Organometallics 2006, 25, 4627-4633
4627
A Solid-Gas Route to Polymorph Conversion in Crystalline
II
5
[
Fe (η -C H COOH) ]. A Diffraction and Solid-State NMR Study
5
4
2
Dario Braga, Fabrizia Grepioni,* and Marco Polito*
Dipartimento di Chimica G Ciamician, UniVersit a` di Bologna, 40126 Bologna, Italy
Michele R. Chierotti, Silvano Ellena, and Roberto Gobetto*
Dipartimento di Chimica IFM, UniVersit a` di Torino, 101256 Torino, Italy
ReceiVed May 29, 2006
5
Crystalline form I (monoclinic) and form II (triclinic) of ferrocene dicarboxylic acid [Fe(η -C
COOH) ] have been employed in solid-gas reactions at room temperature with the gaseous bases NH
NH (CH ), and NH(CH . The two crystal forms behave in exactly the same way in the solid-gas
5 4
reaction, generating the same products, identified as the anhydrous crystalline salts [NH H -
5 4
H -
2
3
,
2
3
3 2
)
5
4
]
2
[Fe(η -C
] (3). Interestingly
though, all these crystals revert via vapor release exclusively to the metastable crystalline form I. Starting
5
5
COO)
2
] (1), [NH
3
CH ]
3 2
[Fe(η -C
5
H
4
COO)
2
] (2), and [NH
2
(CH
3
)
2 2
]
5 4 2
[Fe(η -C H COO)
1
3
15
materials and products have been investigated by single-crystal and powder diffraction and by C,
CPMAS and H MAS methods.
N
1
5
Introduction
[Fe(η -C5H4COOH)2] has already proven to be a very useful
reactant in the preparation of hybrid organic-organometallic
and organometallic-organometallic crystal architectures by both
In previous papers we have shown that solvent-free reactions,
such as those occurring between solid reactants or between a
solid and a vapor,1 provide viable routes, alternative to
conventional reactions in solution, for the preparation of
molecular salts and cocrystals. Reactions between molecular
solids and between a molecular solid and a vapor have been
the subject of investigations for more than a century in the field
6
,7
solution and solid-state methods. For instance, it has been
5
shown that crystalline [Fe(η -C5H4COOH)2] reacts with vapors
of 1,4-diazabicyclo[2.2.2]octane to quantitatively generate the
corresponding organic-organometallic adduct [N(CH2CH2)3-
5
5
8
5
NH][Fe(η -C5H4COOH)(η -C5H4COO)]. The acid [Fe(η -C5H4-
COOH)2] also reacts in mechanochemical reactions with a
2
of organic-solid-state chemistry and are still attracting consider-
6
number of solid bases.
[
3
able interest in the field of “green chemistry”, because these
5
Fe(η -C5H4COOH)2] is known in three crystalline forms, a
reactions do not require recovery, storage, and disposal of
monoclinic form (form I), a triclinic form (form II), and a second
4
solvents. Solvent-free processes have now begun to be ap-
5
triclinic form (form III). The hydrogen-bonded dimer {[Fe(η -
preciated in the field of coordination and organometallic
C5H4COOH)2]}2 is the fundamental supramolecular unit present
in all forms, the major difference in the packing arrangement
arising from the relative orientation of the hydrogen-bonded
dicarboxylic dimers in the solid state. The structure of form III
has been serendipitously determined and recently reported.9
Form I and form II can instead be obtained in a fairly
straightforward manner (see below), which makes the dicar-
boxylic acid a good candidate for separate reactions with gases.
The aim of this work is threefold: (i) to investigate the
behavior of different crystal forms of the same substance toward
5
chemistry.
In this paper we discuss the results of an investigation of
reactivity toward volatile bases of different crystal forms of the
5
sandwich organometallic dicarboxylic acid [Fe(η -C5H4COOH)2].
*
Corresponding authors. E-mail: fabrizia.grepioni@unibo.it.
1) (a) Braga, D.; Grepioni, F. Angew Chem., Int. Ed. 2004, 43, 2. (b)
Braga, D.; Grepioni, F. Chem. Commun. 2005, 29, 3635.
2) (a) Pellizzari, G. Gazz. Chim. Ital. 1884, 14, 362. (b) Paul, I. C.;
(
(
Curtin, D. Y. Science 1975, 187, 19. (c) Miller, R. S.; Curtin, D. Y.; Paul,
I. C. J. Am. Chem. Soc. 1971, 93, 2784. (d) Miller, R. S. Curtin, D. Y.;
Paul, I. C. J. Am. Chem. Soc. 1972, 94, 5117. (e) Miller, R. S.; Curtin, D.
Y.; Paul, I. C. J. Am. Chem. Soc. 1974, 96, 6329. (f) Chiang, C. C.; Lin,
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Applications to organometallic cases are less popular, see for example: (b)
Albrecht, M.; Lutz, M.; Speck, A. L.; van Koten, G. Nature 2000, 406,
970. (c) Albrecht, M.; Gossage, R. A.; Lutz, M.; Speck, A. L.; van Koten,
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(e) Nichols, P. J.; Raston, C. L.; Steed, J. W. Chem. Commun. 2001, 1062.
(f) Belcher, W. J.; Longstaff, C. A.; Neckenig, M. R.; Steed, J. W. Chem.
Commun. 2002, 1602.
(6) Braga, D.; Maini, L.; Polito, M.; Mirolo, L.; Grepioni, F. Chem.--
Eur. J. 2003, 9, 4362.
(7) Braga, D.; Maini, L.; Grepioni, F.; De Cian, A.; Felix, O.; Fischer,
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Commun. 2002, 2960.
(9) Monoclinic form: (a) Palenik, G. J. Inorg. Chem. 1969, 8, 2744.
Triclinic form: (b) Takusagawa, F.; Koetzle, T. F. Acta Crystallogr., Sect.
B 1979, 35, 2888. Triclinic form: (c) Braga, D.; Polito, M.; D’Addario,
D.; Grepioni, F. Cryst. Growth Des. 2004, 1109.
9
1
1
9, 6303. (g) Miller, R. S.; Paul, I. C.; Curtin, D. Y. J. Am. Chem. Soc.
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(
3) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice;
Oxford University Press: New York, 1998.
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(
Kaupp, G. Mol. Cryst. Liq. Cryst. 1994, 242, 153. (c) Kaupp, G.; Schmeyers,
J.; Haak, M.; Marquardt, T.; Herrmann, A. Mol. Cryst. Liq. Cryst. 1996,
2
2
1
1
76, 315. (d) Kaupp, G.; Schmeyers, J.; Boy, J. Chem.--Eur. J. 1998, 4,
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2
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0.1021/om060468w CCC: $33.50 © 2006 American Chemical Society
Publication on Web 08/18/2006