Communication pubs.acs.org/IC
Coinage Metal Pyrazolates [(3,5-(CF3)2Pz)M]3 (M = Au, Ag, Cu) as Buckycatchers Naleen B. Jayaratna,† Marilyn M. Olmstead,‡ Boris I. Kharisov,§ and H. V. Rasika Dias*,† †
Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, Texas 76019-0065, United States Department of Chemistry, University of California, One Shields Avenue, Davis, California 95616-5259, United States § Universidad Autónoma de Nuevo León, Ciudad Universitaria, San Nicolás de los Garza, Nuevo León 66451, Mexico ‡
S Supporting Information *
Buckminsterfullerene C60 is a fascinating molecule13,14 with applications spanning from superconductivity to medicine and biology. Considerable effort has been expended to synthesize supramolecular assemblies consisting of C60 with various molecules like porphyrins, calixarenes, and corranulenes to obtain hybrid materials with interesting structures and novel photochemical, electronic, and redox properties.15−21 In order to accommodate and complement the convex-shaped C60 and to form stronger host−guest interaction, concave hosts are usually preferred. An area of research activity in one of our laboratories concerns the π-acid/π-base chemistry between [M3] and arenes like benzene, mesitylene, and naphthalene. For example, [(3,5(CF3)2Pz)Ag]3 ([Ag3],5 which is the most π-acidic member of the [M3] family, easily forms sandwich molecular assemblies and s t a c k s li ke ( b e n z e n e ) [ A g 3 ]( b e n z e n e ) , ( b e n z e n e ) [Ag3]2(benzene), {(mesitylene)[Ag3](mesitylene)}∞, and {[Ag3](naphthalene)}∞ with planar, electron-rich arenes.22,23 Here we show that it is possible to use nonplanar fullerenes in this chemistry and report our findings involving C60 and [Ag3] and the related [Cu3] and [Au3]. The work by Gabbai ̈ et al. and Petrukhina et al. involving the π-acid [o-C6F4Hg]3 is noteworthy in this regard. They have used this trimeric mercury(II) complex to obtain π-acid/π-base adducts with planar arenes24,25 and 1:1 binary stacks with corannulene and indenocorannulene.26 Interestingly, the treatment of C60 with [Ag3] in a 1:4 molar ratio in CS2 readily produced {C60[Ag3]4}∞ as an air-stable, purple (appeared black to naked eye) crystalline solid. Our first attempt was at a 1:1 molar ratio, which also produced the same product. This cocrystal was moderately soluble in CS2 (less soluble than free C60) and slightly soluble in CH2Cl2 and CHCl3. The related copper and gold analogues, {C60[Cu3]4}∞ and {C60[Au3]4}∞, can also be synthesized using the corresponding metal pyrazolates [Cu3] and [Au3] and C60 in CS2 or CS2/ benzene, respectively. The solubility properties of the copper complex {C60[Cu3]4}∞ are not significantly different from those of {C60[Ag3]4}∞, but the gold complex {C60[Au3]4}∞ is quite insoluble in the above solvents and shows some solubility in benzene. The room temperature 1H, 13C{1H}, and 19F NMR spectra of {C60[Cu3]4}∞ and {C60[Ag3]4}∞ were recorded in CS2/CDCl3, while the low solubility in these solvents prompted us to use
ABSTRACT: The synthesis and characterization of supramolecular assemblies {C60[M3]4}∞ consisting of C60 and coinage metal pyrazolates [M3] (i.e., [(3,5-(CF3)2Pz)M]3, where Pz = pyrazolate and M = Au, Ag, and Cu) are reported. {C60[Cu3]4}∞, {C60[Ag3]4}∞ and {C60[Au3]4}∞ form isomorphous crystals. The [M3] moieties adopt a concave conformation to complement the convex C60 surface. They exist as dimers of trimers (i.e., hexanuclear [M3]2 units) that are held together by three close M···M metallophilic interactions at 3.1580(17), 3.2046(7), and 3.2631(7) Å for copper, silver, and gold systems, respectively. The [M3]2 moieties surround each C60 in a tetrahedral fashion, while each [M3]2 is sandwiched by two C60 molecules to form a supramolecular 3D assembly.
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omoleptic pyrazolate complexes of copper, silver, and gold are of significant interest because of their structural diversity, fascinating luminescent properties, and rich supramolecular chemistry.1−7 Trinuclear units featuring nine-membered M3N6 metallacycles (M = Cu, Ag, Au) are the most common structural motif found in these systems (e.g., [(3,5(CF3)2Pz)M]3 ([M3]; Figure 1).4,5,8 They often aggregate
Figure 1. Trinuclear [M3] systems involving the metal ions (M) copper(I), silver(I), and gold(I) and fluorinated pyrazolate [3,5(CF3)2Pz]−.
further by forming dimers of trimers or columns of trimers with M···M metallophilic interactions.9 These molecules commonly display bright visible luminescence upon exposure to UV radiation in the solid state, which in certain cases can be altered by variation of the temperature or excitation wavelength or by exposure to solvent vapor or pressure.2,5,7,10−12 © XXXX American Chemical Society
Received: July 16, 2016
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DOI: 10.1021/acs.inorgchem.6b01709 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry C6D6 as the NMR solvent for the gold adduct of {C60[Au3]4}∞. The chemical shift values corresponding to the pyrazolyl moiety protons or C60 carbons of {C60[M3]4}∞ remained unchanged or were only slightly different compared to the corresponding signals of the pure components. For example, the 1H NMR spectrum of {C60[Cu3]4}∞ shows a peak at 7.01 ppm for the pyrazolate proton compared to 7.02 ppm of the free [Cu3]. The 13 C{1H} NMR resonance corresponding to C60 in the complex {C60[Cu3]4}∞ was observed at 142.9 ppm compared to the 142.68 ppm peak of free C60.14 This suggests only a weak interaction between C60 and [M3] in solution or that these NMR resonances are not very responsive to [M3]/C60 interaction. X-ray crystallographic data provide definitive evidence for the formation of {C60[Cu3]4}∞, {C60[Ag3]4}∞, and {C60[Au3]4}∞ supramolecules in the solid state. The {C60[M3]4}∞ systems crystallize in the cubic Fd3̅c space group and are isomorphous. The C60 cage resides on a crystallographic special position of 23 and shows positional disorder. The repeating unit of {C60[Au3]4}∞ is illustrated in Figure 2 (showing only one of
Figure 3. View of the supramolecular structure of {C60[Au3]4}∞ (carbon, fluorine, and hydrogen atoms of pyrazolyl moieties have been removed for clarity).
Figure 4. View showing C60 sandwiched [Au3]2 with three intertrimer Au···Au contacts. Figure 2. X-ray structures of {C60[Au3]4}∞ showing the basic stoichiometry and tetrahedrally encapsulated C60 by four [Au3]. {C60[Cu3]4}∞ and {C60[Ag3]4}∞ analogues are isomorphous.
Table 1. Selected Structural Parameters for {C60[M3]4}∞ and Related [M3] Precursors (Distances in Angstroms; Angles in Degrees)
the 12 orientations of the C60 cage). The related copper and silver analogues have very similar structures. The unit cell lengths of {C60[M3]4}∞ are, however, different [a = 36.340(3), 36.963(3), and 36.823(6) Å for M = Cu, Ag, and Au, respectively (at 100 K)], but this is not surprising considering the involvement of different metal ions. In fact, cell dimensions agree well with the trend expected based on the covalent radii of the three coinage metal ions (i.e., 1.13, 1.33, and 1.25 Å for CuI, AgI, and AuI, respectively).27 C60, for comparison, crystallizes in the cubic space group with a unit cell length of 14.052(5) Å.28 Figures 3 and 4 show part of the extended 3D sandwich structure of {C60[Au3]4}∞ featuring each C60 molecule surrounded by four dimers of [Au3] trimers in a tetrahedral fashion (only the Au6N6 core of [Au3]2 is shown), and each [Au3]2 is sandwiched by two C60 molecules. The [Au3] moieties adopt a concave configuration to compliment the convex C60 surface and to facilitate a more intimate union. The [Au3] moieties exist as dimers of trimers ([Au3]2) that are held together by three close Au···Au contacts at 3.2631(7) Å, perhaps assisted by the reduced intertrimer pyrazolyl moiety steric interactions, as a result of an outwardly pointed [Au3] periphery. The related {C60[Ag3]4}∞ and {C60[Cu3]4}∞ adducts also feature three close Ag···Ag and Cu···Cu contacts at 3.2046(7) and 3.1580(17) Å, respectively (see Table 1). For comparison, the closest intertrimer M···M contacts of the parents [Au3] and [Cu3]
{C60[Au3]4}∞ M···M (intratrimer) M···M (intertrimer) M−N closest M···C(C60) N−M−N av. M···M (intratrimer) closest M···M (intertrimer) av. M−N av. N−M−N
3.3435(7) 3.2631(7) 1.993(5) 2.006(6) 3.138 174.1(2) [Au3]5 3.3506(3) 3.885(1) 1.996(4) 179.60(16)
{C60[Ag3]4}∞
{C60[Cu3]4}∞
3.4810(7) 3.2046(7) 2.065(4) 2.081(4) 3.182 172.39(15) [Ag3]5
3.2376(15) 3.1580(17) 1.856(6) 1.868(6) 3.103 172.7(3) [Cu3]5
3.4968(4) 3.2037(4) 2.091(3) 174.81(12)
3.2323(4) 3.813(1) 1.859(2) 178.46(10)
(which stack face-to-face with alternating short−long separations, forming supramolecular columns)5 are significantly longer at 3.885(1) and 3.813(1) Å, respectively, and involve only two and one, rather than three, M···M contacts as in {C60[M3]}∞. The closest intertrimer Ag···Ag separation in [Ag3] [3.2037(4) Å]5 is similar in magnitude to that observed in {C60[Ag3]4}∞ but involves only two argentophilic interactions. In contrast to the 3D sandwich structures of {C60[M3]4}∞ that extend in four directions in a tetrahedral fashion and with intertrimer M···M interactions (Figures 3 and 4), the [o-C6F4Hg]3 and corannulene adducts noted above form 1:1 columnar structures with B
DOI: 10.1021/acs.inorgchem.6b01709 Inorg. Chem. XXXX, XXX, XXX−XXX
Inorganic Chemistry
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alternating [o-C6F4Hg]3 and corannulene moieties and do not feature intertrimer Hg···Hg contacts.26 The intertrimer metallophilic interactions of {C60[Au3]4}∞ and {C60[Ag3]4}∞ are well within Bondi’s van der Waals radii sums (i.e., 3.32 and 3.44 Å for gold and silver),29 while the Cu··· Cu contacts in {C60[Cu3]4}∞ are slightly longer (cf. 2.80 Å). Recent work by Alvarez and others, however, point to the presence of van der Waals interactions at even longer distances than those of Bondi’s [e.g., van der Waals radii sums proposed by Alvarez: 4.76 Å (Cu−Cu), 5.06 Å (Ag−Ag), and 4.64 Å (Au− Au)].30−33 Overall, short and multiple intertrimer M···M contacts of {C60[M3]4}∞ and bowl-shaped [M3] moieties point to significantly enhanced metallophilic bonding interactions in these systems as a result of C60 encapsulation. It is also noteworthy that the twisted trigonal-prismatic geometry (with twist angles of about 21−23°; see Figure S11) adopted by the M6 core of the dimer of trimers of {C60[M3]4}∞ is rare in comparison to the chair configuration with two close intertrimer M···M contacts (as in {[Ag3]2(toluene)}∞, (benzene)[Ag3]2(benzene), and {[Cu3]2(benzene)}∞).5,22,34 The closest M···C (of C60) distances for {C60[M3]4}∞ are also noted in Table 1. Although these values should be treated with caution considering the positional disorder of the C60 cage, they are all below or at Bondi’s van der Waals contact distance and suggest close C60− [M3] interactions in the solid state. These {C60[M3]4}∞ adducts decompose at elevated temperatures, which was observed in the melting point determination and confirmed by thermogravimetric analysis (TGA). All three complexes decompose by the release of metal pyrazolate, leaving C60. This is actually the opposite of what we have see with some of the arene−[M3] stacks.35 This is perhaps not a surprise because C60 has a high sublimation temperature (∼600 °C). In summary, we describe the isolation of three supramolecular assemblies involving C60 and coinage metal pyrazolates [M3]. This work shows that it is possible to use systems like [M3] directly (without any modifications) to effectively catch Buckyballs. The [M3] moieties have the ability to adopt a concave conformation to accommodate curved surfaces of fullerenes. The [M3] units in {C60[M3]4}∞ exit as slightly twisted trigonal-prismatic dimers of trimers with three close metallophilic M···M interactions. Hybrid products like {C60[M3]4}∞ resulting from the combination of two important classes of compounds [fullerenes and metal pyrazolate (or analogous systems)] offer many options to develop new material that may show interesting photochemical, electronic, and redox properties. Further studies are underway in our laboratory to explore the properties of such materials.
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Communication
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel: (+1) 817 272 3813. Web: https:// www.uta.edu/chemistry/faculty/directory/Dias.php. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the Robert A. Welch Foundation (Grant Y-1289) and National Science Foundation (Grant CHE1265807). We also want to thank Dr. Nicola Armaroli (CNR, Italy) for performing preliminary photophysical studies.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01709. Experimental details on the synthesis and characterization, TGA analysis, and additional figures (PDF) X-ray crystallographic data in CIF format (CIF) X-ray crystallographic data in CIF format (CIF) X-ray crystallographic data in CIF format (CIF) C
DOI: 10.1021/acs.inorgchem.6b01709 Inorg. Chem. XXXX, XXX, XXX−XXX
Communication
Inorganic Chemistry (27) Bayler, A.; Schier, A.; Bowmaker, G. A.; Schmidbaur, H. J. Am. Chem. Soc. 1996, 118, 7006−7007. (28) Liu, S.; Lu, Y. J.; Kappes, M. M.; Ibers, J. A. Science 1991, 254, 408−10. (29) Bondi, A. J. Phys. Chem. 1964, 68, 441−51. (30) Alvarez, S. Dalton Trans. 2013, 42, 8617−8636. (31) Schmidbaur, H.; Schier, A. Chem. Soc. Rev. 2008, 37, 1931−1951. (32) Schmidbaur, H.; Schier, A. Angew. Chem., Int. Ed. 2015, 54, 746− 784. (33) Carvajal, M. A.; Alvarez, S.; Novoa, J. J. Chem. - Eur. J. 2004, 10, 2117−2132. (34) Jayaratna, N. B.; Hettiarachchi, C. V.; Yousufuddin, M.; Dias, H. V. R. New J. Chem. 2015, 39, 5092−5095. (35) Rawashdeh-Omary, M. A.; Rashdan, M. D.; Dharanipathi, S.; Elbjeirami, O.; Ramesh, P.; Dias, H. V. R. Chem. Commun. 2011, 47, 1160−1162.
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DOI: 10.1021/acs.inorgchem.6b01709 Inorg. Chem. XXXX, XXX, XXX−XXX
