Table Of Contentstereochemistry of organometallic and inorganic compounds 5
Chains, Clusters, Inclusion
Compounds, Paramagnetic
Labels, and Organic Rings
Edited by
PIERO ZANELLO
Universita di Siena, Dipartimento di Chi mica, Pian dei Mantel I in i 44, 53100 Siena, Italy
ELSEVIER
Amsterdam — London — New York — Tokyo 1994
ELSEVIER SCIENCE B.V.
Sara Burgerhartstraat 25
P.O. Box 211, 1000 AE Amsterdam, The Netherlands
Library of Congress Cataloging-in-Publication Data
Chains, clusters, inclusion compounds, paramagnetic labels, and
organic rings / edited by Piero Zanello.
p. cm. — (Stereochemistry of organometa11ic and inorganic
compounds ; 5)
Includes bibliographical references and index.
ISBN 0-444-81581-3 (acid-free)
1. Organometa11ic compounds. 2. Complex compounds. 3. Cyclic
compounds. I. Zanello, Piero. II. Series.
QD481.S763 no. 5
[QD411]
541 .2'23 s — dc20
[541.2'242] 93-42633
CIP
ISBN: 0-444-81581-3
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V
PREFACE
Volume 5 of Stereochemistry of Organometallic and Inorganic
Compounds appears with a delay of about three years. Due to personal
circumstances, Professor Ivan Bernal, who was the founder of this
Series, has been forced to renounce to his task. I was asked to
conclude the editing of the present Volume, which prematurely closes
a Series planned to cover an important piece of stereochemistry. I
beg preliminarily the readers' forgiviness for my inexperienced
editorship, since the refinement and authoritativeness of Professor
Bernal will be profoundly missed.
In Chapter 1, Drs. Averbuch-Pouquot and Durif accurately depict
the state of art of the cyclic condensation of phosphates. Most of us
have a rather precise idea of the extraordinary and multiple
structural arrangements that the S1O4 units assume in silicates, and
of their practical appliances; we now learn that the PO4 units are
equally able to give interesting aggregates in polyphosphates,
especially in cyclophosphates. We hope that the profound knowledge of
the structural and chemical aspects of polyphosphates brought on by
Averbuch-Pouquot and Durif may stimulate new studies in the field
(for instance, the dramatic problem of eutrophication immediately
comes to mind).
The belief that metal cluster compounds are able to act as
electron sponges is deep-rooted. In Chapter 2, I have tried to show
that such a generalization may lead to misconceptions, in that
multiple electron transfers which do not cause framework destruction
in metal-carbonyl complexes are not so common. In addition, in those
cases where chemically reversible redox changes occur, we have
examined in detail the structural consequences accompanying such
electron addition/removal processes. Coupling electrochemical
measurements to structural parameters may afford a more precise
bonding description of this class of compounds, which have
significant effects on catalysis and material sciences.
VI
In Chapter 3, Professor Harada describes the encapsulation of
organometal complexes in structurally suitable organic receptors
(namely, cyclodextrins) . This has led to pioneering work devoted to
correlate the geometries of inorganic molecules with those of organic
substrates. Supramolecular Chemistry, the most recent branch of
Coordination Chemistry, will find uses in the study of inclusion
compounds, particularly in analysing the bonding forces which keep
together stable organic and stable inorganic molecules.
EPR techniques are ideally suited to characterize paramagnetic
inorganic molecules (e.g., magnetic properties and bonding
parameters). Nevertheless, obtaining stereochemical informations from
EPR spectra is by no means an easy matter. Professors S.S.Eaton and
G.R.Eaton have found that introduction of a paramagnetic nitroxyl
group into a metal complex having unpaired electrons leads to an
internal "electron ping pong" between the two paramagnetic centres.
The analysis of such an electron flow, depicted in Chapter 4, gives
invaluable informations about the structure, conformation, or isomer
constitution of the molecules. Since the distance as well as the
molecular shape of the framework separating the two paramagnetic
centres can be finely tuned by properly varying either the ligand in
the metal complex or the complexity of the nitroxyl radical itself,
it is evident that a more complete body of structural information
will be gained by this unpaired-electron labelling method.
The remaining two Chapters intend to show how the stereochemical
organization of organic assemblies may be properly addressed by
appending to them selected metal complexes. In Chapter 5, Dr.
A.Heumann describes the use of palladium complexes to promote homo-
and hetero-cyclization of organic chains according to well determined
stereochemical pathways. In Chapter 6, Dr. M.Uemura reviews the use
of arenetricarbonylchromium complexes to obtain a wide range of
stereodefined classes of benzene derivatives. The clarity and
completeness of these two Chapters will bring organic chemists'
attention to this kind of inorganic approach to stereoselective
organic syntheses.
VII
To conclude, my gratitude goes to Professor I.Bernal for his
friendly invitation to contribute repeatedly to this Series, as well
as to the Administrative Editor of ELSEVIER for entrusting me with
this editorial task. Likewise, I am indebted to all the co-authors of
the present Volume for their spirit of co-operation, particularly for
their patience to update their manuscripts.
Vlll
List of Contributors
Marie Therese Averbuch-Pouchot Centre National de la Recherche
Scientifique, Laboratoire de
Cristallographie, associe ä
l'Universite J.Fourier, 166X
- 38042 Grenoble Cedex, France
Andre Durif Centre National de la Recherche
Scientifique, Laboratoire de
Cristallographie, associe ä
l'Universite J.Fourier, 166X
- 38042 Grenoble Cedex, France
Gareth R.Eaton Department of Chemistry,
University of Denver,
Denver, Colorado 80208, U.S.A.
Sandra S.Eaton Department of Chemistry,
University of Denver,
Denver, Colorado 80208, U.S.A.
Akira Harada Department of Macromolecular Science,
Faculty of Science, Osaka University,
Japan
Andreas Heumann Ecole Nationale Superieure de
Syntheses, de Procedes et d'Ingenierie
Chimiques d'Aix-Marseille
Faculte de St-Jerome, 13397 Marseille
Cedex 13, France
Motokazu Uemura Faculty of Science, Osaka City
University, Sugimoto 3-3-138,
Sumiyoshi-ku, Osaka 558, Japan
Piero Zanello Dipartimento di Chimica,
Universitä di Siena,
Piano dei Mantellini, 44,
53100 Siena, Italy
CRYSTAL CHEMISTRY OF CYCLOPHOSPHATES
M.T. Averbuch-Pouchot and A. Durif
3
CRYSTAL CHEMISTRY OF CYCLOPHOS PH ATES
M.T. AVERBUCH-POUCHOT and A. DURIF
Centre National de la Recherche Scientifique
Laboratoire de Cristallographie, associe ä l'Universite J. Fourier
166X - 38042 Grenoble Cedex, France.
1. INTRODUCTION
Cyclophosphates constitute an important part of the condensed
phosphate chemistry. This chemistry has been very long to develop and,
even today, is still relatively poor if compared with that of silicates, for
instance.
Let us start explaining what is commonly called a condensed
phosphate. We can very simply say, before proceeding into the subject
with more details, that any phosphoric anion in which exists a P-O-P bond
is a condensed phosphoric anion. Another simple way to define these
salts is to say that any phosphoric anion corresponding to a formula
characterized by a ratio P/O larger than 1/4 is a condensed one. It can be
noticed that this last definition is a direct consequence of the first one,
since the basic unit of all phosphoric anions is the PO4 tetrahedron.
These P-O-P bonds can be obtained by various processes ; one of
the simplest is the reorganization of two molecules of a monohydrogeno-
monophosphate after the elimination of a water molecule :
O O 0 0
I I II
O - P - 0-H + H-0 - P - O - -> O - P - O - P -O + H 0
2
I I II
o o 00
This scheme of condensation illustrates the most common way to prepare,
for instance, tetrasodium diphosphate :
2Na HP0 > Na P20 + H 0
2 4 4 7 2
This condensation phenomenon can generate a great number of phos
phoric anions with various geometries and it is today recognized that no
classification of condensed phosphates is possible unless supported by
the geometry of the anions.
4
1.1. Classification of Condensed Phosphates
In the present state of the crystal chemistry of condensed
phosphates, one observes, for the anions, three very different types of
condensation geometries.
Figure 1.1 Some examples of polyphosphate anions.
The first one corresponds to a progressive linear linkage of PO4
tetrahedra sharing one or two of their oxygen atoms. Fig. 1.1 reports some
examples of such condensed anions. The corresponding phosphates are
usually called polyphosphates. The general formula for this type of anions
is given by : (P 0 n i)(n+2)-.
n 3 +
Phosphorus atoms, belonging to PO4 tetrahedra sharing two of their
oxygen atoms with neighboring PO4, are usually called "internal"
phosphorus, the other ones "terminal" phosphorus.
The second type of condensation is a cyclic one, leading to the
formation of (P 03n)n" rings. Today, phosphoric rings are known for n = 3,
n
4, 5, 6, 8, 10 and 12. The corresponding phosphates are named
cyclophosphates. Fig. 1.2 illustrates some ring-anions.
If in the first two types of condensation, one PO4 tetrahedron shares
one or two of its oxygen atoms with the neighboring PO4 groups, things
are different for the third type of condensation observed in a class of
P205-rich phosphates, called ultraphosphates. Here, in the anion, some
PO4 tetrahedra share three of their oxygen atoms with the neighboring
PO4 groups. This type of condensation leads to very various anion
geometries : finite groups, infinite ribbons, infinite layers or three-
dimensional networks. The phosphorus atom of a PO4 tetrahedron sharing
three of its oxygen atoms with adjacent tetrahedra is named "branching"
5
phosphorus. Fig. 1.3 gives the representation of an ultraphosphate anion.
Figure 1.2 Some examples of ring-anions.
Figure 1.3 An ultraphosphate anion as observed in S1T1P5O14.
1.2. Nomenclature of Condensed Phosphates
Along years, the nomenclature used for condensed phosphates has
been very often confusing. In the few next lines, we simply report what is
today commonly accepted for the appellation of the condensed phos -
phates.
In the case of phosphates containing anions corresponding to the
first type of condensation geometry, the general appellation is polyphos-
phates, but with some variations according to the degree of condensation.
As we said above, in these salts the general formula of the phosphoric
