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PAPER View Article OnlineView Journal | View Issue

CrystEngCommThis journal is © The Royal Society of Chemistry 2014

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the

Structure of Matter, Chinese Academy of Sciences, Fujian, Fuzhou, 350002, China.

E-mail: ygy@fjirsm.ac.cn; Fax: +86 591 83710051

† Electronic supplementary information (ESI) available: X-ray crystallographicfile for 1 and 2 in CIF format, Table S1, Fig. S1–S10. CCDC 930243 (1) and930244 (2). For ESI and crystallographic data in CIF or other electronic formatsee DOI: 10.1039/c3ce42224k

Cite this: CrystEngComm, 2014, 16,

1885

Received 1st November 2013,Accepted 27th November 2013

DOI: 10.1039/c3ce42224k

www.rsc.org/crystengcomm

Constructing heterometallic frameworkswith highly connected topology based onedge-to-edge hexanuclear lanthanide clusters†

Wei-Hui Fang and Guo-Yu Yang*

Hydrothermal reactions of Sm2O3 and CuI with 4-pyridin-4-ylbenzoic acid afford two heterometallic

frameworks, namely, [Sm3Cu5I4L6(μ3-OH)2(OAc)(H2O)3]·ClO4·2H2O (1) (OAc = acetate) and

[Sm6Cu14I12L14(μ3-OH)4(H2O)5]·2ClO4·8H2O (2). X-ray crystal structure analyses reveal that these two 3D

pillared-layer heterometallic frameworks are both constructed from similar ribbon-like edge-to-edge

hexanuclear Ln clusters. Interestingly, the {Sm6}1 cores in 1 and {Sm6}

2 clusters in 2 are both connected

by carboxyls of L ligands into 1D Ln-cluster organic chains along the a axis. In 1, such chains are linked

by [CuL]− pillars and 1D stair-like [Cu4I4]n chains to give a pillared-layer 3D framework. Whereas in 2,

these chains are extended by the [CuL]− pillars and [Cu12I12]n layers to form a 3D framework. Remarkably,

to further stabilize the framework of 2, the [CuL]− pillars connect the {Sm6}2 clusters of neighbouring 1D

Ln-cluster organic chains interpenetrating through the 11-ring windows of [Cu12I12]n layers. Topological

analyses indicate that 1 and 2 possess a highly (6,14)-connected and a rare odd 11-connected topology,

respectively. Furthermore, the IR, TGA, PXRD, UV-Vis spectra of 1 and 2 have also been studied.

Introduction

Metal–organic frameworks (MOFs) have quickly developedinto a fruitful research area due to the aesthetics of diversearchitectures and their potential applications. To betterdescribe and understand these architectures, as well as pro-vide a blueprint for the design of new materials, networktopology is thus employed.1 Despite low connected networksbeing frequently synthesized, highly connected ones havebeen rarely achieved due to the limited coordination sites ofinorganic metal nodes and the steric hindrance of mostorganic ligands. To overcome this barrier and limitation,high-nuclearity metal clusters with larger sizes and morecoordination sites, but smaller steric hindrance, were used tosubstitute the single metal centers as nodes.2 Up to now,some successful instances of 8-,3 9-,4 10-,5 12-,6 and 14-connected7 nets have been realized by this strategy. Neverthe-less, 14-connected networks have been scarcely reported yetand few odd numbered connected cases are known. Thus,there still remains a great challenge for the exploration ofMOFs with highly connected nets.

On the basis of the above mentioned approach, two pri-mary issues should be solved for creating MOFs with highlyconnected nets. The first is how to make high-nuclearity inor-ganic metal clusters. At present, a common synthetic strategyis to control the hydrolysis of metal salts in the presence ofsupporting ligands. According to the documented records,the cluster chemistry of transition metals (TMs) is now well-established, whereas the analogous chemistry of lanthanides(Lns) is less developed for its variable and high coordinationnumbers as well as poor stereochemical preferences. Most ofthe resulting Ln clusters still possess discrete structures.8

Once the high-nuclearity TMs or Ln clusters are obtained, theaccompanying question is how to make them into extendedframeworks. Therefore, the next issue is the judicious choiceof supporting ligands. Inspired by the above strategy, ourgroup initiated a synthetic attempt based on the followingconsiderations: (1) Ln ions often display high and variablecoordination numbers, which make it possible to generatecomplex frameworks showing high connectivities; (2) makingthese Ln ions undergo hydroxo Ln cluster aggregation; (3)incorporating distinct Ln and Cu metal clusters as nodes toconstruct heterometallic MOFs with highly connected nets;(4) according to the hard–soft acid base theory, the (Ln–O)/(Cu–N) donor combinations are effective in framework con-struction as complementary to the hard/soft metal cationicacid and hard/soft donor base, thus, multifunctionalsupporting ligands containing mixed N/O donors should beintroduced. In prior research, hydrothermal reaction of Ln2O3

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and copper halide in the presence of isonicotinic acid (Hin), arigid ligand with O and N donors on opposite sides, has suc-cessfully afforded many heterometallic MOFs.9 In 2008, wereported a series of 3D (6,8)-connected net constructed fromcubane Ln4 and chair-like Cu4 clusters.10 With continuedexploration, we selected lengthened Hin, 4-pyridin-4-ylbenzoicacid (HL) as a ligand to avoid steric crowding around metalclusters. A search of the Cambridge Structural Database (CSD,Version 5.34, May 2013 update) found 73 crystal structuresencompassing HL, in which three quarters are TMs coordina-tion polymers.11 Whereas, our efforts in this area mainly focuson the assembly of the Ln and Ln–Cu analogues.12 In the con-tinuing development of highly connected MOFs incorporatingboth Ln and Cu clusters, we obtain a highly (6,14)-connectedframework and a rare odd 11-connected heterometallic frame-work based on edge-to-edge hexanuclear Ln clusters, formu-lated as, [Sm3Cu5I4L6(μ3-OH)2(OAc)(H2O)3]·ClO4·2H2O (OAc =acetate) (1) and [Sm6Cu14I12L14(μ3-OH)4(H2O)5]·2ClO4·8H2O(2), respectively.

Experimental sectionMaterials and physical measurements

All chemicals were commercially purchased and used withoutfurther purification. The elemental analyses (C, H and N) wereperformed on a Vario EL III elemental analyzer. The FT-IRspectra (KBr pellets) were recorded by using an ABB BomemMB 102 spectrometer over a range of 400–4000 cm−1.Thermogravimetric analyses (TGA) were performed on aMettler TGA/SDTA 851e analyzer with a heating rate of10 °C min−1 from 30 to 1000 °C under air atmosphere. PowderX-ray diffraction (PXRD) data were collected on a Rigaku MiniFlex II diffractometer using CuKα radiation (λ = 1.54056 Å)under ambient conditions. UV-Vis diffuse reflectance spectralmeasurements were carried out using a Perkin-Elmer Lambda950 spectrometer. The absorption spectra were calculatedfrom reflectance spectra using the Kubelka–Munk function.13

Synthesis of [Sm3Cu5I4L6(μ3-OH)2(OAc)(H2O)3]·ClO4·2H2O (1)

A mixture of Sm2O3 (0.5 mmol, 0.174 g), CuI (1 mmol, 0.190 g),HL (1.0 mmol, 0.199 g), NaOAc·3H2O (2.5 mmol, 0.340 g),H2O (16.0 mL, 0.35 mmol) and three drops of HClO4 with thepH value of about 2.0 was sealed in a 30 mL Teflon-lined bombat 200 °C for 8 days, and then cooled to room temperature.Orange prismatic crystals of 1 were recovered by filtration,washed with distilled water and dried at ambient temperature(yield 51% based on Sm2O3). Elemental analysis: calcd. forC74H63ClCu5I4Sm3N6O25: C 32.34, H 2.31, N 3.06. Found:C 32.60, H 2.51, N 3.67. IR (KBr pellet, cm−1): 3449(s), 2369(w),1647(m), 1591(s), 1554(vs), 1419(vs), 1222(w), 1100(s), 1010(w),827(w), 779(w), 735(m), 621(m).

Synthesis of [Sm6Cu14I12L14(μ3-OH)4(H2O)5]·2ClO4·8H2O (2)

A mixture of Sm2O3 (0.7 mmol, 0.244 g), CuI (0.7 mmol,0.133 g), HL (1.0 mmol, 0.199 g), H2O (10.0 mL, 0.22 mmol)

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and three drops of HClO4 with the pH value of about 2.0 wassealed in a 30 mL Teflon-lined bomb at 190 °C for 7 days, andthen cooled to room temperature. Dark red prismatic crystals of2 were recovered by filtration, washed with distilled water anddried at ambient temperature (yield 32% based on Sm2O3).Elemental analysis: calcd. for C168H142Cl2Cu14Sm6I12N14O53:C 30.62, H 2.17, N 2.97. Found: C 30.03, H 2.42, N 3.26. IR (KBrpellet, cm−1): 3431(s), 2365(w), 1642(m), 1604(s), 1554(vs), 1421(vs),1225(w), 1090(s), 1010(w), 827(w), 779(w), 735(m), 615(m).

X-ray crystallography study

The intensity data of 1 and 2 were collected at 293 K on aSuper-Nova, Dual, Atlas diffractometer with graphite-monochromatized CuKα radiation (λ = 1.54178 Å). The struc-ture was solved with the ShelXS structure solution programusing direct methods and refined with the ShelXL refinementpackage using least squares minimisation.14 Non-hydrogenatoms were refined anisotropically. Selected crystallographicdata and refinement details for 1 and 2 are summarized inTable 1, and selected bond lengths are listed in Table S1.†

Results and discussionSynthesis

The majority of the reported Ln–Cu frameworks were madeby means of conventional solution reactions.15 In this work,two heterometallic frameworks were obtained by the hydro-thermal reaction of Ln oxide, copper halide and HL at lowpH value. It should be mentioned that Ln oxides are rarelyused in solvent-based reactions due to their low solubility.16

In fact, contrast experiments have been carried out duringthis period of research, displaying that the final products didnot present any crystallinity if other Cu2+ salts such as copperacetate or nitrate were employed to replace CuI as the coppersource in the reaction system. In addition, the Cu centres in1 and 2 have an oxidation state of +1 according to bondvalence sum calculations.17 As compared to pentanuclear[LnIII

2CuII3(OH)4] without adjusting the pH value,18 the acid-

ity of the mixed solution must be adjusted carefully to pH = 2by adding HClO4, which is crucial for the formation of 1 and2, no single crystals were obtained without it or using otheracids such as H2SO4, HAc or HNO3 under similar conditions.The perchlorate can not only be used in the synthesis as apH regulator, but also be used as a special raw material neu-tralizing the positive charge of the framework. Remarkably,hexa-Ln cluster subunits with identical arrangement of Smions but different coordination geometries, denoted {Sm6}

1

and {Sm6}2 cores, are included in 1 and 2 (Scheme 1). It is

reported that terminal water molecules (OT) of Ni6 cores inPOM–organic frameworks can be substituted by a variety ofrigid carboxylates19 and acetate ligands.20 Similarly, it can beextended to our Ln–Cu systems that OAc− anions as chelatingligands in 1 replace OT from two ends of the hexa-Ln core in2. In acetate (OAc−), the carboxyl group generally acts as thechelating and terminal ligand to bond to a single cluster for

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Table 1 Crystal data and structure refinement for 1 and 2

Compound 1 2

Formula C74H63N6ClCu5I4O25Sm3 C168H142N14Cl2Cu14I12O53Sm6

Mr 2748.10 6590.32Crystal system Triclinic TriclinicSpace group P1̄ P1a/Å 11.1699(2) 11.2148(2)b/Å 14.0489(3) 17.3605(2)c/Å 27.7447(3) 26.9709(5)α/° 102.36(1) 84.0670(1)β/° 97.79(1) 85.012(2)γ/° 100.39(2) 71.920(2)V/Å3 4113.76(1) 4956.71(1)Z 2 1ρ/g cm−3 2.219 2.208μ/mm−1 29.935 5.186F(000) 2618 3120GOF on F2 0.991 1.027Collected reflns 68 085 50 878Unique reflns (Rint) 16 430 (0.0764) 28 838 (0.0322)Obsd reflns [I > 2(I)] 13 602 26 399Refined parameters 1053 2377R1

a /wR2b [I > 2(I)] 0.0760, 0.2019 0.0475, 0.1329

R1a /wR2

b (all data) 0.0881, 0.2164 0.0534, 0.1382

a R1 =P

||Fo| − |Fc||/P

|Fo|.b wR2 = {

P[w(Fo

2 − Fc2)2]/

P[w(Fo

2)2]}1/2.

Scheme 1 Schematic representation of the substitution of peripheralOT in hexa-Ln cores. Carboxylate oxygen atoms (OCOO−) of the Lligands are omitted for clarity. Colour codes: Sm green, O red, OT darkblue, C black.

Scheme 2 Coordination modes of the ligands in 1 (I, II) and 2 (I–III).

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further stabilizing the cluster, and the methyl group not onlypossesses large steric hindrance but also cannot act as thebridging ligands to link adjacent hexa-Ln clusters (Scheme 1).It is rarely observed that the small OAc− ligands act as thebridging ligands to link two large clusters by its two O atomsof the carboxyl because of the large repulsion interactionsbetween two adjacent clusters. If the acetate ligands inScheme 1 were replaced by the oxalate ligands, i.e. the methylof the OAc− ligand is replaced by the carboxyl, the adjacenthexa-Ln cluster can be linked together by the oxalate ligandsto form extended chains and layers based on the hexa-Ln clus-ter units. Therefore, the small size acetate ligands in 1 arehelpful for stabilizing and achieving edge-to-edge hexa-Lnclusters. In fact, when the oxalate ligands were used in thereaction system, 1 cannot be obtained. Accordingly, we specu-late that the remaining OT in 1 will further be substituted bythe acetates if the sterics permit. To some extent, such hexa-Lncluster units are stable under broad experimental conditions.

This journal is © The Royal Society of Chemistry 2014

Structure of [Sm3Cu5I4L6(μ3-OH)2(OAc)(H2O)3]·ClO4·2H2O (1)

A single crystal X-ray diffraction analysis reveals that complex1 is a 3D pillared-layer heterometallic framework and crystal-lizes in the triclinic system with space group P1̄. The asym-metric unit of 1 contains three unique Sm3+ ions, five Cu+

ions, four I− ions, six L ligands, two hydroxyls, one acetateligand, three coordinated water molecules, one ClO4

− groupand two crystallization water molecules (Fig. S1†). In thestructure, six L ligands present two types of coordinationmodes (Scheme 2): μ-L-κ1N,κ2O,O′ (mode I) and μ3-L-κ1N,κ1O,κ1O′ (mode II) in the ratio of 1 : 2, and the acetatedisplays a μ-L-κ1O,κ2O,O′ mode. The Sm1–Sm3 ions areeight-coordinated (Fig. S2a–c†): one hydroxyl and seven OCOO−

from four L ligands as well as one acetate for Sm1; four OCOO−

atoms from two L ligands and one acetate, two hydroxylsand a pair of coordinated water molecules for Sm2; fourOCOO− atoms from four L ligands, three hydroxyls and onecoordinated water molecule for Sm3. The coordinationgeometry is close to that of a distorted square antiprism forSm1, and bicapped trigonal prism for Sm2 and Sm3,

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Fig. 2 (a–b) View of the 1D chain and 2D heterometallic layer alongthe a axis. Acetate ligands are omitted for clarity. (c) Schematicrepresentation of the 6-connected pcu topology. The 1D chains and[CuL2]

− linkers are represented in black and green lines for clarity.

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respectively. The Sm–O distances vary from 2.302(1) to2.599(1) Å, with an average value of about 2.413 Å. TheCu1–Cu4 ions are four-coordinate with distorted tetrahedralgeometries (Fig. S2d†): I1, I1D, I2 and N1D for Cu1NI3; I1, I2,I3 and N2 for Cu2NI3; I2, I3, I4 and N3E for Cu3NI3; I3, I4,I4F and N4G for Cu4NI3, respectively. These Cu atoms arebridged by μ3-I1/I2/I3/I4 to form a chair-like Cu4I4 unit,further linked by identical μ3-I1D/I4F to give a 1Dstair-like [Cu4I4]n chain. The Cu–I bond lengths vary from2.605(1)–2.683(1) Å, which are comparable to related Cu–Icompounds.21 The Cu5 and Cu6 ions (Fig. S2e†) are linked bytwo pyridyl nitrogen (NPY) of L ligands in mode II, generatinglinear [CuL2]

− motifs. Similar linear motifs have also beenobserved in few reported Hin-base Ln–Cu heterometalliccomplexes.22

The Sm1–Sm3 ions are capped by two μ3-OH groups togive a triangular [Sm3(μ3-OH)2]

7+ unit, which is symmetry-related by an inversion center to form a centrosymmetricribbon-like [Sm6(μ3-OH)4]

14+, {Sm6}1, cluster with Sm⋯Sm

distances of 3.703, 3.953 and 4.004 Å (Fig. 1a). The planes ofthe two triangles in the {Sm6}

1 unit are strictly parallel, butnot coplanar, and the perpendicular distance between themis about 1.09 Å (Fig. 1b). The literature survey shows that thehexa-Ln compounds usually arrange in face-capped octahe-dral geometry with an interstitial μ6-O group.23 Other geomet-rical configurations are trigonal prism, macrocyclic clusterand the combination of two triangular Ln3 motifs linkedby the oxygen atoms.24 Compared with the reporteddouble-capped triangles in the head-to-head24c andedge-to-edge24d,24e arrangement, {Sm6}

1 here represents thefirst example of single-capped triangles in the edge-to-edgearrangement (Fig. S3†). Such a ribbon-like hexanuclear Lncore can also be intuitively described as four edge-sharingdefected cubane units. Then, such {Sm6}

1 cores are bridgedby carboxyl groups from the L ligands to form an infinite 1Dchain running along the a axis (Fig. 2a).

Additionally, the {Sm6}1 cores are further joined by [CuL2]

−

moieties into a 4-connected 2D Ln–organic–Cu heterometalliclayer on the bc plane (Fig. 2b). Thus, the total connection ofthe {Sm6}

1 cores by L ligands and [CuL2]− moieties can be

simplified as 6-connected 3D pcu network, which could bemore precisely described with the Schläfli symbol of (412·63)

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Fig. 1 Top (a) and side (b) view of the {Sm6}1 core in 1.

(Fig. 2c). Moreover, the pcu network is further furnished by1D stair-like [Cu4I4]n chains via Cu–N bonds to make a 3Dpillared-layer framework with narrow and long channels,where counterions and lattice water molecules are located(Fig. 3a). If those guest molecules are removed, 1 has a586.5 Å3 potential solvent volume estimated by PLATON,25

accounting for 14.3% of the total cell volume. From theperspective of network topology, each {Sm6}

1 cluster links six ofthe same clusters and eight Cu4I4 units via four linear [CuL2]

−

motifs and twelve L ligands (Fig. 3b). Whereas, each Cu4I4 unitconnects two of the same ones and four {Sm6}

1 clustersthrough four shared I− atoms and four L ligands (Fig. 3c).Therefore, the connection between two different types of metalclusters can be rationalized as a new binodal (6,14)-connectednet with the Schläfli symbol of (320·432·528·611)(38·46·5) byassigning the Cu4I4 as a six-connected node and the {Sm6}

1

cluster as a fourteen-connected node. The pcu net can beviewed as a subnet of this highly connected topology(Fig. 3d).

Structure of [Sm6Cu14I12L14(μ3-OH)4(H2O)5]·2ClO4·8H2O (2)

X-ray diffraction analysis reveals that 2 crystallizes in the tri-clinic system with chiral space group P1. The asymmetricunit of 2 contains six unique Sm3+ ions, fourteen Cu+ ions,twelve I− ions, fourteen L ligands, four hydroxyls, five coordi-nated water molecules, two ClO4

− groups and eight latticewater molecules (Fig. S4†). In the structure, fourteen Lligands present three types of coordination mode (Scheme 2)in the ratio of 3 : 9 : 2 for mode I, mode II and mode III,respectively. The Sm1–Sm4 and Sm6 ions are seven-coordinated with monocapped trigonal prism geometry(Fig. S5a–d, f†): four OCOO− (O1,O4,O17,O21A) from four L ligands,two coordinated water molecules (O1W,O2W) and one μ3-OH(O29) for Sm1; five OCOO− from five L ligands (O2,O5,O7,O15,O16) and two μ3-OH (O29,O30) for Sm2; four OCOO− (O14A,O19,O23,O25) from four L ligands and three μ3-OH groups(O29,O30,O31) for Sm3; four OCOO− (O3B,O8,O9,O22) from

This journal is © The Royal Society of Chemistry 2014

Fig. 3 (a) The overall 3D framework in 1. (b–c) Polyhedral and theschematic view of the linkages of the {Sm6}

1 (green) and the Cu4I4(pink) cores. (d) Schematic representation of the (6,14)-connected net.The pcu net built by Sm chains and [CuL2]

− motifs are marked in greenfor clarity.

Fig. 4 (a) Polyhedral view of the 1D chain in 2. (b) View of theinorganic [Cu12I12]n layer on the ab plane. The Cu nodes in the 11-ringwindows are emphasized in orange. (c) The framework extended bythe 1D Sm chains and the 2D Cu–I layers. The benzene and pyridinerings of the L ligands (mode I and III) are represented in black lines forclarity. (d) Overall framework of 2 showing rhombic channels alongthe a axis.

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four L ligands and three μ3-OH groups (O30,O31,O32) forSm4; four OCOO− (O10,O13,O20B,O28) from four L ligands,two coordinated water molecules (O4W,O5W) and oneμ3-OH group (O32) for Sm6. The Sm5 (Fig. S5e†) is eight-coordinated: five OCOO− (O11,O12,O24,O26,O27) from four Lligands, a coordinated water molecule (O3W) and two μ3-OHgroups (O31,O32). The coordination geometry is close to thatof a square antiprism. The Sm–O distances vary from2.275(8) to 2.510(1) Å, with an average value of about 2.418 Å.Fourteen Cu atoms adopt three types of coordination geome-try (Fig. S5g†): near-linear, distorted trigonal, and distortedtetrahedral geometries. The Cu1–Cu11 ions are all four-coordinated in distorted tetrahedral geometries. The Cu12ion adopts a distorted trigonal coordination geometry. TheCu–I bond lengths vary from 2.573(3) to 2.837(2) Å. Com-pared with linear [CuL2]

− moieties in 1, the Cu13 and Cu14ions in 2 form a near-linear26 [CuL2]

− coordination geometry.They are composed of two N atoms from two bridging Lligands with the Cu–N distance varying from 1.890(1) Å to1.940(1) Å, and angles of N–Cu–N are 160.4(8)° and 172.4(6)°,respectively.

This journal is © The Royal Society of Chemistry 2014

Six Sm3+ ions are linked by four μ3-OH groups to give asimilar four edge-sharing defected cubane [Sm6(μ3-OH)4]

14+

({Sm6}2) core. Each μ3-OH anion links three Sm ions with the

distances in the range of 2.373(9)–2.494(8) Å. In contrast withthe {Sm6}

1 core in 1, there is no inversion centre due to thedifferent coordination environment of Sm3+ ions. Similarly,the {Sm6}

2 cores here are also connected by carboxyls from Lligands to give a 1D chain along the a axis (Fig. 4a). TheCu1–Cu12 ions are linked by I atoms to give the Cu12I12 moi-eties, which are further connected by shared I atoms into aunique inorganic sql [Cu12I12]n layer on the ab plane withpeanut-like 11-ring windows, where the Cu nodes (Cu13,Cu14) are located (Fig. 4b). Although a variety of CuI sub-structures have been well documented,27a,27b 2D-layered CuImotifs are scarce.27c–27e Consequently, the linkage betweenthe 1D Ln-cluster organic chains and the parallel 2D[Cu12I12]n layers formed by L ligands in mode I and III givesrise to a 3D coordination framework (Fig. 4c). Besides theconnections between the 1D Ln–organic chains and the

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parallel [Cu12I12]n layers, the most striking structural featuresof compound 2 are the following linkages between the 1DLn-cluster organic chains along the c axis. To further stabilizethe sandwich framework, the Cu nodes through the 11-ringwindows of the Cu–I layers connect the {Sm6}

2 cores of1D Ln-cluster organic chains via the L ligands in mode II(Fig. 5a). The {Sm6}

2 clusters are projected exactly onto the11-rings of Cu–I layers viewing down the c axis (Fig. 5b).From the perspective of topology, the connections between1D Ln-cluster organic chains and [CuL2]

− can be regarded asa bipillared 4-connected sql net (Fig. 5c, d). Such overwhelm-ing linkages can be simplified as the self-interpenetration oftwo sql subnets (Fig. 5e, f). Remarkably, such interpenetra-tion has not been observed in Ln–Cu systems. In short,there are two types of linkages in 2: the connectionsbetween 1D Ln-cluster organic chains and the parallel Cu–Ilayers through L ligands in mode I and III; and the additionallinkages between 1D Ln-cluster organic chains by L ligandsin mode II. Both of them are indispensable in the formationof this interesting framework (Fig. 4d). All taken into consid-eration, the interpenetration in 2 is substantially differentfrom general n-fold interpenetration, but they both resultfrom stability reasons. The primary requirement for interpen-etration in 2 is the existence of the Cu–I layers. This is thekey reason that no such interpenetration phenomenonwas observed in 1. Another two necessary features are the

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Fig. 5 (a) Perspective drawing of the interpenetration, in which the Cunodes in the 11-ring windows are emphasized in orange. (b) Top viewof the interpenetration. (c–d) View of the bipillared layer and its corre-sponding topology. The Cu nodes are emphasized in orange. (e–f) Sideview and schematic illustration of the interpenetration. The green, andblue atoms represent the {Sm6}

2 cores, and Cu12I12 cores, respectively.The benzene and pyridine rings of L ligands are shown in orange linesfor clarity.

large enough windows on the Cu–I layer and the longenough pillars to link neighbouring hexa-Ln cluster nodes.It is speculated that similar interpenetration might beobserved between two parallel Ln-cluster organic layers. Thecounter-anions ClO4

− and guest water molecules occupy thevoid of the rhombic region of 0.9 × 2.7 nm. PLATON sug-gests a solvent accessible volume of ca. 14.8% (727.7 Å3) ofthe unit cell.

In order to illustrate the complicated framework moreclearly, the network topology is further analyzed. In thisarchitecture, each {Sm6}

2 core is linked by four of thesame cores and seven Cu12I12 moieties through four[CuL2]

− pillars and fourteen L ligands (Fig. 6a). Whereaseach Cu12I12 unit is surrounded by four neighbouringCu12I12 units and seven {Sm6}

2 cores via shared the Iatoms and nine L ligands (Fig. 6b). Therefore, both {Sm6}

2

and Cu12I12 cores can be rationalized as 11-connectednodes, and the resulting structure of 2 is a uninodal11-connected bcu-x net with the Schläfli symbol (318·423·513·6)(Fig. 6c). Although several eight-connected bcu28 networkshave been reported, such a bcu-x network has scarcelybeen documented because it requires a larger metal clusteras the eleven-connected node. According to recentapproaches in the analysis of highly connected frameworksbased on the visualization of the structures as combina-tions of interconnected layered 2D sheets or subnets,2a the11-connected net of 2 can be described as interpenetrated4-connected nets with each center providing seven addi-tional links to each other. So the interpenetrated4-connected net can be regarded as a subunit of the final3D 11-connected net.

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Fig. 6 (a–b) Polyhedral and schematic view of the linkages of {Sm6}2

(green) and Cu12I12 (pink) cores in 2. (c) Schematic representation ofthe 11-connected net. The 4-connected net of heterometallic andcopper halide layers are emphasized in green and pink lines.

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Comparison of structures

In comparison to the discrete hexa-Ln clusters with edge-to-edge arrangement of two double-capped triangles, two single-capped triangles with edge-to-edge arrangement presentedhere are extended by different copper halide motifs into twoheterometallic pillared-layer MOFs with highly connectedtopology. Despite the acetate and terminal water moleculesoccupying the ends of the hexa-Sm cluster in 1 and 2, the{Sm6}

1 in 1 and {Sm6}2 in 2 are both linked by the carboxyls

of L ligands to form 1D chains running along the a axis.However, there are some obvious differences between 1 and2: (1) the space group: 1 crystallizes in centrosymmetric P1̄space group, while 2 crystallizes in chiral P1 space group; (2)1D Ln-cluster organic chains extended by [CuL2]

− into differ-ent nets (Fig. 2b, c; 5c, d). Although the similar hexa-Sm clus-ters are surrounded by four [CuL2]

− motifs in 1 and 2, the{Sm6}

1 core connects four of the same ones, and the {Sm6}2

core is bipillared to two of the same ones. As a result, the 1DLn–organic chains in 1 and 2 are bridged into 6-connectedpcu (Fig. 2c) and 4-connected sql nets (Fig. 5d), respectively;(3) different copper halide motifs: 1D stair-like [Cu4I4]nchains in 1 and 2D rhombic grid [Cu12I12]n layers in 2; (4)overall topology: highly (6,14)-connected topology in 1 and arare odd 11-connected topology in 2. Similar hexa-Ln {Sm6}

1

and {Sm6}2 cores but different linkages exist in 1 and 2, in

which the some coordination sites of the {Sm6}1 and {Sm6}

2

cores are occupied by the acetate groups and terminal watermolecules, resulting in that fewer L ligands bond to the{Sm6}

1 and {Sm6}2 cores (16 and 18 L ligands on {Sm6}

1 and{Sm6}

2 cores, respectively). If the above mentioned acetategroups and coordination water molecules are replaced by thesame number of the L ligands, the number of the L ligandsbonded to the {Sm6}

1 and {Sm6}2 cores will sum to 24 and 23,

respectively (Fig. S6†). In addition, the correspondingcopper(I) halide cluster in 1 is smaller than that of 2,resulting in many more copper(I) halide clusters surroundingthe {Sm6}

1 core, such as 14 Cu4I4 clusters encircleing the{Sm6}

1 core and only 11 Cu12I12 clusters encircling the {Sm6}2

core; (5) sizes and shapes of the channels: long and narrowchannels in 1, whereas rhombic channels exist in 2. The for-mation of 1 and 2 shows that it is possible to make differentMOFs based on the same or similar Ln structural buildingunits.

PXRD

The experimental PXRD patterns of 1 and 2 are in goodagreement with the simulated PXRD patterns from thesingle-crystal X-ray diffraction, indicating the high purity ofthe synthesized samples (Fig. S7†).

IR spectroscopy

The characteristic features of L ligands dominate the IR spec-tra of 1 and 2 (Fig. S8†). The strong and sharp absorptionbands around 3400 cm−1 are assigned as the characteristicpeaks of –OH vibration. The strong vibrations at about 1600

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to 1400 cm−1 are corresponding to the asymmetric andsymmetric stretching vibrations of the carboxyl group, respec-tively. Strong and characteristic Cl–O symmetric stretchingfrequencies around 1100 and 620 cm−1 are observed for theClO4

− counterions. The lack of strong bands around 1700 cm−1

indicate that the HL ligands are deprotonated.

TGA

To examine the thermal stability of the heterometallic frame-works, TGA of 1 and 2 were examined in air atmosphere from30 to 1000 °C (Fig. S9†). Their TG curves show weight lossfrom 30 to 800 °C corresponding to the release of lattice andcoordination water molecules, organic ligands, counterionsand dehydration of hydroxyl groups (calcd/found 1 66.4/66.5%; 2 67.1/66.6%). Assuming that the residue correspondsto Sm2O3 and CuO, the observed weights are in good agree-ment with the calculated values (calcd/found 1 33.6/33.5%;2 32.9/33.3%).

UV-Vis absorption spectra

The diffuse reflectance absorption spectra of 1 and 2 arerecorded. The optical absorption spectra indicate that 1 and2 exhibit strong and similar optical absorption in the visibleregion, with estimated optical band gaps of 2.19 and 2.14 eV(Fig. S10†). These band gap sizes are significantly smallerthan the previous literature value for CuI (2.92 eV).10,14b

Conclusion

In summary, we have synthesized and characterized twopillared-layer frameworks with highly connected topologies.They represent unprecedented examples of heterometallicframeworks with highly and odd connected topology basedon the single-capped edge-to-edge hexa-Ln clusters. Com-pared to our previous Ln–Hin–Cu system, the rare linear andnear-linear [CuL2]

− moieties more frequently appear in theselong pillared frameworks.12c Obviously, the incorporation ofCu(I) halide plays an important role in the formation of thefinal (6,14)-connected and 11-connected net. The successfulisolation of 1 and 2 not only demonstrates that the replace-ment of single metal ions with metal clusters as nodes is afeasible route to make highly connected topologies, but alsoconfirms the significant potential of this strategy. Furthersystematic studies for the synthesis of highly connectedframeworks with high nuclearity Ln-based clusters arecurrently under way.

Acknowledgements

This work was supported by the NNSF of China(nos. 91122028, 21221001, and 50872133), the 973 Program(nos. 2014CB932101 and 2011CB932504), and the NNSF forDistinguished Young Scholars of China (no. 20725101).

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