Unusual Ni−Ag Mixed-Metal, Mixed-Valence, and Cluster-Containing

May 31, 2008 - Complete Ag4M2(DMSA)4 (M = Ni, Pd, Pt, DMSA = Dimercaptosuccinic Acid) Cluster Series: Optical Properties, Stability, and Structural ...
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CRYSTAL GROWTH & DESIGN

Unusual Ni-Ag Mixed-Metal, Mixed-Valence, and Cluster-Containing Coordination Polymers Generated from Nickel-Macrocyclic Ligand and Silver Ion by Metal-Exchange Qiang Zhang, Jian-Ping Ma, Ping Wang, Zhi-Qiang Shi, Yu-Bin Dong,* and Ru-Qi Huang

2008 VOL. 8, NO. 7 2581–2587

College of Chemistry, Chemical Engineering and Materials Science, Key Laboratory of Molecular and Nano Probe, Engineering Research Center of Pesticide and Medicine Intermediate Clean Production, Ministry of Education, Shandong Normal UniVersity, Jinan, 250014, P. R. China ReceiVed March 19, 2008

ABSTRACT: A new nickel-macrocyclic complex [Ni(L)] · CH2Cl2 (1, L ) C24H22N4O3) was synthesized based on a bent oxadiazole bridging ligand terminated by tetradentate N2O2 Schiff-base units. Two novel Ni-Ag mixed-metal, mixed-valence, and clustercontaining coordination polymers, namely, [Ag2Ni(L)](ClO4)2.5 (2) and [Ag2Ni(L)](BF4)2.5 (3), generated from 1 and AgX (X ) ClO4-, BF4-) were synthesized. During the reactions, unexpected metal-exchange and metal valence-change were observed. These two Ni-Ag coordination polymers are isostructural. They all feature a two-dimensional double-layered concavo-convex structure which is composed of a dual-bowl unit and mixed-valent NiII2NiIII2 cluster node. Compounds 1-3 were fully characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction. In addition, the luminescent properties of 1-3 were investigated primarily. Introduction 1

Compared to common coordination polymers, the design and synthesis of mixed-metal, and/or mixed-valence coordination polymers have received considerably less attention. To date, only a handful of such polymeric complexes have been reported.2,3 In principle, the simultaneous presence of different metal centers or different valent metal centers should increase the diversity and complexity of the polymeric structures (influenced by the different oxidation states and coordination predisposition). Additionally, such coordination polymers have great application potential for superior physical properties resulting from the incorporation between the distinct metal ions or different valent metal centers. So far, there are basically two approaches to access mixed-metal or mixed-valence coordination polymers: (1) Two-step approach: starting with the use of presynthesized metal-containing complexes with uncoordinated donors to combine with the second type of metal ion or valent metal ion.2,3 (2) One-step approach: the use of multidentate organic spacers to bind two different types of metal ions or two different valent metal ions in a one-pot reaction.2,3 Both approaches have been proven to be very useful to construct mixed-metal or mixed-valence coordination polymers. We earlier explored the rational design and construction of mixed-metal coordination polymers based on a “two-step approach” by combination of the neutral metalloligand with the second type of metal ion. In our previous cases, however, metalcontaining ligands always retain their molecular geometry, and no metal-exchange and valence-change has been observed during the reactions.2c,d Recently, we have designed and synthesized some neutral metallamacrocycles based on the bent oxadiazole bridging spacers which are end-capped by the chelating N2O2 Schiffbase coordination sites. Considering the uncoordinated oxadiazole-N donors on these neutral bimetallic rings,4 we wondered if these complexes could be used as metal-containing ligands to bind the second type of metal ion into heterometallic * To whom correspondence should be addressed. E-mail: yubindong@ sdnu.edu.cn.

coordination polymers. We report herein the synthesis and structural characterization of a new metal-containing macrocyclic ligand [Ni(L)] · CH2Cl2 (1; L ) C24H22N4O3) and two novel Ni-Ag mixed-metal, mixed-valence, and cluster-containing coordination polymers, namely, [Ag2Ni(L)](ClO4)2.5 (2) and [Ag2Ni(L)](BF4)2.5 (3), generated from 1 and AgX (X ) ClO4and BF4-) (Scheme 1). During the reactions, unexpected metalexchange and metal valence-change were observed. Experimental Section Materials and Methods. AgX (X ) ClO4- and BF4-) and Ni(OAc)2 · 4H2O (Acros) were used as obtained without further purification. The LH was synthesized according to the literature method previously reported by us.4 Infrared spectroscopy (IR) samples were prepared as KBr pellets, and spectra were obtained in the 4000-400 cm-1 range using a Perkin-Elmer 1600 FTIR spectrometer. Elemental analyses were performed on a PE2400II analyzer. X-ray photoelectron spectroscopy data were obtained with an ESCALab220i-XL electron spectrometer from VG Scientific using 300W Al KR radiation. The base pressure was about 3 × 10-9 mbar. The binding energies were referenced to the C1s line at 284.8 eV from adventitious carbon. The metal microanalyses (ICP) were carried out using IRIS INTIETID2 spectrometer. Caution. Two of the crystallization procedures involve metal perchlorate, which is a strong oxidizer. Synthesis of 1. A solution of Ni(OAc)2 · 4H2O (25.4 mg, 0.10 mmol) in EtOH (8 mL) was layered onto a solution of LH (20.0 mg, 0.048 mmol) in CH2Cl2 (8 mL). The solutions were left for about one week at room temperature, and brown crystals were obtained. Yield, 87%. IR (KBr pellet cm-1): 3067 (m), 2917(m), 1612 (vs), 1573(vs), 1554(s), 1517(s), 1482(s), 1404(s), 1284(s), 1229(m), 1191(m), 1064(m), 1024(m), 947(m), 905(m), 861(m), 800(m), 726(s), 690(s). Elemental analysis (%) calcd for C25H24 Cl2N4NiO3: C 53.75, H 4.30, N 10.03; Found: C 53.31, H 4.11, N 9.98. Synthesis of 2. A solution of AgClO4 (20.0 mg, 0.096 mmol) in toluene (8 mL) was layered onto a solution of 1 (20.0 mg, 0.036 mmol) in CH2Cl2 (8 mL). The solutions were left for about three days at room temperature, and light brown crystals Ag2Ni(C24H22N4O3) · 2.5(ClO4) were obtained. Yield, 86.4%. IR (KBr pellet cm-1): 3068(m), 2933(m), 1612(s), 1551(s), 1492(m), 1429(s), 1358(m), 1317(s), 1286 (s), 1218(m), 1196(s), 1090(vs), 1039(vs), 928(m), 853(s), 796(m), 741(m), 701(m), 681(m), 622(m), 539(m), 498(w). Elemental analysis (%) calcd for C24H22Ag2Cl2.50N4NiO13: C 30.72, H 2.35, N 5.97; Found: C 30.44, H 2.11, N 5.73.

10.1021/cg800293x CCC: $40.75  2008 American Chemical Society Published on Web 05/31/2008

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Scheme 1. Synthesis of Ni-Ag Cluster-Containing Heterometallic Mixed-Valence Coordination Polymers

Table 1. Crystallographic Data for 1-4 empirical formula fw cryst syst a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) space group Z value F calc (g/cm3) µ (Mo KR) (mm-1) temp (K) no. of observations (I > 3σ) final R indicesa [I > 2σ(I)]: R; Rw a

C25H24Cl2N4NiO31 (1) 558.09 monoclinic 12.888(2) 14.242(2) 14.886(3) 90 111.843(3) 90 2536.1(8) P2(1)/c 4 1.462 1.010 293(2) 4454 0.1026; 0.2052

C24H22Ag2Cl2.50N4NiO13 (2) 937.53 tetragonal 22.6562(10) 22.6562(10) 12.3186(8) 90 90 90 6323.2(6) P4/n 8 1.970 2.097 293(2) 5577 0.0711; 0.2065

C24H22Ag2B2.50F10N4NiO3 (3) 905.93 tetragonal 22.5368(19) 22.5368(19) 12.143(2) 90 90 90 6167.7(13) P4/n 8 1.951 1.957 293(2) 5451 0.0699; 0.1851

C25H27Ag2Cl5N4O12 (4) 968.50 triclinic 10.144(2) 10.983(2) 16.335(4) 93.147(4) 98.088(4) 104.386(4) 1737.7(7) P1j 2 1.851 1.575 293(2) 5723 0.0967; 0.2908

R1 ) Σ|Fo| - |Fc|/Σ |Fo|. wR2 ) {Σ[w(Fo2 - Fc2)2]/Σ[w(Fo2)2]}1/2.

Synthesis of 3. A solution of AgBF4 (20.0 mg, 0.10 mmol) in toluene (8 mL) was layered onto a solution of 1 (20.0 mg, 0.036 mmol) in CH2Cl2 (8 mL). The solutions were left for about three days at room temperature, and light brown crystals were obtained. Yield, 86%. IR (KBr pellet cm-1): 3076(m), 2923(m), 1611(s), 1559(s), 1499(m), 1477(s), 1378(m), 1356(s), 1320 (s), 1282(m), 1188(s), 1071(vs), 1011(vs), 930(m), 817(s), 744(m), 685(m), 629(m). Elemental analysis (%) calcd for C24H22Ag2B2.50F10N4NiO3: C 31.79, H 2.43, N 6.18; Found: C 31.59, H 2.13, N 6.09. Synthesis of 4. A solution of AgClO4 (0.010 mmol) and Ni(OAc)2 · 4H2O or Ni(ClO4)2 (0.005 mmol) in toluene (8 mL) was carefully layered onto a solution of LH or L2- (0.005 mmol) in CHCl3 (8 mL). The solutions were left for about one week at room temperature, and colorless crystals of 4 were obtained. Yield, 89%. IR (KBr pellet cm-1): 3233(s), 2906(w), 1618(s), 1491(w), 1430(s), 1360(vs), 1318(s), 1289(s), 1118(s) 1089(s) 857(w), 622(s), 540(m) 479 (s). Elemental analysis (%) calcd for Ag2C25H27Cl5N4O12: C 30.98, H 2.78, N 5.78; Found: C 31.29, H 2.53, N 5.59. Single-Crystal Structure Determination. Suitable single crystals of 1-4 were selected and mounted in air onto thin glass fibers. X-ray intensity data were measured at 293 K on a Bruker SMART APEX CCD-based diffractometer (Mo KR radiation, λ ) 0.71073 Å). The raw frame data for 1-4 were integrated into SHELX-format reflection files and corrected for Lorentz and polarization effects using SAINT.5 Corrections for incident and diffracted beam absorption effects were applied using SADABS.5 None of the crystals showed evidence of crystal decay during data collection. All structures were solved by a

Table 2. Interatomic Distances (Å) and Bond Angles (°) with esds () for 1a Ni(1)-O(3)#1 Ni(1)-N(3) N(4)-Ni(1)#1

1.805(5) Ni(1)-O(2) 1.931(6) Ni(1)-N(4)#1 1.936(6) O(3)-Ni(1)#1

O(3)#1-Ni(1)-O(2) 178.5(3) O(2)-Ni(1)-N(3) 92.5(2) O(2)-Ni(1)-N(4)#1 87.9(2) C(17)-N(4)-Ni(1)#1 124.2(5) C(12)-O(2)-Ni(1) 128.3(5)

1.824(5) 1.936(6) 0.805(5)

O(3)#1-Ni(1)-N(3) 87.2(2) O(3)#1-Ni(1)-N(4)#1 92.5(2) N(3)-Ni(1)-N(4)#1 179.3(3) C(19)-N(4)-Ni(1)#1 118.4(5) C(15)-O(3)-Ni(1)#1 131.1(5)

a Symmetry transformations used to generate equivalent atoms: #1 -x, -y + 2, -z.

combination of direct methods and difference Fourier syntheses and refined against F2 by the full-matrix least-squares technique. Crystal data, data collection parameters, and refinement statistics for 1-4 are listed in Table 1. Relevant interatomic bond distances and bond angles for 1-4 are given in Tables 2–5.

Results and Discussion Metalation of LH with Ni(OAc)2 in a EtOH/CH2Cl2 mixed solvent system at room temperature afforded the neutral metallamacrocycle Ni2L2 (1) in high yield. The single crystal structure of 1 revealed that two deprotoned L2- ligands act as

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Table 3. Interatomic Distances (Å) and Bond Angles (°) with esds () for 2a Ag(1)-O(2) Ni(1)-N(1) Ni(1)-N(1′)#2 Ni(1)-Ni(1)#2 O(3)-Ag(2)-C(20) N(1)-Ni(1)-N(1′)# N(1)-Ni(1)-Ni(1)#1 N(1′)#2-Ni(1)-Ni(1)#1 N(1)-Ni(1)-Ni(1)#2) N(1′)#2-Ni(1)-Ni(1)#2 N(2)-N(1)-Ni(1) N(2′)-N(1′)-Ni(1)#1

2.222(5) Ag(1)-C(1) 2.188(10) Ni(1)-N(2′)#1 2.445(11) Ni(1)-Ni(1)#1 2.961(2) 157.0(2) 2115.4(4) 80.0(3) 112.3(3) 70.5(3) 57.5(3) 110.4(8) 112.3(7)

N(1)-Ni(1)-N(2′)#1 N(2′)#1-Ni(1)-N(1′)#2 N(2′)#1-Ni(1)-Ni(1)#1 O(2)-Ag(1)-C(1) N(2′)#1-Ni(1)-Ni(1)#2 Ni(1)#1-Ni(1)-Ni(1)#2 C(10)-N(1)-Ni(1) N(1′)-N(2′)-Ni(1)#2

2.277(6) 2.233(10) 2.961(2)

140.9(5) 99.7(4) 71.0(3) 162.2(2) 120.7(3) 70.79(4) 137.3(7) 112.9(7)

a Symmetry transformations used to generate equivalent atoms: #1 y - 1/2, -x + 1, -z + 2; #2 -y + 1, x + 1/2, -z + 2; #3 -y + 1/2, x, z; #4 y, -x + 3/2, z; #5 -y + 3/2, x, z; #6 y, -x + 1/2, z; #7 -x + 3/ 2, -y + 3/2, z; #8 -x + 1/2, -y + 1/2, z.

Table 4. Interatomic Distances (Å) and Bond Angles (°) with esds () for 3a Ag(1)-O(3) Ag(2)-O(2) Ni(1)-N(2′)#1 Ni(1)-Ni(1)#1 N(1)-Ni(1)#1 N(2′)-Ni(1)#2

2.204(5) 2.179(6) 2.415(12) 2.957(2) 2.442(12) 2.415(12)

O(3)-Ag(1)-C(15) 164.0(2) N(1′)-Ni(1)-N(2)#1 141.8(5) N(2)#1-Ni(1)-N(2′)#1 29.6(4) N(2)#1-Ni(1)-N(1)#2 99.9(5) N(1′)-Ni(1)-Ni(1)#1 79.4(3) N(2′)#1-Ni(1)-Ni(1)# 166.2(3) N(1′)-Ni(1)-Ni(1)#2 68.9(3) N(2′)#1-Ni(1)-Ni(1)# 2134.0(3) Ni(1)#1-Ni(1)-Ni(1)# 269.92(4) N(2)-N(1)-Ni(1)#1 113.1(8) N(2′)-N(1′)-Ni(1) 110.7(8)

Ag(1)-C(15) Ag(2)-C(10) Ni(1)-N(1)#2 Ni(1)-Ni(1)#2 N(2)-Ni(1)#2

O(2)-Ag(2)-C(10) N(1′)-Ni(1)-N(2′)#1 N(1′)-Ni(1)-N(1)#2 N(2′)#1-Ni(1)-N(1)#2 N(2)#1-Ni(1)-Ni(1)#1 N(1)#2-Ni(1)-Ni(1)#1 N(2)#1-Ni(1)-Ni(1)#2 N(1)#2-Ni(1)-Ni(1)#2 C(24)-N(1)-Ni(1)#1 N(1)-N(2)-Ni(1)#2 C(1)-N(2′)-Ni(1)#2

2.262(7) 2.240(8) 2.442(12) 2.957(2) 2.234(11)

158.8(3) 114.5(4) 114.5(4) 129.5(4) 72.4(3) 112.2(3) 121.8(3) 58.3(3) 149.2(9) 111.1(8) 125.8(10)

a Symmetry transformations used to generate equivalent atoms: #1 y - 1/2, -x + 1,-z; #2 -y + 1, x + 1/2, -z; #3 y - 1, -x + 1/2, z. #4 -y + 1/2, x + 1, z; #5 y, -x + 3/2, z; #6 -y + 3/2, x, z; #7 -y + 2, x + 1/2, -z; #8 y - 1/2, -x + 2, -z; #9 y, -x + 1/2, z; #10 -x + 1/2, -y + 1/2, z; #11 -y + 1/2, x, z; #12 -x + 3/2, -y + 3/2, z.

Table 5. Interatomic Distances (Å) and Bond Angles (°) with esds () for 4a Ag(1)-N(1) Ag(1)-O(12) Ag(2)-C(10) N(1)-Ag(1)-O(3)#1 O(3)#1-Ag(1)-O(12) O(2)#2-Ag(2)-O(8) C(1)-N(1)-N(2) N(2)-N(1)-Ag(1)

2.296(8) 2.419(10) 2.306(13) 124.1(3) 126.4(3) 103.6(7) 106.7(9) 114.6(6)

Ag(1)-O(3)#1 Ag(2)-O(2)#2 Ag(2)-O(8) N(1)-Ag(1)-O(12) O(2)#2-Ag(2)-C(10) C(10)-Ag(2)-O(8) C(1)-N(1)-Ag(1)

2.308(8) 2.230(10) 2.421(15) 102.3(3) 134.0(4) 108.2(6) 138.7(8)

a Symmetry transformations used to generate equivalent atoms: #1 -x, -y + 1, -z + 1; #2 -x + 1, -y + 1, -z + 1.

the organic clip to bind two square-coordinated Ni(II) ions into a neutral bimetallic rectangular ring (Figure 1), which is identical to its Cu(II) analogue4 reported by us very recently. Such binuclear complexes are interesting in that (a) the metallamacrocycles are neutral, (b) they possess four uncoordinated outward oxadiazole N-donors, which could act as the metal-containing ligand to bind the second type of metal center to generate the heterometallic coordination polymers or supramolecular complexes, and (c) they are potentially useful as host-guest materials.4 For obtaining the heterometallic coordination polymers, 1 was used as a metal-containing ligand to react with the second type of metal ion. For example, 1 was treated with AgClO4 in a CH2Cl2/toluene mixed solvent system, generating a new com-

Figure 1. The molecular structure of neutral bimetallic macrocycle Ni2L2 (1).

plex 2. The single crystal analysis revealed that 2 features a mixed-metal coordination species which contains both Ni and Ag atoms. It is surprising that two crystallographically independent Ag(I) cations did not coordinate to Noxadiazole donors which were left for them, and, however, occupied Ni’s site but in a different coordination manner. As indicated in Figure 2, two types of Ag(I) centers lie in a {AgOπ} coordination sphere consisting of one carbonyl oxygen and one η1- >CdC< group from the terminal Schiff-base unit on the L. The Ag-C distances lie in a range of 2.2-2.8 Å, which is commonly observed in Ag(I)-π complexes.6 In addition, ClO4- counterions still weakly coordinate to Ag(I) centers through the long O-Ag bonds (2.7-2.9 Å). As shown in Figure 2, four Ag(1) and four Ag(2) atoms are connected by the terminal bidentate Schiffbase groups into two 16-membered Ag4-rings, in which the opposite Ag · · · Ag distances are 7.38 and 7.52 Å, respectively. All L ligands surround Ag(I) atoms and the coordinated ClO4anions are located on the one side of the Ag4 plane; moreover, the ligands spread effectively to generate bowl-shaped containers. Two weakly µ4-κ4-ClO4- anions are situated in the center of the Ag(1)4 and Ag(2)4 rings, respectively, and deviate from the Ag4 plane ca. 1.2 Å, making the bowl bottom. It is interesting that Ag(1)L and Ag(2)L bowls are in different shapes; moreover, the flat Ag(1)L bowl is embedded in the deep Ag(2)L bowl to give rise to a novel dual bowl host-guest system, in which the uncoordinated ClO4- anions are located as the guest (Figure 2). The dimensions of the Ag(1)L and Ag(2)L bowls are as follows: 3.0 and 2.7 nm for the upper-rim diameters (i.e., the distances between the opposite terminal methyl groups of L); 1.2 and 1.8 nm in depth; the dihedral angles between Ag4 plane and L are ca. 137° and 112°, respectively. In contrast, Ni atoms got rid of the NO-chelating coordination sites and were bonded to Noxadiazole donors. Notably, the four Ni atoms self-aggregate into a Ni4 cluster with a Ni-Ni bond distance of 2.961(2) Å.7 Ni4 core is capped by four oxadiazole groups from four L ligands through eight N-Ni bonds (2.188(10)-2.445(11) Å), and the eight terminal Schiff-base moieties stretch outward from the Ni4 core and act as the bidentate binding site to trap 16 Ag(I) atoms at the terminal. Thus, the Ni4L4 herein performs as a 16-connected node which could be considered as a “dendrimer-like node” (Figure 3). 2 reported herein actually provides a new approach to generate the high-connected metal-organic polymers,8 that is, incorporation polynuclear cluster cores with multidentate bent organic ligands possessing middle coordination sites to construct such materials. It is noteworthy that Ni herein exists in both 2+ and

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Figure 2. Top and side view of Ag(I)L molecular bowl units, and representation of formation of the dual bowl host-guest system. Ag, N, C, O, and Cl are colored as orange, blue, gray, red, and green, respectively.

Figure 3. 16-connected node based on Ni4-cluster and multidentate bent ligands (left) and chart representation of the new approach to access to multiconnected “dendrimer-like node” (right).

3+ valence states,3d which was confirmed by XPS (Supporting Information). It is noteworthy that the Ni(III)-N bond lengths herein are slightly longer than the Ni(III)-Ndonor bond lengths in, for example, Tp(Me3)Ni(III)(µ-O)2Ni(III)Tp(Me3) · 4CH2Cl2.9 In order to confirm the presence of Ni and Ag in the same crystal, the ICP was performed on the crystals of 2 and 3. The measured results are in agreement with the single crystal structure well (Supporting Information). In the solid state, compound 2 features a double-layered concavo-convex structure extended in the crystallographic ab plane. In each layer, flat- and deep-bowls are linked to each

other by the Ni4 nodes and face up and down alternately. Two concavo-convex layers are stacked along the crystallographic c axis and mesh one another. The Ni4 cluster cores are sandwiched by these two layers and fixed by eight Ni-N bonds (four Ni-N(2) and four Ni-N(1) from both sides of layers, respectively) (Figure 4). In order to confirm the formation of the unusual complex 2 and synthesize more such novel complexes, AgBF4 was used instead of AgClO4 to perform the reaction under the same reaction conditions. Single crystal analysis revealed that 3 and 2 are isostructural, and features the same Ni-Ag mixed-metal,

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Figure 4. Representation of how the dual net formed (flat and deep bowls are colored blue and red for the sake of clarity) and the top and side views of double-layered 2D net (the Ni4-cluster cores are shown as polyhedron in cyan).

Figure 5. The ORTEP figure of 4 (displacement ellipsoids drawn at the 30% probability level).

mixed-valence, and Ni4 cluster-containing coordination polymer as 2. Two kinds of Ag(I) centers adopt {AgOπ} sphere, but contain a η2- >CdC< coordination moiety (Ag-C distances in the range of 2.2-2.8 Å). In 3, the BF4- anion serves as a µ4-κ4-ligand instead of ClO4- to bind four Ag(I) atoms (F-Ag bond distances from 2.7 to 2.8 Å) to form the bowl bottom (Supporting Information). As mentioned above, there is an unexpected metal-exchange in 2 and 3. The original binding sites of Ni(II) in metalcontaining ligand 1 were occupied by the newcomers of Ag(I) in 2 and 3. This is the first time, we believe, that such an

interesting phenomenon has been observed in the construction of heterometallic coordination polymers based on the two-step approach. The study of exchangeable binding property of metal ions is very important in the understanding of some life processes, for example, in RNA enzymatic activity and DNA binding activity.10 It is worth pointing out that the current result deviates from our intended strategy of creating mixed-metal coordination polymers (Scheme 1). On the other hand, the simply combination of LH (or L2-), Ni(OAc)2 · 4H2O (or Ni(ClO4)2) with AgClO4 in the required mixed solvent system only led to silver-containing complex 4 instead of Ni-Ag

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Figure 6. Side (a) and top (b) views of the one-dimensional chain in 4.

Figure 7. Photoinduced emission spectra of 1 (red line) and 2-3 (blue line) in the solid state.

mixed-metal assembly, which reflected that the preformation of complex 1 is indeed necessary for the formation of complex 2. As shown in Figure 5, there are two different Ag(I) centers in 4. The first Ag(I) center adopts a distorted trigonal coordination environment which consists of one oxadiazole N donor (dAg(1)-N(1) ) 2.296(8) Å), one carbonyl oxygen (dAg(1)-O(3) ) 2.308(8) Å) from the terminal Schiff-base unit on the L and one aquo oxygen atom (dAg(1)-O(12) ) 2.419(10) Å). In addition, the Ag(I) center still weakly coordinates to a ClO4- counterion with a long bond length of 2.7 Å. The second Ag(I) centers lie in a {AgO2π} coordination sphere consisting of two perchlorate oxygen atoms and one η1- >CdC< group from the terminal Schiff-base unit on the L. The Ag-C distance is 2.306(13) Å, which is comparable to the corresponding bond lengths in 2 and 3. As shown in Figure 6, two bent L ligands bind two Ag(2) centers into an elliptical ring (crystallographic dimensions of ca. 14 × 6 Å). These ring units are further linked together

through inter-ring Ag-O(3) bonding interactions to generate the elliptoid channels along the crystallographic a axis. The Ag(1) centers and one of two ClO4- anions are located inside. Compared to the various discrete molecular containers,11 polymeric metal-organic complexes composed of bowl-shaped units are unprecedented. Up to now, a number of homometallic Ag- or Ni-coordination polymers, some metal cluster-containing coordination polymers, and some mixed-metal or mixed-valence coordination polymers have been reported. To the best of our knowledge, 2 and 3 are the first family of mixed-metal, mixedvalence, and cluster-containing coordination polymers. Luminescent Properties of 1-3. Inorganic-organic hybrid coordination complexes have been investigated for fluorescence properties and for potential applications as luminescent materials, such as light-emitting diodes (LEDs).12 Thus, the syntheses of coordination complexes by the judicious choice of conjugated organic spacers and transition metal centers can be an efficient method for obtaining new types of electroluminescent materials.13 We have been exploring the luminescent properties of bent oxadiazole and trizole bridging spacers and metal-organic coordination polymers and supramolecular complexes based on them in the solid state.14 The results indicate that some complexes generated from these ligands do exhibit interesting fluorescent properties. The luminescent properties of 1-3 were investigated in the solid state. As indicated in Figure 7, 1 exhibits one emission maximum at 472 nm (λex ) 273 nm). Owing to the same structural feature, compounds 2 and 3 exhibit the same luminescence in the solid state. Compared to 1, the maximum emission band of 2-3 are blue-shifted to 438 nm (λex ) 200 nm), with a second, less intense band present at 430 nm; however, no obvious enhancement of the fluorescence intensity is realized. Conclusions In conclusion, we have shown the first series of mixed-metal, mixed-valence, and cluster-containing metal-organic polymers

Ni-Ag Coordination Polymers

based on the “two-step approach” by metal-exchange. This finding could be a beneficial complement for the “two-step approach” to heterometallic coordination polymers. Current efforts toward the preparation of new heterometallic coordination polymers based on this type of neutral metallamacrocyclic ligand and other metal ions are underway.

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Acknowledgment. We are grateful for financial support from the National Natural Science Foundation of China (No. 20671060), National Basic Research Program of China (973 Program, 2007CB936000), and Shangdong Natural Science Foundation (Nos. Z2004B01, J06D05 and 2006BS04040). Supporting Information Available: The ORTEP figures of 1-3, XPS spectra, ICP analyses, and structural figures of 3. This material is available free of charge via the Internet at http://pubs.acs.org.

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