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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 (BPDC2)

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 Koreab 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, [MII(H2O)3(BPDC)]nnH2O (M = Co (1), Fe (2)), have been prepared by theself-assembly of cobalt(II) and iron(II) ions, respectively, with 2,2 0-bipyridyl-3,30-dicarboxylic acid (H2BPDC) 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 BPDC2 belonging to the adjacent metal ion and two nitrogen atomsfrom the BPDC2 acting as a chelating ligand. In1 and 2, one carboxylate oxygen atom of coordinated BPDC2 binds to the neighbor-ing metal ion, which give rise to 1-D helical coordination polymers. The helical chains of1 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 abplane. The supramolecules 1 and2 show isomorphous structures regardless ofthe 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 ofcoordination polymers with various architectures, such as

helix, 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 helical

structure 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 ofligand, and the spacers linking the binding sites.Furthermore, hydrogen bonding interactions besides themetalligand 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 metalligand 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 2,20-bipyridyl-4,4 0-dicarboxylic acid (H2BPDC) 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: [email protected] (K.S. Min), [email protected] (B.G. Kim).

www.elsevier.com/locate/ica

Inorganica Chimica Acta 360 (2007) 16781683
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2-D supramolecules consisting of 1-D helical chains,[MII(H2O)3(BPDC)]n nH2O (M = Co (1), Fe (2)), respec-tively, by the self-assembly, where each [MII(H2O)3]

2+ unitis coordinated by BPDC2 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 1and 2.

N

NO

OO

O

M2+

OH2

OH2

H2O

M = Co (1), Fe (2)

n

nH2O

N

N C

C

O

O

OH

OH

H2BPDC

2. Experimental

2.1. General procedures

All chemicals and solvents used in the syntheses were ofreagent grade and were used without further purification.2,2 0-Bipyridyl-3,3 0-dicarboxylic acid (H2BPDC) 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 [CoII(H2O)3(BPDC)]nnH2O (1)

An aqueous solution (10 mL) of H2BPDC (50 mg,0.20 mmol) was added dropwise to an aqueous solution(10 mL) of Co(NO3)26H2O (60 mg, 0.20 mmol). The pHof the solution was adjusted to ca. 8 by the addition of0.1 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 1formed were filtered, washed with MeOH, and dried inair (yield: 45 mg, 60%). Calc. for C12H12CoN2O7: 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 cm1.

2.3. Synthesis of [FeII(H2O)3(BPDC)]n nH2O (2)

This complex was prepared as red microcrystals in amanner similar to the synthesis of 1 except that Fe(S-O4)7H2O (57 mg, 0.20 mmol) instead of Co(NO3)26H2O was used. Yield: 61 mg (82%). Calc. for

C12H18FeN2O10: 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 cm1.

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 usingMo Ka 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 SHELXL97 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 2are summarized inTable 1.

3. Results and discussion

3.1. Synthesis and characterization

1-D helical coordination polymers, [CoII(H2O)3(BPDC)]n nH2O (1) and [Fe

II(H2O)3(BPDC)]n nH2O (2),

were prepared in an aqueous solution by the self-assembly

Table 1Crystallographic data for1 and 2

1 2

Empirical formula C12H14CoN2O8 C12H14FeN2O8Formula weight 373.18 370.10Crystal system monoclinic monoclinicSpace group P21/n P21/n

a(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(A3) 1464.38(19) 1487.5(6)Z 4 4Dcalc(g cm

3) 1.693 1.653

T(K) 173(2) 173(2)k (A) 0.71073 0.71073l (mm1) 1.217 1.058F(0 0 0) 764 760Collected 9134 12934Unique 3457 3543Observed 2650 2854Parameters 240 240

Goodness-of-fit 1.023 1.114R1

a (4rdata) 0.0381 0.0480wR2

b (4rdata) 0.0913 0.1005Largest difference in

peak and hole (e/A3)0.572 and 0.827 0.792 and0. 554

a R1=P

iFoj jFci/P

jFoj.bwR2

PwF2o F

2c

2=P

wF2o21=2.

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of Co(NO3)26H2O and Fe(SO4)7H2O, respectively, with2,2 0-bipyridyl-4,4 0-dicarboxylic acid (H2BPDC) 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, CH2Cl2, and CHCl3.

The infrared spectrum (KBr pellet) of1 shows mOH of thewater molecules at 3350 and mC@O of the carboxylategroups of BPDC2 at 1580 cm1. Similarly, the infraredspectrum of 2 shows mOH of the water molecules at 3400and mC@O of the carboxylate groups of BPDC

2 at1570 cm1. TGA trace of 1 shows a weight loss of18.97% (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 BPDC2 ligand isdecomposed. The final products are grayish black.

3.2. X-ray crystal structures

3.2.1. 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 BPDC2 ion bonded a neighboring cobalt(II)ion and two nitrogen atoms of the bipyridine unit ofBPDC2 as well as three water molecules to display adistorted octahedral coordination geometry. The averageCoOBPDC, CoNbpy, and CoOwater bond distances are2.093(2), 2.130(1), and 2.080(1) A, respectively. Within a

monomeric unit, intramolecular hydrogen bonding interac-tions exist between the uncoordinated oxygen atoms ofcarboxylate 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, \O2WH2AO2 = 155.47), and 11-mem-bered ring (O3W O4 (x + 1.5, 0.5 +y, 0.5z) =2.714(3) A, \O3WH3AO4 = 172.60). The BPDC2

bridging ligand is not planar since the dihedral anglebetween the pyridine rings of BPDC2 ion is 31.65(6).Such distortion is common and has been observed withother complexes bridged by the ligands containing 2,20-bipy or 4,4 0-bipy unit[13].

One carboxylate oxygen atom of coordinated BPDC2

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 BPDC2 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 21-screw axis.Similarly, some examples of 1-D helical coordination poly-mers formed by self-assembly have been reported [5bf].Furthermore, within a 1-D chain, intramolecular hydrogenbonding interaction exists between the aqua ligand and theuncoordinated carboxylate oxygen atom of BPDC2

belonging to the adjacent cobalt(II) ion to form a rigid

1-D chain (O1W O3 (x + 1.5, y0.5, z + 0.5) =

2.719(3) A, \O1WH1AO3 = 161.96) (Fig. 1b). Thehelical chains are linked each other by the hydrogen bond-ing interactions between the carboxylate oxygen atom ofthe BPDC2 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 theabplane (O2W O4 (x1,y, z) =2.631(2) A, \O2WH2BO4 = 169.70)(Fig. 1c). Within a

layer, all 1-D helical chains show the same chirality. On the

Co

C1

C2C3

C4

C5

C6

C7

C8 C9

C10C12

C11

O4

O3

O1

O2O1W

O2W

O3W

O4W

O1'

N1

N2

c

a

b

Fig. 1. (a) ORTEP drawing of 1 with atomic numbering scheme( 0 = 1.5x, 0.5 + y, 0.5z). The atoms are represented by 50% probable

thermal ellipsoids. (b) Perspective view of1 showing the helical 1-D chain.The hydrogen bonding interactions within a chain are indicated as ---. (c)Extended 2-D structure of1. The hydrogen bonding interactions betweenthe chains are indicated as nnn.

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other hand, by arranging in an ABAB fashion along

withc-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 water

molecule forms hydrogen bonds with the aqua ligand(O4W O3W = 2.653(3) A, \O4WH3BO3W = 175.60)and the uncoordinated carboxylate oxygen atoms belongto the neighboring helical chain in which the rigid 2-D layeris formed (O4W O2 (x1, y, z) = 2.803(3) A, \O4WH4AO2 = 154.72, O4W O3 (x1, y, z) = 2.815(3) A,

\O4WH4BO3 = 160.45). Compound 1 crystallizes inthe monoclinic system, and the unit cell parameters are

Table 2Selected bond distances (A) and angles () for 1

CoN1 2.104(2) O1C11 1.244(3)CoN2 2.153(2) O2C11 1.261(3)CoO1a 2.093(2) O3C12 1.252(3)CoO1W 2.121(2) O4C12 1.263(3)CoO2W 2.062(2) C5C6 1.492(3)

CoO3W 2.058(2)N1CoN2 76.04(7) N2CoO3W 166.30(8)N1CoO1a 87.61(7) O1WCoO1a 178.97(7)N1CoO1W 93.39(8) O1WCoO2W 89.59(8)N1CoO3W 91.99(8) O1WCoO3W 91.26(8)N1CoO2W 168.70(8) O2WCoO1a 89.38(7)N2CoO1a 84.00(7) O2WCoO3W 98.84(8)N2CoO1W 96.02(7) O3WCoO1a 88.94(7)N2CoO2W 92.82(8)

Marked atoms are generated by symmetry operations: a 1.5x, 0.5 +y,0.5z.

Fig. 2. Side view (stereoview) perpendicular to the helical axis of the

structure: (a) left-handed, (b) right-handed.

Fe

C1

C2C3

C4

C5

C6

C7

C8 C9

C10C12

C11

O4

O3O2

O1 O1W

O2'

N2

N1

O2W

O3W

O4W

a

b

c

Fig. 3. (a) ORTEP drawing of 2 with atomic numbering scheme(0 = 1.5x, 0.5 +y, 0.5z). The atoms are represented by 50% probablethermal ellipsoids. (b) Perspective view of2showing the helical 1-D chain.The hydrogen bonding interactions within a chain are indicated as ---. (c)Extended 2-D structure of2. The hydrogen bonding interactions between

the helical chains are indicated as nnn.



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very similar to those of [NiII(H2O)3(BPDC)]n nH2O

obtained by hydrothermal synthesis (a= 10.045, b=9.285, c= 16.155 A, b= 96.60, V= 1497 A3, P21/n)[14]. Thus, 1 is isomorphous to [NiII(H2O)3(BPDC)]nnH2O.

3.2.2. Description of structure 2

An ORTEP drawing of 2 is shown in Fig. 3a andselected bond distances and angles are listed in Table 3.The iron(II) ion exhibits a distorted octahedral geometryby coordination of one carboxylate oxygen atom and twonitrogen atoms as well as three water molecules. The aver-age FeOBPDC, FeNbpy, and FeOwaterbond distances are

2.133(2), 2.189(1), and 2.097(1) A, respectively. These bondlengths are slightly longer than those of CoN(O) in 1 (ca.0.0170.059 A) due to the large ionic radius of iron(II) ion(rFe(II)= 0.920 A and rCo(II)= 0.885 A) [15]. In a mono-meric unit, intramolecular hydrogen bonds show betweenthe uncoordinated oxygen atoms of carboxylate and theaqua ligands (O2W O1 (x+ 1.5, 0.5 +y, 0.5z) =2.744(3) A, \O2WH2AO1 = 154.75, O3W O4 (x+ 1.5, 0.5 +y, 0.5z) = 2.717(3) A, \O3WH3AO4 = 167.62). The BPDC2 ligand is distorted with thedihedral angle of 32.79(7) between the pyridine units asdescribed in 1 [13].

One carboxylate oxygen atom of coordinated BPDC2

links to the adjacent iron(II) ion, which leads to a 1-D heli-cal chain (Fig. 3b). In the 1-D helical chain, intramolecularhydrogen bond shows between the aqua ligand and theuncoordinated carboxylate oxygen atom (O1W O3(x+ 1.5, y0.5, z+ 0.5) = 2.736(3) A, \O1WH1AO3 = 159.57) (Fig. 3b). The 1-D helical chains are alsoconnected each other by the hydrogen bondings, whichgives rise to a 2-D network (O2W O4 (x1, y,z) = 2.618(3) A, \O2WH2BO4 = 179.18) (Fig. 3c).Similar to the structure of 1, each 2-D layer has the samechirality, while the adjacent layer is different. Thus, com-pound 2 possesses also two kinds of 1-D chains due to

the inversion center (Fig. 2). The separation between the

layers (8.091 A) is comparable to that of1 (8.012 A). Theshortest Fe Fe distances within a helical chain andbetween the chains are 7.377 and 6.331 A, respectively,and very similar to those of Co Co. Furthermore, the lat-tice water molecule forms hydrogen bonding with the aqualigand (O4W O3W = 2.660(3) A, \O4WH3BO3W =

175.23) and the uncoordinated carboxylate oxygen atoms(O4W O1 (x1, y, z) = 2.826(3) A, \O4WH4AO2 =157.92, O4W O3 (x1, y, z) = 2.824(3) A, \O4WH4BO3 = 164.41). As shown inTable 1, compound 2 isisomorphous to 1 and [NiII(H2O)3(BPDC)]n nH2O[14].

4. Conclusion

Using the 2,2 0-bipyridyl-3,3 0-dicarboxylic acid(H2BPDC) as well as cobalt(II) and iron(II) ions, 1-D heli-cal coordination polymers of [CoII(H2O)3(BPDC)]n nH2O(1) and [FeII(H2O)3(BPDC)]n nH2O (2) have been con-structed in an aqueous solution by self-assembly. Eachcompound is insoluble in common solvents. Compounds1 and 2 lead to 1-D helical structures by the metalligandcoordination between the cobalt(II) or iron(II) ion andBPDC2. The helical chains of 1 and 2 are linked by thehydrogen bonding interactions between the carboxylateoxygen atom of the BPDC2 ions and the water moleculebelonging to the adjacent helical chains, which give riseto 2-D networks. Both compounds, 1 and 2, are isomor-phous structures.

Acknowledgement

The authors acknowledge the Central Instrument Facil-ity of Gyeongsang National University for assistance inobtaining the X-ray crystal structures.

Appendix A. Supplementary material

CCDC 606990 and 606991 contain the supplementarycrystallographic data for1 and2. The data can be obtainedfree of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge CrystallographicData Centre, 12 Union Road, Cambridge CB2 1EZ, UK;fax: (+44) 1223-336-033; or e-mail: [email protected]

c.uk. Supplementary data associated with this article canbe found, in the online version, at doi:10.1016/j.ica.2006.09.010.

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Table 3Selected bond distances (A) and angles () for 2

FeN1 2.207(2) O1C11 1.268(3)FeN2 2.170(2) O2C11 1.246(3)FeO2a 2.1333(19) O3C12 1.248(3)FeO1W 2.134(2) O4C12 1.267(3)FeO2W 2.074(2) C5C6 1.493(4)

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