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1-D, 2-D and 3-D coordination polymers assembled from polynuclear CoII units based on the isophthalate(-2) ligand
Polyhedron 29 (2010) 3335–3341
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1-D, 2-D and 3-D coordination polymers assembled from polynuclear CoII units based on the isophthalate(-2) ligand Eun Young Kim a, Young Joo Song a, Hyo Geun Koo a, Ju Hoon Lee a, Hyun Min Park a, Cheal Kim a,⇑, Tae-Hwan Kwon b, Seong Huh b, Sung-Jin Kim c,⇑, Youngmee Kim c a b c
Department of Fine Chemistry, and Eco-Product and Materials Education Center, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea Department of Chemistry and Protein Research Center for Bio-Industry, Hankuk University of Foreign Studies, Yongin 449-791, Republic of Korea Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
a r t i c l e
i n f o
Article history: Received 11 August 2010 Accepted 9 September 2010 Available online 22 September 2010 Keywords: Isophthalic acid Polynuclear CoII units Coordination polymers CoII complexes Gas sorption
a b s t r a c t Three polymeric complexes containing polynuclear CoII units, [Co2(Cbtp)2(ip)2] (1), [N(CH3)4]2[Co3(ip)4] (2), and [{Co7(ip)5(l-OH)4}(l-bpp)2]2(H2O) (3), have been prepared by solvothermal synthesis. Isophthalic acid (H2ip) has been used for the construction of polynuclear CoII units, and three auxiliary ligands, namely Cbtp, quinazoline, and bpp, have also been employed to change nuclearity of CoII unit and the dimensionality of polymeric CoII compounds: 1-D structure containing dinuclear CoII units with Cbtp, 2-D structure containing trinuclear CoII units without quinazoline, and 3-D structure containing heptanuclear CoII units with bpp. The gas sorption study of 3 revealed a relative high uptake of CO2 over N2 because of small dimension of channels. The thermal stabilities and magnetic properties of these complexes were also examined. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The synthesis and use of multinucleating ligands has become a common strategy for the preparation of polynuclear coordination complexes with new and sophisticated structures and functions [1–3]. The investigation of the properties ensuing from such architectures has found relevance in areas as diverse as bioinorganic chemistry [4], molecular magnetism [5,6], molecular electronics [7] or materials chemistry [8]. Carboxylate-including ligands [9–15] such as phthalate, biphenyldicarboxylate, benzenetricarboxylate, and adamatanedicarboxylate can be used as multinucleating ligands to make multi-dimensional coordination polymers containing polynuclear units. These kinds of ligands have the potential capacity to bridge metal centers to form polymeric structures, and the wide range of stable complexes are due to (a) the various coordination modes for the carboxylate ion, bridging modes (g1:g1:l2), (g2:l2) or (g1:g2:l3), and chelating mode (g1:g1), (b) the stable coordination geometries of CoII ions, such as tetrahedral, trigonal bipyramidal, or octahedral, and (c) the presence of a number of coordinated water or hydroxide ligands [16,17]. Paramagnetic CoII is a good candidate for the construction of multinuclear coordination polymers with carboxylate or dicarboxylate ligands. The study of metal carboxylate complexes has been ⇑ Corresponding authors. Tel.: +82 2 970 6693; fax: +82 2 973 9149 (C. Kim); tel.: +82 2 3277 3589; fax: +82 2 3277 2384 (S.-J. Kim). E-mail addresses: [email protected] (C. Kim), [email protected] (S.-J. Kim). 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.09.013
an interesting topic due to their structures and magnetism, and these properties are based on the carboxylates which can bridge the metal centers to create diverse magnetic interactions. Several examples of polynuclear CoII clusters have been reported, and their magnetic properties were systematically investigated [17–40]. In this paper, isophthalic acid (H2ip) has been chosen for the construction of polynuclear CoII–carboxylate complexes, and auxiliary ligands, such as Cbtp (Cbtp = 2,6-bis((1H-1,2,4-triazol-1yl)methyl)pyridine), quinazoline, and bpp (1,3-bis(4-pyridyl)propane), have been employed to this system to form 1-D, 2-D, and 3-D coordination polymers containing polynuclear CoII units. Three polymeric complexes containing polynuclear CoII cluster units, [Co2(Cbtp)2(ip)2] (1), [N(CH3)4]2[Co3(ip)4] (2), and [{Co7(ip)5(l-OH)4}(l-bpp)2]2(H2O) (3) have been prepared, and their properties including the magnetic susceptibility and the gas sorption ability have been studied. In addition, the thermal stabilities of these complexes were also investigated.
2. Experimental 2.1. Materials 2,6-Bis(bromomethyl)pyridine, sodium-1,2,4-triazolide, quinazoline, 4,40 -trimethylene-dipyridine, isophthalic acid, ammonium hydroxide, methanol, ethanol, DMF, methylene chloride, Co(NO3)26H2O, Co(OAc)24H2O, were purchased from Aldrich and
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were used as received. 4-Fluorophenyl acetate and 4-nitrophenyl benzoate were obtained from Lancaster. 2.2. Instrumentation Elemental analysis for carbon, nitrogen, and hydrogen was carried out by using an EA1108 (Carlo Erba Instrument, Italy) in the Organic Chemistry Research Center of Sogang University, Korea. IR spectra were measured on a BIO RAD FTS 135 spectrometer as KBr pellets. PXRD data were obtained using a Rigaku X-ray diffractometer with Cu Ka radiation (k = 1.5418 Å). Magnetic susceptibility measurements on powder samples were carried out in the temperature range from 5 to 300 K in an applied magnetic field of 5000 G using a Quantum Design MPMS-5 SQUID magnetometer. 2.3. Gas sorption analysis Ultrapure grade (99.999%) N2 and CO2 gases were used for the gas sorption experiments. The N2 sorption analysis was performed on a Belsorp-miniII at 77 K (BEL, Japan). The low-pressure CO2 sorption analyses were performed on a Belsorp-miniII at 196 K. 2-Propanol/dry ice bath was used to maintain 196 K. A moisture trap was equipped at the outlet of the CO2 gas cylinder to avoid moisture contamination during the measurement. The as-prepared samples soaked in CHCl3 in a screw-capped vial were shaken for 2 days. The CHCl3-exchanged samples were dried at 423 K under high vacuum for 2 h before measurements. 2.4. Synthesis of 2,6-bis((1H-1,2,4-triazol-1-yl)methyl)pyridine (Cbtp) Sodium-1,2,4-triazolide (1.21 g, 12 mmol) was added to a solution of 2,6-bis(bromomethyl)pyridine (1.35 g, 5 mmol) in absolute ethanol (100 mL) under N2. The resulting mixture was stirred for 3 days at 77 °C. Subsequently, the solvent was concentrated under vacuum and the residue was purified by column chromatography (silicagel, methylene chloride/methanol v/v, 8/2). Yield was 51%. Anal. Calc. for C11H11N7 (241.29), L: C, 54.75; H, 4.60; N, 40.64. Found: C, 54.47; H, 4.43; N, 40.96%. 1H NMR (CDCl3, 300 MHz): d 8.239 (s, 2H, 3-positions of triazole), d 7.994 (s, 2H, 5-positions of triazole), d 7.770 (t, 1H, 4-position of pyridine ring), d 7.127 and 7.107 (d, 2H, 3- and 5-positions of pyridine ring), and d 5.453 (s, 4H, two methylene groups). IR (KBr): m(cm1) = 3103(s), 1596(s), 1575(m), 1511(s), 1462(m), 1426(s), 1366(s), 1271(s), 1217(m), 1166(m), 1143(s), 1097(w), 1020(s), 961(m), 890(m), 870(m), 770(s), 716(m), 680(s), 651(m), 594(m). 2.4.1. Synthesis of [Co2(Cbtp)2(ip)2] (1) A mixture of Co(OAc)24H2O (35.9 mg, 0.14 mmol), isophthalic acid (20.1 mg, 0.12 mmol), 2,6-bis((1H-1,2,4-triazol-1-yl)methyl) pyridine (29.0 mg, 0.12 mmol), and H2O (5 mL) was placed a Teflon-lined stainless steel vessel (20 mL) and heated at 140 °C for 3 days, and cooled to 25 °C at a rate of 5 °C/h. Red-violet crystals suitable for X-ray analysis were obtained. Yield was 54%. Purity of bulk sample of 1 was checked by powder XRD (see Fig. S1 in Supporting Information). Anal. Calc. for C19H15CoN7O4 (464.31), 1: C, 49.15; H, 3.26; N, 21.12. Found: C, 49.41; H, 3.11; N, 21.00%. IR (KBr): m(cm1) = 3400(brs), 3131(m), 2969(w), 1612(s), 1577(s), 1545(s), 1523(s), 1480(m), 1451(s), 1396(brs), 1282(s), 1210(m), 1130(s), 1019(s), 992(m), 921(m), 875(w), 766(m), 746(s), 719(s), 681(m), 656(m). 2.4.2. Synthesis of [N(CH3)4]2[Co3(ip)4] (2) A mixture of Co(NO3)26H2O (74.2 mg, 0.25 mmol), isophthalic acid (53.0 mg, 0.32 mmol), quinazoline (32.9 mg, 0.25 mmol), ammonium hydroxide (61.0 lL, 0.50 mmol) and DMF/methanol (4/1, v/v, 5 mL) was placed a Teflon-lined stainless steel vessel
(20 mL) and heated at 170 °C for 2 days, and cooled to 25 °C at a rate of 5 °C/h. Blue-violet crystals suitable for X-ray analysis were obtained. Yield was 43%. Purity of bulk sample of 2 was checked by powder XRD (see Fig. S2 in Supporting Information). Anal. Calc. for C40H40Co3N2O16 (981.53), 2: C, 48.94; H, 4.12; N, 2.85. Found: C, 49.12; H, 3.95; N, 2.77%. IR (KBr): m(cm1) = 3034(w), 1614(s), 1571(s), 1483(s), 1395(s), 1306(s), 1272(w), 1159(m), 1076(w), 943(s), 827(w), 811(w), 750(s), 722(s), 710(s), 657(w), 551(w), 468(w). 2.4.3. [{Co7(ip)5(l-OH)4}(l-bpp)2]2(H2O) (3) A mixture of Co(NO3)26H2O (41.6 mg, 0.14 mmol), isophthalic acid (20.1 mg, 0.12 mmol), 1,3-bis(4-pyridyl)propane (24.3 mg, 0.12 mmol), ammonium hydroxide (29.30 lL, 0.24 mmol) and DMF/ethanol (1/4, v/v, 5 mL) was placed a Teflon-lined stainless steel vessel (20 mL) and heated at 160 °C for 2 days, and cooled to 25 °C at a rate of 5 °C/h. Blue-violet crystals suitable for X-ray analysis were obtained. Purity of bulk sample of 3 was checked by powder XRD (see Fig. S3 in Supporting Information). Yield was 92%. C66H48Co7N4O24(H2O)2(C3H7NO) (1801.87), 3: C, 45.97; H, 3.30; N, 3.88. Found: C, 45.72; H, 3.01; N, 3.37%. IR (KBr): m(cm1) = 3441(brm), 1666(w), 1635(s), 1612(s), 1557(s), 1482(w), 1437(m), 1385(s), 1219(w), 1073(w), 1018(w), 812(m), 740(s), 713(s), 658(w), 518(w), 453(w). 2.5. Crystallography The diffraction data for compounds 1–3 were collected on a Bruker SMART AXS diffractometer equipped with a monochromator in the Mo Ka (k = 0.71073 Å) incident beam. The crystal was mounted on a glass fiber. The CCD data were integrated and scaled using the Bruker-SAINT software package, and the structure was solved and refined using SHEXTL V6.12 [41]. Hydrogen atoms were located in the calculated positions. For 3, the largest peak in the final difference Fourier map of 1.912 e Å3 indicates that there might be disordered solvent molecules in the structure. The crystallographic data for compounds 1–3 are listed in Table 1. 3. Results and discussion Isophthalic acid (H2ip) was selected as a multinucleating ligand for paramagnetic CoII centers, and three different auxiliary ligands, namely Cbtp, quinazoline, and bpp, were employed to form 1-D, 2-D, and 3-D coordination polymers, respectively. A new ligand 2,6-bis((1H-1,2,4-triazol-1-yl)methyl)pyridine (Cbtp) has been synthesized for construction of CoII coordination polymers, and it was characterized by NMR, IR, and elemental analysis. In 1, Cbtp ligands bridge two CoII ions, and these Cbtp-bridged Co2 units are connected by ip to form a 1-D chain. In 2, the use of quinazoline ligands in the synthesis led to a 2-D layer compound containing trinuclear Co3 units, but without auxiliary quinazoline ligands. With bpp auxiliary ligands, compound 3, a porous 3-D framework containing heptanuclear Co7 units was synthesized. All three compounds are shown in Scheme 1. 3.1. Structure description of [Co2(Cbtp)2(ip)2] (1) The asymmetric unit contains a CoII ion, an ip, and a Cbtp ligand; there is an inversion center at the mid point of the Co Co contact between adjacent CoII ions that are bridged by two Cbtp ligands. The symmetry operations (x + 1, y + 1, z + 2), (x, y 1, z), and (x, y + 1, z) generate 1-D chains (Fig. 1). The coordination geometry around CoII ion is distorted octahedral constructed by four carboxylate oxygen atoms and two Cbtp nitrogen atoms. Two carboxylates in ip show two different coordination modes:
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E.Y. Kim et al. / Polyhedron 29 (2010) 3335–3341 Table 1 Crystal data and structure refinement for 1–3.
Empirical formula Formula weight T (K) k (Å) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (Mg/m3) Absorption coefficient (mm1) Crystal size (mm3) Reflections collected Independent reflections (Rint) Data/restraints/parameters Goodness-of-fit (GOF) on F2 Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)
1
2
3
C19H15CoN7O4 464.31 293(2) 0.71073 P1
C40H40Co3N2O16 981.53 293(2) 0.71073 P21/n 18.4972(14) 10.1886(8) 23.0512(16) 90.00 112.3890(10) 90.00 4016.8(5) 4 1.623 1.302 0.15 0.10 0.10 20 610 7834 [Rint = 0.0562] 7834/0/558 0.983 R1 = 0.0621, wR2 = 0.1714 R1 = 0.0880, wR2 = 0.1939 0.888 and 1.310
C66H52Co7N4O26 1729.63 170(2) 0.71073 C2/c 24.038(5) 23.217(5) 15.263(3) 90.00 115.73(3) 90.00 7673(3) 4 1.494 1.552 0.20 0.10 0.08 17 110 6472 [Rint = 0.1489] 6472/2/480 0.917 R1 = 0.0755, wR2 = 0.1790 R1 = 0.1372, wR2 = 0.1976 1.912 and 0.902
9.0408(12) 10.0189(12) 11.6879(14) 82.641(2) 76.649(2) 76.098(2) 996.9(2) 2 1.547 0.904 0.15 0.05 0.05 5627 3829 [Rint = 0.0562] 3829/0/280 0.804 R1 = 0.0387, wR2 = 0.0759 R1 = 0.0599, wR2 = 0.0786 0.371 and 0.679
Scheme 1. 1-D, 2-D and 3-D coordination polymers assembled from dinuclear and polynuclear CoII units based on the isophthalate(-2) ligand.
Fig. 1. 1-D chain of 1. All hydrogen atoms were omitted for clarity.
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chelating (g1:g1) and bridging (g1:g1:l2) (Scheme 2). One side carboxylate of ip bridges Cbtp-bridged Co2 units, and the other side carboxylate chelates the CoII ion in the neighboring Co2 units. The Co Co separation is 4.317 Å. 3.2. Structure description of [N(CH3)4]2[Co3(ip)4] (2) There are three independent CoII ions (Co1, Co2, and Co3) with four ip ligands and two tetramethylammonium cations. The symmetry operations (x + 1/2, y 1/2, z + 1/2), (x + 1/2, y + 1/2, z + 1/2), (x 1/2, y + 1/2, z + 1/2), (x 1/2, y 1/2, z + 1/ 2), (x, y 1, z), and (x, y + 1, z) generate a 2-D sheet as shown in Fig. 2(a). The three CoII ions are joined together by six carboxylate groups from six ip ligands. The geometry around Co1 is distorted octahedral. Co2 is five-coordinated, and from the angular structural parameter as a general descriptor of five-coordinate centric molecules [42], the irregular coordination geometry of Co2 is described as being 42.6% along Berry pseudorotation from trigonal bipyramidal toward square pyramidal. The geometry around Co3 can be described as distorted octahedral considering long Co–O bonds (2.346 and 2.696 Å) as the weak coordination from PLATON analysis. There are trimethylammonium cations between 2-D layers (Fig. 2(b)). There are two different ip ligands showing different coordination modes in both carboxylate groups: one contains two carboxylates with the bridging (g1:g1:l2) and the chelating (g1:g1) modes, and the other does them with the bridging (g1:g1:l2) and (g2:g1:l2) modes (Scheme 2). The intra-cluster separations of Co1 Co2, Co1 Co3 and Co2 Co3 are 3.25(1), 3.282(1) and 6.529(1) Å, respectively. 3.3. Structure description of [{Co7(ip)5(l-OH)4}(l-bpp)2]2(H2O) (3) The asymmetric unit contains four crystallographically independent CoII ions (Co1, Co2, Co3, and Co4) with two and half of ip ligands and two independent hydroxyl groups and one water solvent molecule. The symmetry operations (x, y + 2, z + 1/2), (x, y + 2, z 1/2), (x + 1, y, z + 1/2), (x + 1/2, y + 3/2, z), (x, y, z 1/2), (x + 1/2, y + 1/2, z), (x 1/2, y 1/2, z) produce a 3-D framework with 1-D pores (Fig. 3(a)). The water solvate molecules occupy the 1-D pores. The seven cobalt ions are joined together by 10 bridged carboxylate groups and four hydroxyl groups. In a Co7 unit, there is an inversion center on Co1 ion surrounded by six other CoII ions, and the Co7 unit is almost in a plane. The neutral wheel-shaped Co7 unit has the formula [{Co7(ip)10/2
(l-OH)4}(l-bpp)4/2] (Fig. 3(b)). The coordination geometry around Co1 is distorted octahedral constructed by all six oxygen atoms from two carboxylate groups and four bridging hydroxyl (l3-OH) groups. The coordination geometry around Co2 and Co3 on the rim is also distorted octahedral, but it has different environment from Co1, in which NO5 belongs to four carboxylate oxygen atoms, a bridging hydroxyl group, and a bpp nitrogen atom. The remaining Co4 ion has distorted tetrahedral geometry constructed by all four oxygen atoms from three carboxylate groups and bridging hydroxyl group. There are three different ip ligands showing different coordination modes in both carboxylate groups: two ip ligands contain both carboxylates with the bridging (g1:g1:l2) modes, and the remaining one does both with the bridging (g1:g2:l3) modes (Scheme 2). The intra-cluster separations of Co1 Co2, Co1 Co3, Co1 Co4, Co2 Co3, Co2 Co4, and Co3 Co4 are 3.67(4), 3.25(2), 3.353(4), 3.441(1), 3.39(2), and 3.47(4) Å, respectively. For 3, the framework without the water and DMF solvates possesses 21.5% of solvent accessible void in the unit cell based on a PLATON calculation. The as-made 3 framework with the water solvents also possesses 19.2% voids. The PLATON/Squeeze routine indicates the total potential solvent accessible void volume is 1651.4 Å3. Benzenedicarboxylic acids have been used for designing coordination polymers and open framework structures [43–51]. Among them, isophthalic acid (H2ip) has been used as a multinucleating ligand with paramagnetic CoII ions to produce multinuclear CoII complexes. There were two examples of ip ligand bridged polynuclear CoII complexes: 3-D network containing trinuclear CoII units connected by melamine (ma), {[Co3(ma)(ip)3]2H2O}n [20] and porous 3-D magnet containing heptanuclear CoII units, [KCo7(OH)3(ip)6(H2O)4]12H2O [30]. Although 2 and 3 are similar to those reported complexes Co3 and Co7 units, the structural study using varying auxiliary ligands has not been reported, to our best knowledge. Basically, ip ligands bridge CoII ions to produce dinuclear Co2, trinuclear Co3, and heptanuclear Co7 units, and then appropriate auxiliary ligands can be employed to connect those units to 1-D, 2-D, and 3-D networks (Scheme 1). With Cbtp, one end of the carboxylate of ip bridges Cbtp-bridged Co2 units, and the other end carboxylate chelates the Co ion in the neighboring Co2 units to produce 1-D chains, 1. Quinazoline ligands were not included in this system, and instead a 2-D sheet 2 containing ip-bridged Co3 units was contained. With bpp, a 3-D network 3 containing ip-bridged Co7 units was obtained. These results clearly indicate that judicious
Scheme 2. Coordination modes of ip ligands in coordination polymers assembled from polynuclear CoII units.
E.Y. Kim et al. / Polyhedron 29 (2010) 3335–3341
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Fig. 2. (a) 2-D Sheet of 2 including a trinuclear Co3 unit. All hydrogen atoms were omitted for clarity. (b) Packing diagram containing 2-D sheets and tetraammonium cations between them.
choice of auxiliary ligands can control not only the nuclearity of the CoII units from dinuclear, trinuclear to heptanuclear structure but also the dimensionality of CoII complexes containing ipbridged polynuclear CoII units from 1-D, 2-D to 3-D networks. 3.4. Magnetic property Variable-temperature magnetic susceptibility data of 1 and 2 were collected in the temperature range 4–300 K under a field of
0.5 T, and the resulting plots of vM, vM1 versus T are depicted (see the Supporting information: Figs. S4 and S5). The effective magnetic moment at room temperature, leff of 1, was 4.77 lB which is larger than the spin-only effective moment of 3.87 lB which is due to the orbital contribution. The vM1 values obey the Curie–Weiss law well with a Curie constant of 2.87 emuT/ mol and a h value of 1.22 K for 1, and there was no evidence of magnetic exchange coupling between the CoII in the chain. The leff value (8.49 lB) per a Co3 unit of 2 at room temperature is larger
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Fig. 3. (a) 3-D Framework of 3 along c axis. All hydrogen atoms were omitted for clarity. (b) Drawing for a heptanuclear Co7 unit.
than that (6.71 lB) for three non-interacting cobalt ions of S = 3/2 which is also due to the orbital contribution. The vM1 values of 2 obey the Curie–Weiss law well with a Curie constant of 2.62 emuT/mol and a h value of 0.29 K, which also suggests that there is no significant interaction between the Co3 units within the 2-D layer 2. The variable-temperature magnetic susceptibilities and magnetic moments of 3 per a Co7 unit are shown (see the Supporting information: Fig. S6). The leff value (11.99 lB) per a Co7 unit of 3 at room temperature is larger than that (10.25 lB) for spin-only cobalt ions of S = 3/2 indicating significant orbital contributions of the distorted octahedral CoII ions. Between 10 and 300 K, 3 obeys the Curie–Weiss law with a Curie constant of 19.85 emuT/ mol and a h value of 34.22 K.
3.5. Thermogravimetric analysis To study the thermal stabilities of these complexes, thermal gravimetric analysis (TGA) of compounds 1–3 was performed (see the Supporting information: Figs. S7-S9). The compound 1 showed no discernible weight loss up to 365 °C. The compound 2 gradually lost its weight because of the potential decomposition of the N(CH3)4+ cations. The TGA curve for 3 displayed a weight loss of 5.82% (theoretical weight loss: 5.12%) at 176.3 °C and which is attributed to the loss of two solvate water and DMF molecules.
3.6. Gas sorption We have tested the gas sorption ability of the sample 3 by using N2 and CO2 (Fig. 4). The as-prepared 3 was solvent exchanged with CHCl3 by shaking for 2 days. The sample dried at 150 °C for 2 h exhibited CO2 uptake value of 76.7 cm3/g at STP (3.42 mmol/g) at 196 K. In contrast, relatively small amount of N2 sorption was observed at 77 K: 30.9 cm3/g at STP. The Brunauer–Emmett–Teller (BET) surface area is merely 47.2 m2/g. Nevertheless, the relative high uptake of CO2 over N2 can be attributed to the different kinetic diameters of the gases: CO2 3.30 Å and N2 3.64 Å [52]. Therefore, 3 showed selective sorption ability of CO2 over N2 possibly because of small dimension of channels.
4. Conclusions
Fig. 4. Gas sorption isotherms for CO2 (diamonds) and N2 (circles) by the activated 1. Adsorption branches (closed symbols) and desorption branches (open symbols) are indicated.
Three coordination polymers containing polynuclear CoII units, [Co2(Cbtp)2(ip)2] (1), [N(CH3)4]2[Co3(ip)4] (2), and [{Co7(ip)5(lOH)4}(l-bpp)2]2(H2O) (3), have been reported. Isophthalic acid (H2ip) has been used for the construction of polynuclear CoII units, and three auxiliary ligands, namely Cbtp, quinazoline, and bpp, have also been employed to change nuclearity of CoII unit and the dimensionality of polymeric CoII compounds: 1-D structure containing dinuclear CoII units with Cbtp, 2-D structure containing trinuclear CoII units without quinazoline, and 3-D structure containing heptanuclear CoII units with bpp. The gas sorption study of 3 revealed a relative high uptake of CO2 over N2 because of small dimension of channels.
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Acknowledgements Financial support from Korea Ministry Environment ‘‘ET-Human resource development Project”, the Korean Science & Engineering Foundation (R01-2008-000-20704-0 and 2009-0074066), the Converging Research Center Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0082832), and the SRC program of the Korea Science and Engineering Foundation (KOSEF) through the Center for Intelligent Nano-Bio Materials at Ewha Womans University (Grant R11-2005-008-00000-0) is gratefully acknowledged. Appendix A. Supplementary data CCDC 777826, 7777825, and 777827 contains the supplementary crystallographic data for 1–3. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.poly.2010.09.013. References [1] J.-P. Sauvage, M.W. Hosseini, in: J.-M. Lehn (Ed.), Comprehensive Supramolecular Chemistry, vol. 9, Pergamon Press, Oxford, 1995. [2] M. Fujita, K. Umemoto, M. Yoshizawa, N. Fujita, T. Kusukawa, K. Biradha, Chem. Commun. (2001) 509. [3] G. Aromí, H. Stoeckli-Evans, S.J. Teat, J. Cano, J. Ribas, J. Mater. Chem. 16 (2006) 2635. [4] J.E. Bol, W.L. Driessen, R.Y.N. Ho, B. Maase, L. Que, J. Reedijk, Angew. Chem., Int. Ed. 36 (1997) 998. [5] M. Ruben, U. Ziener, J.M. Lehn, V. Ksenofontov, P. Gütlich, G.B.M. Vaughan, Chem. Eur. J. 11 (2004) 94. [6] L.K. Thompson, T.L. Kelly, L.N. Dawe, H. Grove, M.T. Lemaire, J.A.K. Howard, E.C. Spencer, C.J. Matthews, S.T. Onions, S.J. Coles, P.N. Horton, M.B. Hursthouse, M.E. Light, Inorg. Chem. 43 (2004) 7605. [7] B.J. Coe, N.R.M. Curati, Comments Inorg. Chem. 25 (2004) 147. [8] O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature 423 (2003) 705. [9] S. Noro, S. Kitagawa, M. Kondo, K. Seki, Angew. Chem., Int. Ed. 39 (2000) 2081. [10] Z.L. Huang, M. Drillon, N. Masciocchi, A. Sironi, J.T. Zao, P. Rabu, P. Panissod, Chem. Mater. 12 (2000) 2805. [11] L. Pan, N. Ching, X. Huang, J. Li, Inorg. Chem. 39 (2000) 5333. [12] L. Pan, B.S. Finkel, X. Huang, J. Li, Chem. Commun. (2001) 105. [13] P.S. Mukherjee, N. Das, Y.K. Kryshenko, A.M. Arif, P.J. Stang, J. Am. Chem. Soc. 126 (2004) 2464. [14] N.L. Rosi, J. Kim, M. Eddaoudi, B. Chen, M. O’Keeffe, O.M. Yaghi, J. Am. Chem. Soc. 127 (2005) 1504. [15] Z. Wang, G. Chen, K. Ding, Chem. Rev. 109 (2009) 322. [16] B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629. [17] T. Duangthongyou, S. Jirakulpattana, C. Phakawatchai, M. Kurmoo, S. Siripaisarnpipat, Polyhedron 29 (2010) 1156. [18] K.S. Gavrilenko, Y.L. Gal, O. Cador, S. Golhen, L. Ouahab, Chem. Commun. (2007) 280.
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Polyhedron journal homepage: www.elsevier.com/locate/poly
1-D, 2-D and 3-D coordination polymers assembled from polynuclear CoII units based on the isophthalate(-2) ligand Eun Young Kim a, Young Joo Song a, Hyo Geun Koo a, Ju Hoon Lee a, Hyun Min Park a, Cheal Kim a,⇑, Tae-Hwan Kwon b, Seong Huh b, Sung-Jin Kim c,⇑, Youngmee Kim c a b c
Department of Fine Chemistry, and Eco-Product and Materials Education Center, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea Department of Chemistry and Protein Research Center for Bio-Industry, Hankuk University of Foreign Studies, Yongin 449-791, Republic of Korea Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Republic of Korea
a r t i c l e
i n f o
Article history: Received 11 August 2010 Accepted 9 September 2010 Available online 22 September 2010 Keywords: Isophthalic acid Polynuclear CoII units Coordination polymers CoII complexes Gas sorption
a b s t r a c t Three polymeric complexes containing polynuclear CoII units, [Co2(Cbtp)2(ip)2] (1), [N(CH3)4]2[Co3(ip)4] (2), and [{Co7(ip)5(l-OH)4}(l-bpp)2]2(H2O) (3), have been prepared by solvothermal synthesis. Isophthalic acid (H2ip) has been used for the construction of polynuclear CoII units, and three auxiliary ligands, namely Cbtp, quinazoline, and bpp, have also been employed to change nuclearity of CoII unit and the dimensionality of polymeric CoII compounds: 1-D structure containing dinuclear CoII units with Cbtp, 2-D structure containing trinuclear CoII units without quinazoline, and 3-D structure containing heptanuclear CoII units with bpp. The gas sorption study of 3 revealed a relative high uptake of CO2 over N2 because of small dimension of channels. The thermal stabilities and magnetic properties of these complexes were also examined. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction The synthesis and use of multinucleating ligands has become a common strategy for the preparation of polynuclear coordination complexes with new and sophisticated structures and functions [1–3]. The investigation of the properties ensuing from such architectures has found relevance in areas as diverse as bioinorganic chemistry [4], molecular magnetism [5,6], molecular electronics [7] or materials chemistry [8]. Carboxylate-including ligands [9–15] such as phthalate, biphenyldicarboxylate, benzenetricarboxylate, and adamatanedicarboxylate can be used as multinucleating ligands to make multi-dimensional coordination polymers containing polynuclear units. These kinds of ligands have the potential capacity to bridge metal centers to form polymeric structures, and the wide range of stable complexes are due to (a) the various coordination modes for the carboxylate ion, bridging modes (g1:g1:l2), (g2:l2) or (g1:g2:l3), and chelating mode (g1:g1), (b) the stable coordination geometries of CoII ions, such as tetrahedral, trigonal bipyramidal, or octahedral, and (c) the presence of a number of coordinated water or hydroxide ligands [16,17]. Paramagnetic CoII is a good candidate for the construction of multinuclear coordination polymers with carboxylate or dicarboxylate ligands. The study of metal carboxylate complexes has been ⇑ Corresponding authors. Tel.: +82 2 970 6693; fax: +82 2 973 9149 (C. Kim); tel.: +82 2 3277 3589; fax: +82 2 3277 2384 (S.-J. Kim). E-mail addresses: [email protected] (C. Kim), [email protected] (S.-J. Kim). 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.09.013
an interesting topic due to their structures and magnetism, and these properties are based on the carboxylates which can bridge the metal centers to create diverse magnetic interactions. Several examples of polynuclear CoII clusters have been reported, and their magnetic properties were systematically investigated [17–40]. In this paper, isophthalic acid (H2ip) has been chosen for the construction of polynuclear CoII–carboxylate complexes, and auxiliary ligands, such as Cbtp (Cbtp = 2,6-bis((1H-1,2,4-triazol-1yl)methyl)pyridine), quinazoline, and bpp (1,3-bis(4-pyridyl)propane), have been employed to this system to form 1-D, 2-D, and 3-D coordination polymers containing polynuclear CoII units. Three polymeric complexes containing polynuclear CoII cluster units, [Co2(Cbtp)2(ip)2] (1), [N(CH3)4]2[Co3(ip)4] (2), and [{Co7(ip)5(l-OH)4}(l-bpp)2]2(H2O) (3) have been prepared, and their properties including the magnetic susceptibility and the gas sorption ability have been studied. In addition, the thermal stabilities of these complexes were also investigated.
2. Experimental 2.1. Materials 2,6-Bis(bromomethyl)pyridine, sodium-1,2,4-triazolide, quinazoline, 4,40 -trimethylene-dipyridine, isophthalic acid, ammonium hydroxide, methanol, ethanol, DMF, methylene chloride, Co(NO3)26H2O, Co(OAc)24H2O, were purchased from Aldrich and
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were used as received. 4-Fluorophenyl acetate and 4-nitrophenyl benzoate were obtained from Lancaster. 2.2. Instrumentation Elemental analysis for carbon, nitrogen, and hydrogen was carried out by using an EA1108 (Carlo Erba Instrument, Italy) in the Organic Chemistry Research Center of Sogang University, Korea. IR spectra were measured on a BIO RAD FTS 135 spectrometer as KBr pellets. PXRD data were obtained using a Rigaku X-ray diffractometer with Cu Ka radiation (k = 1.5418 Å). Magnetic susceptibility measurements on powder samples were carried out in the temperature range from 5 to 300 K in an applied magnetic field of 5000 G using a Quantum Design MPMS-5 SQUID magnetometer. 2.3. Gas sorption analysis Ultrapure grade (99.999%) N2 and CO2 gases were used for the gas sorption experiments. The N2 sorption analysis was performed on a Belsorp-miniII at 77 K (BEL, Japan). The low-pressure CO2 sorption analyses were performed on a Belsorp-miniII at 196 K. 2-Propanol/dry ice bath was used to maintain 196 K. A moisture trap was equipped at the outlet of the CO2 gas cylinder to avoid moisture contamination during the measurement. The as-prepared samples soaked in CHCl3 in a screw-capped vial were shaken for 2 days. The CHCl3-exchanged samples were dried at 423 K under high vacuum for 2 h before measurements. 2.4. Synthesis of 2,6-bis((1H-1,2,4-triazol-1-yl)methyl)pyridine (Cbtp) Sodium-1,2,4-triazolide (1.21 g, 12 mmol) was added to a solution of 2,6-bis(bromomethyl)pyridine (1.35 g, 5 mmol) in absolute ethanol (100 mL) under N2. The resulting mixture was stirred for 3 days at 77 °C. Subsequently, the solvent was concentrated under vacuum and the residue was purified by column chromatography (silicagel, methylene chloride/methanol v/v, 8/2). Yield was 51%. Anal. Calc. for C11H11N7 (241.29), L: C, 54.75; H, 4.60; N, 40.64. Found: C, 54.47; H, 4.43; N, 40.96%. 1H NMR (CDCl3, 300 MHz): d 8.239 (s, 2H, 3-positions of triazole), d 7.994 (s, 2H, 5-positions of triazole), d 7.770 (t, 1H, 4-position of pyridine ring), d 7.127 and 7.107 (d, 2H, 3- and 5-positions of pyridine ring), and d 5.453 (s, 4H, two methylene groups). IR (KBr): m(cm1) = 3103(s), 1596(s), 1575(m), 1511(s), 1462(m), 1426(s), 1366(s), 1271(s), 1217(m), 1166(m), 1143(s), 1097(w), 1020(s), 961(m), 890(m), 870(m), 770(s), 716(m), 680(s), 651(m), 594(m). 2.4.1. Synthesis of [Co2(Cbtp)2(ip)2] (1) A mixture of Co(OAc)24H2O (35.9 mg, 0.14 mmol), isophthalic acid (20.1 mg, 0.12 mmol), 2,6-bis((1H-1,2,4-triazol-1-yl)methyl) pyridine (29.0 mg, 0.12 mmol), and H2O (5 mL) was placed a Teflon-lined stainless steel vessel (20 mL) and heated at 140 °C for 3 days, and cooled to 25 °C at a rate of 5 °C/h. Red-violet crystals suitable for X-ray analysis were obtained. Yield was 54%. Purity of bulk sample of 1 was checked by powder XRD (see Fig. S1 in Supporting Information). Anal. Calc. for C19H15CoN7O4 (464.31), 1: C, 49.15; H, 3.26; N, 21.12. Found: C, 49.41; H, 3.11; N, 21.00%. IR (KBr): m(cm1) = 3400(brs), 3131(m), 2969(w), 1612(s), 1577(s), 1545(s), 1523(s), 1480(m), 1451(s), 1396(brs), 1282(s), 1210(m), 1130(s), 1019(s), 992(m), 921(m), 875(w), 766(m), 746(s), 719(s), 681(m), 656(m). 2.4.2. Synthesis of [N(CH3)4]2[Co3(ip)4] (2) A mixture of Co(NO3)26H2O (74.2 mg, 0.25 mmol), isophthalic acid (53.0 mg, 0.32 mmol), quinazoline (32.9 mg, 0.25 mmol), ammonium hydroxide (61.0 lL, 0.50 mmol) and DMF/methanol (4/1, v/v, 5 mL) was placed a Teflon-lined stainless steel vessel
(20 mL) and heated at 170 °C for 2 days, and cooled to 25 °C at a rate of 5 °C/h. Blue-violet crystals suitable for X-ray analysis were obtained. Yield was 43%. Purity of bulk sample of 2 was checked by powder XRD (see Fig. S2 in Supporting Information). Anal. Calc. for C40H40Co3N2O16 (981.53), 2: C, 48.94; H, 4.12; N, 2.85. Found: C, 49.12; H, 3.95; N, 2.77%. IR (KBr): m(cm1) = 3034(w), 1614(s), 1571(s), 1483(s), 1395(s), 1306(s), 1272(w), 1159(m), 1076(w), 943(s), 827(w), 811(w), 750(s), 722(s), 710(s), 657(w), 551(w), 468(w). 2.4.3. [{Co7(ip)5(l-OH)4}(l-bpp)2]2(H2O) (3) A mixture of Co(NO3)26H2O (41.6 mg, 0.14 mmol), isophthalic acid (20.1 mg, 0.12 mmol), 1,3-bis(4-pyridyl)propane (24.3 mg, 0.12 mmol), ammonium hydroxide (29.30 lL, 0.24 mmol) and DMF/ethanol (1/4, v/v, 5 mL) was placed a Teflon-lined stainless steel vessel (20 mL) and heated at 160 °C for 2 days, and cooled to 25 °C at a rate of 5 °C/h. Blue-violet crystals suitable for X-ray analysis were obtained. Purity of bulk sample of 3 was checked by powder XRD (see Fig. S3 in Supporting Information). Yield was 92%. C66H48Co7N4O24(H2O)2(C3H7NO) (1801.87), 3: C, 45.97; H, 3.30; N, 3.88. Found: C, 45.72; H, 3.01; N, 3.37%. IR (KBr): m(cm1) = 3441(brm), 1666(w), 1635(s), 1612(s), 1557(s), 1482(w), 1437(m), 1385(s), 1219(w), 1073(w), 1018(w), 812(m), 740(s), 713(s), 658(w), 518(w), 453(w). 2.5. Crystallography The diffraction data for compounds 1–3 were collected on a Bruker SMART AXS diffractometer equipped with a monochromator in the Mo Ka (k = 0.71073 Å) incident beam. The crystal was mounted on a glass fiber. The CCD data were integrated and scaled using the Bruker-SAINT software package, and the structure was solved and refined using SHEXTL V6.12 [41]. Hydrogen atoms were located in the calculated positions. For 3, the largest peak in the final difference Fourier map of 1.912 e Å3 indicates that there might be disordered solvent molecules in the structure. The crystallographic data for compounds 1–3 are listed in Table 1. 3. Results and discussion Isophthalic acid (H2ip) was selected as a multinucleating ligand for paramagnetic CoII centers, and three different auxiliary ligands, namely Cbtp, quinazoline, and bpp, were employed to form 1-D, 2-D, and 3-D coordination polymers, respectively. A new ligand 2,6-bis((1H-1,2,4-triazol-1-yl)methyl)pyridine (Cbtp) has been synthesized for construction of CoII coordination polymers, and it was characterized by NMR, IR, and elemental analysis. In 1, Cbtp ligands bridge two CoII ions, and these Cbtp-bridged Co2 units are connected by ip to form a 1-D chain. In 2, the use of quinazoline ligands in the synthesis led to a 2-D layer compound containing trinuclear Co3 units, but without auxiliary quinazoline ligands. With bpp auxiliary ligands, compound 3, a porous 3-D framework containing heptanuclear Co7 units was synthesized. All three compounds are shown in Scheme 1. 3.1. Structure description of [Co2(Cbtp)2(ip)2] (1) The asymmetric unit contains a CoII ion, an ip, and a Cbtp ligand; there is an inversion center at the mid point of the Co Co contact between adjacent CoII ions that are bridged by two Cbtp ligands. The symmetry operations (x + 1, y + 1, z + 2), (x, y 1, z), and (x, y + 1, z) generate 1-D chains (Fig. 1). The coordination geometry around CoII ion is distorted octahedral constructed by four carboxylate oxygen atoms and two Cbtp nitrogen atoms. Two carboxylates in ip show two different coordination modes:
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E.Y. Kim et al. / Polyhedron 29 (2010) 3335–3341 Table 1 Crystal data and structure refinement for 1–3.
Empirical formula Formula weight T (K) k (Å) Space group a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z Dcalc (Mg/m3) Absorption coefficient (mm1) Crystal size (mm3) Reflections collected Independent reflections (Rint) Data/restraints/parameters Goodness-of-fit (GOF) on F2 Final R indices [I > 2r(I)] R indices (all data) Largest difference in peak and hole (e Å3)
1
2
3
C19H15CoN7O4 464.31 293(2) 0.71073 P1
C40H40Co3N2O16 981.53 293(2) 0.71073 P21/n 18.4972(14) 10.1886(8) 23.0512(16) 90.00 112.3890(10) 90.00 4016.8(5) 4 1.623 1.302 0.15 0.10 0.10 20 610 7834 [Rint = 0.0562] 7834/0/558 0.983 R1 = 0.0621, wR2 = 0.1714 R1 = 0.0880, wR2 = 0.1939 0.888 and 1.310
C66H52Co7N4O26 1729.63 170(2) 0.71073 C2/c 24.038(5) 23.217(5) 15.263(3) 90.00 115.73(3) 90.00 7673(3) 4 1.494 1.552 0.20 0.10 0.08 17 110 6472 [Rint = 0.1489] 6472/2/480 0.917 R1 = 0.0755, wR2 = 0.1790 R1 = 0.1372, wR2 = 0.1976 1.912 and 0.902
9.0408(12) 10.0189(12) 11.6879(14) 82.641(2) 76.649(2) 76.098(2) 996.9(2) 2 1.547 0.904 0.15 0.05 0.05 5627 3829 [Rint = 0.0562] 3829/0/280 0.804 R1 = 0.0387, wR2 = 0.0759 R1 = 0.0599, wR2 = 0.0786 0.371 and 0.679
Scheme 1. 1-D, 2-D and 3-D coordination polymers assembled from dinuclear and polynuclear CoII units based on the isophthalate(-2) ligand.
Fig. 1. 1-D chain of 1. All hydrogen atoms were omitted for clarity.
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chelating (g1:g1) and bridging (g1:g1:l2) (Scheme 2). One side carboxylate of ip bridges Cbtp-bridged Co2 units, and the other side carboxylate chelates the CoII ion in the neighboring Co2 units. The Co Co separation is 4.317 Å. 3.2. Structure description of [N(CH3)4]2[Co3(ip)4] (2) There are three independent CoII ions (Co1, Co2, and Co3) with four ip ligands and two tetramethylammonium cations. The symmetry operations (x + 1/2, y 1/2, z + 1/2), (x + 1/2, y + 1/2, z + 1/2), (x 1/2, y + 1/2, z + 1/2), (x 1/2, y 1/2, z + 1/ 2), (x, y 1, z), and (x, y + 1, z) generate a 2-D sheet as shown in Fig. 2(a). The three CoII ions are joined together by six carboxylate groups from six ip ligands. The geometry around Co1 is distorted octahedral. Co2 is five-coordinated, and from the angular structural parameter as a general descriptor of five-coordinate centric molecules [42], the irregular coordination geometry of Co2 is described as being 42.6% along Berry pseudorotation from trigonal bipyramidal toward square pyramidal. The geometry around Co3 can be described as distorted octahedral considering long Co–O bonds (2.346 and 2.696 Å) as the weak coordination from PLATON analysis. There are trimethylammonium cations between 2-D layers (Fig. 2(b)). There are two different ip ligands showing different coordination modes in both carboxylate groups: one contains two carboxylates with the bridging (g1:g1:l2) and the chelating (g1:g1) modes, and the other does them with the bridging (g1:g1:l2) and (g2:g1:l2) modes (Scheme 2). The intra-cluster separations of Co1 Co2, Co1 Co3 and Co2 Co3 are 3.25(1), 3.282(1) and 6.529(1) Å, respectively. 3.3. Structure description of [{Co7(ip)5(l-OH)4}(l-bpp)2]2(H2O) (3) The asymmetric unit contains four crystallographically independent CoII ions (Co1, Co2, Co3, and Co4) with two and half of ip ligands and two independent hydroxyl groups and one water solvent molecule. The symmetry operations (x, y + 2, z + 1/2), (x, y + 2, z 1/2), (x + 1, y, z + 1/2), (x + 1/2, y + 3/2, z), (x, y, z 1/2), (x + 1/2, y + 1/2, z), (x 1/2, y 1/2, z) produce a 3-D framework with 1-D pores (Fig. 3(a)). The water solvate molecules occupy the 1-D pores. The seven cobalt ions are joined together by 10 bridged carboxylate groups and four hydroxyl groups. In a Co7 unit, there is an inversion center on Co1 ion surrounded by six other CoII ions, and the Co7 unit is almost in a plane. The neutral wheel-shaped Co7 unit has the formula [{Co7(ip)10/2
(l-OH)4}(l-bpp)4/2] (Fig. 3(b)). The coordination geometry around Co1 is distorted octahedral constructed by all six oxygen atoms from two carboxylate groups and four bridging hydroxyl (l3-OH) groups. The coordination geometry around Co2 and Co3 on the rim is also distorted octahedral, but it has different environment from Co1, in which NO5 belongs to four carboxylate oxygen atoms, a bridging hydroxyl group, and a bpp nitrogen atom. The remaining Co4 ion has distorted tetrahedral geometry constructed by all four oxygen atoms from three carboxylate groups and bridging hydroxyl group. There are three different ip ligands showing different coordination modes in both carboxylate groups: two ip ligands contain both carboxylates with the bridging (g1:g1:l2) modes, and the remaining one does both with the bridging (g1:g2:l3) modes (Scheme 2). The intra-cluster separations of Co1 Co2, Co1 Co3, Co1 Co4, Co2 Co3, Co2 Co4, and Co3 Co4 are 3.67(4), 3.25(2), 3.353(4), 3.441(1), 3.39(2), and 3.47(4) Å, respectively. For 3, the framework without the water and DMF solvates possesses 21.5% of solvent accessible void in the unit cell based on a PLATON calculation. The as-made 3 framework with the water solvents also possesses 19.2% voids. The PLATON/Squeeze routine indicates the total potential solvent accessible void volume is 1651.4 Å3. Benzenedicarboxylic acids have been used for designing coordination polymers and open framework structures [43–51]. Among them, isophthalic acid (H2ip) has been used as a multinucleating ligand with paramagnetic CoII ions to produce multinuclear CoII complexes. There were two examples of ip ligand bridged polynuclear CoII complexes: 3-D network containing trinuclear CoII units connected by melamine (ma), {[Co3(ma)(ip)3]2H2O}n [20] and porous 3-D magnet containing heptanuclear CoII units, [KCo7(OH)3(ip)6(H2O)4]12H2O [30]. Although 2 and 3 are similar to those reported complexes Co3 and Co7 units, the structural study using varying auxiliary ligands has not been reported, to our best knowledge. Basically, ip ligands bridge CoII ions to produce dinuclear Co2, trinuclear Co3, and heptanuclear Co7 units, and then appropriate auxiliary ligands can be employed to connect those units to 1-D, 2-D, and 3-D networks (Scheme 1). With Cbtp, one end of the carboxylate of ip bridges Cbtp-bridged Co2 units, and the other end carboxylate chelates the Co ion in the neighboring Co2 units to produce 1-D chains, 1. Quinazoline ligands were not included in this system, and instead a 2-D sheet 2 containing ip-bridged Co3 units was contained. With bpp, a 3-D network 3 containing ip-bridged Co7 units was obtained. These results clearly indicate that judicious
Scheme 2. Coordination modes of ip ligands in coordination polymers assembled from polynuclear CoII units.
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Fig. 2. (a) 2-D Sheet of 2 including a trinuclear Co3 unit. All hydrogen atoms were omitted for clarity. (b) Packing diagram containing 2-D sheets and tetraammonium cations between them.
choice of auxiliary ligands can control not only the nuclearity of the CoII units from dinuclear, trinuclear to heptanuclear structure but also the dimensionality of CoII complexes containing ipbridged polynuclear CoII units from 1-D, 2-D to 3-D networks. 3.4. Magnetic property Variable-temperature magnetic susceptibility data of 1 and 2 were collected in the temperature range 4–300 K under a field of
0.5 T, and the resulting plots of vM, vM1 versus T are depicted (see the Supporting information: Figs. S4 and S5). The effective magnetic moment at room temperature, leff of 1, was 4.77 lB which is larger than the spin-only effective moment of 3.87 lB which is due to the orbital contribution. The vM1 values obey the Curie–Weiss law well with a Curie constant of 2.87 emuT/ mol and a h value of 1.22 K for 1, and there was no evidence of magnetic exchange coupling between the CoII in the chain. The leff value (8.49 lB) per a Co3 unit of 2 at room temperature is larger
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Fig. 3. (a) 3-D Framework of 3 along c axis. All hydrogen atoms were omitted for clarity. (b) Drawing for a heptanuclear Co7 unit.
than that (6.71 lB) for three non-interacting cobalt ions of S = 3/2 which is also due to the orbital contribution. The vM1 values of 2 obey the Curie–Weiss law well with a Curie constant of 2.62 emuT/mol and a h value of 0.29 K, which also suggests that there is no significant interaction between the Co3 units within the 2-D layer 2. The variable-temperature magnetic susceptibilities and magnetic moments of 3 per a Co7 unit are shown (see the Supporting information: Fig. S6). The leff value (11.99 lB) per a Co7 unit of 3 at room temperature is larger than that (10.25 lB) for spin-only cobalt ions of S = 3/2 indicating significant orbital contributions of the distorted octahedral CoII ions. Between 10 and 300 K, 3 obeys the Curie–Weiss law with a Curie constant of 19.85 emuT/ mol and a h value of 34.22 K.
3.5. Thermogravimetric analysis To study the thermal stabilities of these complexes, thermal gravimetric analysis (TGA) of compounds 1–3 was performed (see the Supporting information: Figs. S7-S9). The compound 1 showed no discernible weight loss up to 365 °C. The compound 2 gradually lost its weight because of the potential decomposition of the N(CH3)4+ cations. The TGA curve for 3 displayed a weight loss of 5.82% (theoretical weight loss: 5.12%) at 176.3 °C and which is attributed to the loss of two solvate water and DMF molecules.
3.6. Gas sorption We have tested the gas sorption ability of the sample 3 by using N2 and CO2 (Fig. 4). The as-prepared 3 was solvent exchanged with CHCl3 by shaking for 2 days. The sample dried at 150 °C for 2 h exhibited CO2 uptake value of 76.7 cm3/g at STP (3.42 mmol/g) at 196 K. In contrast, relatively small amount of N2 sorption was observed at 77 K: 30.9 cm3/g at STP. The Brunauer–Emmett–Teller (BET) surface area is merely 47.2 m2/g. Nevertheless, the relative high uptake of CO2 over N2 can be attributed to the different kinetic diameters of the gases: CO2 3.30 Å and N2 3.64 Å [52]. Therefore, 3 showed selective sorption ability of CO2 over N2 possibly because of small dimension of channels.
4. Conclusions
Fig. 4. Gas sorption isotherms for CO2 (diamonds) and N2 (circles) by the activated 1. Adsorption branches (closed symbols) and desorption branches (open symbols) are indicated.
Three coordination polymers containing polynuclear CoII units, [Co2(Cbtp)2(ip)2] (1), [N(CH3)4]2[Co3(ip)4] (2), and [{Co7(ip)5(lOH)4}(l-bpp)2]2(H2O) (3), have been reported. Isophthalic acid (H2ip) has been used for the construction of polynuclear CoII units, and three auxiliary ligands, namely Cbtp, quinazoline, and bpp, have also been employed to change nuclearity of CoII unit and the dimensionality of polymeric CoII compounds: 1-D structure containing dinuclear CoII units with Cbtp, 2-D structure containing trinuclear CoII units without quinazoline, and 3-D structure containing heptanuclear CoII units with bpp. The gas sorption study of 3 revealed a relative high uptake of CO2 over N2 because of small dimension of channels.
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Acknowledgements Financial support from Korea Ministry Environment ‘‘ET-Human resource development Project”, the Korean Science & Engineering Foundation (R01-2008-000-20704-0 and 2009-0074066), the Converging Research Center Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2009-0082832), and the SRC program of the Korea Science and Engineering Foundation (KOSEF) through the Center for Intelligent Nano-Bio Materials at Ewha Womans University (Grant R11-2005-008-00000-0) is gratefully acknowledged. Appendix A. Supplementary data CCDC 777826, 7777825, and 777827 contains the supplementary crystallographic data for 1–3. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.poly.2010.09.013. References [1] J.-P. Sauvage, M.W. Hosseini, in: J.-M. Lehn (Ed.), Comprehensive Supramolecular Chemistry, vol. 9, Pergamon Press, Oxford, 1995. [2] M. Fujita, K. Umemoto, M. Yoshizawa, N. Fujita, T. Kusukawa, K. Biradha, Chem. Commun. (2001) 509. [3] G. Aromí, H. Stoeckli-Evans, S.J. Teat, J. Cano, J. Ribas, J. Mater. Chem. 16 (2006) 2635. [4] J.E. Bol, W.L. Driessen, R.Y.N. Ho, B. Maase, L. Que, J. Reedijk, Angew. Chem., Int. Ed. 36 (1997) 998. [5] M. Ruben, U. Ziener, J.M. Lehn, V. Ksenofontov, P. Gütlich, G.B.M. Vaughan, Chem. Eur. J. 11 (2004) 94. [6] L.K. Thompson, T.L. Kelly, L.N. Dawe, H. Grove, M.T. Lemaire, J.A.K. Howard, E.C. Spencer, C.J. Matthews, S.T. Onions, S.J. Coles, P.N. Horton, M.B. Hursthouse, M.E. Light, Inorg. Chem. 43 (2004) 7605. [7] B.J. Coe, N.R.M. Curati, Comments Inorg. Chem. 25 (2004) 147. [8] O.M. Yaghi, M. O’Keeffe, N.W. Ockwig, H.K. Chae, M. Eddaoudi, J. Kim, Nature 423 (2003) 705. [9] S. Noro, S. Kitagawa, M. Kondo, K. Seki, Angew. Chem., Int. Ed. 39 (2000) 2081. [10] Z.L. Huang, M. Drillon, N. Masciocchi, A. Sironi, J.T. Zao, P. Rabu, P. Panissod, Chem. Mater. 12 (2000) 2805. [11] L. Pan, N. Ching, X. Huang, J. Li, Inorg. Chem. 39 (2000) 5333. [12] L. Pan, B.S. Finkel, X. Huang, J. Li, Chem. Commun. (2001) 105. [13] P.S. Mukherjee, N. Das, Y.K. Kryshenko, A.M. Arif, P.J. Stang, J. Am. Chem. Soc. 126 (2004) 2464. [14] N.L. Rosi, J. Kim, M. Eddaoudi, B. Chen, M. O’Keeffe, O.M. Yaghi, J. Am. Chem. Soc. 127 (2005) 1504. [15] Z. Wang, G. Chen, K. Ding, Chem. Rev. 109 (2009) 322. [16] B. Moulton, M.J. Zaworotko, Chem. Rev. 101 (2001) 1629. [17] T. Duangthongyou, S. Jirakulpattana, C. Phakawatchai, M. Kurmoo, S. Siripaisarnpipat, Polyhedron 29 (2010) 1156. [18] K.S. Gavrilenko, Y.L. Gal, O. Cador, S. Golhen, L. Ouahab, Chem. Commun. (2007) 280.
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