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Inorganic Chemistry Communications 10 (2007) 1026–1030

Two novel anion-directed Cu(II) double betaine coordinationpolymers with different open frameworks: Inorganic chains

[Cu3(l3–OH)2(l2–H2O)2]n as secondary building unitswith unusual chair-like [Cu3O4] cores

Yan Li a,b, Jian-Ping Zou a,b, Wen-Qiang Zou a,b, Fa-Kun Zheng a,*,Guo-Cong Guo a,*, Can-Zhong Lu a, Jin-Shun Huang a

a State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences,

Fuzhou, Fujian 350002, PR Chinab Graduate School, Chinese Academy of Sciences, Beijing 100039, PR China

Received 18 April 2007; accepted 14 May 2007Available online 2 June 2007

Abstract

The reaction of double betaine ligand L1 (L1 = 1,3-bis(pyridinio-4-carboxylato)-propane) with Cu(ClO4)2 and Cu(NO3)2, respectively,afforded two novel anion-directed coordination polymers with different open frameworks. The structure of [Cu3(L1)2(OH)2(H2O)2]-(ClO4)4Æ2H2O 1 is a unique 3-D open-framework with large S-shape channels, while [Cu3(L1)2(OH)2(H2O)2](NO3)4Æ2H2O 2 has a 2-Dtubular structure. There exist inorganic copper-oxo chains [Cu3(l3–OH)2(l2–H2O)2]n in both 1 and 2 as secondary building units, inwhich the [Cu3O4] cores exhibit a rarely observed chair-like configuration. The anion template of ClO�4 and NO�3 , and labile coordinationorientation of L1 ligand prompt the formation of different polymeric networks in 1 and 2.� 2007 Elsevier B.V. All rights reserved.

Keywords: Anion template; Coordination polymers; Crystal structure; Double betaine; Inorganic chain

Ever-increasing interests have been paid to the designand construction of metal-organic open-frameworks(MOFs) due to their various structural architectures andpotential applications, such as in molecular adsorption,catalysis, fluorescence and magnetic materials [1,2]. A num-ber of 1-D, 2-D, and 3-D coordination polymers possessingspecific geometries capable of accommodating anions andguest molecules have been developed [3]. It is well-knownthat most of them with cavities or channels of various sizesand shapes have been designed and assembled by appropri-ate choice of the well-defined coordination geometries ofthe naked metal ions or mononuclear metal complexes as

1387-7003/$ - see front matter � 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.inoche.2007.05.020

* Corresponding authors. Tel.: +86 591 83704827; fax: +86 59183714946.

E-mail address: zfk@fjirsm.ac.cn (F.-K. Zheng).

nodes and organic ligands as linkers [4]. However, metal-organic coordination polymers constructed by polynuclearmetal clusters or inorganic chains and organic bridgingligands have not been well documented so far [5]. Inorganicchains serving as secondary building units (SBUs) have theadvantage of synthesizing and designing functional porouscoordination polymers.

The metal carboxylates have been shown to be animportant family of MOFs, and have continuouslyreceived great attentions for decades due to their excellentcoordination capability and the possibility of offering newfunctional materials [1c,6]. Compared to other carboxylateligands, the chemistry of double betaine ligands (betaine:Me3NþCH2CO�2 ) has been investigated limitedly so far[7,8]. Two carboxylate groups and flexibilities of backbonesof double betaine ligands may result in structural diversi-

Y. Li et al. / Inorganic Chemistry Communications 10 (2007) 1026–1030 1027

ties on the formation of complexes. Our previous studieshave mainly been focused on the research of the influencesof metal ions and double betaine ligands on the polymericstructures by employing different metal centers and variousdouble betaine ligands [9]. As an extension of this research,we present two novel Cu(II) coordination polymers withdouble betaine ligand L1 (Scheme 1) [10], [Cu3(L1)2(OH)2-(H2O)2]X4Æ2H2O (X ¼ ClO�4 1, NO�3 2), obtained by theself-assembly of Cu(X)2 (X ¼ ClO�4 and NO�3 ) with L1

N+-OOC CH2 CH2 CH2+N OO-C

Scheme 1. Chemical structural diagram of L1.

Fig. 1. (a) ORTEP drawing of the coordination environment around Cu1 andonly atoms coordinated to copper atom are labeled (symmetry code A: �x,inorganic copper-oxo chain of 1, consisting of chair-like trinuclear [Cu3O4] uS-shape channels, which are filled by discrete perchlorate groups and lattice w

ligand [11]. Their structures have been characterized byX-ray single-crystal diffraction analyses [12]. Interestingly,their polymeric structures are completely different fromeach other originating from anion template and the flexiblecoordination orientation of L1. It is worth noting that both1 and 2 are constructed by inorganic copper-oxo chains[Cu3(l3–OH)2(l2-H2O)2]n containing rarely observedchair-like trinuclear [Cu3O4] units.

The structure of 1 is a unique 3-D open-framework withlarge S-shape channels, constructed by the cross-linkage ofinorganic copper-oxo chains [Cu3(l3–OH)2(l2-H2O)2]n andL1 ligands. There are two crystallographically independentCu(II) centers in an asymmetric unit, which exhibit differ-ent coordination environments (Fig. 1a). The Cu1 atompresents a distorted square pyramidal coordination, which

Cu2 in 1 with thermal ellipsoids at 30% probability. For the sake of clarity,�y, �z; B: 1 � x, �y, �z; C: 0.5 � x, 0.5 + y, 0.5 � z). (b) View of 1-Dnits. (c) The 3-D network of 1 constructed by L1 ligands with 1-D largeater molecules.

1028 Y. Li et al. / Inorganic Chemistry Communications 10 (2007) 1026–1030

involves a CuO4 equatorial plane comprising of two car-boxylate oxygen atoms from two symmetrically relatedL1 ligands and two symmetrically related hydroxyl oxygenatoms with the normal Cu–O lengths varying from 1.934(3)to 1.981(3) A [13]. The axial position is occupied by a coor-dinated water molecule with a long Cu–O length of2.399(3) A due to the Jahn–Teller effect of Cu(II) ion.The Cu2 atom sits at a symmetry inversion center andhas an elongated octahedral coordination geometry. Theequatorial positions are defined by four oxygen atoms fromtwo centrosymmetric L1 ligands and two centrosymmetrichydroxyl groups with the Cu–O lengths between 1.973(3)and 1.981(3) A. Two elongated axial positions are occupiedby two centrosymmetric water molecules with the length of2.305(3) A. It is expected in 1 that the Cu–O(hydroxyl) dis-tances (1.963(3)–1.981(3) A) are obviously shorter thanthe Cu–O(water) distances (2.305(3)–2.399(3) A). An inter-esting structural characteristic of 1 is that in inorganicchains [Cu3(l3–OH)2(l2-H2O)2]n the basic trinuclear[Cu3O4] unit features an unusual chair-like configurationwith the equatorial plane of the octahedral coordinationsphere of the Cu2 atom as a cushion, as shown inFig. 1b. The Cu1 and Cu2 atoms are bridged by a l3–OH group, a l2–H2O molecule and a bidendate L1 ligand.The neighbouring units [Cu3O4] are connected by two sym-metrically related Cu1–l3–OH bonds, which results in theformation of infinite inorganic copper-oxo chains alongthe a direction. The nearest separations between metalatoms are 3.010(1) A (Cu1–Cu1) and 3.024(1) A (Cu1–Cu2), respectively. To our best knowledge, only two exam-ples of coordination polymers built up by inorganic chains[Cu3(l3–OH)2(l2-H2O)2]n have been reported [14]. In[Cu3(OH)2(H2O)2(Me3NCH2CO2)4](ClO4)4 [14a], the threeCu atoms are in a triangular arrangement, while three Cuatoms are in line in 1. As for another example of[Cu3(L)2(OH)2(H2O)4] 3 (L = adipate dianion), the[Cu3O4] fragment displays the same chair-like configura-tion as that in 1 [14b]. Nevertheless, it is noted that an

Fig. 2. The 2-D layered structure of 2 linked by L

equatorial position of the square pyramidal coordinateCu atom is terminated by one water molecule in 3 insteadof betaine ligand L1 in 1, which leads to the 1-D arrays in 3,and 3-D and 2-D networks in 1 and 2, respectively.

Two carboxylate groups in both ends of L1 ligand adoptdifferent coordination modes: one is syn monodentate andthe other syn–syn bridging bidentate. L1 ligand not onlylinks two neighboring Cu(II) centers within the samemetallo-chain through the bidentate carboxylate group,but also coordinates to a third Cu(II) atom in anotherchain through the monodentate carboxylate group, result-ing in the final 3-D framework with large S-shape channels,which accommodate lattice water molecules and perchlo-rate ions (Fig. 1c). The (syn–syn)-syn tridentate coordina-tion mode of L1 ligand is the same as that in the reportedAg(I)-L1 complex [9a].

There exist hydrogen bonding interactions in 1, whichplay an important role in crystal packing and stabilizingthe structure. The geometrical parameters pertaining tothe H-bonds of 1 are collected in Supplementary dataTable S1. One of two crystallographically independent per-chlorate groups (O23 and O24) are hydrogen bonded byboth the coordinated water molecules (O1W) and hydroxylgroups (O1H). The strong hydrogen bonding betweencoordinated water molecule (O1W) and uncoordinated car-boxylate oxygen atom (O3) has also occurred.

The structure of 2 has a 2-D tubular network,containing inorganic copper-oxo chains [Cu3(l3–OH)2

(l2–H2O)2]n connected through L1 ligands (Fig. 2). Thesituation of inorganic chain [Cu3(l3–OH)2(l2–H2O)2]nand the coordination mode of L1 ligands is almost equalto that in 1. The Cu–Oequatorial distances (1.925(3)–1.971(3) A for Cu1 and 1.950(3)–1.958(3) A for Cu2,respectively) and the Cu1–Oaxial distance (2.384(4) A) arecomparable to those in 1, while, the Cu2–Oaxial bond dis-tance of 2.445(4) A is obviously longer than that in 1.The nearest metal–metal distances are 2.9982(11) and3.0309(13) A for Cu1–Cu2 and Cu1–Cu1, respectively.

1 ligands (symmetry code A: 1 � x, �y, 1 � z).

Scheme 2. The different polymeric structures of 1 (a) and 2 (b).

Y. Li et al. / Inorganic Chemistry Communications 10 (2007) 1026–1030 1029

Notably, despite the same conformation of inorganicchains and the same coordination mode of L1 ligand, thefinal frameworks of 1 and 2 are completely different fromeach other. In 2, the adjacent inorganic metallo-chainsare connected through two [Cu3(l3–OH)2(l2-H2O)2] unitsand two L1 ligands along the [01�1] direction to yield a2-D framework, while in 1 through two [Cu3(l3–OH)2

(l2–H2O)2] units and one L1 ligand in two directions([01 1] and [0�11]) to afford a 3-D network, as shown inScheme 2.

There also exists extensive hydrogen bonding in thepacking of the 2-D molecular framework in 2. The geomet-rical parameters pertaining to the H-bonds of 2 arecollected in Supplementary data Table S2. The lattice watermolecule is hydrogen bonded by its symmetry-related oneto form a (H2O)2 dimer, which is further linked to twonitrate ions by hydrogen bonds to produce a (H2O)2-(NO3)2 aggregate. The adjacent layers are joined by(H2O)2(NO3)2 aggregates through hydrogen bonding con-cerned with nitrate ions and hydroxyl groups to generatea 3-D open network with hydrogen-bonded (H2O)2-(NO3)2 aggregates filled in the channels, as plotted in Sup-plementary data Figure S1.

The TGA curve of 2 (Supplementary data Figure S2)reveals that 2 is thermally stable up to 112 �C. Above thistemperature, in the range 112–142 �C, the loss of latticewater molecules took place with a weight loss of 3.52%(calcd. 3.22%). Then the framework of 2 collapsed above218 �C and the black inorganic residuals were formed.

In the present study, the dissimilarities of polymericframeworks between 1 and 2 can be ascribed to anions tem-plate, namely anion-directed assembly [15], which isslightly different from that observed in a series of Ag(I)coordination polymers in our earlier work [9a]. In thereported Ag(I) coordination polymers, the variation ofthe anions of the silver salts in the synthetic procedureresults in different polymeric frameworks, subunits, coordi-nation modes of carboxylate groups and geometries of theAg(I) atoms. However, in 1 and 2, different anions lead toformation of two conformational supramolecular isomers[16] with the same inorganic copper-oxo chains, but differ-ent MOFs. Although both ClO�4 in 1 and NO�3 in 2 are notinvolved in coordination with metal ions, anions templatewith different shapes and sizes between ClO�4 and NO�3 ionsinduces conformational transformation and consequent

distinct coordination orientation of L1 ligand [17]. The L1

ligand displays the M-like conformation in 1 with a dihe-dral angle of 55.60(15)� between the two pyridine ringsand the L-like one in 2 with a dihedral angle of81.01(13)�, as illustrated in Supplementary data FigureS3. The intrinsic flexibility of L1 ligand is attributed tothe free rotation around sp3 hybridized H2C–CH2 bondsand offers the ability of adjusting the polymeric networks.

Finally, it is interesting to find that the Cu(II) centers in1 and 2 not only coordinate to the carboxylate oxygenatoms of double betaine ligands but also to the water mol-ecules and hydroxyl groups to form the inorganic chains[Cu3(l3–OH)2(l2–H2O)2]n. Thus, the coordinated watermolecules and hydroxyl groups may play a key role inbuilding inorganic metallo-chains, which can be used toconstruct novel inorganic–organic hybrid compounds [18].

In summary, we have successfully prepared two novelanion-directed Cu(II) double betaine coordination poly-mers with different open frameworks. It is attractive thatthe inorganic chains [Cu3(l3–OH)2(l2–H2O)2]n with theunusual chair-like [Cu3O4] moieties are used as secondarybuilding units in construction of MOFs, which may pro-vide a feasible synthetic route in novel inorganic–organichybrid compounds.

Acknowledgements

The authors gratefully acknowledge the financial sup-port of 973 Program (2006CB932900), National NaturalScience Foundation of China (20671091) and Fujian Prov-ince (A0420002 and 2005I017).

Appendix A. Supplementary material

CCDC 609058 contains the supplementary crystallo-graphic data for 1 and CCDC 609285 contains the supple-mentary crystallographic data for 2. These data can beobtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallo-graphic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated with thisarticle can be found, in the online version, atdoi:10.1016/j.inoche.2007.05.020.

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[10] The double betaine ligands L1 was prepared according to theliterature [8a]. Anal. Calc. for L1Æ4H2O (C15H22N2O8, %): C, 50.27;H, 6.19; N, 7.82. Found (%): C, 50.38; H, 6.17; N, 7.67. Selective IRdata (KBr, cm�1): 1642, 1626 (vs, mas (COO)), 1568, 1509, 1470,1454(m, mC@C(phenyl and pyridyl rings)), 1370(vs, ms(COO)), 795,784(s, dC–H), 699 (m, dC@C).

[11] Complexes 1 and 2 were obtained by the same reaction method. Anaqueous solution (15 ml) of copper salt (0.2 mmol) (Cu(ClO4)2Æ6H2Ofor 1, Cu(NO3)2Æ3H2O for 2) and double betaine ligands L1

(0.32 mmol) was stirred at about 80 �C for several hours and thenfiltered. The filtrate was kept at room temperature for two weeks togive blue prismatic crystals suitable for X-ray analyses. Both obtainedcomplexes are stable in air. Yield: 37% (based on L1) for 1. Anal. Calc.(C30H38Cl4Cu3N4O30, %): C, 28.44; H, 3.02; N, 4.42%. Found (%): C,28.39; H, 3.05; N, 4.37%. Selective IR data (KBr, cm�1): 1645(vs,mas(COO)), 1575(m), 1488(m), 1464(w, mC@C(phenyl and pyridyl rings)),1416(vs, ms(COO)), 1096(s, m(ClO)), 780(m, dC�H), 695(m, dC@C),625(m, m(ClO)). Yield: 43% (based on L1) for 2. Anal. Calc.(C30H38Cu3N8O26, %): C, 32.25; H, 3.43; N, 10.03%. Found (%): C,32.34; H, 3.45; N, 10.12%. Selective IR data (KBr, cm�1): 1641(sh),1618(vs, mas(COO)), 1561(m), 1459(w, mC@C(phenyl and pyridyl rings)),1413(sh), 1383(vs, ms(COO)), 783(s, dC�H), 693(m, dC@C). Notes:Perchlorate salts of metal complexes are potentially explosive andshould be handled with care.

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