Inorganic Chemistry Communications 12 (2009) 426–429

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Inorganic Chemistry Communications

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A neodymium coordination polymer with mixed m-phenylenediacrylate andformate bridges: Synthesis, unprecedented topology, and magnetism

Qian Sun, Jian-Yong Zhang, Hua Tian, Yan-Qin Wang, En-Qing Gao *

Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, Shanghai 200062, China

a r t i c l e i n f o

Article history:Received 24 December 2008Accepted 6 March 2009Available online 17 March 2009

Keywords:LanthanideCoordination polymerSolvothermal synthesisMagnetic properties

1387-7003/$ - see front matter � 2009 Elsevier B.V. Adoi:10.1016/j.inoche.2009.03.002

* Corresponding author. Tel./fax: +86 21 62233404E-mail address: eqgao@chem.ecnu.edu.cn (E.-Q. G

a b s t r a c t

A new lanthanide(III) coordination polymer with mixed m-phenylenediacrylate (mpda) and formatebridges, [Nd(mpda)(HCOO)(H2O)]n was synthesized by a solvothermal reaction involving the in situ for-mation of formate from N,N-dimethyl formamide. The three-dimensional metal-organic framework con-tains l3-formate-bridged Nd(III) layers pillared by the mpda ligand and exhibits an unprecedented 3,7-connected topology with Schläfli symbol (4,62)2(42,6)(47,64,810). The magnetic properties are typical ofthe Nd(III) 4I9/2 ground state perturbed by ligand field and probable antiferromagnetic exchange throughtriple l2-oxygen bridges.

� 2009 Elsevier B.V. All rights reserved.

Metal-organic coordination polymers have been under intenseinvestigations because of their diverse architectures and potentialapplications in catalysis, gas storage, molecular recognition, optics,and magnetism [1–7]. To get designed and predictable frameworksand properties, an enormous amount of research is being focusedon constructing novel coordination polymers by choosing versatileorganic ligands and functional metal ions [8–10]. Lanthanide met-als are good choices for building multidimensional coordinationpolymers and have attracted more and more attentions for theirfantastic coordination properties and special chemical/physicalcharacteristics arising from 4f electrons [11–14]. Although greatachievements have been made in the crystal engineering of somecoordination networks with specific topologies properties, preciseprediction of the outcome is not always possible, especially forthe f-block metal ions due to their versatile coordination numbersand flexible coordination geometry. As far as the ligands are con-cerned, the rigid aromatic polycarboxylates, such as benzenedi-carboxylates, benzenetricarboxylates and biphenyldicarboxylates,are the most extensively studied organic ligands in the construc-tion of metal-organic coordination materials [15–20]. The searchof new organic ligands with different coordination habits is still afundamental task for the crystal engineering of coordination poly-mers. Here we report a new lanthanide polymer arising from m-phenylenediacrylate (mpda), which has not yet been explored incoordination chemistry. The ligand resembles m-phenylenedicarb-oxylate in coordination orientations and rigidity but has expandedspace between the carboxylate groups. The present compound[Nd(mpda)(HCOO)(H2O)]n (1) contains mixed mpda and formate

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.ao).

ligands and exhibits a 3D coordination framework in which l3-for-mate bridged Nd(III) layers are pillared by the mpda ligand in a l4

mode (Scheme 1). The structure displays a new and complicated(4,62)2(42,6)(47,64,810) topology. The magnetic properties have alsobeen investigated.

The title compound 1 was synthesized from the hydrothermalreaction of Nd(NO3)3 � 6H2O and H2mpda in an mixed solvent ofDMF, water and pyridine [21]. The FT-IR spectrum shows the char-acteristic absorption peaks of the main functional groups for the ti-tle compound. The strong absorption bands at 1645 and 1600 cm�1

are assignable to the asymmetric carboxylate vibrations [vas(COO)]for mpda and formate, respectively, and the very strong band at1380 cm�1 and the shoulder absorption at 1400 cm�1 can beattributed to vas(COO). It should be noted that the formate ligandis generated from the in situ hydrolysis of DMF. The in situ hydro-lysis of DMF under hydrothermal conditions to give coordinationcompounds with formate has been documented previously [22–26]. However, compound 1 could not be synthesized in the absenceof DMF, using formic acid or sodium formate as the formate source.We have also performed the experiment in the water or alcoholsystem, yet not any characterizable materials were obtained. Thethermal stability of the title compound was investigated on thecrystalline samples under nitrogen atmosphere from 25 to1000 �C (Fig. S1). The first weight loss of 4.0% begins at 180 �Cand completes at 260 �C (centered around 250 �C, according tothe differentiate curve), corresponding to the loss of coordinationwater molecules (calc. 4.1%). The compound undergoes a rapidand large weight loss above 380 �C, due to the decomposition ofthe formate and mpda ligands. The curve reaches a constant valueabove 950 �C, the residue weight (62%) corresponding to Nd2O3

(calc. 61%).

Table 1Selected bond distances (Å) and angles (�) for 1

Nd1–O4 2.414(4) Nd1–O2A 2.470(4)Nd1–O6B 2.491(4) Nd1–O5C 2.504(4)Nd1–O1 2.522(4) Nd1–O3D 2.530(4)Nd1–O5E 2.551(4) Nd1–O7 2.608(5)Nd1–O6D 2.677(4) Nd1–O2 2.865(5)

O4–Nd1–O2A 140.87(15) O4–Nd1–O6B 140.28(15)O2A–Nd1–O6B 67.57(14) O4–Nd1–O5C 129.58(16)O2A–Nd1–O5C 70.44(14) O6B–Nd1–O5C 79.47(13)O4–Nd1–O1 80.44(16) O2A–Nd1–O1 138.04(14)O6B–Nd1–O1 83.00(14) O5C–Nd1–O1 75.43(14)O4–Nd1–O3D 68.99(15) O2A–Nd1–O3D 72.46(14)O6B–Nd1–O3D 132.80(14) O5C–Nd1–O3D 109.79(13)

O1–Nd1–O3D 144.05(15) O4–Nd1–O5E 95.42(14)O2A–Nd1–O5E 65.96(14) O6B–Nd1–O5E 69.66(13)O5C–Nd1–O5E 133.43(10) O1–Nd1–O5E 131.32(14)O3D–Nd1–O5E 71.86(13) O4–Nd1–O7 69.76(16)O2A–Nd1–O7 128.12(16) O6B–Nd1–O7 70.61(14)O5C–Nd1–O7 129.24(14) O1–Nd1–O7 61.29(15)O3D–Nd1–O7 120.71(15) O5E–Nd1–O7 71.73(15)O4–Nd1–O6D 78.75(15) O2A–Nd1–O6D 81.65(14)O6B–Nd1–O6D 140.86(5) O5C–Nd1–O6D 67.44(13)

O1–Nd1–O6D 107.10(13) O3D–Nd1–O6D 49.78(13)O5E–Nd1–O6D 119.68(13) O7–Nd1–O6D 147.66(14)O4–Nd1–O2 70.18(14) O2A–Nd1–O2 125.83(13)O6B–Nd1–O2 120.90(13) O5C–Nd1–O2 60.77(13)O1–Nd1–O2 47.58(13) O3D–Nd1–O2 102.43(13)O5E–Nd1–O2 165.58(12) O7–Nd1–O2 101.48(14)O6D–Nd1–O2 59.59(12)

Transformations used to generate equivalent atom: A: �x + 1, y � 1/2, �z + 3/2; B:�x + 2, y � 1/2, �z + 3/2; C: x, �y + 1/2, z � 1/2; D: x � 1, y, z; E: �x + 1, �y, �z + 2;

Scheme 1. Coordination modes of the ligands in 1.

Q. Sun et al. / Inorganic Chemistry Communications 12 (2009) 426–429 427

Single crystal X-ray analyses [27] revealed that compound 1 is athree-dimensional framework containing formate ion and mpda asbridging ligands, with 10-coordinated neodymium centers. The lo-cal environment around Nd(III) ion is depicted in Fig. 1. The asym-metric unit contains one Nd(III) ion, one mpda ligand, one formateion and a water molecule. Each Nd(III) ion is coordinated by twochelating carboxylate groups from two mpda ligands, two carbox-ylate oxygen atoms from another two mpda ligands, three oxygenatoms from three formats, and a water molecule, defining a dis-torted polyhedron with 16 triangular faces. The Nd–O bond dis-tances range from 2.414(4) to 2.865(5) Å (Table 1), close to thepreviously reported Nd–O lengths [28–30]. The formate ions actas l3-O,O0:O bridges and link Nd(III) ions into a 2D layer alongthe bc plane (Fig. 2a). The intra-layer Nd–Nd distances separatedby the l2-O atom (O5) and the OCO group are 4.05 and 7.00 Å,respectively. The 2D layer is unprecedented in the domain of lan-thanide chemistry and features two types of cyclic structural mo-tifs: the eight-membered bimetallic ring in which metal ions arelinked by two OCO bridges, and the 12-membered tetrametallicring in which metal ions are linked by alternating l2-O and OCObridges. Topologically, the l2-O atoms as well as the Nd atomscan be taken as three-connecting nodes, and thus the Nd-formatelayer can be regarded as a binodal 2D net with Schläfli symbol 4�82.

The mpda ligand adopts a bis(bidentate) bridging coordinationmode connecting four Nd atoms and serves as a V-shaped pillarinterlinking the Nd-formate layers. Each carboxylate group che-lates a Nd atom and binds an additional Nd atom through an oxy-gen atom (O2 or O6), which acts as additional l2-O bridge betweenthe Nd atoms bridged by l2-O from formate. Actually, the nearestneighboring Nd atoms in 1 are bridged by three l2-O atoms, one(O5) from a formate ion and two (O2 and O6) from two different

Fig. 1. Coordination environment of Nd(III) in 1 with the ellipsoids draw

mpda ligands. As a result, a 1D chain motif with triple l2-O bridgesis formed along the b direction (Fig. 2b). The chains are interlinkedinto a complicated 3D network by the formate O–C–O groups inthe c direction and by the mpda ligands in the a direction (Fig. 3).

For topological analysis, it is convenient to take all the l2-Oatoms as three-connecting nodes and reduce the other parts ofthe ligands to simple linkers between nodes. Then the Nd atomscan be regarded as seven-connecting nodes, and the network is re-duced to a complicated trinodal 3,7-connected 3D net with Schläflisymbol (4,62)2(42,6)(47;64;810) (Fig. S2). To our knowledge, thistopology is unprecedented in the literature [31,32].

The temperature dependence of the magnetic susceptibility inthe range of 2–300 K for 1 was measured at 1000 Oe and is shownas vM–T and vMT–T plot in Fig. 4. For Nd(III) ions, the 4I9/2 groundstate is well separated (by about 2000 cm�1) in energy from thefirst excited state, and hence only the ground state is thermallypopulated at room temperature and below. The vMT of 1 at room

n at the 50% probability level, hydrogen atoms omitted for clarity.

Fig. 2. (a) The 2D layer constructed from Nd(III) and formate ions. (b) The 1D chainwith triple l2-O bridges along the b direction.

Fig. 3. The 3D structure of compound 1 (hydrogen atoms and water molecules areomitted for clarity).

Fig. 4. Magnetic susceptibility of 1 plotted as vM versus T (left axis) and vMT versusT (right axis). Inset: Thermal variation of v�1

M of 1.

428 Q. Sun et al. / Inorganic Chemistry Communications 12 (2009) 426–429

temperature is equal to 1.64 emu mol�1 K. This value is in goodagreement with the value (1.64 emu mol�1 K) calculated accordingto the equation v = (Nb2gJ

2J(J + 1)/3kT (J = 9/2, gJ = 8/11) [33]. As T islowered, vMT decreases more and more rapidly, and finally reaches0.87 emu mol�1 K at 2 K. The data above 120 K follows the Curie–Weiss law with C = 1.84 emu mol�1 K and h = �38.5 K [34]. Thethermal dependence of vMT should mainly arise from two concur-rent effects. (i) Ligand-field perturbation, which splits the 4I9/2

ground term into several sub-levels, the details dependent uponthe local symmetry around the metal ion. At room temperature,all the sub-levels are populated, and upon cooling, the sub-levelsof higher energy are progressively depopulated. (ii) The magneticexchange between the neighboring Nd(III) ions that are closelybridged by three l2-O atoms. The exchange between 4f ions is ex-pected to be small but its influence on vMT becomes important atlow temperature. The theoretical simulation of the magnetic prop-erties of 1 is impossible, because no model combining single-ionspin-orbit coupling, ligand field, magnetic exchange, and Zeemanperturbation is available.

In conclusion, a novel 3D lanthanide coordination polymer withhigh thermal stability has been synthesized from Nd(III) andH2mpda by a solvothermal technique and characterized by X-raydiffraction analysis and magnetic measurements. The structurecontains l3-formate-bridged Nd(III) layers pillared by the mpda li-gand and exhibits an unprecedented 3,7-connected net topology.The magnetic properties are typical of the 4I9/2 ground state per-turbed by ligand field and antiferromagnetic exchange.

Acknowledgements

The authors thank the NSFC (20571026 and 20771038), Shang-hai Leading Academic Discipline Project (B409), and STCSM(06SR07101) for financial supports.

Appendix A. Supplementary material

CCDC 714518 contains the supplementary crystallographic datafor 1. These data can be obtained free of charge from The Cam-bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-ta_request/cif. Supplementary data associated with this articlecan be found, in the online version, at doi:10.1016/j.inoche.2009.03.002.

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