A Three-Dimensional Mixed-Ligand Coordination Polymer Featuring Strongly Antiferromagnetically Coupled Dinuclear Copper Paddlewheels Linked into a 6-Connected Self-Penetrated Network
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 10 3518–3520
David P. Martin,† Ronald M. Supkowski,‡ and Robert L. LaDuca*,† Lyman Briggs College, E-30 Holmes Hall, Michigan State UniVersity, East Lansing, Michigan 48825, and Department of Chemistry and Physics, King’s College, Wilkes-Barre, PennsylVania 18711 ReceiVed July 10, 2008
ABSTRACT: The coordination polymer {[Cu2(glu)2(bpmp)] · 4H2O}n (1, glu ) glutarate, bpmp ) N,N′-bis(4-pyridyl)piperazine) was prepared via solution-phase methods. Single-crystal X-ray diffraction revealed the presence of [Cu2(glu)2]n layers containing “paddlewheel” dinuclear units. These layers are connected by tethering bpmp ligands into a self-penetrated three-dimensional covalent network with 6-connected 446108 topology. Variable-temperature magnetic studies indicated the presence of very strong antiferromagnetic coupling (J ) -283(8) cm-1) within the {Cu2} dinuclear units of 1. Incipient channels within the self-penetrated framework are occupied by ”infinite” C(4) water molecule chains. Mutual interpenetration is frequently encountered in the structures of two-dimensional (2D) and three-dimensional (3D) coordination polymers,1 with long ditopic tethering ligands able to promote higher degrees of interpenetration.2,3 In comparison, self-penetrated coordination polymers are much rarer.4-10 This intriguing class of materials exhibits structures wherein the rods (connecting ligands) of the framework penetrate through the shortest internodal circuits. A variety of unique topologies have been identified in recently prepared self-penetrated coordination polymers. For example, {[Ni(1,3,5-tri(4-pyridyl) triazine)](NO3)2}4 adopts an unprecedented chiral regular (12,3)-net self-penetrated topology. Although the deliberate design of self-penetrated structures is as yet elusive, it has been demonstrated that conformationally flexible difunctional tethering ligands, such as succinate, can prove advantageous for their self-assembly.8-10 {[Cd(succinate)(L)] · H2O} (L ) N,N′-bispyridin-4-ylmethylsuccinamide) exhibits [Cd(L)] triple helices, connected into a very rare 2D self-penetrated layer by gauche conformation succinate dianions.8 Recently we reported a unique self-penetrated 3D 5-connected net with a uniform 610 topology in {[Ni(dpa)2(succinate)0.5]Cl} (dpa ) 4,4′-dipyridylamine), constructed by the interconnection of quadruply interpenetrated [Ni(dpa)2]n2n+ diamondoid nets through gauche conformation succinate linkers.9 We thus decided to undertake synthetic explorations toward mixed-ligand divalent coordination polymers incorporating the conformationally flexible glutarate (glu) and N,N′-bis(4-pyridyl)piperazine (bpmp) ligands. We felt that the greater conformational freedom of the glu ligand relative to succinate could potentially promote the self-assembly of coordination polymers with novel interwoven topologies. In this communication, we report the synthesis and structural characterization of {[Cu2(glu)2(bpmp)] · 4H2O}n (1), a 3D coordination polymer with a relatively simple yet extremely uncommon self-penetrated 6-connected topology. Magnetic and thermal studies of 1 are also reported herein. Room temperature layering of an aqueous solution of copper(II) nitrate and glutaric acid with a methanolic solution of bpmp11 resulted in the deposition of green crystals of 1 in good yield.12 The infrared spectrum of 1 was consistent with the inclusion of both glu and bpmp ligands, with features corresponding to pyridyl ring puckering (743-839 cm-1) and stretching (1227-1454 cm-1). * Corresponding author. E-mail:
[email protected]. † Michigan State University. ‡ King’s College.
Figure 1. Coordination environment of 1, highlighting the dinuclear ”paddle-wheel” motif and complete glu and bpmp ligands.
Asymmetric and symmetric carboxylate stretching modes were observed at 1605 and 1416 cm-1, respectively. Single-crystal X-ray diffraction13 revealed that 1 contains an asymmetric unit consisting of a copper atom, one glu ligand, and one-half of a bpmp ligand, along with two water molecules of crystallization. The coordination environment is a nearly perfect [CuO4N] square pyramid, with an Addison τ factor14 of 0.01. The bond lengths and angles are standard for a Jahn-Teller active square pyramidal Cu2+ ion, with Cu-O bond lengths ranging from 1.958 to 1.982 Å and a “long” axial bond length to the pyridyl nitrogen atom of the bpmp ligand (2.190 Å). Four glu carboxylate termini bridge two Cu2+ ions in a syn-syn manner to generate a commonly seen {Cu2} dinuclear “paddlewheel” pattern (Figure 1).15 The Cu · · · Cu contact distance across the dinuclear unit is 2.651 Å. The aliphatic chains of the glu ligands, which adopt a gauche-anti conformation (four C atom torsion angles ) 58.8, 176.8°), conjoin the {Cu2} dinuclear units into a [Cu2(glu)2]n rectangular gridlike layer motif that lies parallel to the bc crystal plane (Figure 2). The closest through-ligand Cu · · · Cu distances within the layer measure 7.169 and 8.003 Å; the closest through-space Cu · · · Cu distances across the grid apertures are 8.713 and 13.568 Å, which represent the c and b lattice parameters, respectively. Neighboring [Cu2(glu)2]n layers are linked by tethering bpmp ligands, with a Cu · · · Cu through ligand distance of 16.501 Å, to form the 3D covalent coordination polymer structure for 1 (Figure 3). Incipient channels running through the network, which occupy 15.7% of the crystal volume as calculated with PLATON,16 contain “infinite” 1D water molecule chains with C(4) morphology.17 These interact with the coordination polymer matrix by hydrogen-bonding
10.1021/cg800743a CCC: $40.75 2008 American Chemical Society Published on Web 08/20/2008
Communications
Crystal Growth & Design, Vol. 8, No. 10, 2008 3519
Figure 2. View down a of the [Cu2(glu)2]n layer motif in 1. Figure 5. Network perspective of the self-penetrated 6-connected 446108 topology of 1. The green spheres represent the centroids of the {Cu2} dinuclear units. The red and blue lines represent the glu and bpmp ligands, respectively.
Figure 6. View of the self-penetration of the eight-membered circuits in the 446108 network of 1. Figure 3. View down c of the 3D network in 1. Orange spheres represent water molecules of crystallization within the incipient voids.
Figure 4. Transverse view of a C(4) water chain residing within the incipient channels in the self-penetrated structure of 1.
interactions with carboxylate oxygen atoms and the piperazinyl nitrogen atoms of the bpmp ligands. Within the [Cu2(glu)2]n layers, the apical sites of the square pyramidal coordination environments in adjacent {Cu2} paddlewheels are titled by ∼41° with respect to each other and project above and below the layers at an ∼58° angle. Because of this canting, bpmp ligands do not connect {Cu2} paddlewheels directly along the a crystal direction. In addition, this distance (13.054 Å, the a lattice parameter) is too short to be spanned by a fully extended bpmp ligand. Each {Cu2} unit therefore connects to two others in different [Cu2(glu)2]n layers, translated by +b or -b, respectively. As a result, the overall connectivity of 1 differs dramatically from a standard primitive cubic network (pcu, 41263 topology), as seen in many 6-connected mixed-ligand coordination polymers.18 The topology of 1 also varies from that of the previously reported copper glutarate/organodiimine coordination polymers {[Cu2(glu)2(4,4′-bipyridine)] · 3H2O}n and {[Cu2(glu)2(1,2-(di-4-pyridylethane)] · 5H2O}n,19 both of which adopt a rare 48668 (rob) 6-connected network. Instead, the connectivity of 1 represents an extremely rare 6-connected covalent network with 446108 topology (Figure 5) as analyzed by TOPOS software.20 This particular topology has been observed only once in the coordination polymer family [M(dicyanamide)(1,2-bis(4-pyridyl)ethane-N,N′-dioxide)] (M
) Mn, Fe, Co, Ni, Cu) prepared by Gao and Batten,21 and once in a supramolecular net formed by the salt {[Co(H2O)4(Hdpa)2][pyromellitate]}.22 A closer examination of a portion of the network (Figure 6) reveals that the eight-membered circuits formed by the connection of {Cu2} units within three different layers weave through each other without sharing a single connecting node. Yet the circuits also connect through tethering glu ligands. Thus, 1 can be reckoned as another entry in the small genre of self-penetrated coordination polymers. Thermogravimetric analysis (see the Supporting Information, Figure S1) of a sample of crystalline 1 indicated the expulsion of the unligated water molecule chains between 25 and 50 °C, with a mass loss of 9.6% (calcd 9.9%). Ejection of the organic components began at ∼180 °C, with a final mass remnant of 21.3% at 900 °C, consistent with deposition of CuO (21.9% predicted). A variable-temperature magnetic susceptibility study was carried out in order to ascertain the level of magnetic communication within and between the {Cu2} paddlewheel units. The value of the χmT product at 300 K is 0.29 cm3 mol-1 K, consistent with an uncoupled S ) 1 d9 Cu2+ ion. This value decreased rapidly upon cooling, reaching 0.10 cm3 mol-1 K at 150 K and 0.005 cm3 mol-1 K at 8 K, indicative of antiferromagnetic coupling across the {Cu2} paddlewheel dinuclear units. The variable-temperature magnetic susceptibility data were fit to the well-known Bleaney-Bowers expression for a dimer of spin S ) 1/2 ions,23 with best fit parameters of g ) 2.27(4) and J ) -283(8) cm-1 with R ) 2.2 × 10-4 for the data above 100 K (see the Supporting Information, Figure S2). The strength of the antiferromagnetic interaction is ascribed to the equatorial-equatorial bridging mode enforced by the tetracarboxylate paddlewheel motif, as well as a modicum of δ-type through-space interaction between the magnetic dx2-y2 orbitals.15
3520 Crystal Growth & Design, Vol. 8, No. 10, 2008 In conclusion, the length mismatch between the glu and bpmp ligands has provided access to an extremely rare 6-connected selfpenetrated 446108 topology during the self-assembly of the coordination polymer {Cu2(glu)2(bpmp)] · 4H2O}n. The {Cu2} paddlewheel building blocks within the structure of 1 exhibit very strong antiferromagnetic coupling. It is clear that employing flexible aliphatic dicarboxylate ligands and long, hydrogen-bonding capable tethering organodiimines can promote the generation of selfpenetrated coordination polymer structures. Further efforts in this direction are ongoing in our laboratory.
Acknowledgment. We thank Michigan State University for funding this work. We also thank Dr. Rui Huang for the elemental analysis and Dr. Reza Loloee for use of the SQUID magnetometer. Supporting Information Available: Crystallographic data in CIF format; magnetic susceptibility plot, thermogravimetric analysis plot for 1 (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.
References (1) (a) Batten, S. R. CrystEngComm 2001, 3, 67–73. (b) Carlucci, L.; Ciani, G.; Proserpio, D. M. Coord. Chem. ReV. 2003, 246, 247–289. (2) Blatov, V. A.; Carlucci, L.; Ciani, G.; Proserpio, D. M. CrystEngComm 2004, 6, 377–395. (3) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460– 1494. (4) Abraham, B. F.; Batten, S. R.; Grannas, M. J.; Hamit, H.; Hoskins, B. F.; Robson, R. Angew. Chem., Int. Ed. 1999, 38, 1475–1477. (5) Wang, X.-L.; Qin, C.; Wang, E.-B.; Su, Z.-M. Chem. sEur. J. 2006, 12, 2680–2691. (6) Bi, M.; Li, G.; Zou, Y.; Shi, Z.; Feng, S. Inorg. Chem. 2007, 46, 604–606. (7) Niel, V.; Thompson, A. L.; Goeta, A. E.; Enachescu, C.; Hauser, A.; Galet, A.; Munoz, M. C.; Real, J. A. Chem.sEur. J. 2005, 11, 2047– 2060. (8) Lloyd, G. O.; Atwood, J. L.; Barbour, L. J. Chem. Commun. 2005, 1845–1847. (9) Montney, M. R.; Mallika Krishnan, S.; Patel, N. M.; Supkowski, R. M.; LaDuca, R. L. Cryst. Growth Des. 2007, 7, 1145–1153. (10) Wang, X. L.; Qin, C.; Wang, E.-B.; Li, Y.-G.; Su, Z.-M.; Xu, L.; Carlucci, L. Angew. Chem., Int. Ed. 2005, 44, 5824–5827.
Communications (11) Pocic, D.; Planeix, J.-M.; Kyritsakas, N.; Jouaiti, A.; Abdelaziz, H.; Wais, M. CrystEngComm 2005, 7, 624–628. (12) Cu(NO3)2 · 6H2O (0.058 g, 0.19 mmol) and glutaric acid (0.024 g, 0.19 mmol) were added to 4 mL of distilled H2O in a borosilicate glass tube that had been sealed at one end. A solution of bpmp (0.050 g, 0.19 mmol) in 4 mL of methanol was then carefully layered on top of the aqueous solution. Green blocks of 1 (0.038 g, 0.10 mmol, 53% yield based on Cu) deposited after ∼1 week. Anal. Calcd for C26H40Cu2N2O6 (1): C, 42.91; H, 5.54; N, 7.70%. Found: C, 42.80; H, 5.75; N, 7.57. IR (cm-1): 3375(w, br), 2945(w), 2849(w), 1605(s), 1454(m), 1416(s), 1346(w), 1311(m), 1283(w), 1271(w), 1227(w), 1142(w), 1119(w), 1061(w), 1010(w), 998(m), 940(w), 880(w), 857(m), 839(m), 807(m), 793(m), 743(w). (13) Crystal data for 1: monoclinic, space group P21/c, a ) 13.054(3) Å, b ) 13.568(3) Å, c ) 8.7130(18) Å, β ) 90.184(3)°, V ) 1543.3(6) Å3, Z ) 4, Fcalc’d ) 1.566 g/cm3, µ(Mo KR) ) 1.445 mm-1, F(000) ) 756, R ) 0.0678, wR ) 0.0679, GOF ) 1.020, T ) 173(2) K, CCDC No. 687612. (14) Addison, A. W.; Rao, T. N. J. J. Chem. Soc., Dalton Trans. 1984, 1349–1356. (15) Youngme, S.; Cheansirisomboon, A.; Danvirutai, C.; Pakawatchai, C.; Chaichit, N.; Engkagul, C.; van Albada, G. A.; Costa, J. S.; Reedijk, J. Polyhedron 2008, 27, 1875–1882. (16) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool; Utrecht University: Utrecht, The Netherlands, 1998. (17) (a) Infantes, L.; Motherwell, S. CrystEngComm 2002, 4, 454–461. (b) Infantes, L.; Chisholm, J.; Motherwell, S. CrystEngComm 2003, 5, 480–486. (18) (a) Long, L.-S.; Wu, Y.-R.; Huang, R.-B.; Zheng, L.-S. Inorg. Chem. 2004, 43, 3798–3800. (b) Hu, R.-F.; Kang, Y.; Zhang, J.; Li, Z.-J.; Qin, Y.-Y.; Yao, Y.-G. Z. Anorg. Allgem. Chem. 2005, 631, 3053– 3057. (c) Zheng, Y.-Q.; Lin, J.-L.; Kong, Z.-P. Inorg. Chem. 2004, 43, 2590–2596. (19) Rather, B.; Zaworotko, M. J. Chem. Commun. 2003, 830–831. (20) Blatov, V. A.; Shevchenko, A. P.; Serezhkin, V. N. J. Appl. Crystallogr. 2000, 33, 1193. (21) Sun, H.-L.; Gao, S.; Ma, B.-Q.; Batten, S. R. CrystEngComm 2004, 6, 579–583. (22) Braverman, M. A.; LaDuca, R. L. CrystEngComm 2008, 10, 117– 124. (23) Bleaney, B.; Bowers, K. D. Proc. R. Soc. London, Ser. A 1952, 214, 451.
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