DOI: 10.1021/cg900748r
Different Structural Networks Determined by Variation of the Ligand Skeleton in Copper(II) Diphosphinate Coordination Polymers
2010, Vol. 10 7–10
Ferdinando Costantino,† Andrea Ienco,*,‡ and Stefano Midollini‡ † Dipartimento di Chimica e CEMIN, Universit a di Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy, and ‡Istituto di Chimica dei Composti Organo Metallici, CNR, Via Madonna del Piano 10, 50019 Sesto fiorentino (Florence), Italy
Received July 2, 2009; Revised Manuscript Received November 10, 2009
ABSTRACT: A new polymeric copper(II)-organic framework, [[Cu(4,40 -bipy)(p(xyl)p)(H2O)2] 3 2(H2O)]n (1; p(xyl)p=P,P0 -diphenyl-
p-xylenediphosphinate, 4,40 -bipy=4,40 -bipyridine), has been synthesized. Single-crystal X-ray diffraction revealed that the structure of 1 consists of 2D grids connected by solvent water molecules. The temperature-dependent X-ray powder diffraction analysis of 1 has shown the formation of a dehydrated phase well modeled by a 3D structure with a binodal 4,6 connected topology. Crystal engineering based on metal-organic framework materials (MOFs) is a topic of large, growing interest of modern coordination chemistry.1 As a matter of fact, these compounds possess unique open-framework structures and can have applications in the storage of gases, as catalysts, and in separation and exchange reactions (zeolitic-like MOFs).2 Recently, new fascinating MOFs, having flexible networks, which can change their structures to respond to external stimuli, have been reported.3 Actually, most coordination polymers have been assembled through processes either not completely clarified or serendipitous. Therefore, it is a great challenge for the chemists in this field to design rational strategies for the synthesis of networks having determined compositions and structures. Unfortunately, even small variations of only one of the several factors influencing the synthetic process (metal ion, ligand, solvent, temperature, pH, etc.) can dramatically change the framework structure.4 We have shown in the last years that P,P0 -diphenyl-diphosphinate anions are useful ligands to bridge metal ions in polymeric networks of different geometries (1D, 2D, 3D).5 As a matter of fact, we found that the two closely related H2pcp and H2pc2p acids (see Scheme 1) react with the Cu(acetate)2/4,40 -bipy system, under the same reaction conditions, to assemble MOFs of different topology: namely, a 1D tubelike network, in the case of H2pcp,5g and a metastable 3D cds one which spontaneously changes into a 2D grid, in the case of H2pc2p.5i Some peculiar properties of the latter networks are consistent with the ability of the ethylene chain to assume different conformations. To further investigate the influence of the skeleton connecting the diphosphinate moieties to the structure of the resulting MOF, now we allowed the system Cu(acetate)2/4,40 -bipy to react, under the same usual conditions, with the P,P0 -diphenyl p-xylene diphosphinic acid, H2p(xyl)p, synthesized by us.6 In this latter, the skeleton should be more rigid and the two phosphinic groups are quite far away; therefore, the p(xyl)p2- anion ligand should be unable to chelate a single metal center.8 Reaction of Cu(CH3COO) 3 6H2O, H2p(xyl)p, and 4,40 -bipyridine (ratio of 1:1:1) in water allowed the formation of light blue crystals of formula [[Cu(4,40 -bipy)(p(xyl)p)(H2O)2] 3 2H2O)]n 1.10 These were characterized by elemental analysis, TGA, and XPRD. Single-crystal X-ray analysis11 of the complex revealed a 2D layered structure with guest solvent water molecules, which connect the 2D slabs through hydrogen bonding interactions. The architecture of the network is the same previously found for
Figure 1. Portion of the structure of 1, showing the copper coordination and the complete connectivity. The hydrogen atoms bonded to carbon atoms are omitted. Selected distances (A˚) and angles (deg): Cu1-O2=Cu1-O20 =1.973(4), Cu1-N1=2.022(6), Cu1N200 =2.002(6), Cu1-O3=Cu1-O30 =2.574(5), O2-Cu1-O20 = 177.3(2), O20 -Cu1-N200 =88.68(10), O2-Cu1-N200 =88.67(10), O20 -Cu1-N1 = 91.33(10), O2-Cu1-N1 = 91.32(10), N200 Cu1-N1 = 179.9990(10), O20 -Cu1-O3 = 90.46(16), O2-Cu1O3 = 89.75(16), N200 -Cu1-O3 = 94.56(10), N1-Cu1-O3 = 85.44(10). Symmetry transformations used to generate equivalent atoms: 0 = -x þ 3/2, y, -z þ 3/2, 00 = x, y - 1, z.
Scheme 1
*To whom correspondence should be addressed. Fax: þþ39-055-5225203. Telephone: þþ39-055-5225201. E-mail:
[email protected].
the complex [[Cu(4,40 -bipy)(pc2p)(H2O)] 3 3H2O]n (2), isolated from the Cu(acetate)2/H2pc2p/4,40 -bipy system.5i
r 2009 American Chemical Society
Published on Web 12/15/2009
pubs.acs.org/crystal
8 Crystal Growth & Design, Vol. 10, No. 1, 2010
Costantino et al.
Figure 2. Single 2D slab (on the left), the packing of the slabs, and a view of the hydrogen bonding interactions connecting two slabs (on the right). The bipys are omitted. The p(xyl)p group is simplified. Only the carbon atoms bonded to the P atoms are shown, and the xylil group is represented by a single line connecting the two CH2 groups.
Figure 3. Comparison of the observed and calculated powder diffraction patterns. (a) Observed diffraction pattern for 1a. (b) Calculated diffraction pattern using the structural model for 1a. Packing view of the 3D anhydrous 1a network.
Figure 4. Schematic representation of the solid state transformation of 1 in 1a. After the removal of the water molecules from 1, it is possible to approach simultaneously the PO groups to the nearly metal, as indicated by the red arrows.
The unit cell of 1 consists of a Cu(II) cation, a p(xyl)p2- anion, a 4,40 -bipy molecule, and four water molecules, of which only two are coordinated to the metal as shown in Figure 1. The metal coordination polyhedron, which is located on a C2 axis, is a distorted octahedron with the equatorial positions occupied by two nitrogen atoms of two different bipy molecules and by two symmetry related oxygen atoms of two different phosphinate
anions. (Cu-O2 = Cu-O20 = 1.973(4) A˚, where the symmetry transformation is -x þ 3/2, y, -z þ 3/2). Finally, two axially coordinated and symmetry related water molecules complete the coordination sphere around the copper ion (Cu-O3=Cu-O30 = 2.576(5) A˚; -x þ 3/2, y, -z þ 3/2). Figure 2 shows the rectangular grid resulting from the connection of the Cu-p(xyl)p-Cu rows through the bipy molecules.
Communication The meshes of the rectangular grid have almost the same length in the direction of the bipy Cu-Cu0 (11.073(5) in 1 and 11.087(4) in 2), while in the Cu-p(xyl)p-Cu direction the Cu-Cu distance is longer by almost 2 A˚ (11.314(2) vs 9.316(2) in 1 and 2, respectively). The slabs are staggered with respect to one another. Hydrogen bonding interactions (as highlighted in Figure 2) between the coordinated and uncoordinated solvent water molecules, as well as the noncoordinated oxygen atoms of the p(xyl)p moieties, connect the 2D slabs. The most important hydrogen bonds are as follows: O1 3 3 3 O3=2.792(8) A˚, O2 3 3 3 O3=3.236(7) A˚, O4 3 3 3 O1 = 2.747(7) A˚, and O3 3 3 3 O4 = A˚ (-x þ 2, -y þ 1, -z þ 2). The coordinated and the solvent water molecules, as shown by the thermogravimetric analysis (see Figure S1), are lost at 120° (weight loss of 10.7% calcd, 11.0% exp). The temperaturedependent X-ray powder diffraction analysis of compound 1 shows that a new crystalline phase (1a) is formed at 120 °C. The latter is stable also at room temperature (see Figure S2). The original hydrated phase 1 is regenerated if 1a is placed in contact with water for a few minutes (see Supporting Information). We were able to index this diffraction pattern using the TREOR program,15 finding a monoclinic cell with the following parameters: a = 11.387(2) A˚, b = 11.100(2) A˚, c = 22.612(4) A˚, β = 97.45(1)°, M(20)=14.16 We propose here a structural model of 1a obtained from 1 by removing the solvent and Copper coordinated water molecules and by approaching the PO groups to the metal atoms. A second structural model 1b was also considered, but it was discarded, since its transformations from 1 were energetically unfavored, as shown in the Supporting Information. The refinement details are described in the reference section. The comparison of the calculated and observed powder diffraction patterns of 1a is shown in Figure 3. The model 1a phase is a 3D phase. The network is a 4,6 connected binodal net with the Copper metals as the six connected nodes and the p(xyl)p ligands as four connected nodes.17 The assigned topology is tcj/hc.18 As shown by Figure 4, the series of infinite strips formed by copper(II) metal atoms and 4,40 bipyridine are still present, as suggested also by the similar length of the b axis in 1 and 1a. This is evidence that the model structure 1a is a reasonable one. The copper metal now adopts a pseudooctahedral coordination with two nitrogen atoms and with four oxygen atoms of four independent p(xyl)p groups. Two Cu-O distances are shorter (Cu1-O1 = 2.25(1) A˚ and Cu1-O4 = 2.12(1) A˚) with respect to the others (Cu1-O2=2.40(1) A˚ and Cu1-O3=2.35(1)A˚). From the comparison of structures 1 and 1a, the rearrangement occurring upon the temperature transformation is a slipping of the 2D slabs with a facile formation of two new copper oxygen bonds as illustrated in Figure 4. It is noteworthy that we have previously reported that the compound [[Cu(4,40 -bipy)(pc2p)(H2O)] 3 3H2O)]n (2) at 130 °C gives an amorphous phase which, as in case of 1, can be regenerated by treatment with water.5i The different solid states (amorphous/crystalline) of the two dehydrated phases may be related to the different number of solvent water molecules per unit formula in 1 and 2 and consequently the percentage of the total volume occupied by the solvent water molecule (3.8% in 1 and 6.4% in 2). Also, the presence of the p(xyl)p group may help the packing of the slabs in 1 (see the additional p(xyl)p/bipyridine π-π interactions highlighted in Figure S4) and their easier recombination in the crystalline phase 1a. In summary, we have shown how in hybrids based on diphosphinate ligands the elongation of the chain connecting the two diphosphinate moieties favors the formation of stable 2D networks. In the case of p(xyl)p, no formation of 3D highly hydrated metastable phases is observed as for the pc2p ligand; however, the xyl spacer between the diphosphinate moieties blocks the conformation of the hybrid polymer through the π-π interactions
Crystal Growth & Design, Vol. 10, No. 1, 2010 9 between the xyl and phenyl groups, favoring the formation of a 3D crystalline anhydrous Cu/p(xyl)p/4,40 bipy network. Acknowledgment. We thank Prof. Davide Maria Proserpio for helpful suggestions. This work has been performed under the FIRENZE HYDROLAB project sponsored by Ente Cassa di Risparmio di Firenze, and it was supported by MIUR (Rome) through PRIN project 2007X2RLL2: Nuove strategie per il controllo delle reazioni metallo assistite: interazioni non convenzionali di frammenti molecolari. Supporting Information Available: X-ray crystallographic information files (CIF) and supplementary graphics. This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) Long, J. R.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1213–1214. (2) Ferey, G.; Mellot-Draznieks, C.; Serre, C.; Millange, F. Acc. Chem. Res. 2005, 38, 217–225. Kitagawa, S.; Kitaura, R.; Noro, I. S. Angew. Chem., Int. Ed. 2004, 43, 2334–2375. Rao, C. N. R.; Natarajan, S.; Vaidhyanathan, R. Angew. Chem., Int. Ed. 2004, 43, 1466–1496. Yaghi, O. M.; O'Keeffe, M.; Ockwig, N. W.; Chae, H. M.; Eddaudi, H.; Kim, J. Nature 2003, 423, 705–714. (3) Ferey, G. Chem. Soc. Rev. 2008, 37, 191–214. Kitagawa, S.; Uemura, K. Chem. Soc. Rev. 2005, 34, 109–119. (4) Eddaudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, O. M. Science 2002, 295, 469–472. Seo, J. S.; Whang, D.; Lee, H.; Jun, S. I.; Oh, J.; Jeon, Y. J.; Kim, K. Nature 2000, 404, 982– 986. Masaoka, S.; Tanaka, D.; Nakanishi, Y.; Kitagawa, S. Angew. Chem., Int. Ed. 2004, 43, 2530–2534. (5) (a) Berti, E.; Cecconi, F.; Ghilardi, C. A.; Midollini, S.; Orlandini, A.; Pitzalis, E. Inorg. Chem. Commun. 2002, 5, 1041. (b) Cecconi, F.; Dakternieks, D.; Duthie, A.; Ghilardi, C. A.; Gili, P.; Lorenzo-Luis, P.; Midollini, S.; Orlandini, A. J. Solid State Chem. 2004, 177, 786. (c) Ciattini, S.; Costantino, F.; Lorenzo-Luis, P.; Midollini, S.; Orlandini, A.; Vacca, A. Inorg. Chem. 2005, 44, 4008. (d) Beckmann, J.; Costantino, F.; Dakternieks, D.; Duthie, A.; Ienco, A.; Midollini, S.; Mitchell, C.; Orlandini, A.; Sorace, L. Inorg. Chem. 2005, 44, 9416. (e) Midollini, S.; Lorenzo-Luis, P.; Orlandini, A. Inorg. Chim. Acta 2006, 359, 3275. (f) Costantino, F.; Midollini, S.; Orlandini, A.; Sorace, L. Inorg. Chem. Commun. 2006, 9, 591. (g) Bataille, T.; Costantino, F.; Lorenzo-Luis, P.; Midollini, S.; Orlandini, A. Inorg. Chem. Acta 2008, 361, 9–15. (h) Costantino, F.; Midollini, S.; Orlandini, A. Inorg. Chim. Acta 2008, 361, 327–344. (i) Bataille, T.; Costantino, F.; Ienco, A.; Guerri, A.; Marmottini, F.; Midollini, S. Chem. Commun 2008, 6381–6383. (6) Synthesis of P,P0 -diphenyl p-xylene diphoshinic acid, H2p(xyl)p. The acid was prepared following the general method of alkylation of phenyl phosphinic acid previously described by Garst.7 To a 16 M commercial solution of n-butyl lithium in hexane (100 mL, 160 mmol), at 0 °C, under nitrogen, was added 150 mL of anhydrous tetrahydrofuran. Then a solution of 10.8 g (76 mmol) of phenylphosphinic acid in 150 mL of THF was added dropwise over 10 min, under magnetical stirring. The resulting suspension was stirred at 0 °C for 1 h and then treated with 6.60 g (30 mmol) of R,R0 dichloro-p-xylene in 50 mL of tetrahydrofuran, over 10 min. This mixture was stirred for 1 h at 0 °C, at reflux for 6 h, and at room temperature for 12 h. Removal of the solvent left a solid which was treated with 200 mL of water and 8 mL of concentrated ammonium hydroxide. The mixture was stirred at room temperature for 2 h, and then the remaining solid material was filtered off. The solution was washed with 200 mL of ether, and then the aqueous layer was acidified with 20% aqueous hydrochloric acid. An oil precipitated which solidified to give a whitish powder. This was filtered, washed with water and then with ether, and dried in air. The product can be recrystallized from methanol. The acid is almost insoluble in water and is sparingly soluble in ethanol or methanol. Yield: 3.2 g (28%). Anal. Calc for C20H20O4P2: C, 62.18; H, 5.22. Found: C, 61.78; H, 5.34. 1HNMR (DMSO-d6): δ 3.23 (d, 2JP-H =17 Hz, 4H, CH2-P) ppm, 6.99 (s, H4, C6H4) 7.7-7.7 (m, 10H, C6H5), 8.36 (s, 2H, P-OH); 31P NMR {1H}=34.0(s) ppm. (7) Garst, M. E. Synth. Commun. 1979, 9, 261–266. (8) The pcp usually chelates the metal center, but we recently found that also pc2p can chelate a metal center under certain conditions.9
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(9) Costantino, F.; Ienco, A.; Midollini, S.; Orlandini, A.; Sorace, L.; Vacca, A. Eur. J. Inorg. Chem. 2008, 3046–3055. (10) Synthesis of [[Cu(4,40 -bipy)(p(xyl)p)(H2O)2] 3 2(H2O)]n. Thirty milligrams (0.08 mmol) of H2p(xyl)p and 12 mg (0.08 mol) of 4,40 -bipy were added to a solution of 15.4 g (0.08 mmol) of Cu(CH3COO)2 3 H2O in 30 mL of water. The resulting mixture was heated for 48 h at 80 °C, without stirring. Well shaped light blue crystals precipitated. The supernatant solution was decanted off, and the crystals were washed two times with the water, by decantation. The complex was dried in air. XRD data of complex 1 were collected on a X’Pert PRO diffractometer with Cu KR radiation (λ=1.5418). The experimental XRD patterns agreed well with the simulated ones generated on the basis of the single-crystal analyses for 1, suggesting the phase purity of the products. Yield: 29 mg (53%) . Anal. Calc for C30H34CuN2O8P2: C, 53.30; H, 5.07; N, 4.14. Found: C, 53.18; H, 5.20; N, 4.10. (11) (a) Crystal data for 1: C30H34CuN2O8P2, MW=676.07, monoclinic, P2/n, a = 11.4560(10), b = 11.073(5), c = 12.449(2), β = 112.050(10), V = 1463.7(7) A˚3, Z = 2, Fcalc = 1.534 Mg/m3, μ = 2.559 mm-1, F(000) = 702, crystal size = 0.6 0.1 0.03 mm3, reflections collected=4274, independent reflections=2171, goodness-of-fit on F2 =1.174, R1=0.0668, wR2=0.1722 [I > 2σ(I)], R indices (all data) R1=0.0834, wR2=0.1873, largest difference peak and hole 0.410 and -0.436 e 3 A˚3-. The data collection was performed at 293(2) K on a Philips PW 1100 diffractometer equipped with Cu KR radiation. The structure was solved using direct methods using Sir9712 and refined on F2 by full-matrix least squares techniques with the SHELXL program.13 All non-hydrogen atoms were refined anisotropically. The water hydrogen atoms were found in the Fourier map and freely refined. The other hydrogen atoms were introduced in calculated positions. (b) The structural model of 1a was derived from that of 1 by removing the copper-coordinating water molecules and by approaching the
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(12) (13) (14) (15) (16) (17)
(18)
PO groups to the Cu atoms. This model was correctly positioned in the new unit cell by placing the Cu atoms in special positions. The bad quality of the diffraction pattern and the high number of light independent atoms (36) did not allow a good refinement. For that reason, a partial Rietveld refinement has been performed. The model of 1a was refined using the GSAS program.14 Only the p(xil)p atoms were refined, using severe bond and angle restraints, whereas the bipyridine groups were fixed. Also, the profile and the background parameters were refined. At the end of the refinement, the agreement factors were the following: C30H34CuN2O6P2, MW = 644.07, monoclinic, P21/c, a = 11.403(3) A˚, b = 11.092(3) A˚, c = 22.580(5) A˚, β = 97.59(2)°, number of data points = 6476, number of parameters = 106, number of restraints = 138, goodness-of-fit on P F2 = 4.30, a b c Rp = 0.057 , Rwp F2 = 0.104 . (a) R p = P= 0.078 , 2RP P |I2o - I2c|/ P 2 1/2 PIo; 2(b) Rwp=[ w(Io - Ic) / wIo ] ; (c) RF2 = |Fo - Fc |/ |Fo |. Altomare, A.; Burla, M. C.; Cavalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. C.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115–119. Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122. Larson, C.; von Dreele, R. B. Generalized Crystal Structure Analysis System; Los Alamos National Laboratory, NM, 2001. Werner, P. E.; Eriksson, L.; Westdahl, M. C. J. Appl. Crystallogr. 1985, 18, 367–370. de Wolff, P. M. J. Appl. Crystallogr. 1968, 1, 108–113. (a) Carlucci, L.; Ciani, G.; Proserpio, D. M. In Making Crystals by Design. Methods, Techniques and Applications; Braga, D., Grepioni, F., Eds.; Wiley: Darmstadt, 2007; pp 58-85. (b) TOPOS ver 4.0, http:// www.topos.ssu.samara.ru/. Blatov, V. A. IUCr CompComm Newsletter 2006, 7, 4-38. Blatov, V. A.; Proserpio, D. M. Acta Crystallogr. 2009, A65, 202– 212.
