Synthesis and characterization of controlled dendritic architectures by association of two phosphorus dendrons through a metallic center

Article abstract of DOI:10.1080/10426500902947971

The reactions of RuCl2(PPh3)3 with either a small amino diphosphine or a first-generation phosphorus-containing dendron possessing an aminodiphosphine as the core induce the formation of complexes in which two amino diphosphines are associated through the

Full text of DOI:10.1080/10426500902947971

This article was downloaded by: [University of Delaware]
On: 05 October 2014, At: 02:51
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Phosphorus, Sulfur, and Silicon
and the Related Elements
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/gpss20
Synthesis and Characterization
of Controlled Dendritic
Architectures by Association
of Two Phosphorus Dendrons
Through a Metallic Center
Valérie Maraval a , Régis Laurent a , Bruno
Donnadieu a , Anne-Marie Caminade a & Jean-Pierre
Majoral a
a Laboratoire de Chimie de Coordination du CNRS ,
Toulouse Cedex, France
Published online: 06 Jun 2009.
To cite this article: Valérie Maraval , Régis Laurent , Bruno Donnadieu , Anne-Marie
Caminade & Jean-Pierre Majoral (2009) Synthesis and Characterization of Controlled
Dendritic Architectures by Association of Two Phosphorus Dendrons Through a Metallic
Center, Phosphorus, Sulfur, and Silicon and the Related Elements, 184:6, 1612-1620,
DOI: 10.1080/10426500902947971
To link to this article: http://dx.doi.org/10.1080/10426500902947971
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the

Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,
and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Phosphorus, Sulfur, and Silicon, 184:1612–1620, 2009
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500902947971
Synthesis and Characterization of Controlled Dendritic
Architectures by Association of Two Phosphorus
Dendrons Through a Metallic Center
´
´
Valerie Maraval, Regis Laurent, Bruno Donnadieu,
Anne-Marie Caminade, and Jean-Pierre Majoral
Laboratoire de Chimie de Coordination du CNRS, Toulouse Cedex,
France
The reactions of RuCl (PPh ) with either a small amino diphosphine or a first-
3 3
2
generation phosphorus-containing dendron possessing an aminodiphosphine as
the core induce the formation of complexes in which two amino diphosphines are
associated through the metallic center. Determination of the structure of the smallest
complex by X-ray diffraction shows that the metal is surrounded by a square-based
bi-pyramid defined by the four phosphorus atoms of both diphosphines in a single
plane, with the chlorine atoms at both summits. The first generation dendrons
behave in the same way as the small compound, and allow us to isolate an original
bis dendron, associated through the ruthenium atom.
Keywords Crystal structure; dendrimers; dendrons; diphosphine; ruthenium
INTRODUCTION
Dendritic architectures have been strongly stirring up the imagina-
tion of the scientific community for more than 20 years, due to the
numerous unique properties they possess, in particular in the fields of
catalysis, materials, and biology. Most of these compounds have a regu-
lar multibranched architecture emanating from a central core, and are
named dendrimers.1 In contrast with all the other types of artificial
polymers, dendrimers are not synthesized by polymerization reactions
but step-by-step. The synthesis of dendrimers is of particular interest,
because it constitutes one of the rare examples of perfectly controlled
Received 5 February 2008; accepted 26 February 2008.
Dedicated to Professor Marian Mikolꢀajczyk, CBMiM PAN in Lꢀ o´dz´, Poland, on the
occasion of his 70th birthday.
Address correspondance to Anne-Marie Caminade or Jean-Pierre Majoral, Labora-
toire de Chimie de Coordination du CNRS, 205 route de Narbonne, 31077 Toulouse
Cedex 4, France. E-mail: caminade@lcc-toulouse.fr or majoral@lcc-toulouse.fr
1612

Controlled Dendritic Architectures
1613
and highly reproducible processes able to afford nano-objects. However,
more complex dendritic architectures can be also developed, thanks
to the step-by-step syntheses; they generally employ the use of “den-
drons. ” Dendrons are reminiscent of dendrimers, but in contrast to
dendrimers, they possess one reactive function at the level of the core.
Most dendrons are obtained by a convergent strategy introduced by
2
´
Hawker and Frechet, and are generally synthesized only up to gener-
ation 2, 3, or 4 in order to avoid the steric crowding of the core function.
Depending on the type of function, several dendrons can be associated
by their core in a spontaneous self-assembly,3 around a metal,4 or by
reaction with a multifunctional core.5
Since 1994, we have synthesized dendrimers6 and special dendritic
architectures7 possessing phosphorus atoms as branching points. Fig-
ure 1 illustrates the various types of dendritic architectures that
we have already prepared thanks to the versatility of the chem-
istry of phosphorus: layered dendrimers,8 “multiplurifunctionalized”
dendrimers,9 layer-block dendrimers,10 surface-block dendrimers,11
star polymers,12 and even highly sophisticated architectures in which
dendrons are linked to the interior of a dendrimer.13
FIGURE 1 Various types of phosphorus-containing dendritic architectures
built with one phosphorus at each branching point.

1614
V. Maraval et al.
In this article, we report our attempts to synthesize new phosphorus-
containing dendritic architectures by associating two dendrons by their
core around a metal.
RESULTS AND DISCUSSION
As indicated in the Introduction, associating two dendrons through a
metallic center has some precedents.4 The type of metal used includes
in several cases transition metals (often with the aim of performing
catalysis experiments), but to the best of our knowledge, such an ex-
periment has not been attempted previously with ruthenium deriva-
tives. We have already grafted ruthenium to the core of dendrons to
perform diastereoselective Michael additions.14 We will show here that
the same metal is able to accommodate two dendrons.
Pincer diphosphino derivatives are generally stable ligands for
ruthenium, thus the dendrons that will be used should possess such
a ligand at the core. The first experiment is conducted with two equiv-
alents of a small model of the dendron that is the diphosphine 1 (ob-
tained by reaction of Ph2PCH2OH with 1,1ꢀ -dimethylhydrazine14), and
RuCl2(PPh3)3,15 chosen because it was previously shown to be able to
accommodate two diphosphines.16 The complexation reaction, moni-
tored by 31P NMR, displays the disappearance of the signal at δ 31P =
−24 ppm corresponding to compound 1, on behalf of a new singlet at δ
31P = 0.2 ppm corresponding to the complex 2, together with a singlet
at −7 ppm, corresponding to free PPh3 (Scheme 1). After workup, only
the signals corresponding to 2 are detected by 31P NMR. This com-
1
pound is also characterized by H NMR, which displays in particular
SCHEME 1

Controlled Dendritic Architectures
1615
FIGURE 2 ORTEP drawing of compound 2. Selected bond lengths (Å) and
bond angles (◦): Ru P1 2.4317(13); Ru P2 2.3752(12); Ru Cl 2.4294(10);
P1 Ru P1’ 180.00(5); P2 Ru P2ꢀ 180.0; P1 Ru P2ꢀ 92.55(4); P1 Ru P2
87.45(4); P1 Ru Cl1 100.56(4); P1 Ru Cl1ꢀ 79.44(4); P2 Ru Cl1 91.73(4);
P2 Ru Cl1ꢀ 88.27(4).
a deshielding of the signal corresponding to the P-CH2-N groups, from
3.6 ppm in 1 to 3.9 ppm in 2.
To further characterize compound 2, and in particular the arrange-
ment around the metallic center, orange single crystals of compound
2 were grown in dichloromethane from a concentrated solution. The
ORTEP drawing of compound 2 is shown in Figure 2. It is worth not-
ing that both Cl are in the trans position, and that they constitute the
summits of a square-based bi-pyramid defined by the four phosphorus
atoms around Ru.
Having demonstrated the viability of our method with a small com-
pound, we decided to apply the same methodology to a real dendron.
For this purpose, the first generation dendron 1-G1 possessing a diphos-
phine as core was synthesized as indicated previously.17 Reaction of two
equivalents of 1-G1 with one equivalent of RuCl2(PPh3)3 affords as ex-
pected the bis-dendron 2-[G1]2 (Scheme 2). 31P NMR is again the best
method to characterize this compound, which displays two singlets
and two doublets. The most characteristic signal is the singlet at δ

1616
V. Maraval et al.
SCHEME 2
31P = 1.1 ppm, corresponding to the complexed diphosphine, whereas
the other singlet at 62.9 ppm corresponds to the P(S)(OPh)2 end groups.
It is worth noting that the two doublets characteristic of the P N P S
linkages in 2-[G1]2 (δ 31P = 18.7 and 51.6 ppm, respectively with 2JPP
=
31.8 Hz) are identical to those found for 2-G1, thus this linkage is not
implied in the complexation. Indeed, we have previously shown that
complexation of P N P S linkages (for instance by gold), induces a
significant shielding of the doublet corresponding to the P S group
(ꢀδ = 17 ppm).18 1H NMR is also useful to characterize the bis dendron
2-[G1]2; it displays also the same deshielding than the one observed
in the reaction 1 → 2 for the P-CH2-N groups from 3.5 ppm for 2-G1
to 3.9 ppm for 2-[G1]2. In view of these data, we can deduce that the
structure of the bis dendron 2-[G1]2 at the level of the core is the same
than that of compound 2.
CONCLUSION
We have shown in this article our preliminary results for the synthesis
of original bis dendrons, coupled by their core through a ruthenium
center. The coupling occurs as easily with the first generation dendron
as with a very simple model, thus such methodology should be usable
for the coupling of larger dendrons. Furthermore, 31P NMR appears
again as a very valuable and sensitive tool to characterize sophisticated
macromolecules.
EXPERIMENTAL
All manipulations were carried out using standard high vacuum and
dry-argon techniques. 1H, 13C, and 31P NMR spectra were recorded
with Bruker AC 200, AC 250, or DPX 300 spectrometers. References for
NMR chemical shifts are 85% H3PO4 for 31P and SiMe4 for 1H. Solvents

Controlled Dendritic Architectures
1617
were dried and distilled prior to use (THF over sodium/benzophenone,
CH2Cl2 over phosphorus pentoxide) and degassed when phosphines are
used. Compounds 1,14 1-G1,17 and RuCl2(PPh3)135 were synthesized as
previously published.
Synthesis and Characterization of Compound 2
0.190 g (0.417 mmol) of compound 1 in solution in dichloromethane
(5 mL) was added to 0.200 g (0.208 mmol) of dichloro tris-(triphenyl-
phosphine) ruthenium (II) in solution in dichloromethane (15 mL). The
resulting mixture was stirred for 2 h at room temperature, then evap-
orated to dryness to afford an orange powder. This powder was washed
twice with ether, then twice with pentane, to afford compound 2 as an
orange powder in 76% yield. Single crystals suitable for X-ray charac-
terization were grown at room temperature from a concentrated solu-
tion of 2 in dichloromethane.
1
31P{ H} NMR (CDCl3): δ = 0.2 (s) ppm. 1H NMR (CDCl3): δ = 2.3 (s,
12H, CH3), 3.9 (d, 2JHP = 10.0 Hz, 8H, CH2), 6.8–7.7 (m, 40H, CHarom)
ppm. Anal. Calcd for C56H60N4P4Cl2Ru: C, 61.99; H, 5.57; N, 5.16.
Found: C, 61.93; H, 5.50; N, 5,09.
Synthesis and Characterization of the Bis Dendron 2-[G1]2
0.318 g (0.208 mmol) of dendron 1-G1 in solution in dichloromethane
(5 mL) was added to 0.100 g (0.104 mmol) of dichloro tris-
(triphenylphosphine) ruthenium (II) in solution in dichloromethane
(10 mL). The resulting mixture was stirred for 2 h at room temperature,
then evaporated to dryness to afford an orange powder. This powder
was washed three times with a mixture ether/pentane, to afford the bis
dendron 2-[G1]2 as an orange powder in 88% yield.
1
2
31P{ H} NMR (CDCl3): δ = 1.1 (s, PPh2), 18.7 (d, JPP = 31.8 Hz,
2
P N P S), 51.6 (d, JPP = 31.8 Hz, P N P S), 62.9 (s, NNP S)
1
ppm. H NMR (CDCl3): δ = 2.3 (br s, 6H, CH3 N CH2), 2.9 (m, 8H,
3
2
CH2 CH2 P), 3.3 (d, JHP = 10.4 Hz, 12H, CH3 N P), 3.9 (d, JHP
=
10.8 Hz, 8H, N CH2 PPh2), 6.8–7.8 (m, 120H, CHarom, CH N) ppm.
Anal. Calcd for C162H154N14O12P12S6Cl2Ru: C, 60.33; H, 4.81; N, 6.08.
Found: C, 60.28; H, 4.75; N, 5.98.
X-Ray Structure Determination for Compound 2
Measurement was carried out on a one circle IPDS STOE X-ray diffrac-
tometer system (Mo-radiation, λ = 0.71073 Å, 50KV/30mA power), at
low temperature (T = 160(2) K). Frames were integrated with the aid

1618
V. Maraval et al.
of STOE, X-RED, Data Reduction for STADI4 and IPDS, Revision 1.08.
Stoe software.19
A total of 167 frames were collected for a hemisphere of reflections.
Based on a triclinic crystal system (P -1), the integrated frames yielded
a total of 12053 reflections at a maximum 2θ angle of 45.98 degrees, of
which 4428 were independent reflections (Rint = 0.0486, Rsig = 0.0695,
completeness = 94.8%) and 3134 (70.8%) reflections were greater than
2σ (I). The unit cell parameters were a = 12.0173(15) Å, b = 12.4932(16)
Å, c = 13.2869(17) Å, α = 87.307(16)◦, β = 66.722(14)◦, γ = 67.290(15)◦,
V =1677.2(4) Å3, Z = 1, calculated density Dc = 1.553 g/cm3. Absorp-
tion corrections were applied (absorption coefficient µ = 0.929 mm;−1
max/min transmission 0.691 and −0.626) using the Difabs program.20
Structure was solved by using direct methods, with the aid of SIR9220
and refined by least-squares procedures on F2, using SHELXL-9721 in-
cluded in the WinGX programs.22 Direct methods of phase determina-
tion followed by some Fourier cycles of refinement led to an electron
density map, from which most of the non-hydrogen atoms were iden-
tified. With subsequent isotropic refinement, all of the non-hydrogen
atoms were identified, atomic coordinates, isotropic and anisotropic
displacement parameters of all the non-hydrogen atoms were refined
by means of a full matrix least-squares procedure on F2. The hydrogen
atoms were included in the refinement in calculated positions, riding on
the carbon atoms to which they were connected. Drawing of molecule
was realized with the aid of ORTEP32.23 Atomic scattering factors were
taken from International Tables for X-Ray Crystallography.24
The refinement converged at R1 = 0.0359, wR2 = 0.0752, with in-
tensity I>2σ (I). The largest peak/hole in the final difference map was
0.691 and -0.626 e.Å−3. Further details on the crystal structure inves-
tigation are available on request from the Director of the Cambridge
Crystallographic Data Centre, 12 Union Road, GB-Cambridge CB21EZ
UK, by quoting the full journal citation.
Supplementary Data
Crystallographic data for the structures reported in this article have
been deposited with the Cambridge Crystallographic Data Centre and
allocated the deposition number CCDC (2). Copies of the data can be
obtained free of charge via www.ccdc.cam.uk/data request/cif.
REFERENCES
[1] (a) G. R. Newkome, F. Vo¨gtle, and C.N. Moorefield, Dendrimers and dendrons (John
Wiley and Sons, Weinheim, Germany, 2001); (b) J. M. J. Fre´chet and D. A. Tomalia,

Controlled Dendritic Architectures
1619
Dendrimers and other dendritic polymers (John Wiley and Sons, Chichester, UK,
2001); (c) J. P. Majoral and A. M. Caminade, Chem. Rev., 99, 845 (1999).
[2] C. J. Hawker and J. M. J. Fre´chet, J. Am. Chem. Soc., 112, 7638 (1990).
[3] (a) S. C. Zimmerman, F. Zeng, D. E. C. Reichert, and S. V. Kolotuchin, Science, 271,
1095 (1996); (b) W. T. S. Huck, R. Hulst, P. Timmerman, F. C. J. M. van Veggel, and
D. N. Reinhoudt, Angew. Chem. Int. Ed., 36, 1006 (1997); (c) V. Percec, W. D. Cho,
P. E. Mosier, G. Ungar, and D. J. P. Yeardley, J. Am. Chem. Soc.,120, 11061 (1998);
(d) M. Suarez, J. M. Lehn, S. C. Zimmerman, A. A Skoulios, and B. Heinrich, J. Am.
Chem. Soc., 120, 9526 (1998).
[4] See for example (a) H. F. Chow, I. Y. K. Chan, D. T. W. Chan, and R. W. M. Kwok,
Chem. Eur. J., 2, 1085 (1996); (b) V. Catalano and N. Parodi, Inorg. Chem., 36,
537 (1997); (c) J. Issberner, F. Vo¨gtle, L. De Cola, and V. Balzani, Chem. Eur. J.,
3, 706 (1997); (d) G. R. Newkome, E. He, and L. A Godinez, Macromolecules, 31,
4382 (1998); (e) M. Kawa and J. M. J. Fre´chet, Chem. Mater., 10, 286 (1998); (f) M.
Plevoets, F. Vo¨gtle, L. De Cola, and V. Balzani, New J. Chem., 23, 63 (1999) ; (g)
M. Enomoto and T. Aida, J. Am. Chem. Soc., 121, 874 (1999); (h) V. V. Narayanan
and E. C. Wiener, Macromolecules, 33, 3934 (2000); (i) B. S. Balaji, Y. Obora, D.
Ohara, S. Koide, and Y. Tsuji, Organometallics, 20, 5342 (2001); (j) M. Enomoto, A.
Kishimura, and T. Aida, J. Am. Chem. Soc., 123, 5608 (2001); (k) R. W. Saalfrank,
C. Deutscher, H. Maid, A. M. Ako, S. Sperner, T. Nakajima, W. Bauer, F. Hampel,
A. B. Hess, N. J. R. van Eikema Hommes, R. Puchta, and F. W. Heinemann, Chem.
Eur. J., 10, 1899 (2004); (l) N. S. Baek, Y. H. Kim, S. G. Roh, B. K. Kwak, and H. K.
Kim, Adv. Func. Mater., 16, 1873 (2006).
[5] See for example: (a) C. J. Hawker and J. M. J. Fre´chet, J. Chem. Soc. Chem. Com-
mun., 1010 (1990); (b) K. Wooley and C. J. Hawker, J. Am. Chem. Soc.,115, 9836
(1993); (c) P. R. Ashton, S. E. Boyd, C. L. Brown, N. Jayaraman, S. A. Nepogodiev,
and J. F. Stoddart, Chem. Eur. J., 2, 1115 (1996); (d) J. W. Leon, M. Kawa, and J. M.
J. Fre´chet, J. Am. Chem. Soc., 118, 8847 (1996); (e) D. B. Amabilino, P. R. Ashton,
V. Balzani, C. L. Brown, A. Credi, J. M. J. Fre´chet, J. W. Leon, F. M. Raymo, N.
Spencer, J. F. Stoddart, and M. Venturi, J. Am. Chem. Soc., 118, 12012 (1996); (f)
X. Camps, H. Scho¨nberger, and A. Hirsch, Chem. Eur. J., 3, 561 (1997); (g) D. K.
Smith and F. Diederich, Chem. Commun., 2501 (1998); (h) C. C. Mak, N. Bampos,
J. K. M. Sanders, Angew. Chem. Int. Ed., 37, 3020 (1998); (i) A. Ritze´n and T. Frejd,
Chem. Commun., 207 (1999); (j) V. Sartor, L. Djakovitch, J. L. Fillaut, F. Moulines,
F. Neveu, J. C. Blais, and D. Astruc, J. Am. Chem. Soc., 121, 2929 (1999).
[6] N. Launay, A. M. Caminade, R. Lahana, and J. P. Majoral, Angew. Chem. Int. Ed.
Engl., 33, 1589 (1994); (b) N. Launay, A. M. Caminade, and J. P. Majoral, J. Am.
Chem. Soc., 117, 3282 (1995).
[7] J. P. Majoral, A. M. Caminade, and V. Maraval, Chem. Commun., 2929 (2002).
[8] (a) L. Brauge, G. Magro, A. M. Caminade, and J. P. Majoral, J. Am. Chem. Soc., 123,
6698 (2001), correction: J. Am. Chem. Soc., 123, 8446 (2001); (b) V. Maraval, A. M.
Caminade, J. P. Majoral, and J. C. Blais, Angew. Chem. Int. Ed., 42, 1822 (2003);
(c) V. Maraval, J. Pyzowski, A. M. Caminade, and J. P. Majoral, J. Org. Chem., 68,
6043 (2003).
[9] (a) N. Launay, M. Slany, A. M. Caminade, and J. P. Majoral, J. Org. Chem., 61, 3799
(1996); (b) M. L. Lartigue, M. Slany, A. M. Caminade, and J. P. Majoral, Chem. Eur.
J., 2, 1417 (1996); (c) M. Slany, A. M. Caminade, and J. P. Majoral, Tetrahedron Lett.,
37, 9053 (1996); (d) M. L. Lartigue, A. M. Caminade, and J. P. Majoral, Tetrahedron
Asymmetry, 8, 2697 (1997); (e) M. Severac, J. Leclaire, P. Sutra, A. M. Caminade,
and J. P. Majoral, Tetrahedron Lett., 45, 3019 (2004).

1620
V. Maraval et al.
[10] V. Maraval, R. Laurent, B. Donnadieu, M. Mauzac, A. M. Caminade, and J. P.
Majoral, J. Am. Chem. Soc., 122, 2499 (2000).
[11] (a) A. M. Caminade, A. Maraval, and J. P. Majoral, Eur. J. Inorg. Chem., 887 (2006);
(b) V. Maraval, A. Maraval, G. Spataro, A. M. Caminade, J. P. Majoral, D. H. Kim,
and W. Knoll, New J. Chem., 30, 1731 (2006).
[12] V. Darcos, D. Taton, Y. Gnanou, P. Marchand, A. M. Caminade, J. P. Majoral, M.
Destarac, and F. Lesing, Chem. Commun., 2110 (2004).
[13] (a) C. Galliot, C. Larre´, A. M. Caminade, and J. P. Majoral, Science, 277, 1981
(1997); (b) C. Larre´, D. Bressolles, C. Turrin, B. Donnadieu, A. M. Caminade, and
J. P. Majoral, J. Am. Chem. Soc., 120, 13070 (1998); (c) V. Cadierno, A. Igau, B.
Donnadieu, A. M. Caminade, and J. P. Majoral, Organometallics, 18, 1580 (1999);
(d) V. Maraval, R. Laurent, S. Merino, A. M. Caminade, and J. P. Majoral, Eur. J.
Org. Chem., 3555 (2000).
[14] V. Maraval, R. Laurent, A. M. Caminade, and J. P. Majoral, Organometallics, 19,
4025 (2000).
[15] T. A. Stephenson and G. Wilkinson, J. Inorg. Nucl. Chem., 28, 945 (1966).
[16] J. V. Barkley, S. J. Higgins, M. K. McCart, and T. J. Pounds, Inorg. Chem., 36, 6188.
[17] V. Maraval, R. M. Sebastian, F. Ben, R. Laurent, A. M. Caminade, and J. P. Majoral,
Eur. J. Inorg. Chem., 1681 (2001).
[18] C. Larre´, B. Donnadieu, A. M. Caminade, and J. P. Majoral, Chem. Eur. J., 4, 2031
(1998).
[19] STOE, X-RED, Data Reduction for STADI4 and IPDS, Revision 1.08.
[20] A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M.C. Burla, G. Polidori,
and M. Camalli, J. Appl. Cryst., 27, 435 (1994).
[21] G. M. Sheldrick, SHELX97 [Includes SHELXS97, SHELXL97, CIFTAB]—Programs
for Crystal Structure Analysis (Release 97-2), Institu¨t fu¨r Anorganische Chemie der
Universita¨t, Go¨ttingen, Germany, 1998.
[22] L. J. Farrugia, J. Appl. Cryst., 32, 837 (1999).
[23] L. J. Farrugia, J. Appl. Crystallogr., 30, 565 (1997).
[24] International Tables for X-Ray Crystallography (Kynoch Press, Birmingham, Eng-
land, 1974), vol. IV.