Polymorphism of Molecular Organometallic Crystals. A Third Form of the Supramolecular Hydrogen-Bonded Dimer {[FeII(η5-C5H4COOH)2]}2 Dario Braga,* Marco Polito, and Daniela D’Addario Dipartimento di Chimica G Ciamician, Universita` di Bologna, 40126 Bologna, Italy
CRYSTAL GROWTH & DESIGN 2004 VOL. 4, NO. 6 1109-1112
Fabrizia Grepioni* Dipartimento di Chimica, Universita` di Sassari, Via Vienna 2, 07100, Sassari, Italy Received July 28, 2004;
Revised Manuscript Received September 6, 2004
ABSTRACT: A third polymorphic form of the ferrocene dicarboxylic acid [FeII(η5-C5H4COOH)2], already known as a monoclinic (form I) and a triclinic (form II) crystal form, has been obtained and structurally characterized. This third form III presents dimers {[FeII(η5-C5H4COOH)2]}2 of doubly hydrogen-bonded carboxylic rings in the solid state, with O(H)‚‚‚O distances in the range 2.613(9)-2.646(10) Å. The hydrogen-bonded dimer {[FeII(η5-C5H4COOH)2]}2 is the fundamental supramolecular unit present also in forms I and II. The difference between the three crystal forms arises from the relative orientation of the hydrogen-bonded dicarboxylic dimers in the solid state. In form III, the cyclopentadienyl rings of neighboring molecules are at graphitic separation (3.40 Å vs an intrasandwich distance of 3.30 Å). The controlled preparation and characterization of crystal polymorphs,1 e.g., of different crystal forms of the same substance, has become one of the major issues of modern crystal engineering and solid-state chemistry.2 This is not only because of the economical issues arising from patent litigation of polymorphs of drugs but also because studies of polymorphism afford fundamental information on molecular recognition, crystal nucleation, crystallization, and the relationship between solid phases.3 Several groups have long been interested in the utilization of organometallic building blocks in the crystal engineering4 of hydrogen-bonded organometallic, or hybrid organic-organometallic and inorganic-organometallic molecular crystalline materials.5 In this respect, the ferrocene dicarboxylic acid [FeII(η5-C5H4COOH)2] has proven to be a very useful reactant in the preparation of hybrid organicorganometallic and organometallic-organometallic crystal architectures by both solution6a and solid-state6b methods. Clearly, the use of a given polymorphic form of a starting reactant when the reaction takes place in solution cannot be expected to affect the recognition and subsequent selfassembly that lead to formation of a new product or supramolecular adduct.7 On the contrary, when the process is based on a co-grinding of molecular materials, i.e., when the process is an inter-solid reaction,8 different polymorphic modifications may be expected, at least in principle, to yield different results or to behave in different ways in the course of the mechanochemical treatment. Crystalline ferrocene dicarboxylic acid [FeII(η5-C5H4COOH)2] has already been characterized in two crystal forms, a monoclinic9a and a triclinic9b form, respectively. These forms contain exactly the same type of supramolecular hydrogen-bonded dimeric unit, {[FeII(η5-C5H4COOH)2]}2, although in different arrangements in the solid state. The commercial form of [FeII(η5-C5H4COOH)2] is the monoclinic form I, and this is the polymorph that we have been using thus far in all reactions. This is the case also of the mechanochemical reaction between the organometallic complex and a number of solid bases, which we have described recently.6b We wondered if the reaction products * To whom correspondence should be addressed. E-mail: dario.braga@ unibo.it;
[email protected].
Table 1. Relevant Intramolecular Structural Parameters (Å) Concerning the -COOH Groups in Form III of Crystalline [FeII(η5-C5H4COOH)2] C11 O2 1.226(9) C12 O4 1.240(9) C23 O6 1.214(9) C24 O8 1.228(9) C35 O10 1.254(9) C36 O12 1.230(9)
C11 O1 1.304(9) C12 O3 1.284(9) C23 O5 1.304(9) C24 O7 1.314(9) C35 O9 1.285(9) C36 O11 1.290(9)
of the solid-solid process would be affected by the use of the other known form, i.e., the triclinic form II. In this paper we report, while searching for the conditions to crystallize form II, we have isolated and characterized a different triclinic modification of this fundamental organometallic molecular crystal. In this paper we report a comparison between the three forms of [FeII(η5-C5H4COOH)2]. In the attempt to obtain the triclinic form II, the commercial monoclinic form I of [FeII(η5-C5H4COOH)2] (10 mg) was dissolved in MeOH (5 mL); a mixture of CHCl3/ Et2O (drops) was then added slowly. After the sample stood in the freezer for 3 days orange crystals were obtained from this solvent mixture. X-ray investigation of the unit cell parameter yielded a cell that was neither that of form I nor that of form II. Structural analysis revealed formation of a third, previously unknown, form of the same acid. In view of the fact that the density of the different polymorphs is often good measure of the stability of different crystal forms, it is worth noting that the calculated densities increase progressively on passing from form I to III [room temperature, 1.713, 1.728, and 1.763 for form I, II, and III, respectively, see also below]. Even though, thus far, we have been unable to produce this new form in a quantity sufficient for the desired characterization by a variety of solid-state studies, we have been able to obtain single crystals suitable for X-ray diffraction17 and to determine the packing arrangement. Before comparing the three packing patterns, however, let us spend few words on the molecular structure (see Table 1) and hydrogen-bonding parameters (see Table 2). Both intra- and intermolecular parameters appear to agree with a localized hydrogen-bonding picture, with fully ordered -COOH groups. The data are also in good agreement with those available for forms I and II,9 confirming
10.1021/cg0497400 CCC: $27.50 © 2004 American Chemical Society Published on Web 09/18/2004
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Table 2. Relevant Hydrogen Bonda Distances (Å) and Angles (deg) in Form III of Crystalline [FeII(η5-C5H4COOH)2]
a
interaction
O-H
H‚‚‚O
O‚‚‚O
O-H‚‚‚O
symmetry
O(1)-H(1)‚‚‚O(6) O(3)-H(2)‚‚‚O(8) O(5)-H(3)‚‚‚O(2) O(7)-H(4)‚‚‚O(4) O(9)-H(5)‚‚‚O(12) O(11)-H(6)‚‚‚O(10)
1.07(10) 1.00(11) 0.95(8) 1.09(13) 0.84(10) 1.06(11)
1.57(10) 1.74(12) 1.68(8) 1.55(13) 1.81(11) 1.56(12)
2.632(8) 2.622(8) 2.622(8) 2.628(8) 2.646(10) 2.613(9)
176(9) 145(11) 175(9) 170(8) 171(10) 168(9)
-2 + x, y, -1 + z -2 + x, y, -1 + z 2 + x, y, 1 + z 2 + x, y, 1 + z 1 -x, -y, 1 - z 1 - x, -y, 1 - z
Hydrogen atoms as located from the Fourier maps and not corrected for X-ray foreshortening effects.
Figure 2. Space filling projections of the superimposed second layers of {[FeII(η5-C5H4COOH)2]}2 that generate the threedimensional packings of (a) form I (monoclinic), (b) form II (triclinic), and (c) form III of crystalline {[FeII(η5-C5H4COOH)2]}2. Figure 1. An in-plane, space filling projection of the packing in (a) form I (monoclinic), (b) form II (triclinic), and (c) form III of crystalline {[FeII(η5-C5H4COOH)2]}2. Note how form III is closely related to form I. In III, the dimers {[FeII(η5-C5H4COOH)2]}2 pack in a sort of “dimers of dimers” with almost superimposed ferrocenyl cyclopentadienyl rings.
that, in terms of molecular structure, the ferrocenyl dicarboxylic acid is a relatively stiff and “conservative” supramolecular system. The simplest way to compare the three crystal structures is by looking at molecular layers formed by the supramolecular dimers {[FeII(η5-C5H4COOH)2]}2. A space-filling representation of a section of the packings in the known monoclinic and triclinic forms of [FeII(η5-C5H4COOH)2] is provided in Figure 1, panels a and b, respectively. Figure 1c shows the layer present in form III, projected in a similar way as for the other two forms (compare with Figure 1, panels a and b). It is possible to appreciate how the structure of III is closely related to that of the other two forms, but in particular to that of I. In III, the hydrogen-
bonded dimmers {[FeII(η5-C5H4COOH)2]}2 pack in a sort of “dimers of dimers” fashion with almost superimposed ferrocenyl cyclopentadienyl rings. These tetramolecular units are separated by another {[FeII(η5-C5H4COOH)2]}2 dimer rotated roughly 90 deg. By comparing Figure 1, panels a and c one can see how structure III can be ideally derived from that of I by sliding in plane molecular dimers. Interestingly, in form III the cyclopentadienyl ligands of molecules forming the “dimers of dimers” are at very close “graphitic-like” separation (intersandwich separation 3.40 vs an intrasandwich distance of 3.30 Å). The three-dimensional packing is easily reconstructed by adding a second layer of {[FeII(η5-C5H4COOH)2]}2 on each layer shown in Figure 1. Figure 2 shows how the cyclopentadienyl ligands of the three forms I, II, and III tend to overlap with the oxygen atoms of the carboxylic groups beneath and above; in such a way, interactions of the C-H‚‚‚O type are likely to be optimized. It is worth comparing the unit cell parameters of the three forms, in particular, those of the two triclinic
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Table 3. Comparison of the Unit Cell Parameters, Cell Volumes, and Calculated Densities between Form I, II, and III of [FeII(C5H4COOH)2] compound
space group
cell parameters
2.635 2.593
P21/c
triclinic9b
2.625 2.671 2.643 2.620
P1 h
form III triclinic
2.632(8) 2.622(8) 2.622(8) 2.628(8) 2.646(10) 2.613(9)
P1 h
a ) 8.403(10) b ) 8.910(10) c ) 14.192(18) β ) 90.41(8) a ) 7.477(1) b ) 7.895(1) c ) 18.235(3) R ) 99.04(1) β ) 91.35(3) γ ) 97.41(2) a ) 7.919(3) b ) 14.375(9) c ) 14.605(3) R ) 110.68(3) β ) 90.07(3) γ ) 94.78(5)
monoclinic9a
O‚‚‚O (Å)
modifications, as reported in Table 3, together with cell volumes and calculated densities. Table 3 shows also that the three forms differ in calculated densities, form III being apparently denser than the others by ca. 3.5%. Whether this fact reflects a difference in stability of the three crystal forms is difficult to say in the absence of accurate measurements of observed densities. It is a fact, however, that form III has been obtained by crystallization at low temperature, even though cell dimensions and X-ray data have been subsequently collected at room temperature (see Experimental Section, Supporting Information). In this note, we have reported the crystal structure of a third form of the dicarboxylic organometallic acid [FeII(η5C5H4COOH)2] and compared the packing arrangement and hydrogen bonding with that observed in the two previously known forms. The three crystal forms contain essentially identical supramolecular objects, namely, {[FeII(η5-C5H4COOH)2]}2, and yet they show far from trivial differences in packing. One may be tempted to think that crystal polymorphism would be more common with flexible molecular species, such as ferrocene itself,10 which may yield different compromises between the optimization of molecular and crystal structures than more rigid systems. The cases discussed in this paper tell us another story. Even though it is well-known that different packings are available for many substantially rigid systems,1,2 it is interesting to note that, in this case, the conserved object is not a molecular but a supramolecular ensemble, viz. {[FeII(η5C5H4COOH)2]}2. Studies of polymorphism in organometallic crystal chemistry have been much less widespread than in the motherfield of organic solid-state chemistry.11 Besides the classical case of ferrocene, known in three polymorphic modification, there are only few examples of systematic investigations. For instance, two polymorphic modifications are known for the complex [(η2-fumaric acid)Fe(CO)4] (designated forms I and II).12a,b In form I, the fumaric acid ligands form ribbons of ligands joined by carboxylic rings. Interestingly, the same arrangement is observed in crystalline fumaric acid,12c,d which also possesses two polymorphic forms both based on molecular chains interlinked via hydrogen-bonded carboxylic rings. In form II of [(η2-fumaric acid)Fe(CO)4] the carboxylic rings form a catemer-type pattern. The complex HMn(CO)5, one of the first carbonyl hydrides to be structurally characterized by X-ray and neutron diffraction,13 is known in two polymorphic forms, both monoclinic, designated R-HMn(CO)5 and β-HMn(CO)5. Two polymorphic modifications of the oxidation product of the neutral complex [Cr0(η6-C6H5COOH)2], namely, [CrI(η6C6H5COOH)2][PF6], have been separately obtained depending on the crystallization conditions.14 Both forms contain
Vcell (Å3)
dcalc (g cm-3)
1062.5 (Z ) 4)
1.713 (T ) 293)
1053.1 (Z ) 4)
1.728 (T ) 293)
1549.2(12) (Z ) 6)
1.763 (T ) 293 K)
chains of cations held together by hydrogen bonds between the carboxyl groups. A related structural situation is shown by [MoH(η5-C5H5)2(CO)][Mo(η5-C5H5)(CO)3], which crystallizes in two different forms.15 A few other examples are known.16 It has been asserted that the number of polymorphic modifications of a given compound is a function of the time and energy spent in investigating polymorphism.1 It can be expected that the increasing awareness that the investigation of different polymorphic modifications of the same substance provides important information on molecular recognition and intermolecular bonding will make studies of polymorphism more popular also in the wide field of organometallic chemistry. However, we have not yet addressed the initial question of this paper, and to this end we need to improve the preparation of form III to carry out solid-solid reactions and compare the results with those previously obtained with form I. The main outcome of this study is not as much that we have a third crystal form of the molecule [FeII(η5C5H4COOH)2], but rather that we have a third crystal form of the supramolecular hydrogen-bonded adduct [FeII(η5C5H4COOH)2], which appears to be the truly robust unit transferable from one crystal architecture to another. Acknowledgment. We thank MIUR (COFIN and FIRB), the Universities of Bologna (D.B.) and Sassari (F.G.) for financial support. Supporting Information Available: Details about the X-ray crystal structures, including Experimental Section, tables of crystal data and structure refinement, atomic coordinates, bond lengths and angles, anisotropic displacement parameters, ORTEP figures for all compounds described herein. This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) McCrone, W. C. In Polymorphism in Physics and Chemistry of the Organic Solid State; Fox, D., Labes, M. M., Weisseberger, A., Eds.; Interscience: New York, 1965; Vol. II, p 726. (b) Threlfall, T. L. Analyst 1995, 120, 2435. (c) Bernstein, J. Polymorphism in Molecular Crystals; Oxford University Press: Oxford, 2002. (2) (a) Bernstein, J.; Davey, R. J.; Henck, J.-O. Angew. Chem., Int. Ed. Eng. 1999, 38, 3440. (b) See also Bladgen, N.; Davey, R. J. Chem. Br. 1999, 35, 44. (c) Braga, D. Chem. Commun. 2003, 2751. (3) (a) Dunitz J.; Bernstein, J. Acc. Chem. Res. 1995, 28, 193. (b) Blagden, N.; Davey, R. J. Cryst. Growth Des. 2003, 3, 873. (c) Davey, R. J.; Allen, K.; Blagden, N.; Cross, W. I.; Lieberman, F. H.; Quayle, M. J.; Righini, S.; Seton, L.; Tiddy, G. J. T. CrystEngComm 2002, 4, 257. (d) Jetti, R. K. R.; Boese, R.; Sarma, J. A. R. P.; Reddy, L. S.; Vishweshwar P.; Desiraju G. R. Angew. Chem., Int. Ed. Eng. 2003, 42, 1963.
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(4) (a) Braga, D., Grepioni, F., Orpen, A. G., Eds. Crystal Engineering: From Molecules and Crystals to Materials; Kluwer Academic Publishers: Dordrecht, 1999. (b) Hollingsworth, M. D. Science 2002, 295, 2410. (c) Desiraju, G. R. Crystal Engineering: The Design of Organic Solids; Elsevier: Amsterdam, 1989. (d) Aakero¨y, C. B.; Borovik, A. S. Coord. Chem. Rev. 1999, 183, 1. (e) Braga, D.; Grepioni, F.; Desiraju, G. R. Chem. Rev. 1998, 98, 1375. (f) Rivas, J. C. M.; Brammer, L. Coord. Chem. Rev. 1999, 183, 43. (5) (a) Braga, D.; Grepioni, F. J. Chem. Soc., Dalton 1999, 1, 1. (b) Braga, D.; Maini, L.; Polito, M.; Rossini, M.; Grepioni, F. Chem. Eur. J. 2000, 6, 4227. (c) Braga, D.; Maini, L.; Prodi, L.; Caneschi, A.; Sessoli, R.; Grepioni, F. Chem. Eur. J. 2000, 6, 1310. (d) Braga, D.; Maini, L.; Polito, M.; Grepioni, F. Organometallics 1999, 18, 2577. (e) Tse, M. C.; Cheung, K. K.; Chan, M. C. W.; Che, C. M. Chem. Commun. 1998, 21, 2295. (f) Kim, Y. J.; Verkade, J. G. Inorg. Chem. 2003, 42, 4262. (g) Oh, M.; Carpenter, G. B.; Sweigart, D. A. Organometallics 2003, 22, 2364. (h) Oh, M.; Carpenter, G. B.; Sweigart, D. A. Angew. Chem., Int. Ed. 2002, 41, 3650. (i) Oh, M.; Carpenter, G. B.; Sweigart, D. A. Chem. Commun. 2002, 18, 2168. (j) Elschenbroich, C.; Schiemann, O.; Burghaus, O.; Harms, K., J. Am. Chem. Soc. 1997, 119, 7452. (6) (a) Braga, D.; Maini, L.; Grepioni, F.; De Cian, A.; Felix, O.; Fischer, J.; Hosseini, M. W. New J. Chem. 2000, 24, 547. (b) Braga, D.; Maini, L.; Polito, M.; Mirolo, L.; Grepioni, F. Chem. Eur. J. 2003, 9, 4362. (7) One should keep in mind, however, that starting an experiment with a particular crystal form necessarily introduces seeds of that form into the environment, and these seeds can influence the outcome of the experiment. They do not necessarily influence the outcome, but they can; that depends on how aggressive the seeding is, and how robust other processes are to the influence of those seeds. The effect of this kind of unintentional seeding is noted in ref 3a. (8) Braga, D.; Grepioni, F. Angew. Chem., Int. Ed. 2004 43, 2. (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.
Communications (10) (a) Seiler, P.; Dunitz, J. D. Acta Crystallogr., Sect. B 1979, B35, 2020; (b) Takusagawa, F.; Koetzle, T. F. Acta Crystallogr., Sect. B 1979, B35, 1074; (c) Seiler, P.; Dunitz, J. D. Acta Crystallogr., Sect. B 1979, B35, 1068; (d) Braga, D.; Grepioni, F. Organometallics 1992, 11, 711; (e) Dunitz, J. D. Acta Crystallogr., Sect B 1995, B51, 619. (11) Braga, D.; Grepioni, F. Chem. Soc. Rev. 2000, 29, 229. (12) (a) Pedone, C.; Sirigu, A. Inorg. Chem. 1968, 7, 2614. (b) Hsiou, Y.; Wang, Y.; Liu, L. K. Acta Crystallogr., Sect. C 1989, 45, 721. (c) Brown, C. J. Acta Crystallogr. 1966 21, 1. (d) Bednowitz, A. L.; Post, B. Acta Crystallogr. 1966, 21, 566. (13) La Placa, S. J.; Hamilton, W. C.; Ibers, J. A.; Davison, A. Inorg. Chem. 1969, 8, 1928. (14) Braga, D.; Maini, L.; Grepioni, F.; Elschenbroich, C.; Paganelli, F.; Schiemann, O. Organometallics 2001, 20, 1875. (15) (a) Antsyshkina, A. S.; Dikareva, L. M.; Porai-Koshits, M. A.; Ostrikova, V. N.; Skripkin, Y. V.; Volkov, O. G.; Pasynskii, A. A.; Kalinnikov, V. T. Koord. Khim. 1985, 11, 82. (b) Marsella, J. A.; Huffman, J. C.; Caulton, K. G.; Longato, B.; Norton, J. R. J. Am. Chem. Soc. 1982, 104, 6360. (16) See, for instance, Braga, D.; Abati, A.; Scaccianoce,L.; Johnson, B. F. G.; Grepioni F. Solid State Sci. 2001, 3, 783; Miller J. L. Adv. Mater. 1998, 10, 1553. (17) The solid-state structure of [FeII(η5-C5H4COOH)2] (form III) was determined at 293 K by single-crystal X-ray diffraction on a Nonius CAD4 diffractometer equipped with a graphitemonochromator (Mo-KR radiation, λ ) 0.71073 Å). C12H10FeO4, FW ) 274.05, triclinic, space group P1 h , Z ) 6, a ) 7.919(3), b ) 14.375(9), c ) 14.605(3) Å, R ) 110.68(3), β ) 90.07(3), γ ) 94.78(5), V ) 1549.2(12) Å3, 5426 independent reflections (5659 measured), R1 ) 0.048, wR2 ) 0.1523, GOF ) 0.961. All non-H atoms refined anisotropically.
CG0497400
