Article abstract of DOI:10.1039/b407244h

The molecular structure of aluminium and iron(III) complexes with 3-phenyl and 3-(4-pyridyl) (HL) substituted acetylacetonate ligands is appreciably distorted. For AlL₃ and FeL₃ this shows that the orientation of the side pyridyl-N donor atoms lone pairs is about 90 and 135° which favours the assembly of heterobimetallic square patterns in Al(Fe)L₃ complexes with metal ions. This was employed for the modular construction of semi-regular heterobimetallic networks, in which the pyridyldiketonate ligands bridge pairs of Fe(Al)/Cd(Co) metal ions and support the structure of 1D and 2D coordination polymers. The unprecedented 2D structure of [Cd{AlL₃}(CH₃OH){NO₃} ₂]·2CHCl₃ and Cd{AlL₃}-(CH ₃OH)Br₂]·2CHCl₃·2CH ₃OH is based upon plane tiling by a set of heterobimetallic squares and octagons, while [Cd{FeL₃}₂(NO₃) ₂]·2H₂O and [Co{AlL₃}₂Cl ₂]·4CHCl₃·2CH₃OH are 1D polymers and exist as chains of heterobimetallic squares sharing opposite vertices.

Full text of DOI:10.1039/b407244h

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F U L L P A P E R
Extended coordination frameworks incorporating
heterobimetallic squares†
Volodimir D. Vreshch,a Andrey B. Lysenko,a Alexander N. Chernega,b Judith A. K. Howard,c
Harald Krautscheid,d Joachim Sielerd and Konstantin V. Domasevitch*a
a
Inorganic Chemistry Department, Kiev University, Volodimirska Street 64, Kiev 01033, Ukraine.
E-mail: dk@anorgchemie.univ.kiev.ua
Institute of Organic Chemistry, Murmanskaya Str.4, Kiev 253660, Ukraine
Dept. of Chemistry, University of Durham, Durham, UK DH1 3LE
Institut für Anorganische Chemie, Universität Leipzig, Linnéstraße 3, D-04103 Leipzig,
b
c
d
Deutschland
Received 13th May 2004, Accepted 14th July 2004
First published as an Advance Article on the web 13th August 2004
The molecular structure of aluminium and iron(III) complexes with 3-phenyl and 3-(4-pyridyl) (HL) substituted
acetylacetonate ligands is appreciably distorted. For AlL3 and FeL3 this shows that the orientation of the side pyridyl-N
donor atoms lone pairs is about 90 and 135° which favours the assembly of heterobimetallic square patterns in Al(Fe)L3
complexes with metal ions. This was employed for the modular construction of semi-regular heterobimetallic networks,
in which the pyridyldiketonate ligands bridge pairs of Fe(Al)/Cd(Co) metal ions and support the structure of 1D and
2D coordination polymers. The unprecedented 2D structure of [Cd{AlL3}(CH3OH){NO3}2]·2CHCl3 and Cd{AlL3}-
(CH3OH)Br2]·2CHCl3·2CH3OH is based upon plane tiling by a set of heterobimetallic squares and octagons, while
[Cd{FeL3}2(NO3)2]·2H2O and [Co{AlL3}2Cl2]·4CHCl3·2CH3OH are 1D polymers and exist as chains of heterobimetallic
squares sharing opposite vertices.
Introduction
Properties of network solids1 originate in their structure and
thus they can be designed in a rational manner using a crystal
engineering approach.1,2 Many important and attractive synthetic
targets for the coordination frameworks are illustrated by 2D
semi-regular topologies that are sustained with sets of closely
packed (molecular triangles, squares) and very open (cf. molecular
hexagons, octagons) regions within the network.3 This feature could
be especially suited for the construction of zeolite-like structures4,5
that possess relatively low overall porosity while maintaining the
large cages for guest molecules.6 However, these clear prototypes
still remain unexplored in the chemistry of coordination polymers7
and it is difficult to anticipate such connectivity in metal–organic
systems. For example, each of the semi-regular three-connected nets
(Scheme 1) has angles at the net vertices that cannot be sustained
with a typical coordination around metal ions.
A promising tool for tuning the coordination architecture may
Scheme 1 Three-connected semi-regular nets. Angles at the net vertices
be found by incorporating into the network more than a single type
of coordination geometry, if one can achieve a highly controllable
assembly of heterometallic polymers with the desired distribution
of different metal centers in the lattice and particularly employ-
ing secondary building blocks (‘metal complexes as secondary
ligands’)8 whose conformation inherently matches the metrics
of the semi-regular nets. Thus, tridentate ligands supporting very
uncommon binding directions,  = 90° and 2 × 135°, could favor
the assembly of the square/octagonal net (Scheme 1(a)). We report
an approach for modular engineering of such unprecedented semi-
regular nets incorporating mixed-metal square motifs. This was
feasible with two-step utilization of the ligand functionality and
pre-construction of a suitable building block as an initial step.9
are uncommon for coordination polymers: 90 and 2 × 135° (a); 90, 120 and
150° (b); 60 and 2 × 150° (c).
tris-diketonates and considering metal 3-phenylpentane-2,4-
dionates Al(PhAcac)3·2PhH 1 and Fe(PhAcac)3 2 as a suitable
molecular model. Though the compounds exist as neutral com-
plexes with expected octahedral six-fold coordination of the metal
ion, the molecular structure at first glance is unusual. Two of three
chelate metallocycles are non-planar, with an appreciable bend
along the OO line, and this facilitates the closer disposition of
two coordinated ligands (Scheme 2, Fig. 1). Such a tight packing
of two ligands within the coordination sphere allows the molecule
to adopt a more compact configuration and it minimizes the moiety
volume, i.e. leads to a “collapse” of the molecular structure. This
was observed also for molecular metal complexes with a 3-(4-
pyridyl) substituted acetylacetonate ligand that possesses a very
similar shape and steric volume, AlL3·3H2O 3 and FeL3 4. The
maximal deviation of the metal ion from the mean plane of the che-
late fragment, 0.81 Å, was observed for 4. The “collapsed structure”
may be regarded as an inherent feature of metal tris-diketonates
bearing large aromatic substituents in 3-position of the ligand and
it is unlikely to be predetermined purely by packing effects since
Results and discussion
The desired irregular configuration of the tecton binding
sites was readily accessible for functionally substituted metal
† Electronic supplementary information (ESI) available: Details for
preparations, crystal structure determination and refinement. See http:
//www.rsc.org/suppdata/
T h i s j o u r n a l i s
©
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4
D a l t o n T r a n s . , 2 0 0 4 , 2 8 9 9 – 2 9 0 3
2 8 9 9

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Scheme 2 Distortion of the molecular tris-diketonate structure.
Fig. 2 Inherent conformation of the tris-complexes ML3 (M = Al 2) (a)
facilitates assembly of heterobimetallic squares with d-metal ions coordinat-
ing side nitrogen atoms of the ML3 tecton, for example the Co2Al2 square
pattern seen in structure 6 (b).
Fig. 1 The distorted structure of the aluminium complex 1 showing
immobilization of the guest benzene molecule by trifurcated CHO
hydrogen bonding.10 Bond lengths Al–O are in the range 1.858–
1.882(2) Å.
either unsolvated complexes 2, 4 or water and benzene solvates 3, 1
manifest an equally appreciable distortion of the molecules.
As a result of the “molecular collapse”, the angles between the
vectors of nitrogen atoms lone pairs for 4-pyridyl functionalized
species 3 ( = 88.6, 134.5, 136.9°) and 4 ( = 71.7, 135.3, 152.9°)
are far from evident values of 3 × 120° (Fig. 2). There are no suit-
able structural prototypes for direct comparison, while 64 of 67
neutral metal tris-diketonate moieties observed as yet in crystal
structures11 had a simple regular geometry (120 ± 10°). The only
exceptions are somewhat more distorted iron(III) and manganese(III)
dipivaloylmethanides12 and a bismuth(III) compound, in which a
lone pair of the metal ion is stereoactive.13
Scheme 3 Network topologies originating in combination of the
‘collapsed triangles’ ML3 and T-shape [M′N3] (a) and square [M′N4]
(b) coordination of octahedral metal ions.
Heterobimetallic squares are a basic motif for the coordina-
tion networks based upon ML3 building blocks. The structure of
[Cd{FeL3}2(NO3)2]·2H2O 5 with alternating Cd and Fe centres
exemplifies a 1D array of heterobimetallic squares sharing opposite
vertices (Fig. 3). FeL3 units serve as angular bidentate connectors
( = 87.6°) and the organic ligands bridge pairs of Fe and Cd atoms
at 10.0 Å. The typical six-fold coordination of the cadmium atoms
includes pyridyl nitrogen atoms (Cd–N 2.33, 2.37 Å) of four FeL3
molecules and two trans-situated nitrate groups (Table 1). The
non-coordinated pyridine groups form hydrogen bonds with water
of crystallization, that preclude interdigitation of the coordination
bands [Cd{FeL3}2(NO3)2]n in a fashion found for the 1D ‘railroad
motifs’formed by 4,4′-bipyridine.17 Actually the same structure was
observed for Co/Al complex [Co{AlL3}2Cl2]·4CHCl3·2CH3OH 6.
Chloride ions, which are trans-coordinated to cobalt(II) centres
(Co–Cl 2.44 Å, Fig. 2(b)), have a smaller size than the nitrate groups
in 5, and in the present case, the liberated crystal volume is occupied
by guest chloroform molecules, four per cobalt atom.
Coordination of the remaining third binding site of the ML3
module could increase the dimensionality of the structure and
allow the generation of extended arrays, while preserving the basic
heterobimetallic squares, unlike those for simpler bifunctional self-
assembly ligands.18 The configuration of the binding sites that are
situated at the angles 90° and 2 × 135°, is especially suitable for
generation of semi-regular three-connected topologies support-
ing metal–organic squares and octagons (Scheme 3). This new
possibility has been demonstrated by the 2D network formed in
Mixed-metal coordination frameworks
The above features of the molecular structure are a key pre-requisite
for the rational application of the ‘triangular’ building blocks ML3,
for the design of semi-regular coordination polymers, using coordi-
nation of the side pyridyl-N donors to additional octahedral metal
ions. Supramolecular structures of the resulting heterobimetallic
compounds thus could be pre-programmed at the molecular level
sincefacileorthogonalorientation( = 90°)oftheperipheralpyridyl
groups within the ML3 tecton frame predetermines the formation of
the densest mixed-metal squares, instead of regular open hexagons,
with  = 120° (Fig. 2). A target 2D semi-regular topology origi-
nates in combination of the ‘collapsed triangles’ ML3 with T-shape
[M′N3] metal ion coordination, while square planar [M′N4] centres
can not afford a 2D net and a simpler 1D chain may by anticipated
as a structure motif (Scheme 3). We therefore explored the bind-
ing of ML3 to octahedral metal ions, which typically adopt either
T-shape [M′N3] or planar [M′N4] coordination geometries with the
pyridyl N-donor ligands.14,15 That the molecular metal complexes
of this type retain donor properties of the pyridyl functions and can
be exploited as efficient bridging metalloligands were proved by
examination of the simpler ML2 (M = Be, Cu) systems.16
2 9 0 0
D a l t o n T r a n s . , 2 0 0 4 , 2 8 9 9 – 2 9 0 3

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Table 1 Selected bond distances (Å) and angles (°) for complexes 5–8
[Cd{FeL3}2(NO3)2]·2H2O 5
Cd(1)–N(3)
Cd(1)–N(1)
Cd(1)–O(7)
2.333(3) × 2
2.373(3) × 2
2.396(7) × 2
Fe(1)–O
1.978(3)–2.019(3)
93.20(13)
89.40(19)
N(3)–Cd(1)–N(1)
N(3)–Cd(1)–O(7)
N(1)–Cd(1)–O(7)
101.2(2)
[Co{AlL3}2Cl2]·4CHCl3·2CH3OH 6
Co(1)–N(1)
Co(1)–N(2)
Co(1)–Cl(1)
2.232(4) × 2
2.203(7) × 2
2.445(1) × 2
Al(1)–O
1.859(4)–1.896(5)
86.4(2)
91.1(1)
N(2)–Co(1)–N(1)
N(1)–Co(1)–Cl(1)
N(2)–Co(1)–Cl(1)
90.0(1)
[Cd{AlL3}(CH3OH){NO3}2]·2CHCl3 7
Cd(1)–N(1)
Cd(1)–N(2)
Cd(1)–N(3)
Cd(1)–O(8)
Cd(1)–O(10)
Cd(1)–O(13)
2.390(4)
2.361(4)
2.374(4)
2.453(6)
2.415(8)
2.348(4)
Al(1)–O
1.861(3)–1.886(3)
N(3)–Cd(1)–N(1)
N(2)–Cd(1)–N(3)
N(2)–Cd(1)–N(1)
N(3)–Cd(1)–O(8)
88.5(1)
90.1(1)
164.3(1)
89.08(19)
[Cd{AlL3}(CH3OH)Br2]·2CHCl3·2CH3OH 8
Cd(1)–N(1)
Cd(1)–N(2)
Cd(1)–N(3)
Cd(1)–O(7)
Cd(1)–Br(1)
Cd(1)–Br(2)
2.386(7)
2.374(8)
2.376(7)
2.389(7)
2.706(1)
2.689(1)
Al(1)–O
1.854(6)–1.883(6)
N(2)–Cd(1)–N(3)
N(2)–Cd(1)–N(1)
N(3)–Cd(1)–N(1)
Br(2)–Cd(1)–Br(1)
91.7(3)
87.7(2)
174.2(3)
172.09(4)
Fig. 3 One-dimensional motif incorporating Cd/Fe heterobimetallic
squares in structure 5.
the Cd/Al complexes [Cd{AlL3}(CH3OH){NO3}2]·2CHCl3 7 and
[Cd{AlL3}(CH3OH)Br2]·2CHCl3·2CH3OH 8 (Fig. 4), where all
available side functionality of the metalloligand is employed for
binding with cadmium atoms and results in the generation of the
polymer (7:  = 95.2, 126.1, 138.6°). In 7 the cadmium atoms adopt
a distorted hepta coordination including three pyridyl nitrogen
atoms (“T-shape”) and oxygen atoms of monodentate and asym-
metric-bidentate nitrate groups and a methanol molecule, while for
8 the six-fold coordination of the cadmium atoms is retained with
two trans-situated bromine atoms and also with three equatorial
pyridyl N-donors and a methanol molecule (Fig. 4(a)). Thus both
the aluminium and cadmium atoms provide three-connected verti-
ces for the polymeric structure.19
The resulting coordination network is very open and for 7 it
occupies 3117.9 Å3 per unit cell or only 59.8% of the crystal
volume (62.0% for network in 8).20 It is even more interesting that,
unlike the more usual three-connected 4,4′-bipyridine polymers,1,7,15
the network consists of two kinds of regions in equal proportions—
dense molecular squares and very open octagons, and only the
octagons provide large enough voids, ca. 21 × 7 Å, for hosting
the guest molecules (Fig. 4(b)). This topology is unprecedented
for metal–organic polymers and it may be related to the tellurium
sublattice in the Cs3Te22 structure.21
Fig. 4 Cd/Al heterobimetallic squares sustained with T-shape [CdN3]
coordination of cadmium atoms in structure 8 (a) and resulting 2D
coordination pattern in the form of a semi-regular net (b). Each large
octagonal Cd4Al4 void is populated with four chloroform molecules.
molecules and these topologies are clearly predictable on the
basis of molecular structure. The results demonstrate a potential
of the multi-step approach towards heterometallic coordination
polymers that could be anticipated for ambifunctional ligands
bridging pairs of suitable tetra-, hexa- and octa-coordinate p-and
d-metal ions (cf. Al3+, Ga3+, Fe3+, Zr4+, lanthanides). Pre-assembly
of the secondary tectons using coordination interactions illustrates
also cost- and time-effective alternatives to common organic
preparations of desired tectons and will simplify many other tasks
of supramolecular synthesis.
Conclusion
Our study suggests wider possibilities for the construction of a
number of semi-regular networks incorporating dense molecular
squares and larger polygons that were categorized by Wells,3
but currently are relatively unknown. Either 1D or 2D networks
designed using ‘triangular building blocks’ ML3 have an imprint
of the inherent symmetry and the configuration of the ML3
D a l t o n T r a n s . , 2 0 0 4 , 2 8 9 9 – 2 9 0 3
2 9 0 1

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Experimental
3-Phenylpentane-2,4-dione22 and 3-(4-pyridyl)pentane-2,4-dione
(HL)23 were prepared according to the literature methods.
For preparation of the complex 1, solid NaHCO3 (0.56 g,
6.67 mmol) was added, in several portions during 20 min period,
to a well-stirred solution of 1.2 g (6.77 mmol) 3-phenylpentane-
2,4-dione in 15 ml MeOH and 5 ml H2O. Then the mixture was
combined with a solution of 0.68 g (1.8 mmol) Al(NO3)3·9H2O
in 6 ml H2O and the colorless precipitate was recrystallized from
benzene to give 0.82 g (64% yield) of pure Al(PhAcac)3·2PhH 1.
The solvate loses the incorporated solvent in air within hours. The
complex 3 was prepared similarly and was recrystallized from aque-
ous methanol to give AlL3·3H2O (60%). The iron(III) diketonates
were synthesized in a similar fashion, reacting the components in a
water–methanol mixture. Brown precipitates were dissolved in dry
methanol and slowly evaporated to ca. 2 ml volume, yielding pure
complexes 2 (88%) and 4 (39%). The compounds 1–4 are soluble
in methanol and chloroform.
For preparation of [Cd{FeL3}2(NO3)2]·2H2O 5, 10 mg
(0.032 mmol) Cd(NO3)2·4H2O was dissolved in 5 ml MeOH and
mixed with a solution of 20 mg (0.035 mmol) FeL3 in 4 ml MeOH.
The resulting orange mixture was filtered and left overnight giving
15 mg of brown platelets 5 in a 60% yield. It was not possible to
obtain the Al analog in the same fashion, using the AlL3 tecton.
Crystals of the compounds 6–8 were obtained using a
layering technique. In a typical synthesis, a solution of 40 mg
(0.08 mmol) CoCl2·6H2O in 4 ml MeOH was layered over
a solution of 70 mg (0.126 mmol) AlL3 in 1 ml MeOH and
3 ml CHCl3. Slow interdiffusion of the layers, in a 7–8 days
period, led to crystallization of 45 mg (40% yield) of the light-
blue prisms [Co{AlL3}2Cl2]·4CHCl3·2CH3OH 6. Compounds
[Cd{AlL3}(CH3OH){NO3}2]·2CHCl3 7 and [Cd{AlL3}(CH3OH)
Br2]·2CHCl3·2CH3OH 8 were synthesized in a similar way, in
40–45% yields.
Complexes 6–8 readily lose incorporated solvent molecules with
disintegration of the structure. They are also unstable under the
mother solution since the initially formed crystals lose crystallinity
and dissolve in a period of 15–20 days. It was not possible to obtain
any crystals by the layering method for any mixed-metal FeL3 spe-
cies and the only isolable materials were isomorphous products of
the ion exchange: M{L}2(H2O)2·3H2O, M = Cd and Co (trigonal,
space group R3, a = 22.350(3), c = 13.222(2) Å).
Crystallography
The data were collected using CAD-4 Enraf Nonius (1, Cu-K,
 = 1.54178 Å), Siemens SMART CCD (2–3, 5–7) and Stoe IPDS
(4, 8) diffractometers (Mo-K,  = 0.71073 Å) (Table 2). The struc-
tures were solved by direct methods and refined by least-squares
techniques using SHELXS-86, SHELXL-9724 and CRYSTALS
(1, 2).25 The non-hydrogen atoms were refined anisotropically and
hydrogen atoms were added as fixed contributions with invari-
ant isotropic U values at 0.08 Å2. The hydrogen atoms of solvate
methanol and water molecules in 5, 6 and 8 were not included. One
of three solvate water molecules in 3 is disordered and correspond-
ing hydrogen atoms were not included. In 5 the coordinated nitrate
groups are disordered over two positions that were resolved with
partial contributions of 0.75 and 0.25 and fixed standard geometry
of NO3− ions. Thermal parameters for one of two coordinated nitrate
groups in 7 also were suggestive of possible disorder, but we were
not successful in resolving it. The geometry of the nitrate group
was constrained, N–O 1.25(3), and this led to a stable model. Part
of solvate chloroform molecules in structures 6–8 were refined
with restrained geometry (C–Cl 1.74(1) Å) in order to improve the
refinement stability.
CCDC reference numbers 224037–224041 and 238710–
238712.
See http://www.rsc.org/suppdata/dt/b4/b407244h/ for crystallo-
graphic data in CIF or other electronic format.
2 9 0 2
D a l t o n T r a n s . , 2 0 0 4 , 2 8 9 9 – 2 9 0 3

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10 G. R. Desiraju and T. Steiner, The Weak Hydrogen Bond (IUCr Mono-
Acknowledgements
graph on Crystallography 9), Oxford Science Publ., Oxford, 1999.
11 Cambridge Crystallographic Data Center, CSD, Release October 2003.
12 P. Magnus, A. H. Payne, M. J. Waring, D. A. Scott and V. Lynch,
Tetrahedron Lett., 2000, 41, 9725; I. A. Baidina, P. A. Stabnikov,
V. I. Alexeev, I. K. Igumenov and S. V. Borisov, Zh. Strukt. Khim., 1986,
27, 102.
We acknowledge support from Deutsche Forschungsgemeinschaft
(J. S. and K. V. D.), Royal Society (A. N. Ch.) and the EPSRC for a
Senior Research Fellowship (J. A. K. H.).
References
13 L. Armelao, G. Bandoli, M. Casarin, G. Depaoli, E. Tondello and
A. Vittadini, Inorg. Chim. Acta, 1998, 275, 340.
1 C. Janiak, Dalton Trans., 2003, 2781.
2 R. Robson, J. Chem. Soc., Dalton Trans., 2000, 3735; A. J. Blake,
N. R. Champness, P. Hubberstey, W. S. Li, M. A. Withersby and
M. Schröder, Coord. Chem. Rev., 1999, 183, 117; J. A. R. Navarro and
B. Lippert, Coord. Chem. Rev., 2001, 222, 219.
14 S. A. Barnett and N. R. Champness, Coord. Chem. Rev., 2003, 246,
145.
15 H. Gudbjartson, K. Biradha, K. M. Poirier and M. J. Zaworotko, J. Am.
Chem. Soc., 1999, 121, 2599.
3 A. F. Wells, Three-Dimensional Nets and Polyhedra, Wiley-Inter-
science, New York, 1977; A. F. Wells, Structural Inorganic Chemistry,
Clarendon, Oxford, 5th edn., 1986.
16 B. Chen, F. R. Fronczek and A. W. Maverick, Chem. Commun., 2003,
2166; V. D. Vreshch, A. N. Chernega, J. A. K. Howard, J. Sieler and
K. V. Domasevitch, Dalton Trans., 2003, 1707.
4 S. Noro, S. Kitagawa, M. Kondo and K. Seki, Angew. Chem., Int. Ed.,
2000, 39, 2082.
17 O. M. Yaghi, H. Li and T. L. Groy, Inorg. Chem., 1997, 36, 4292.
18 R. Song, K. M. Kim and Y. S. Sohn, Inorg. Chem., 2003, 42, 821.
19 Recent overviews on three-connected inorganic and coordination nets:
A. Ienco, D. M. Proserpio and R. Hoffman, Inorg. Chem., 2004, 43,
2526; L. Öhrström and K. Larsson, Dalton Trans., 2004, 347.
20 A. L. Spek, PLATON/PLUTON, Jan. 1999, Acta Crystallogr., Sect. A,
1990, 46, C34.
5 K. Seki, Chem. Commun., 2001, 1496; H. Li, M. Eddaoudi,
M. O’Keeffe and O. M. Yaghi, Nature, 1999, 402, 276; M. Eddaoudi,
H. Li and O. M. Yaghi, J. Am. Chem. Soc., 2000, 122, 1391; L. C.
Tabares, J. A. R. Navarro and J. M. Salas, J. Am. Chem. Soc., 2001,
123, 383.
6 E. B. Rusanov, V. V. Ponomarova, V. V. Komarchuk, H. Stoeckli-Evans,
E. Fernandez-Ibañez, F. Stoeckli, J. Sieler and K. V. Domasevitch,
Angew. Chem., Int. Ed., 2003, 42, 2499.
7 B. Moulton and M. J. Zaworotko, Chem. Rev., 2001, 101, 1629.
8 B. D. Chandler, A. P. Ĉoté, D. T. Cramb, J. M. Hill and G. K. H.
Shimizu, Chem. Commun., 2002, 1900.
21 W. S. Sheldrick and M. Wachhold, Angew. Chem., Int. Ed., 1995, 34,
450; M. G. Kanatzidis, Angew. Chem., Int. Ed., 1995, 34, 2109.
22 F. Ramirez, S. B. Bhatia, A. V. Patwardhan and C. P. Smith, J. Org.
Chem., 1967, 32, 3547.
23 L. G. Mackay, H. L. Anderson and J. K. M. Sanders, J. Chem. Soc.,
Perkin Trans. 1, 1995, 2269.
9 A. Kamiyama, T. Noguchi, T. Kajiwara and T. Ito, Angew. Chem.,
Int. Ed., 2000, 39, 3130; S. Noro, S. Kitagawa, M. Yamashita and
T. Wada, Chem. Commun., 2002, 222; L. Carlucci, G. Ciani, F. Porta,
D. M. Proserpio and L. Santagostini, Angew. Chem., Int. Ed., 2002, 41,
1907; V. F. Slagt, P. W. N. M. van Leeuwen and J. N. H. Reek, Chem.
Commun., 2003, 474.
24 G. M. Sheldrick, SHELXL97,Asystem of computer programs for X-ray
structure determination, University of Göttingen, Göttingen, Germany,
1997; G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.
25 D. J. Watkin, C. K. Prout, J. R. Carruthers and P. W. Betteridge, CRYS-
TALS Issue 10. Chemical Crystallography Laboratory, Oxford, UK,
1996.
D a l t o n T r a n s . , 2 0 0 4 , 2 8 9 9 – 2 9 0 3
2 9 0 3