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One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2' -bipyridyl-3,3' -dicarboxylate (BPDC 2-)

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One-dimensional helical coordination polymers of cobalt(II) and iron(II) ions with 2,2 0 -bipyridyl-3,3 0 -dicarboxylate (BPDC 2À ) Ock Keum Kwak a , Kil Sik Min b, * , Bong Gon Kim a, * a Department of Chemistry Education and Institute of Basic Science, Gyeongsang National University, Jinju 660-701, Republic of Korea b Department of Chemistry, University of Utah, Salt Lake City, UT 84112-0850, USA Received 22 May 2006; received in revise
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  One-dimensional helical coordination polymers of cobalt(II)and iron(II) ions with 2,2 0 -bipyridyl-3,3 0 -dicarboxylate (BPDC 2  ) Ock Keum Kwak  a , Kil Sik Min  b,* , Bong Gon Kim  a,* a Department of Chemistry Education and Institute of Basic Science, Gyeongsang National University, Jinju 660-701, Republic of Korea b Department of Chemistry, University of Utah, Salt Lake City, UT 84112-0850, USA Received 22 May 2006; received in revised form 29 August 2006; accepted 7 September 2006Available online 26 September 2006 Abstract One-dimensional (1-D) helical coordination polymers, [M II (H 2 O) 3 (BPDC)] n  Æ  n H 2 O (M = Co ( 1 ), Fe ( 2 )), have been prepared by theself-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2 0 -bipyridyl-3,3 0 -dicarboxylic acid (H 2 BPDC) in an aqueous solution. X-ray crystal structures of compounds  1  and  2  show that each metal ion displays a distorted octahedral coordination geometry includingthree water oxygen atoms, one oxygen atom of the carboxylate of a BPDC 2  belonging to the adjacent metal ion and two nitrogen atomsfrom the BPDC 2  acting as a chelating ligand. In  1  and  2 , one carboxylate oxygen atom of coordinated BPDC 2  binds to the neighbor-ing metal ion, which give rise to 1-D helical coordination polymers. The helical chains of   1  and  2  are linked by the hydrogen bondinginteractions between the carboxylate oxygen atom of the BPDC 2  ion belonging to a chain and the water molecule of the adjacent helicalchain, which lead to 2-D networks extending along the  ab  plane. The supramolecules  1  and  2  show isomorphous structures regardless of the metal ions.   2006 Elsevier B.V. All rights reserved. Keywords:  Cobalt(II) complex; Iron(II) complex; Coordination polymer; Crystal structure; Hydrogen bonding 1. Introduction The contemporary interest in supramolecular chemistryreflects not only their relevance to the design and construc-tion of new coordination polymers from molecular build-ing blocks [1], but also their potential applications tosorption, catalysis, and magnetism [2]. Construction of coordination polymers with various architectures, such ashelix, zigzag chain, honeycomb, square grid, ladder, andinterwoven diamondoid, have been studied extensively[3]. In particular, coordination polymers with helical mor-phology have been attracted to chemists because theyinvolved in the areas such as memory devices and biomi-metic chemistry [4]. However, the self-assembly of helicalstructure is still a challenging subject due to the difficultyof the selection of optimal components, although manycoordination polymers with helical structures have beenreported [5]. The construction depends on the coordinationgeometry of metal ions, the shape and binding mode of ligand, and the spacers linking the binding sites.Furthermore, hydrogen bonding interactions besides themetal–ligand coordination are utilized to induce intra-/inter-molecular interactions in the assembly of supramole-cules [6]. Such interactions are also of great importance dueto the various applications to molecular recognition andcrystal engineering [7,8].In this paper, to prepare helical coordination polymerswhich are constructed by the metal–ligand coordinationas well as the extensive hydrogen bonding interaction, wehave employed the cobalt(II) and iron(II) metal ions asmetal building blocks and the tetradentate ligand 2,2 0 -bipyridyl-4,4 0 -dicarboxylic acid (H 2 BPDC) as organicbuilding block in the reaction. Thus, we have obtained 0020-1693/$ - see front matter    2006 Elsevier B.V. All rights reserved.doi:10.1016/j.ica.2006.09.010 * Corresponding authors. Tel.: +1 801 5814229; fax: +1 801 5818433(K.S. Min). E-mail addresses:  minks@chem.utah.edu (K.S. Min), ombgkim@gsnu.ac.kr (B.G. Kim). www.elsevier.com/locate/ica Inorganica Chimica Acta 360 (2007) 1678–1683  2-D supramolecules consisting of 1-D helical chains,[M II (H 2 O) 3 (BPDC)] n  Æ  n H 2 O (M = Co ( 1 ), Fe ( 2 )), respec-tively, by the self-assembly, where each [M II (H 2 O) 3 ] 2+ unitis coordinated by BPDC 2  ligand to form helical structuresand each 1-D chain is linked by hydrogen bonding interac-tions. Hence, herein we report the synthesis and X-ray crys-tal structures of the isomorphous series  1  and  2 . NNOOOOM 2+ OH 2 OH 2 H 2 OM = Co ( 1 ), Fe ( 2 )nnH 2 ONNCCOOOHOHH 2 BPDC 2. Experimental  2.1. General procedures All chemicals and solvents used in the syntheses were of reagent grade and were used without further purification.2,2 0 -Bipyridyl-3,3 0 -dicarboxylic acid (H 2 BPDC) was pre-pared according to the literature method previouslyreported [9]. Infrared spectra were recorded with a MattsonGenisi Series FT-IR spectrophotometer. Elemental analy-ses were performed by the analytical laboratory of Gyeong-sang National University.  2.2. Synthesis of [Co II  (H   2 O) 3 (BPDC)] n  Æ  nH   2 O ( 1 ) An aqueous solution (10 mL) of H 2 BPDC (50 mg,0.20 mmol) was added dropwise to an aqueous solution(10 mL) of Co(NO 3 ) 2  Æ  6H 2 O (60 mg, 0.20 mmol). The pHof the solution was adjusted to ca. 8 by the addition of 0.1 N NaOH solution. And then the mixture solution washeated for 12 h at 40   C. After the reaction, the solutionwas cooled to room temperature. Upon standing at roomtemperature for several days, pink microcrystals of   1 formed were filtered, washed with MeOH, and dried inair (yield: 45 mg, 60%). Calc. for C 12 H 12 CoN 2 O 7 : C,40.58; H, 3.41; N, 7.89. Found: C, 40.52; H, 3.54; N,7.87%. IR (KBr pellet): 3350, 2900, 1610, 1580, 1400,1160, 780 cm  1 .  2.3. Synthesis of [Fe II  (H   2 O) 3 (BPDC)] n  Æ  nH   2 O ( 2 ) This complex was prepared as red microcrystals in amanner similar to the synthesis of   1  except that Fe(S-O 4 )  Æ  7H 2 O (57 mg, 0.20 mmol) instead of Co(NO 3 ) 2  Æ 6H 2 O was used. Yield: 61 mg (82%). Calc. forC 12 H 18 FeN 2 O 10 : C, 35.49; H, 4.46; N, 6.90. Found: C,35.57; H, 3.93; N, 6.76%. IR (KBr pellet): 3400, 2900,1600, 1570, 1390, 1150, 770 cm  1 .  2.4. Single crystal X-ray structures Single crystals of   1  and  2  were mounted on Bruker P4diffractometer equipped with the SMART CCD system.X-ray data for  1  and  2  were collected at 173 K and usingMoK a  radiation ( k  = 0.71073 A˚, graphite monochroma-tor). The raw data were processed to give structure factorsusing the  SAINT  program and corrected for Lorentz andpolarization effects [10]. No absorption corrections weremade. The crystal structures were solved by direct methods[11] and refined by full-matrix least-squares refinementusing the  SHELXL 97 computer program [12]. All non-hydro-gen atoms were refined anisotropically. All hydrogen atomswere positioned geometrically and refined using a ridingmodel, except those of all water molecules of   1  and  2 ,respectively. The hydrogen atoms of water molecules werelocated from the difference Fourier maps and refined iso-tropically. The detailed crystallographic data of   1  and  2 are summarized in Table 1. 3. Results and discussion 3.1. Synthesis and characterization 1-D helical coordination polymers, [Co II (H 2 O) 3 (BPDC)] n  Æ  n H 2 O ( 1 ) and [Fe II (H 2 O) 3 (BPDC)] n  Æ  n H 2 O ( 2 ),were prepared in an aqueous solution by the self-assembly Table 1Crystallographic data for  1  and  21 2 Empirical formula C 12 H 14 CoN 2 O 8  C 12 H 14 FeN 2 O 8 Formula weight 373.18 370.10Crystal system monoclinic monoclinicSpace group  P  2 1 / n P  2 1 / na  (A˚) 9.9530(7) 9.958(3) b  (A˚) 9.2443(7) 9.314(2) c  (A˚) 16.023(1) 16.183(4) b  (  ) 96.636(2) 97.671(4) V   (A˚ 3 ) 1464.38(19) 1487.5(6) Z   4 4 D calc  (g cm  3 ) 1.693 1.653 T   (K) 173(2) 173(2) k  (A˚) 0.71073 0.71073 l  (mm  1 ) 1.217 1.058 F  (000) 764 760Collected 9134 12934Unique 3457 3543Observed 2650 2854Parameters 240 240Goodness-of-fit 1.023 1.114 R 1a (4 r  data) 0.0381 0.0480 wR 2b (4 r  data) 0.0913 0.1005Largest difference inpeak and hole (e/A˚ 3 )0.572 and   0.827 0.792 and   0. 554 a R 1 = P i F  o j  j F  c i / P j F  o j . b wR 2  ¼ ½ P w ð  F   2o    F   2c Þ 2 = P w ð  F   2o Þ 2  1 = 2 . O.K. Kwak et al. / Inorganica Chimica Acta 360 (2007) 1678–1683  1679  of Co(NO 3 ) 2  Æ  6H 2 O and Fe(SO 4 )  Æ  7H 2 O, respectively, with2,2 0 -bipyridyl-4,4 0 -dicarboxylic acid (H 2 BPDC) at pH 8and 40   C for 12 h. The solids  1  (pink) and  2  (red) wereobtained in good yield (60% and 82%) within several days.Both compounds are insoluble in common solvents such aswater, MeOH, EtOH, DMF, DMSO, CH 2 Cl 2 , and CHCl 3 .The infrared spectrum (KBr pellet) of   1  shows  m OH  of thewater molecules at 3350 and  m C @ O  of the carboxylategroups of BPDC 2  at 1580 cm  1 . Similarly, the infraredspectrum of   2  shows  m OH  of the water molecules at 3400and  m C @ O  of the carboxylate groups of BPDC 2  at1570 cm  1 . TGA trace of   1  shows a weight loss of 18.97% (calculated, 19.31%) at 120   C, corresponding tothe loss of four water molecules per unit formula. Nochemical decomposition was observed up to 291   C. TheTGA trace also shows the onset of decomposition at291   C, indicating that the coordinated BPDC 2  ligand isdecomposed. The final products are grayish black. 3.2. X-ray crystal structures3.2.1. Description of structure  1 An ORTEP drawing of   1  is shown in Fig. 1a andselected bond distances and angles are listed in Table 2.The cobalt(II) ion is coordinated by one carboxylate oxy-gen atom of BPDC 2  ion bonded a neighboring cobalt(II)ion and two nitrogen atoms of the bipyridine unit of BPDC 2  as well as three water molecules to display adistorted octahedral coordination geometry. The averageCo–O BPDC , Co–N bpy , and Co–O water  bond distances are2.093(2), 2.130(1), and 2.080(1) A˚, respectively. Within amonomeric unit, intramolecular hydrogen bonding interac-tions exist between the uncoordinated oxygen atoms of carboxylate and the aqua ligands to form a stable six-mem-bered ring (O2W    O2 (  x  + 1.5, 0.5 +  y , 0.5    z ) =2.736(3) A˚,  \ O2W–H2A–O2 = 155.47  ), and 11-mem-bered ring (O3W    O4 (  x + 1.5, 0.5 +  y , 0.5    z ) =2.714(3) A˚,  \ O3W–H3A–O4 = 172.60  ). The BPDC 2  bridging ligand is not planar since the dihedral anglebetween the pyridine rings of BPDC 2  ion is 31.65(6)  .Such distortion is common and has been observed withother complexes bridged by the ligands containing 2,2 0 -bipy or 4,4 0 -bipy unit [13].One carboxylate oxygen atom of coordinated BPDC 2  binds to the adjacent cobalt(II) ion, which gives rise to a1-D helical coordination polymer (Fig. 1b). The chainshows that the coordination modes of the BPDC 2  ligandand the configuration of the cobalt(II) ion with three watermolecules in a facial fashion lead to helical chain in whichthe corresponding atoms are translated by a 2 1 -screw axis.Similarly, some examples of 1-D helical coordination poly-mers formed by self-assembly have been reported [5b–f].Furthermore, within a 1-D chain, intramolecular hydrogenbonding interaction exists between the aqua ligand and theuncoordinated carboxylate oxygen atom of BPDC 2  belonging to the adjacent cobalt(II) ion to form a rigid1-D chain (O1W    O3 (  x + 1.5,  y    0.5,   z + 0.5) =2.719(3) A˚,  \ O1W–H1A–O3 = 161.96  ) (Fig. 1b). The helical chains are linked each other by the hydrogen bond-ing interactions between the carboxylate oxygen atom of the BPDC 2  ion belonging to a chain and the water mole-cule of the adjacent helical chain, which leads to a 2-D net-work extending along the  ab  plane (O2W    O4 ( x    1,  y , z ) =2.631(2) A˚, \ O2W–H2B–O4 = 169.70  ) (Fig. 1c). Within a layer, all 1-D helical chains show the same chirality. On the CoC1C2C3C4C5C6C7C8C9C10C12C11O4O3O1O2O1WO2WO3WO4WO1 '   N1N2 cab Fig. 1. (a) ORTEP drawing of   1  with atomic numbering scheme( 0 = 1.5    x , 0.5 +  y , 0.5    z ). The atoms are represented by 50% probablethermal ellipsoids. (b) Perspective view of   1  showing the helical 1-D chain.The hydrogen bonding interactions within a chain are indicated as ---. (c)Extended 2-D structure of   1 . The hydrogen bonding interactions betweenthe chains are indicated as  nnn .1680  O.K. Kwak et al. / Inorganica Chimica Acta 360 (2007) 1678–1683  other hand, by arranging in an     ABAB     fashion alongwith  c -axis, the neighboring layers have the different chiral-ity. Thus, compound  1  has two kinds of 1-D chains by symmetry which is involved in an inversioncenter, e.g. right-handed and left-handed (Fig. 2). The sep-aration between the layers is 8.012 A˚. The shortestCo    Co distance within a helical chain is 7.307 A˚and thatbetween the chains is 6.332 A˚. In addition, the lattice watermolecule forms hydrogen bonds with the aqua ligand(O4W    O3W = 2.653(3) A˚,  \ O4W–H3B–O3W = 175.60  )and the uncoordinated carboxylate oxygen atoms belongto the neighboring helical chain in which the rigid 2-D layeris formed (O4W    O2 ( x    1,  y ,  z ) = 2.803(3) A˚,  \ O4W– H4A–O2 = 154.72  , O4W    O3 ( x    1,  y ,  z ) = 2.815(3) A˚, \ O4W–H4B–O3 = 160.45  ). Compound  1  crystallizes inthe monoclinic system, and the unit cell parameters are Table 2Selected bond distances (A˚) and angles (  ) for  1 Co–N1 2.104(2) O1–C11 1.244(3)Co–N2 2.153(2) O2–C11 1.261(3)Co–O1 a 2.093(2) O3–C12 1.252(3)Co–O1W 2.121(2) O4–C12 1.263(3)Co–O2W 2.062(2) C5–C6 1.492(3)Co–O3W 2.058(2)N1–Co–N2 76.04(7) N2–Co–O3W 166.30(8)N1–Co–O1 a 87.61(7) O1W–Co–O1 a 178.97(7)N1–Co–O1W 93.39(8) O1W–Co–O2W 89.59(8)N1–Co–O3W 91.99(8) O1W–Co–O3W 91.26(8)N1–Co–O2W 168.70(8) O2W–Co–O1 a 89.38(7)N2–Co–O1 a 84.00(7) O2W–Co–O3W 98.84(8)N2–Co–O1W 96.02(7) O3W–Co–O1 a 88.94(7)N2–Co–O2W 92.82(8)Marked atoms are generated by symmetry operations:  a 1.5    x , 0.5 +  y ,0.5    z .Fig. 2. Side view (stereoview) perpendicular to the helical axis of thestructure: (a) left-handed, (b) right-handed. FeC1C2C3C4C5C6C7C8 C9C10C12C11O4O3O2O1 O1WO2 '   N2N1O2WO3WO4W abc Fig. 3. (a) ORTEP drawing of   2  with atomic numbering scheme( 0 = 1.5    x , 0.5 +  y , 0.5    z ). The atoms are represented by 50% probablethermal ellipsoids. (b) Perspective view of   2  showing the helical 1-D chain.The hydrogen bonding interactions within a chain are indicated as ---. (c)Extended 2-D structure of   2 . The hydrogen bonding interactions betweenthe helical chains are indicated as  nnn . O.K. Kwak et al. / Inorganica Chimica Acta 360 (2007) 1678–1683  1681
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