Ferrocenyl Functional Coordination Polymers Based on Mono-, Bi

Dec 2, 2008 - Seven ferrocenyl functional coordination polymers have been synthesized based on three kinds of organometallic building blocks. Polymers...
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Ferrocenyl Functional Coordination Polymers Based on Mono-, Bi-, and Heterotrinuclear Organometallic Building Blocks: Syntheses, Structures, and Properties Erpeng Zhang, Hongwei Hou,* Xiangru Meng, Yaru Liu, Yun Liu, and Yaoting Fan

CRYSTAL GROWTH & DESIGN 2009 VOL. 9, NO. 2 903–913

Department of Chemistry, Zhengzhou UniVersity, Zhengzhou, Henan, 450052 P. R. China ReceiVed June 23, 2008; ReVised Manuscript ReceiVed October 6, 2008

ABSTRACT: Seven ferrocenyl functional coordination polymers with the formulas [Zn2(µ2-O2CRFc)4(4,4′-bpy)]n [(R ) (CH2)m with m ) 0 (1), 1 (2), 2 (3), 3 (4)], [Zn(O2C(CH2)4Fc)2(H2O)2(4,4′-bpy)]n (5), [Zn2Ca(µ2-O2CCH2Fc)6 · Zn2(µ2-O2CCH2Fc)4(4,4′bpy)2]n (6) and [Zn2Ca(µ2-O2C(CH2)2Fc)6(4,4′-bpy)]n (7) (Fc ) ferrocene) have been synthesized and characterized. Single-crystal X-ray diffraction studies reveal that their one-dimensional (1-D) chain structures consist of various organometallic building blocks held together by 4,4′-bpy linkers. Polymers 1-4 are based on the paddle-wheel binuclear motif [Zn2(O2CRFc)4]. Polymer 5 is built from the mononuclear unit [Zn(O2CRFc)2(H2O)2]. Polymer 7 is assembled by the linear heterotrinuclear cluster [Zn2Ca(O2CRFc)6] which has been rarely reported up to now. The structure of polymer 6 is a particularly fascinating 1-D chain in which two kinds of building blocks ([Zn2(O2CRFc)4] and [Zn2Ca(O2CRFc)6]) are connected alternately by 4,4′-bpy linkers. These results demonstrate that the total numbers of incorporated ferrocene moieties as well as the structures of 1-7 are closely related to the variation of metal nuclearity (from mononuclear to trinuclear) of the three kinds of organometallic building blocks. The electrochemical studies reveal a good correlation between the Fc/Fc+ redox potentials of 1-7 and the number of methylene in ferrocenyl carboxylates. Introduction The design and construction of metal-organic materials (MOMs, e.g. metal-organic frameworks, coordination polymers, metallodendrimers, and metal-organic polyhedra) have received much attention1-5 owing to their myriad potential applications: gas storage, ion exchange, catalysis, magnetism, nonlinear optics, and biomimetic materials.2,3 Considerable progress has been made on the theoretical forecast and practical approaches of “controlled” syntheses of MOMs.4 Of the many “rational” approaches to the design of these materials, the building block route has been proved to be an efficient strategy with eminent success.1,5,6 Typically, the in situ formed building block with multifold connectivity can be used in concert with polytypic linkers to produce different given architectures in a pseudocontrolled fashion,6 although the precise prediction of the solid-state structure and property still remains a long-term challenge for the crystal engineer. In addition to topological control, ongoing interests in MOMs have been focused on the functionalization of these materials.7 A number of functional MOMs with special properties have been obtained by the traditional self-assembly of organometallic ligands with metal ions.8,9 Recently, the concept of organometallic building block has been introduced into the designing of MOMs. For example, several π-bonded benzoquinone manganese(II), rhodium(II) and copper(I) complexes have been used as organometallic building blocks to construct metal-organometallic networks.10 However, the systematic study of organometallic building blocks has until now remained an underdeveloped area comparing with the well-studied aromatic carboxylate metal cluster. Hence, our group has started on a program aimed at constructing new functional materials by rational utilization of organometallic building blocks and elaborate selection of organic linkers.11 Inspired by the successful application of paddle-wheel binuclear cluster M2(CO2)4 (M ) Cu,12 Zn,13 etc.) and linear trinuclear cluster [M3(CO2)6] * To whom correspondence should be addressed. Fax: (86) 371-67761744. E-mail: [email protected].

(M ) Zn,14 Mg,15 Co,16 Cd,17 etc.) formed by aromatic carboxylates, our synthesis strategy focuses on designing a series of in situ-generated ferrocenyl multinuclear metal cluster building blocks using ferrocenyl carboxylates instead of aromatic carboxylates, and we hope to construct some new MOMs by the assembly of organometallic building blocks with suitable organic linkers. Furthermore, we attempt to control the structures and properties of final products by tuning the structural characteristics of these building blocks rather than adopting the usual strategy of selecting various organic linkers. By this means, not only the structural information but also the functional group is “preprogrammed” into the organometallic building blocks during the synthesis of MOMs. Herein, we report the syntheses of seven ferrocenyl coordination polymers based on three kinds of organometallic building blocks, namely, mononuclear unit [Zn(O2CRFc)2(H2O)2] (type I), paddle-wheel binuclear cluster [Zn2(O2CRFc)4] (type II), and linear heterotrinuclear cluster [Zn2Ca(O2CRFc)6] (type III) (Scheme 1). The crystal structures along with the electrochemical properties of these polymers are represented in this paper. As expected, the fine-tuning of metal nuclearity (from mononuclear to trinuclear) of these building blocks allows for the easy control over the total numbers of incorporated ferrocene moieties as well as the structures of resulting polymers. This group of building blocks, especially the ferrocenyl linear heterotrinuclear cluster, have enriched the varieties of organometallic building blocks and facilitated the design of MOMs with anticipated structures and properties. Experimental Section General. All reagents were obtained from commercial suppliers and used as received. Ferrocenecarboxylic acid (FcCO2H),18 ferrocenylacetic acid (FcCH2CO2H),19 3-ferrocenylpropanoic acid (Fc(CH2)2CO2H),20 4-ferrocenylbutanoic acid (Fc(CH2)3CO2H),19 and 5-ferrocenylpentanoic acid (Fc(CH2)4CO2H)19 were prepared by literature methods. IR data were recorded on a BRUKER TENSOR 27 spectrophotometer with KBr pellets in the 400-4000 cm-1 region. Elemental analyses (C, H, and N) were carried out on a FLASH EA 1112 elemental analyzer. Thermal analyses were performed on a Netzsch STA 449C

10.1021/cg800661g CCC: $40.75  2009 American Chemical Society Published on Web 12/02/2008

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Scheme 1. Three Types of Organometallic Building Blocks in Coordination Polymers 1-7

thermal analyzer from 30 to 800 °C at a heating rate of 10 °C · min-1 in air. The calcium content was measured with a HITACHI Z-8000 atomic absorption spectrophotometer in the flame mode. Powder X-ray diffraction (PXRD) patterns were recorded using Cu KR1 radiation on a PANalytical X’Pert PRO diffractometer. Molecular weights measurements were conducted on a Waters 150C gel permeation chromatography (GPC) instrument using DMF as the eluent and polystyrene as the calibration standard. Cyclic voltammetric experiments were performed by employing a CHI 660B electrochemical analyzer. A three-electrode system was used, which consists of a platinum working electrode, a platinum wire auxiliary electrode, and a Ag/AgCl reference electrode. The measurements were carried out in DMF solutions with 0.1 mol · dm-3 tetrabutylammonium perchlorate (TBAP) as a supporting electrolyte. {[Zn2(µ2-O2CFc)4(4,4′-bpy)] · H2O}n (1). A methanol solution (2 mL) of FcCO2Na (0.04 mmol) was added into 2 mL methanol solution of Zn(NO3)2 · 6H2O (0.02 mmol), then 2 mL methanol solution of 4,4′bpy (0.02 mmol) was added dropwise to the above mixture. The resulting orange solution was allowed to stand at room temperature in the dark. Red crystals were obtained after several weeks (49% yield based on Zn). mp 245-247 °C (dec). Anal. Calcd for C27H23Fe2NO4.5Zn: C, 53.11; H, 3.80; N, 2.29%. Found: C, 53.50; H, 3.75; N, 2.34%. IR (KBr, cm-1): 3420 m, 3100 m, 1604 s, 1556 s, 1472 s, 1390 s, 1350 s, 1104 m, 1017m, 813 m, 513 m. [Zn2(µ2-O2CCH2Fc)4(4,4′-bpy)]n (2). The procedure was similar to that of 1 except that FcCH2CO2Na was used instead of FcCO2Na. Red crystals of 2 were obtained with the yield of 45% based on Zn. mp 218-220 °C (dec). Anal. Calcd for C58H52Fe4N2O8Zn2: C, 55.32; H, 4.16; N, 2.22%. Found: C, 54.90; H, 4.25; N, 2.19%. IR (KBr, cm-1): 3421 m, 3089 m, 1610 s, 1421 s, 1283 m, 1223 m, 1104 m, 1001m, 814 s, 696 m, 487 s. [Zn2(µ2-O2C(CH2)2Fc)4(4,4′-bpy)]n (3). The procedure was similar to that of 1 except that Fc(CH2)2CO2Na was used instead of FcCO2Na. Red crystals of 3 were obtained with the yield of 40% based on Zn. mp 183-185 °C. Anal. Calcd for C62H60Fe4N2O8Zn2: C, 56.62; H, 4.60; N, 2.13%. Found: C, 56.50; H, 4.69; N, 2.15%. IR (KBr, cm-1): 3425 m, 3093 m, 1610 s, 1413 s, 1319 m, 1222 m, 1105 m, 1000m, 812 m, 485 m. [Zn2(µ2-O2C(CH2)3Fc)4(4,4′-bpy)]n (4). The procedure was similar to that of 1 except that Fc(CH2)3CO2Na was used instead of FcCO2Na. Red crystals of 4 were obtained with the yield of 38% based on Zn. mp 158-160 °C. Anal. Calcd for C33H34Fe2NO4Zn: C, 57.80; H, 5.00; N, 2.04%. Found: C, 57.50; H, 4.75; N, 2.23%. IR (KBr, cm-1): 3426 m, 3092 m, 2931 m, 1577 s, 1413 s, 1319 m, 1225 m, 1105 m, 1001m, 814 s, 486 m. [Zn(O2C(CH2)4Fc)2(H2O)2(4,4′-bpy)]n (5). A methanol solution (2 mL) of Fc(CH2)4CO2Na (0.04 mmol) was added into 2 mL aqueous solution of Zn(NO3)2 · 6H2O (0.02 mmol), then 2 mL methanol solution of 4,4′-bpy (0.02 mmol) was added dropwise to the above mixture. The resulting orange solution was allowed to stand at room temperature. Red crystals were obtained after several weeks (58% yield based on Zn). mp 168-170 °C. Anal. Calcd for C40H46Fe2N2O6Zn: C, 58.03; H, 5.60; N, 3.38%. Found: C, 58.37; H, 5.26; N, 3.53%. IR (KBr, cm-1): 3080 m, 2924 m, 1601 s, 1566 s, 1410 s, 1385 s, 1305 m, 1219 m, 1105 m, 1002m, 810 s, 625 s, 482 m.

[Zn2Ca(µ2-O2CCH2Fc)6 · Zn2(µ2-O2CCH2Fc)4(4,4′-bpy)2]n (6). A methanol solution (2 mL) of FcCH2CO2Na (0.03 mmol) was added into 2 mL aqueous solution of Zn(NO3)2 · 6H2O (0.01 mmol) and Ca(NO3)2 · 4H2O (0.005 mmol), then 2 mL methanol solution of 4,4′bpy (0.015 mmol) was added dropwise to the above mixture. The resulting orange solution was allowed to stand at room temperature in the dark. Red crystals were obtained after several days (33% yield based on Zn). mp 240-242 °C (dec). Anal. Calcd for C140H126CaFe10N4O20Zn4: C, 55.23; H, 4.17; N, 1.84%. Found: C, 55.09; H, 4.27; N, 1.83%. IR (KBr, cm-1): 3448 m, 3092 m, 1606 s, 1421 s, 1222 m, 1104 m, 1001m, 815 m, 694 m, 488 m. [Zn2Ca(µ2-O2C(CH2)2Fc)6(4,4′-bpy)]n (7). The procedure was similar to that of 6 except that Fc(CH2)2CO2Na was used instead of FcCH2CO2Na. Red crystals of 7 were obtained with the yield of 36% based on Zn. mp 238-240 °C (dec). Anal. Calcd for C88H86CaFe6N2O12Zn2: C, 56.53; H, 4.64; N, 1.50%. Found: C, 56.52; H, 4.65; N, 1.40%. IR (KBr, cm-1): 3453 m, 3090 m, 1614 s, 1421 s, 1368 m, 1223 m, 1104 m, 1001 m, 813 m, 485 m. X-ray Crystallographic Analyses. The data of 2, 3 and 4 were collected on a Bruker Apex CCD diffractomer (Mo-KR, λ ) 0.71073 Å) at temperature of 20 ( 1 °C. Absorption corrections were applied by using multiscan program SADABS.21 The data of 1, 5, 6, and 7 were collected on a Rigaku Saturn 724 CCD diffractomer (Mo KR, λ ) 0.71073 Å) at temperature of 20 ( 1 °C. The empirical absorption corrections were applied to them. The data were corrected for Lorentz and polarization effects. The structures were solved by direct methods and refined with a full-matrix least-squares technique based on F2 with the SHELXL-97 crystallographic software package.22 Examination by PLATON23 program indicates that the crystal structure of 1 contains solvent accessible voids of 107.00 Å3 per unit cell volume, but the atomic positions of the hydrogen atoms of the water molecules were not calculated. The result of TG analysis further confirmed the existence of water molecules in 1 (see Figure S1 in the Supporting Information). To assist the refinement, several restraints were applied: for 1, the atom C24 was restrained by ISOR; for 2, the thermal parameters of all the carbon atoms in Cp rings were restrained by SIMU, and the atoms Fe3, C27 to C36 were further restrained by ISOR and DELU; for 3, the C-C bond lengths in Cp rings were restrained by SADI, and the thermal parameters of carbon atoms in Cp rings were restrained by SIMU; for 4, the disorder of the 4,4′-bpy ligand was resolved and refined with the aid of restraints on the geometry and anisotropic displacement parameters; for 6, the thermal parameters of disordered atoms in Cp rings were refined with the ISOR instruction. Other nonhydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms except for those riding on H2O oxygen atoms for 5 were placed in idealized positions and refined isotropically to be constrained to ride on their parent atom. Table 1 shows crystallographic crystal data and structure processing parameters of 1-7. Selected bond lengths and bond angles of 1-7 are listed in Table 2.

Results and Discussion Synthesis. Ferrocenyl carboxylate ligands have been proved to be good candidates for building organometallic materials,

a

610.53 293(2) triclinic P1j 10.051(2) 11.728(2) 12.039(2) 62.20(3) 78.96(3) 85.23(3) 1232.1(4) 2 1.643 2.164 618 12635 4329 0.0588 1.020 0.0555 0.1214

R1 ) Σ|Fo| - |Fc|/Σ|Fo|. b wR2 ) [Σw(Fo2 - Fc2)2/Σw(Fo2)2]1/2.

1315.26 293(2) monoclinic C2/c 34.373(4) 14.0358(18) 11.3722(15) 90 90.187(2) 90 5486.5(12) 4 1.592 1.949 2696 16863 6227 0.0414 1.056 0.0495 0.1414

C62H60Fe4N2O8Zn2

C58H52Fe4N2O8Zn2

C27H23Fe2NO4.5Zn

formula

fw T/K cryst syst space group a/Å b/Å c/Å R/deg β/deg γ/deg V/Å3 Z Dc/g · cm-3 abs coeff/mm-1 F(000) reflns collected unique reflns R(int) GOF R1 [I > 2σ(I)]a wR2 (all data)b

1259.16 293(2) monoclinic P21/n 12.159(3) 32.718(7) 13.924(3) 90 112.369(3) 90 5123(2) 4 1.633 2.083 2568 32633 9516 0.0998 1.007 0.0564 0.1383

3 685.68 293(2) triclinic P1j 8.4653(11) 10.4233(13) 17.341(2) 95.9810(10) 99.9330(10) 95.4180(10) 1489.0(3) 2 1.529 1.799 706 11402 5502 0.0221 1.042 0.0331 0.0779

C33H34Fe2NO4Zn

4 827.86 293(2) monoclinic C2/c 28.347(6) 11.537(2) 10.987(2) 90 101.47(3) 90 3521.3(12) 4 1.562 1.541 1720 20461 3996 0.0336 1.020 0.0324 0.0946

C40H46Fe2N2O6Zn

5

Table 1. Crystallographic Data and Structure Refinement Details for 1-7 2

1

3044.51 293(2) triclinic P1j 10.6838(3) 16.8693(5) 18.8666(6) 73.368(3) 74.888(3) 75.342(3) 3086.30(16) 1 1.638 2.010 1554 31034 10837 0.0740 0.992 0.0642 0.1750

C140H126CaFe10N4O20Zn4

6

1869.51 293(2) triclinic P1j 12.6640(12) 12.8431(13) 13.3132(13) 90.598(15) 100.892(15) 105.459(15) 2045.2(3) 1 1.518 1.733 960 20969 7196 0.0679 0.988 0.0677 0.1311

C88H86CaFe6N2O12Zn2

7

Ferrocenyl Functional Coordination Polymers Crystal Growth & Design, Vol. 9, No. 2, 2009 905

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Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) for 1-7a 1 N(1)-Zn(1) O(4)-Zn(1) Zn(1)-O(3)#2 O(2)#2-Zn(1)-N(1) O(3)#2-Zn(1)-N(1)

2.054(4) 2.056(3) 2.052(3) 99.44(16) 100.95(15)

Zn(1)-N(2A) Zn(1)-O(3) Zn(1)-O(7) Zn(2)-O(4) Zn(2)-O(8) N(2)#1-Zn(1)-O(1) N(2)#1-Zn(1)-O(7) N(1)-Zn(2)-O(4) N(1)-Zn(2)-O(8)

2.027(5) 2.065(4) 2.051(4) 2.040(4) 2.053(4) 101.73(18) 99.92(18) 102.28(19) 97.36(18)

Zn(1)-O(1) Zn(1)-N(2)#2 Zn(2)-O(2) O(1)-Zn(1)-N(2)#2 N(1)-Zn(2)-O(2)

2.038(3) 2.046(4) 2.039(3) 101.18(8) 98.98(9)

Zn(1)-O(1) Zn(1)-O(2)#2 Zn(1)-N(1) O(1)-Zn(1)-N(1) O(4)#2-Zn(1)-N(1)

4 2.043(2) 2.038(2) 2.056(12) 105.2(3) 103.0(3)

5 O(1)-Zn(1) Zn(1)-O(2)#2

2.037(4) 2.029(4)

O(1)-Zn(1)-N(1) N(1)-Zn(1)-O(4)

100.65(16) 99.18(16)

Zn(1)-O(1) Zn(1)-O(5) Zn(2)-O(2) Zn(2)-O(6) Zn(2)-N(1) N(2)#1-Zn(1)-O(5) N(2)#1-Zn(1)-O(3) N(1)-Zn(2)-O(6) N(1)-Zn(2)-O(2)

2.030(4) 2.040(4) 2.063(4) 2.044(4) 2.021(5) 97.24(19) 97.12(18) 99.08(19) 99.15(19)

Zn(1)-O(3) Zn(2)-N(1) Zn(2)-O(4) N(2)#2-Zn(1)-O(3) N(1)-Zn(2)-O(4)

2.070(3) 2.039(4) 2.053(4) 98.66(9) 101.75(10)

2

3

Zn(1)-O(3) Zn(1)-O(4)#2 O(3)-Zn(1)-N(1) O(2)#2-Zn(1)-N(1)

2.034(2) 2.034(2) 96.5(3) 94.5(3)

Zn(1)-N(1) Zn(1)-O(1) O(1)-Zn(1)-N(1) O(3)-Zn(1)-N(2)#3 O(3)#1-Zn(1)-O(3) N(2)#3-Zn(1)-N(1)

2.223(2) 2.1132(17) 88.19(4) 93.75(5) 172.50(10) 179.998(1)

Zn(1)-O(5) Zn(1)-O(3) Ca(1)-O(4) Ca(1)-O(6) Zn(2)-O(10)#1 Zn(2)-O(8)#1 O(1)-Zn(1)-N(1) O(5)-Zn(1)-N(1) O(2)#2-Ca(1)-O(2) O(8)#1-Zn(2)-N(2) N(2)-Zn(2)-O(10)#1

1.948(6) 1.958(7) 2.287(7) 2.355(5) 2.053(5) 2.043(6) 101.3(3) 95.5(2) 180.0(2) 104.4(2) 100.0(2)

Zn(1)-O(2)#1 Zn(1)-O(3) Ca(1)-O(4) Ca(1)-O(5) O(2)#1-Zn(1)-N(1) O(3)-Zn(1)-N(1) O(1)-Ca(1)-O(1)#1

1.929(3) 1.958(4) 2.275(4) 2.314(4) 93.38(16) 99.13(17) 180.00(1)

Zn(1)-N(2)#3 O(3)-Zn(1) O(3)-Zn(1)-N(1) O(1)-Zn(1)-N(2)#3 O(1)#1-Zn(1)-O(1)

2.204(2) 2.1026(18) 86.25(5) 91.81(4) 176.37(8)

Zn(1)-O(1) Zn(1)-N(1) Ca(1)-O(2) Zn(2)-N(2) Zn(2)-O(7) Zn(2)-O(9) O(3)-Zn(1)-N(1) O(4)#2-Ca(1)-O(4) O(6)-Ca(1)-O(6)#2 O(9)-Zn(2)-N(2) N(2)-Zn(2)-O(7)

1.951(6) 2.085(6) 2.345(6) 2.040(6) 2.075(6) 2.047(5) 93.6(3) 180.00(1) 180.00(1) 98.7(2) 95.0(2)

6

7 Zn(1)-O(6)#1 Zn(1)-N(1) Ca(1)-O(1) O(6)#1-Zn(1)-N(1) O(4)-Ca(1)-O(4)#1 O(5)#1-Ca(1)-O(5)

1.938(3) 2.078(4) 2.307(4) 98.49(17) 180.0 180.00(1)

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

Scheme 2. Scheme Syntheses of Coordination Polymers 1-7

owing to the unique properties of the ferrocene moiety and various coordination modes of the carboxylate group.24 Among large numbers of ferrocenyl carboxylate complexes, some ferrocenyl monocarboxylate complexes contain the following representative structural units: (1) the mononuclear unit [M(O2CRFc)2(H2O)2], in which each ferrocenyl carboxylate binds to one metal center in the monodentate fashion, such as these in {[Mn(O2CC6H4Fc)2(µ2-OH2)(H2O)2]}n25 and {[Zn(O2CC6H4COFc)2(H2O)2(4,4′-bpy)] · 2MeOH · 2H2O}n;9d (2) the binuclear paddle-wheel motif [M2(µ2-O2CRFc)4], in which each ferrocenyl carboxylate binds to two metal centers in the syn-syn-µ2 mode, such as these in [Cu2(µ2-O2CFc)4(THF)2] · THF26a and Zn2(µ2O2CFc)4(3-PyCO2CH3)2.26b Obviously, both the mononuclear unit and the binuclear motif can be used as organometallic building blocks to construct new coordination polymers. In addition, inspired by the linear trinuclear cluster [M3(CO2)6] formed by aromatic carboxylates,14-17 we presumed that the analogous ferrocenyl linear trinuclear building block [M3(FcRCO2)6] could be obtained by using the ferrocenyl carboxylate instead of aromatic carboxylates. Thus, if the three kinds of organometallic building blocks can be generated in situ during the syntheses of new ferrocenyl coordination polymers, the increase in the number of metal centers

(from mononuclear to trinuclear) would induce the corresponding increase in the number of ferrocene moieties (from 2 to 6) in the building block. This interesting dependency relationship may be useful to design and synthesize anticipated ferrocenyl coordination polymers. In this work, we explored the syntheses of a series of ferrocenyl coordination polymers by the reactions of Zn(NO3)2 · 6H2O and 4,4′-bpy with various ferrocenyl carboxylates. In order to achieve the in situ formation of the three kinds of organometallic building blocks, we conducted these reactions by varying the kinds of ferrocenyl carboxylates as well as the reaction conditions. The results are summarized in Scheme 2. As expected, polymers 1-4 based on the paddle-wheel binuclear building blocks were obtained successfully when Zn(NO3)2 · 6H2O and 4,4′-bpy were combined with FcCO2Na, FcCH2CO2Na, Fc(CH2)2CO2Na, or Fc(CH2)3CO2Na in methanol. Polymer 5 built from the mononuclear building block was also formed by the reaction of Fc(CH2)4CO2Na, Zn(NO3)2 · 6H2O and 4,4′-bpy in the mixed solvents of methanol and water. We have made many attempts to obtain the ferrocenyl coordination polymer based on the linear trinuclear unit, namely [Zn3(O2CRFc)6(4,4′-bpy)]n, by treating Zn(NO3)2 · 6H2O and 4,4′bpy with different ferrocenyl carboxylates in various solvents. Unfortunately, we have not identified any desired product.

Ferrocenyl Functional Coordination Polymers

Crystal Growth & Design, Vol. 9, No. 2, 2009 907

Figure 1. Perspective views showing the coordination environment for the paddle-wheel binuclear building blocks in 1 (a), 2 (b), 3 (c), and 4 (d). All the hydrogen atoms are omitted for clarity.

Instead, a fascinating polymer 6 consisting of two kinds of building blocks was obtained as a byproduct by the reaction of FcCH2CO2Na, Zn(NO3)2 · 6H2O and 4,4′-bpy in the mixed solvents of methanol and water. In the structure of 6, an unexpected linear heterotrinuclear cluster [Zn2Ca(O2CCH2Fc)6] was formed together with the paddle-wheel binuclear motif [Zn2(O2CCH2Fc)4]. The calcium in 6 has been confirmed by the results of atomic absorption spectrum determinations. The calcium was presumably derived from impurities in water. Several crystals of 6 can be separated manually from the major product, which has been identified as 2. In a deliberate synthesis, FcCH2CO2Na and 4,4′-bpy were treated with Zn(NO3)2 · 6H2O and a trace of Ca(NO3)2 · 4H2O in the mixed solvents of methanol and pure water yielding 2 and tiny amounts of 6. Repetition of this reaction but with a larger amount of calcium (Zn:Ca:FcCH2CO2Na ) 2:1:6) afforded pure crystals of 6. Although the formation of the heterotrinuclear cluster is accidental, it is still an effective organometallic building block having the ability to tune the structures and properties of final products. Thus, we developed this method to give polymer 7 which was assembled by the linear heterotrinuclear cluster [Zn2Ca(O2C(CH2)2Fc)6] in similar reaction conditions except that Fc(CH2)2CO2Na was used instead of FcCH2CO2Na. Crystalline phase purity of the bulk materials of 1-7 was confirmed by the experimental PXRD patterns, which match well with the corresponding simulated ones obtained from the single-crystal diffraction data (see Figure S2 in the Supporting Information).

Coordination Polymers 1-4 Based on Paddle-Wheel Binuclear Building Blocks. Single-crystal X-ray diffraction studies reveal that the analogous 1-D chain structures of 1-4 are built from paddle-wheel binuclear units [Zn2(O2CRFc)4]. The perspective views showing the coordination environment for these organometallic building blocks in {[Zn2(µ2-O2CFc)4(4,4′bpy)] · H2O}n (1), [Zn2(µ2-O2CCH2Fc)4(4,4′-bpy)]n (2), [Zn2(µ2O2C(CH2)2Fc)4(4,4′-bpy)]n (3), and [Zn2(µ2-O2C(CH2)3Fc)4(4,4′bpy)]n (4) are depicted in Figure 1. In the structures of 1-4, each Zn(II) ion is coordinated by four equatorial oxygen atoms of ferrocenyl carboxylates and one axial nitrogen atom of a 4,4′bpy molecule to furnish a slightly distorted square pyramidal geometry. The Zn(II) ions are deviated by the range of 0.3384-0.3571 Å from the equatorial planes toward the axial nitrogen atoms. In each paddle-wheel unit, two Zn(II) ions are bridged by four ferrocenyl carboxylates bonded in the bridging bidentate fashion to give the [Zn2(O2CRFc)4] fragment. As seen from Table 2, the corresponding bond lengths and angles around Zn(II) ions in 1-4 are close respectively. For example, the Zn-O distances range from 2.023 to 2.065 Å, the Zn-N distances range from 2.021 to 2.059 Å, and the N-Zn-O angles range from 94.5 to 105.2°. The intraunit Zn · · · Zn distances in each [Zn2(O2CRFc)4] unit range from 2.8786 to 2.9515 Å. These [Zn2(O2CRFc)4] units are linked together by 4,4′-bpy molecules to generate 1-D infinite polymeric chains. As a representative example, the 1-D chain structure of 1 is shown in Figure 2. Two pyridyl rings of the 4,4′-bpy molecule in 2 and 3 are twisted

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Figure 2. 1-D chain of 1 consisting of the paddle-wheel binuclear building block connected together by 4,4′-bpy linker, hydrogen atoms are omitted for clarity.

Figure 3. 1-D chain of 5 consisting of the mononuclear building block connected together by 4,4′-bpy linker, hydrogen atoms are omitted for clarity.

by 41° and 46.4°, respectively, in contrast to those in 1 in which they are coplanar with the dihedral angle of 0°. Similar results can be found for other complexes containing 4,4′-bpy ligand.27 In the crystal of 4, the 4,4′-bpy molecule is found to be disordered, which leads to the difficulty of getting exact value of the twist angle of two pyridyl rings. The Zn(II) ions in each chain are separated by 4,4′-bpy molecule with the distance of 11.180 Å for 1, 11.075 Å for 2, 11.133 Å for 3 and 11.159 Å for 4. The dissimilarities of binuclear building blocks in 1-4 are expressed by the distributions of ferrocenyls around each Zn2 core. As shown in Figure 1a, the [Zn2(O2CFc)4] unit in 1 is quite similar to those in the literature.26,28 Around the Zn2 core, each adjacent ferrocenyl is pointing away from its neighbor, and this structure viewed down the Zn-Zn axis has a skeletal regular carrousel-like shape. However, more skeletal structure types of the binuclear building blocks in 2-4 result from the conformation variation of ferrocenyl carboxylates. Concretely, in 2, ferrocenyls are distributed around each Zn2 core in a noncentrosymmetric fashion (Figure 1b). In 3, 3-ferrocenylpropanoic carboxylate displays trans conformation with the torsion angle of 173.13° for Ccarboxyl-CCH2-CCH2-CCp and gauche conformation with the corresponding torsion angle of 75.44°. In 4, 4-ferrocenylbutanoic carboxylate also adopts two conformations of TG (where T ) trans, and G ) gauche, the torsion angles of the fragments of C1-C2-C3-C4 and C2-C3-C4-C5 are 178.39 and 66.94°, respectively) and GT (the torsion angles ofthefragmentsofC15-C16-C17-C18andC16-C17-C18-C19 are 63.23 and 178.78°, respectively). Thus the similar cen-

trosymmetric skeletal structure type of the two paddle-wheel building blocks in 3 and 4 are observed (Figure 1, panels c and d). Coordination Polymer 5 Based on the Mononuclear Building Block. Single-crystal X-ray structural analysis reveals that 5 crystallizes in a space group C2/c and the structure consists of 1-D polymeric chains extending along the b-axis. A view of this chain structure is depicted in Figure 3. Each Zn(II) ion is coordinated with two terminal monodentate carboxylate groups and two coordinated water molecules (Zn-O 2.103-2.113 Å), together with 4,4′-bpy molecules via nitrogen atoms (Zn-N 2.204-2.223 Å) to complete the octahedral coordination geometry. The deviation of Zn(II) ion from the mean plane formed by the four equatorial oxygen atoms is about 0.1022 Å. The bond angles around Zn(II) ion vary from 86.25° to 180.0°. The [Zn(O2C(CH2)4Fc)2(H2O)2] unit in this polymer can be regarded as mononuclear organometallic building block, in which two 5-ferrocenylpentanoic carboxylates adopt the same TTG conformation (the torsion angles of the fragments of methylene chains between ferrocenyl and carboxyl are 177.75, 171.77 and -96.32°) and situated on opposite sides of the central metal ion. The 4,4′-bpy molecules act as organic linkers to connect these building blocks forming the 1-D polymeric chain. The intrachain Zn · · · Zn separation across the 4,4′-bpy linker is 11.537 Å and two pyridyl rings of 4,4′bpy molecule are twisted by 22.4°.

Ferrocenyl Functional Coordination Polymers

Crystal Growth & Design, Vol. 9, No. 2, 2009 909

Figure 4. (a) Perspective view showing the coordination environment for the paddle-wheel binuclear building block in 6. (b) Perspective view showing the coordination environment for the linear heterotrinuclear building block in 6. (c) 1-D chain of 6 consisting of the binuclear and heterotrinuclear building blocks connected together by 4,4′-bpy linker. All the hydrogen atoms are omitted for clarity.

Coordination Polymer 6 Based on Binuclear and Heterotrinuclear Building Blocks. Single crystal X-ray diffraction study reveals that 6 crystallize in the space group P1j. The polymeric chain consists of two kinds of organometallic building blocks: the paddle-wheel binuclear cluster [Zn2(µ2-O2CCH2Fc)4] (Figure 4a) and the linear heterotrinuclear cluster [Zn2Ca(µ2O2CCH2Fc)6] (Figure 4b). Quite similar to the paddle-wheel binuclear motif in 2, the [Zn2(µ2-O2CCH2Fc)4] unit in 6 is also formed by four ferrocene acetoxy ligands bridging two Zn(II) ions with the Zn2-Zn2A distance of 2.920 Å. Around each Zn(II) ion, four oxygen atoms from four µ2-O2CCH2Fc ligands take up the equatorial positions and a nitrogen atom of 4,4′bpy occupies the axial position to complete a square pyramidal coordination geometry. The deviation of Zn(II) ion from the equatorial plane is about 0.3475 Å, which is slightly larger than the value of 0.3384 Å in 2. The Zn-O distances are in the range of 2.043-2.075Å and the Zn2-N2 distance is 2.040 Å. Although the same ferrocenyl ligand is contained in 2 and 6, the binuclear building block in 6 displays a skeletal structure shape similar to that in 3 and 4 rather than that in 2, which further shows the important influence of the conformation diversity of ferrocenyl carboxylates. The heterotrinuclear [Zn2Ca(µ2-O2CCH2Fc)6] unit in 6 contains a linear array of one Ca(II) ion and two Zn(II) ions connected by six ferrocene acetoxy ligands (Zn-Ca-Zn angle ) 180°). Each of the two Zn · · · Ca pairs is connected through three carboxylate groups by syn-syn-µ2 bonding modes with Zn · · · Ca distance of 3.791 Å. The central Ca(II) ion occupies a crystallographic inversion center and coordinates to six ferrocenyl carboxylate oxygen atoms. The coordination of Ca(II) ion is reasonably ideal octahedral with all O-Ca-O angles of 180° and Ca-O distances in the range of 2.287-2.355 Å. The terminal Zn(II) ion lies in a distorted trigonal pyramidal

geometry in which three carboxylate oxygen atoms take up the equatorial positions and a nitrogen atom of 4,4′-bpy occupies the axial position. The Zn(II) ion locates at 0.2247Å above the O1-O3-O5 equatorial plane, which is much larger than the corresponding deviation value in the paddle-wheel binuclear cluster. The Zn-O bond lengths are in the range of 1.948-1.958 Å and the O-Zn-N angles vary from 93.6 to 101.3°. The carboxyl of ferrocenyl ligand is not symmetrical with one shorter C-O bond coordinated to Zn(II), and one longer C-O bond coordinated to Ca(II). Similar to that in polymers 2-4, the skeletal structure of this centrosymmetric trinuclear building block viewed down the Zn-Ca-Zn axis is also irregular due to the diverse conformation of ferrocene acetoxy ligand. Both kinds of building blocks, [Zn2(µ2-O2CCH2Fc)4] and [Zn2Ca(µ2-O2CCH2Fc)6], can act as nodes, are connected alternately by 4,4′-bpy linker to form a particularly fascinating infinite 1-D chain extending along the b axis direction (Figure 4c). The dihedral angle between two pyridyl rings of 4,4′-bpy linker is 37° which is close to the corresponding value in 2. The Zn · · · Zn separation in 6 across the 4,4′-bpy linker is 11.166 Å. Coordination Polymer 7 Based on the Heterotrinuclear Building Block. Single crystal X-ray diffraction study reveals that the 1-D chain of 7 is built from the linear heterotrinuclear unit [Zn2Ca(µ2-O2C(CH2)2Fc)6] which is quite similar to that of 6. As shown in Figure 5a, in the linear Zn2Ca cluster (Zn-Ca-Zn angle ) 180°), each of the two Zn · · · Ca pairs is connected through three ferrocenyl carboxylates by syn-syn-µ2 bonding modes, and Zn · · · Ca distance (3.791 Å) is identical to the corresponding value in 6. The Ca(II) ion is octahedrally coordinated by six ferrocenyl carboxylate oxygen atoms. Each of the adjacent Zn(II) ions with distorted trigonal pyramidal geometry is deviated by 0.2342Å from the equatorial plane

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Figure 5. (a) Perspective view showing the coordination environment for the linear heterotrinuclear building block in 7. (b) A snowflake-like skeletal structure of the heterotrinuclear building block in 7 viewed down the Zn-Ca-Zn axis. (c) 1-D chain of 7 consisting of the heterotrinuclear building block connected together by 4,4′-bpy linker. All the hydrogen atoms are omitted for clarity.

formed by three carboxyl oxygen atoms toward the axial nitrogen atom of 4,4′-bpy. The carboxyl of ferrocenyl ligand is also not symmetrical with Zn-O and Ca-O distances in the range of 1.929-1.958 Å and 2.275-2.314 Å, respectively. In contrast to that in 3, All the 3-ferrocenylpropanoic carboxylates in 7 display only one conformation of trans with the torsion angles of fragments Ccarboxyl-CCH2-CCH2-CCp in the range of 173.83-179.78°. In this way, a beautiful snowflake-like skeletal structure of this building block viewed down the Zn-Ca-Zn axis is formed by the well-regulated arrangement of six ferrocenyls around the Zn2Ca core (Figure 5b). Each of two terminal Zn(II) ions is further coordinated by a nitrogen atom of 4,4′-bpy linker. Consequently, an infinite 1-D polymeric chain extending along the b axis direction is formed by using these linear trinuclear [Zn2Ca(µ2-O2C(CH2)2Fc)6] units act as nodes (Figure 5c). Like that in 1, the two pyridyl rings of 4,4′-bpy molecule in 7 are also coplanar with the dihedral angle of 0°. The Zn · · · Zn separation in 7 across the 4,4′-bpy linker is 11.223 Å, which is slightly larger than those in 1-4. Effect of Ferrocenyl Carboxylate Conformation on the Skeletal Structure of Organometallic Building Blocks. As an important structural characteristic affecting the crystal packing of 1-7, the skeletal structure of the organometallic building block, i.e., the arrangement of pendant ferrocenyls

around each metal or metal cluster core, deserves to be studied. As shown in the structures, polymers 1-4 and 6 contain the analogous paddle-wheel binuclear building blocks, but the skeletal structures of these paddle-wheel motifs are multifarious (Figures 1a-d and 4a). The reason can be attributed to the conformation variation of these ferrocenyl carboxylates. In fact, this group of ferrocenyl carboxylates, except for ferrocenecarboxylate, may display more than one conformations since the decrease in steric crowding that occurs as the chain length between carboxyl and ferrocenyl increases allows for greater freedom of rotation around the CCp-Cchain bond.28a Therefore, in 1, four ferrocenecarboxylates around each Zn2 core adopt the similar conformation, which results in a regular carrousellike skeletal shape of the building block. In the binuclear building blocks in 2, 3, 4, and 6, all the ferrocenyl carboxylates display two different conformations at the same time, which leads to the irregular arrangements of pendant ferrocenyls around the Zn2 cores. As for the two heterotrinuclear building blocks in 6 and 7 (Figures 4b and 5a), the conformation of ferrocenyl carboxylates also have remarkable effect on the skeletal structure of this kind of organometallic building block. In 6, six ferrocene acetoxy ligands in each heterotrinuclear building block adopt two distinct

Ferrocenyl Functional Coordination Polymers

conformations leading to a centrosymmetric but irregular skeletal structure. But the 3-ferrocenylpropanoic carboxylate in 7 only adopts one conformation, thus a beautiful snowflake-like trinuclear building block is observed. In a word, the conformational variations of ferrocenyl carboxylates lead to various arrangements of pendant ferrocenyls in these organometallic building blocks and subsequent spatial array of 1-D chains in the solid structure. Formation of Three Kinds of Organometallic Building Blocks. Through the rational selection of ferrocenyl carboxylates and elaborate control of reaction conditions, polymers 1-7 containing three kinds of organometallic building blocks have been synthesized successfully. However, the precise prediction of the final structures still remains a challenge because the formation of the organometallic building block is influenced by many factors, such as the coordination fashion and structural characteristic of the ferrocenyl carboxylate ligand, the coordination geometry of the central metal ion, and reaction solvents. It has been reported that the coordination modes of carboxylate ligands have important influences on the metal nuclearity of building blocks:17 the monodentate mode determines that the central ion has no choice but to exist in a mononuclear fashion; the bridging syn-syn-µ2 bidentate mode is essential in chelating metal ions and locking their positions into the popular paddlewheel cluster.29 In our cases, the reason for generating different building blocks of the mononuclear unit and binuclear motif can be attributed to the different coordination fashions of ferrocenyl carboxylates. The root cause leading to the different coordination modes of ferrocenyl carboxylates is not very clear, but it may be ascribed to the structural characteristic of these carboxylates. Comparing with the other four carboxylates, 5-ferrocenylpentanoic carboxylate has the longest alkyl chain between the carboxyl group and the ferrocene moiety. Probably due to the conformation requirement of the longest alkyl chain, 5-ferrocenylpentanoic carboxylate adopts the monodentate mode rather than the syn-syn-µ2 mode, to form a mononuclear building block which is totally different from the paddle-wheel motif. On the other hand, the monodentate mode of 5-ferrocenylpentanoic carboxylate may be associated with the reaction solvents because the coordination modes of carboxylate can be modulated via the choice of solvent system in some cases.30 However, for the Ca-containing polymers 6 and 7, beside the influence of coordination mode, the key role of the introduction of calcium ion for the formation of linear heterotrinuclear building blocks should not be neglected. For example, in 6, although all the ferrocene acetoxy ligands display the synsyn-µ2 mode, the heterotrinuclear cluster is formed simultaneously with the paddle-wheel binuclear motif. This might reasonably be attributed to the fact that the larger ionic radius of Ca(II) ion allows for the acceptance of more coordination atoms in the inner sphere,31 which brings out a notable stabilization for the heterotrinuclear clusters in 6 and 7. In a word, the coordination modes of ferrocenyl carboxylates and the introduction of Ca(II) ion, together with reaction conditions, work together to affect the formation of the building blocks and final structures; it is difficult to separate and rationalize them. Electrochemistry Properties. The molecular weights of these coordination polymers have been determined in DMF solution. The number-average molecular weights (Mn) of 1-7 are 9.544 × 104, 7.721 × 104, 6.803 × 104, 6.113 × 104, 10.803 × 104, 5.203 × 104, and 4.863 × 104, respectively. The results show that these polymers are general intact in DMF solution.

Crystal Growth & Design, Vol. 9, No. 2, 2009 911 Table 3. Electrochemical Data for Coordination Polymers 1-7a coordination polymersb

Ea/V

Ec/V

∆Ep/mVc

E1/2/Vd

ia/ic

1 (FcCO2H) 2 (FcCH2CO2H) 6 (FcCH2CO2H) 3 (Fc(CH2)2CO2H) 7 (Fc(CH2)2CO2H) 4 (Fc(CH2)3CO2H) 5 (Fc(CH2)4CO2H)

0.823 0.612 0.609 0.550 0.547 0.549 0.534

0.683 0.514 0.530 0.474 0.470 0.472 0.457

140 98 79 76 77 77 77

0.753 (0.743) 0.563 (0.558) 0.570 (0.558) 0.512 (0.512) 0.509 (0.512) 0.510 (0.511) 0.496 (0.490)

1.40 1.25 1.13 1.02 1.00 1.02 0.99

a All potentials are referred to Ag/AgCl in DMF solution, V ) 100 mV/s. b The formulas in brackets are the corresponding ferrocenyl carboxylate acids. c ∆Ep ) (Ea - Ec). d E1/2 ) (Ea + Ec)/2. The values given in brackets are the redox potentials of free acids.

Figure 6. Cyclic voltammetrys of polymer 7 at scan rates of 50-300 mV/s.

The electrochemical behaviors of 1-7 were studied by cyclic voltammetry in DMF solutions (ca. 1 × 10-3 M total Fc concentrations) containing 0.1 M tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte. The data are summarized in Table 3. As a representative example, the cyclic voltammetrys of polymer 7 at scan rates of 50-300 mV/s are shown in Figure 6. Under the present experimental conditions, the redox potential (E1/2) of ferrocene is located at 0.544 V vs Ag/AgCl. Polymer 1 exhibits a nearly irreversible redox wave with inordinately large peak to peak separation (∆Ep) and anodic to cathodic peak current ratio (ia/ic), which is attributed to substrate deposition at the working electrode.28 Similar phenomena have been observed for several ferrocenecarboxylate-containing complexes.28 In contrast to 1, the other six polymers display reversible or quasi-reversible redox waves of Fc/Fc+ couple within the whole potential range (from ca. 0.1 to 0.9 V), indicating that the iron centers are independent and equivalent. The peak to peak separations are found to be larger than the theoretical value of 59 mV · s-1 for a fully reversible oneelectron redox reaction.32 This may be due to a combination of uncompensated solution ohmic resistance and slightly slow electron transfer kinetics.33 It is well-known that the electron-withdrawing ability of the carboxyl group and coordinated metal centers serves to raise the potential above that of free ferrocene.28,34 As shown in Table 3, polymer 1 locates at a much higher potential (0.753 V) with a positive shift of 209 mV comparing with the redox potential of free ferrocene (0.544 V). The corresponding potential shifts of ferrocene acetoxy-containing polymers 2 and 6 are ca. +10 mV, which is much smaller than that of 1. In contrast, the redox potentials of 3, 4, 5, and 7 are very close to each other and they all are slightly lower than that of ferrocene with the negative shifts of 32-48 mV. Furthermore, the redox potentials become

912 Crystal Growth & Design, Vol. 9, No. 2, 2009

more negative as the length of the saturated methylene spacers increases in the ferrocenyl carboxylates. These results are in accordance with the previous reports.28,35 The origin of this behavior can be traced back to the presence of the saturated methylene spacers between the electroactive ferrocenyl and carboxyl group. The electron-donating ability of the methylene spacer group serves to partially or entirely cancel the electronwithdrawing inductive effect of the carboxyl group and central metal ions. Therefore, the redox potentials of this group of polymers, except for 1, are close to or lower than the value of free ferrocene. In particular, the redox potentials of 3, 4, 5, and 7 are nearly identical to the corresponding free ferrocenyl carboxylate acids, which further indicates that the coordination of Zn(II) ions to the ferrocenyl ligands does not have significant effect on the redox potential of the ferrocene center. Analogously, it is easy to understand that the CV behaviors of Cacontaining polymers 6 and 7 are similar to that of polymers 2 and 3, respectively. Conclusion By simultaneous use of 4,4′-bpy as organic linker, seven ferrocenyl coordination polymers have been successfully synthesized based on three kinds of organometallic building blocks, namely, mononuclear unit [Zn(O2CRFc)2(H2O)2], paddle-wheel binuclear motif [Zn2(O2CRFc)4], and linear heterotrinuclear cluster [Zn2Ca(O2CRFc)6]. Comparing with the well-studied paddle-wheel binuclear metal clusters, the reports on the linear heterotrinuclear metal cluster are infrequent. To the best of our knowledge, no ferrocenyl coordination polymer based on the linear heterotrinuclear building block has been reported. A comparison of coordination polymers 1-7 reveals that the metal nuclearity of organometallic building blocks plays a significant role in tuning the redox center concentration36 of these polymers, which helps to provide a greater understanding of the influence on electrochemistry caused by structural factors. This indicates that the rational selection of organometallic building block including “preprogrammed” structural information and functional group is an effective strategy for tuning the structures and porperties of functional MOMs. We believe that the precise prediction of the solid-state structure and specific property of the final products would become easier, and more variety of functional materials would be produced by elaborate design and utilization of suitable organometallic building blocks. Acknowledgment. This work was financially supported by the National Natural Science Foundation (No. 20671082), NCET, and the Ph.D. Programs Foundation of Ministry of Education of China. Supporting Information Available: X-ray crystallographic files in CIF format for 1-7, TGA curve for 1, and powder X-ray patterns for 1-7 (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.

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