Designed Assemblies of Metal Halo and Pseudohalo Coordination

Apr 8, 2008 - A-1060 Vienna, Austria, College of Chemistry, Jilin UniVersity, Changchun, Jilin ... ReceiVed August 17, 2007; ReVised Manuscript ReceiV...
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Designed Assemblies of Metal Halo and Pseudohalo Coordination Polymers with Bridging 1-Substituted Ditetrazoles Jie-Hui Yu,†,‡ Kurt Mereiter,§ Nader Hassan,†,⊥ Claudia Feldgitscher,| and Wolfgang Linert*,†

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 5 1535–1540

Institute of Applied Synthetic Chemistry, Vienna UniVersity of Technology, Getreidemarkt 9/163-AC, A-1060 Vienna, Austria, College of Chemistry, Jilin UniVersity, Changchun, Jilin 130023, China, Institute of Chemical Technologies and Analytics, Vienna UniVersity of Technology, Getreidemarkt 9/164, A-1060 Vienna, Austria, and Institute of Material Chemistry, Vienna UniVersity of Technology, Getreidemarkt 9/165, A-1060 Vienna, Austria ReceiVed August 17, 2007; ReVised Manuscript ReceiVed December 20, 2007

ABSTRACT: The simple reactions between inorganic salts [CuX2 or M(SCN)2] and 1-ditetrazoles [btzb ) 1,4-bis(tetrazol-1yl)butane or btze ) 1,2-bis(tetrazol-1-yl)ethane] at room temperature produced seven new coordination polymers: three-dimensional (3-D) CuX2(1,4-btzb) (X- ) Cl- 1, Br- 2), two-dimensional (2-D) Cd(SCN)2(1,4-btzb) (3) and Cd(SCN)2(1,2-btze) (4), and onedimensional (1-D) M(SCN)2(1,4-btzb)2 (M ) Ni 5, Co 6) and Ni(SCN)2(1,2-btze)2 (7). With 1-ditetrazoles as the bridges, the 2-D grid-like CuX2 secondary building units (SBUs) are extended into 3-D network compounds 1 and 2, the 1-D chained Cd(SCN)2 SBUs based on Cd(SCN)2Cd units are linked into 2-D layered compounds 3 and 4 with the macrocyclic rings, whereas the mononuclear trans-M(SCN)2 units are connected into 1-D chained compounds 5-7 based on M(1-ditetrazole)2M macrocyclic rings. It deserves mentioning that 1-ditetrazoles show different shapes in different complexes: Z-shape in 1-4 and V-shape in 5-7. All the complexes are characterized by elemental analysis (CHNS), infrared spectroscopy, and thermogravimetric analysis. Introduction During the past decade, the design and construction of novel hybrid metal halo or pseudohalo coordination polymers with cavities has become one of the hot topics in the field of coordination chemistry due to their fascinating structural features and potential as functional materials in some fields such as ion exchange, absorption, separation and catalysis.1 Owing to a diversity of bridging modes of halo or pseudohalo ions, as we know, inorganic metal halides or pseudohalides themselves can form various discrete clusters, 1-D chains or 2-D sheets, namely, so-called secondary building units (SBUs).2 The literature shows that three construction strategies as stated below are feasible to propagate these SBUs into the porous frameworks: (i) with quaternary ammonium salts or metal complexes as the guest species, the SBUs interact with each other through the covalent M-X bonds, producing 3-D networks as in the cases of [Cu(en)2]2[Cu7Cl11] (en ) ethanyldiamine)1b and a series reported by Martin and his co-worker;1a (ii) using metal complex bridges such as the reported [Cu2(OH)2(2,2′-bypyridine)2]2+,3 [Cu4(OH)4(1,10-phenanthroline)4]4+,4 [Ln4(OH)2(isonicotinate)8(Ac)3]-,5 and [Cu(pyrazinecarboxylate)2]n+,6 the interactions between SBUs and the bridges are the covalent Mcomplex bridgeXSBU or MSBU-Lcomplex bridge bonds; (iii) using organic ligands as the connector, the most general method. Up to now, the organic connectors used include 4,4′-bipyridine,7 piperazine,8 pyrazine,9 1,3,5-triazine,10 isonicotinate,11 and similar species. Recently, the 1-substituted ditetrazoles, exhibiting a flexible and bridging nature, became candidates to act as organic linker not only by virtue of the excellent spin-crossover properties of some iron(II) 1-ditetrazole complexes12 but also due to the interesting network architectures of several structurally characterized †

Institute of Applied Synthetic Chemistry, Vienna University of Technology. On leave from College of Chemistry, Jilin University. Institute of Chemical Technologies and Analytics, Vienna University of Technology. | Institute of Material Chemistry, Vienna University of Technology. ⊥ On leave from Department of Chemistry, Faculty of Science, Suez Canal University, Ismaila, Egypt. ‡ §

coordination polymers, 1-D [Fe(1,2-btze)3] · (BF4)2,13 [Cu(1,2btze)3] · (ClO4)2,14 [Fe(1,2-btzp)3] · (ClO4)2 (btzp ) 1,2-bis(tetrazol-1-yl)propane),15 and 3-D [Fe(1,4-btzb)3] · (PF6)2.16 In this paper, we would like to present seven new coordination polymers with 1-ditetrazole connectors assembled by simple direct synthesis of metal halides or pseudohalides as the inorganic precursors: 3-D CuX2(1,4-btzb) (X- ) Cl- 1, Br2), 2-D Cd(SCN)2(1,4-btzb) 3 and Cd(SCN)2(1,2-btze) 4, and 1-D M(SCN)2(1,4-btzb)2 (M ) Ni 5, Co 6) and Ni(SCN)2(1,2btze)2 7. Experimental Section Materials and General Methods. The inorganic chemicals CuCl2 · 2H2O, CuBr2, CdCl2, NiCl2 · 6H2O, CoCl2 · 6H2O, and NH4SCN were obtained from a commercial source and used without further purification, and the organic ligands 1,4-btzb and 1,2-btze were prepared according to the reported literature.13,16,17 Elemental analyses (CHNS) were performed by the Mikroanalytisches Laboratorium, Institute for Physical Chemistry, Vienna University, Währingerstrasse 42, A-1090 Vienna, Austria. Infrared (IR) spectra were recorded with a PerkinElmer 16PC FTIR spectrophotometer in the 4000-450 cm-1 region using a powdered sample on a KBr plate. Thermogravimetric (TG) behaviors were investigated on a Netzsch TG209C instrument with a heating rate of 5 °C min-1 in flowing synthetic air (25 mL min-1). All X-ray diffraction data were collected with Mo KR radiation (λ ) 0.71073 Å) on a Bruker SMART CCD diffractometer at a temperature of 100 K by ω-scan frames of ∆ω ) 0.3° covering at least hemispheres of the reciprocal space. After data integrations with the program SAINT, the intensities were corrected for absorption with the multi-scan method using the program SADABS. With the SHELXTL program suite, all structures were solved using the Patterson method and subsequent difference Fourier syntheses. The metal atoms of all structures were found in special positions with x,y,z ) 0,0,0 and point symmetry Ci. The structures were refined by full-matrix least-squares techniques on F2 using the program SHELXL97. For structures 1 and 2 twinning with [001] as the twin axis was found and taken into account by removing those reflections which were most affected by twinsuperposition (mainly hk0, hk4, and hk8 reflections). The non-hydrogen atoms for all structures were assigned anistropic displacement parameters. The hydrogen atoms were at first located from difference Fourier syntheses and were then included in the refinement with a riding model.

10.1021/cg700778b CCC: $40.75  2008 American Chemical Society Published on Web 04/08/2008

1536 Crystal Growth & Design, Vol. 8, No. 5, 2008

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Table 1. Crystal Data and Structure Refinement for the Title Compounds

formula formula weight crystal system space group T, K a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z D, g cm-3 µ, mm-1 F(000) reflns measured obsd reflns Ra, wR2b a

1

2

3

4

5

6

7

C6H10N8CuCl2 328.67 monoclinic P21/c 100 11.221(2) 6.6610(13) 7.2330(14)

C6H10N8CuBr2 417.57 monoclinic P21/c 100 11.083(2) 6.8479(14) 7.7026(15)

C6H6N10CdS2 394.73 monoclinic P21/n 100 9.9821(5) 5.5553(3) 10.8937(6)

97.71(3)

538.70(18) 2 2.026 2.513 330 3962 1109 0.0601, 0.1214

579.31(19) 2 2.394 8.773 402 2923 1099 0.0684, 0.1627

C14H20N18NiS2 563.31 triclinic P1j 100 6.5042(6) 9.1377(8) 10.9420(10) 66.8350(10) 82.5310(10) 78.5260(10) 584.97(9) 1 1.599 1.053 290 4723 3274 0.0266, 0.0686

C14H20N18CoS2 563.53 triclinic P1j 100 6.5009(2) 9.1392(3) 10.9637(4) 67.5360(10) 83.2810(10) 78.8730(10) 589.97(3) 1 1.586 0.949 289 9573 3422 0.0219, 0.0599

C10H12N18NiS2 507.21 monoclinic P21/c 100 8.2816(17) 18.081(4) 6.9398(14)

94.82(3)

C8H10N10CdS2 422.78 triclinic P1j 100 5.6244(4) 7.4089(4) 9.1061(7) 100.7790(10) 103.4000(10) 94.7110(10) 359.47(4) 1 1.953 1.819 208 6508 2083 0.0131, 0.0349

102.3260(10) 590.17(5) 2 2.221 2.207 384 4284 1704 0.0149, 0.0375

103.89(3) 1009.1(4) 2 1.699 1.211 516 10979 2928 0.0268, 0.0696

R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo2 - Fc2)2/∑w(Fo)2)2]1/2 (both R for observed reflections).

All structures have been deposited with the Cambridge Crystallographic Data Centre, the CCDC numbers of compounds 1–7 being 656829–656835, respectively. Basic information pertaining to the crystal parameters and structure refinement of the title compounds is summarized in Table 1. Selected bond lengths and bond angles are listed in Table 2. Synthesis of Complexes. WARNING. Tetrazole compounds are potentially explosiVe and should be handled with care. CuCl2(1,4-btzb) (1). A solution of 1,4-btzb (19.4 mg, 0.1 mmol) in acetone (6 mL) was carefully layered over an aqueous solution (1 mL) of CuCl2 · 2H2O (17.1 mg, 0.1 mmol). Green needle crystals of 1 were obtained after 3 days. Yield: 30% (10 mg) based on Cu. Anal. Calcd for C6H10N8CuCl2: C, 21.92; H, 3.07; N, 34.10. Found: C, 22.44; H, 2.95; N, 33.43%. IR (KBr, cm-1): 3108 (s), 2945 (w), 1497 (s), 1443 (m), 1361 (w), 13263 (w), 1171 (s), 1094 (s), 1030 (w), 1014 (m), 883 (m), 668 (m), 642 (m). CuBr2(1,4-btzb) (2). The method is the same as that for 1 except for using CuBr2 (22.3 mg, 0.1 mmol) in place of CuCl2 · 2H2O. Darkred needle crystals of 2 were obtained after 2 days. Yield: 24% (10 mg) based on Cu. Anal. Calcd for C6H10N8CuBr2: C, 17.26; H, 2.41; N, 26.84. Found: C, 17.97; H, 2.08; N, 26.93%. IR (KBr, cm-1): 3112 (s), 2945 (w), 1493 (s), 1431 (m), 1365 (w), 1263 (w), 1166 (m), 1092 (s), 1010 (m), 874 (m), 668 (w), 640 (m). Cd(SCN)2(1,4-btzb) (3). A solution of 1,4-btzb (19.4 mg, 0.1 mmol) in acetone (6 mL) was carefully layered over an aqueous solution (1 mL) of a mixture of CdCl2 (18.3 mg, 0.1 mmol) and NH4SCN (15.2 mg, 0.2 mmol). Colorless needle crystals of 3 were obtained after 1 day. Yield: 24% (10 mg) based on Cd. Anal. Calcd for C8H10N10CdS2: C, 22.73; H, 2.38; N, 33.14; S, 15.17. Found: C, 22.51; H, 1.99; N, 32.40; S, 13.48%. IR (KBr, cm-1): 3120 (s), 2938 (w), 2085 (s), 1496 (w), 1463 (w), 1378 (w), 1244 (w), 1168 (m), 1099 (m), 994 (m), 890 (m), 661 (m), 615 (w). Cd(SCN)2(1,2-btze) (4). A solution of 1,2-btze (16.6 mg, 0.1 mmol) in water (6 mL) was carefully injected into an aqueous solution (1 mL) of a mixture of CdCl2 (18.3 mg, 0.1 mmol) and NH4SCN (15.2 mg, 0.2 mmol). Colorless (sometimes light pink) columnar crystals of 4 were obtained after 1 day. Yield: 23% (9 mg) based on Cd. Anal. Calcd for C6H6N10CdS2: C, 18.26; H, 1.53; N, 35.49; S, 16.25. Found: C, 18.17; H, 1.04; N, 34.95; S, 16.01%. IR (KBr, cm-1): 3118 (m), 2953 (w), 2088 (s), 1483 (m), 1443 (w), 1318 (w), 1267 (w), 1171 (s), 1092 (s), 1018 (w), 975 (m), 685 (w), 662 (m). Ni(SCN)2(1,4-btzb)2 (5). A solution of 1,4-btzb (38.8 mg, 0.2 mmol) in acetone (6 mL) was carefully layered over an aqueous solution (1 mL) of a mixture of NiCl2 · 6H2O (23.7 mg, 0.1 mmol) and NH4SCN (15.2 mg, 0.2 mmol). Blue-purple prism crystals of 5 were obtained after 4 days. Yield: 27% (15 mg) based on Ni. Anal. Calcd for C14H20N18NiS2: C, 29.85; H, 3.58; N, 44.77; S, 11.38. Found: C, 29.96; H, 2.95; N, 44.06; S, 10.76%. IR (KBr, cm-1): 3146 (m), 2928 (w), 2076 (s), 1509 (m), 1455 (m), 1358 (w), 1240 (w), 1175 (m), 1100 (s), 1049 (w), 1000 (s), 872 (m), 648 (s). Co(SCN)2(1,4-btzb)2 (6). The method is the same as that for 5 except for using CoCl2 · 6H2O (23.8 mg, 0.1 mmol) in place of NiCl2 · 6H2O.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for the Title Compoundsa Compound 1 Cu(1)-N(1) 1.979(3) Cu(1)-Cl(1) 2.2810(9) Cu(1)-Cl(1)#1 2.9514(10) N(1)-Cu(1)-Cl(1) 90.76(9) N(1)-Cu(1)-Cl(1)#1 90.70(9) Cl(1)-Cu(1)-Cl(1)#1 92.99(2) Compound 2 Cu(1)-N(1) 1.974(5) Br(1)-Cu(1)#2 3.0662(8) N(1)-Cu(1)-Br(1) 90.07(13) Br(1)-Cu(1)-Br(1)#2 91.57(2)

Br(1)-Cu(1)

2.4408(7)

N(1)-Cu(1)-Br(1)#2 90.86(14)

Compound 3 Cd(1)-N(1) Cd(1)-S(1) N(1)-Cd(1)-S(1) S(1)-Cd(1)-N(5)#3

2.3650(9) 2.7373(3) 92.59(2) 92.26(3)

Cd(1)-N(5)#3

Cd(1)-N(1) Cd(1)-S(1)#4 N(5)-Cd(1)-N(1) N(5)-Cd(1)-S(1)#4

2.4079(11) Cd(1)-N(5) 2.7048(3) 89.36(4) N(1)-Cd(1)-S(1)#4 90.57(3)

Ni(1)-N(8)#5 Ni(1)-N(9) N(9)-Ni(1)-N(1) N(9)-Ni(1)-N(8)#5

2.1098(10) Ni(1)-N(1) 2.0569(10) 90.78(4) N(1)-Ni(1)-N(8)#5 87.28(4)

Co(1)-N(9) Co(1)-N(1) N(9)-Co(1)-N(1) N(9)-Co(1)-N(8)#6

2.0844(8) 2.1687(8) 86.74(3) 89.44(3)

Ni(1)-N(8)#7 Ni(1)-N(9) N(1)-Ni(1)-N(8)#7 N(9)-Ni(1)-N(8)#7

2.1135(10) Ni(1)-N(5) 2.0433(11) 91.66(4) N(9)-Ni(1)-N(1) 89.25(4)

2.2877(10)

N(1)-Cd(1)-N(5)#3 87.19(3)

Compound 4 2.2706(11) 91.87(3)

Compound 5 2.0911(10) 88.22(4)

Compound 6 Co(1)-N(8)#6

2.1435(8)

N(1)-Co(1)-N(8)#6 92.30(3)

Compound 7 2.1016(12) 88.06(4)

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

Orange needle crystals of 6 were obtained after 1 week. Yield: 68% (38 mg) based on Co. Anal. Calcd for C14H20N18CoS2: C, 29.84; H, 3.58; N, 44.75; S, 11.38. Found: C, 29.82; H, 3.09; N, 44.29; S, 11.24%. IR (KBr, cm-1): 3141 (m), 2922 (w), 2066 (s), 1505 (m), 1454 (w),

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Crystal Growth & Design, Vol. 8, No. 5, 2008 1537

1357 (w), 1240 (w), 1174 (m), 1101 (s), 995 (m), 870 (m), 784 (m), 664 (m), 647 (s). Ni(SCN)2(1,2-btze)2 (7). The method is the same as that for 5 except for using 1,2-btze (33.2 mg, 0.2 mmol) in place of 1,4-btzb. Bluepurple platelet crystals of 7 were obtained after 4 days. Yield: 22% (11 mg) based on Ni. Anal. Calcd for C10H12N18NiS2: C, 23.68; H, 2.38; N, 49.72; S, 12.64. Found: C, 23.77; H, 2.12; N, 48.77; S, 12.13%. IR (KBr, cm-1): 3146 (m), 2938 (w), 2087 (s), 1499 (s), 1445 (m), 1357 (w), 1260 (w), 1179 (m), 1101 (s) 1001 (m), 882 (w), 714 (w), 651 (s).

Results and Discussion Synthetic Analysis. When metal-1-ditetrazole complexes are prepared, three basic factors are worthy of consideration: (i) The necessity of counteranions. For the 5-substituted tetrazole ligand, after losing the H atom attached to the N atom, it can act as the counteranion itself. Through multi-N donors, it extends the metal ions into a metal-organic framework (MOF).18 But for the 1-substituted tetrazole ligand, the extra counteranion must be considered because of no H atom on the N atom. At present, the generally used counteranions in metal-1-tetrazole complexes are ClO4-, PF6-, BF4-, and X- ions. In this paper, SCN- ion is used as the counteranion. (ii) The election of solvent used to dissolve the ligand. In general, water, methanol, or ethanol can not dissolve the 1-ditetrazole ligands at room temperature, but acetone or acetonitrile can. An unfavorable factor for acetone as solvent is the volatility leading to poor-quality crystals like compound 2. It should be mentioned that water can dissolve small amounts of 1,2-btze at room temperature. Therefore, water is chosen to dissolve 1,2-btze when compound 4 is prepared. (iii) The molar ratio of precursors. Whether the molar ratio of CuX2 or M(SCN)2 and 1-ditetrazole is 1:1 or 1:2, the same products will be obtained with similar yields. Therefore, the molar ratio of precursors is not an important factor for determining the structures of products for this system. Structure Description. Several 1:1 adducts of CuX2 and 1-substituted monotetrazoles have been reported. It is easy to find that through the semicoordination Cu-X bonds, CuX2 forms two types of structures. With the ancillary 1-tertbutyltetrazole (Cu-Clsemi- ) 2.8, 3.0 Å)19 or 1-(2,4,6-trimethylphenyl)tetrazole (Cu-Clsemi- ) 2.9, 3.0 Å),20 the cis-CuCl2 units are linked into a 1-D infinite chain based on CuCl2Cu rings, while in complexes [CuX2(1-ethyltetrazole)2] (X- ) Cl-,21 Br-;22 Cu-Clsemi- ) 3.0 Å, Cu-Brsemi- ) 3.1 Å), [CuBr2(1-hexanyltetrazole)2] (Cu-Brsemi- ) 3.1 Å),22 [CuCl2(1(2-azidoethyl)tetrazole)2] (Cu-Clsemi- ) 3.0 Å),23 and [CuX2(1(2-chloroethyl)tetrazole)2] (X- ) Cl-, Br-;Cu-Clsemi- ) 3.0 Å, Cu-Brsemi- ) 3.1 Å),24 the trans-CuX2 units are propagated into a 2-D grid-like sheet. Obviously, the size of 1-monotetrazole determines the configuration of CuX2 unit. Compounds 1 and 2 are the first 1:1 adducts of CuX2 and 1-substituted ditetrazole. X-ray analyses reveal that both compounds are isostructural. Hence, only the structure of compound 1 as the representative will be described herein. Compound 1 exhibits a 3-D network, consisting of 2-D CuCl2 SBUs extended by bridging 1,4-bztb ligands. The crystallographically independent Cu(II) atom is involved in an elongated octahedral site with CuCl4N2 core. The equatorial plane is occupied by two Cl atoms and two 1,4-bztb ligands. The Cu-N bond length is within the normal range of 1.98–1.99 Å, and the equatorial Cu-Cl distance, 2.2810(9) Å, is practically identical for all reported analogues.21,23,24 Two Cl atoms from the neighboring CuN2Cl2 units are located in the axial positions with the axial Cu-Cl length of 2.9514(10) Å. As shown in Figure 1, each CuCl2 unit is in a trans position. Through the semicoor-

Figure 1. 2-D grid-like CuCl2 SBUs in 1.

Figure 2. 3-D network of 1 viewed along c (top) and b (bottom) axes.

dination Cu-Cl bond, all the CuCl2 units are connected into a 2-D grid-like sheet like those found in some 2-D CuX2-1monotetrazole adducts.21–24 A comparison of semicoordination bonds in compound 1 and preciously reported CuX2(1-monotetrazole) complexes, to our surprise, the Cu-Clsemi- bonds, approximately 2.8–3.0 Å, are only slightly shorter than the Cu-Brsemi- ones, equal to 3.0–3.1 Å. With these 2-D inorganic CuCl2 sheets as SBUs, the bridging 1,4-btzb ligands link them into an interesting 3-D network with 1-D channels in different directions. As shown in Figure 2, along the c axis, compound 1 exhibits calabash-like channels, whereas along the b axis, the channel is a Z-shape column. For the structure of 2, please see Figures S1 and S2, Supporting Information. For the three pairs of 1:1 CuX2-1-tetrazole adducts [1-tetrazole ) 1,4-btzb, 1-ethyltetrazole, or 1-(2-chloroethyl)tetrazole], differences in the value of the cell angle β are found. Sometimes the difference is large as in CuX2(1-(2-chloroethyl)tetrazole)2

1538 Crystal Growth & Design, Vol. 8, No. 5, 2008

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Figure 3. 2-D layered structures of 3 (top) and 4 (bottom). -

-

-

- 24

(98.054° for X ) Cl , 91.491° for X ) Br ), and sometimes it is small as in compounds 1 (94.82°) and 2 (97.71°). The difference in complexes [CuX2(1-ethyltetrazole)] (107.39° for X- ) Cl-, 103.053° for X- ) Br-) is intermediate.21,22 The larger difference has an influence on the packing mode of the inorganic CuX2 sheet. For example, in CuBr2(1-(2-chloroethyl)tetrazole)2, the grids lie on top of each other, whereas in its chloride complex, an even larger distance (1.945 Å) is exhibited between two layers. Small differences merely have an effect on the distances between the neighboring layers. For instance, in complexes 1 and 2, there is no shift between the two layers, and the unique difference is the nearest interlayer Cu · · · Cu separation, being 11.22 Å for 1 and 11.08 Å for 2, respectively. Compounds 3 and 4 are the 1:1 adducts of Cd(SCN)2 and 1,4-btzb or 1,2-btze. As displayed in Figure 3, both possess a similar layered structure, which can be better described as a linkage of 1-D chained Cd(SCN)2 SBUs by 1-ditetrazol bridges. In each layer, the crystallographically independent Cd(II) center in an octahedral site bonds to two 1-ditetrazole ligands and four SCN- anions. The average Cd-N distances of 2.33 Å for 3 and 2.34 Å for 4 and Cd-S distances of 2.7373(3) Å for 3 and 2.7048 (3) Å for 4 are basically in agreement with those observed in known complex [Cd(SCN)2(bpo)] · CH3CN (bpo ) 2,5-bis(4-pyridyl)-1,3,4-oxodiazole; Cd-Naverage ) 2.33 Å, Cd-S ) 2.76 Å).25 The Cd(SCN)2 unit adopts a trans conformation, and each interacts with the adjacent two through longer Cd-S bonds to form a 1-D Cd(SCN)2 SBU based on Cd(SCN)2Cd rings. Next, the bridging 1-ditetrazoles with their 4,4′-position N atoms propagate these 1-D Cd(SCN)2 SBUs into 2-D layers with macrocyclic rings with 30 members for 3 and 26 members for 4. The intrachain Cd · · · Cd separations are almost identical, 5.6 Å for 3 and 5.5 Å for 4, but the interchain Cd · · · Cd separation (14 Å) in 3 is much larger than that in 4 (12 Å) because of different space length of the two 1-ditetra-

Figure 4. 1-D chains of 5 (top) and 7 (bottom).

zoles. Even though the ligand’s length is different, via the weak interlayer S · · · S interactions, the 2-D layers are further selfassembled into a similar 3-D supramolecular network as illustrated in Figure S3, Supporting Information. The S · · · S contact in 3 (3.9 Å) is longer than that in 4 (3.5 Å), but both are within the range of the sum of van der Waals radii of two S atoms. The reactions at room temperature between M(SCN)2 (M ) Co, Ni) and 1,4-btzb or 1,2-btze produced three 1-D chained coordination polymers M(SCN)2(1,4-btzb)2 (M ) Ni 5, Co 6) and Ni(SCN)2(1,2-btze)2 7. Herein only the structures of two Ni complexes 5 and 7 will be discussed because compounds 5 and 6 are isostructural with each other. As shown in Figure 4, both contain a similar chain arrangement. The SCN- ions do not bridge Ni(II) ions into a infinite cluster, as observed in 3 and 4, but coordinate monodentately to the nickel centers with N donor [Ni-N ) 2.0569(10) Å for 5 and 2.0433(11) Å for 7]. While the 1-ditetrazoles, as shown in known complexes, bridge bidentately to the Ni(II) ions with 4,4′-position N donors with the average Ni-N bond lengths of 2.10 Å for 5 and 2.11 Å for 7. In each chain, the crystallographically unique Ni(II) center with a octahedral geometry is coordinated by six N atoms, in which two are from SCN- anions and four are from 1-ditetrazole ligands. The Ni(SCN)2 unit adopts the trans configuration. Each of the two Ni(SCN)2 units is linked by two 1-ditetrazoles, forming 1-D infinite chains with M(1ditetrazole)2M macrocyclic rings with sizes of 8.3 Å × 5.6 Å for 5 and 6.6 Å × 5.5 Å for 7. The intrachain Ni · · · Ni separations are 10.0 Å for 5 and 8.2 Å for 7, respectively. The 1-D chain of 6 is provided as Supporting Information, please see Figure S4. In contrast to those in compounds 3 and 4, the intermolecular S atoms from SCN- ions form different supramolecular synthons in packing structures of both 5 and 7. As displayed in Figure 5, in compound 5 each S atom shows van der Waals

Metal Halo and Pseudohalo Coordination Polymers

Crystal Growth & Design, Vol. 8, No. 5, 2008 1539 Scheme 1

Table 3. A Comparison of Aromatic C-H Stretching Vibration in Metal-1-Ditetrazole Complexes νC-H (cm-1) shape of 1-tetrazole 1,4-btzb 1 2 3 5 6 [Fe(1,4-btzb)3] · (PF6)2 9 1,2-btze 4 7 [Fe(1,2-btze)3] · (BF4)2 8

Figure 5. A 2-D supramolecular layer in 5 (top) and a 3-D supramolecular network in 7 (bottom) extended by weak intermolecular S · · · S interactions.

interactons with only one S atom from the neighboring chain, extending 1-D chains into a 2-D supramolecular layer in the bc plane, while in compound 7, each S atom makes van der Waals contacts with two S atoms from the neighboring chains, as a result of producing a 3-D supramolecular network. The S · · · S separation, being 3.6 Å in 5, is well-comparable with those observed in known complexes, but somewhat shorter than that in 7, 3.8 Å.26 The interchain Ni · · · Ni separations are 12.0 Å for 5 and 9.6 Å for 7, respectively. What in fact determines the structures of resulting products? The answer to this, we think, can be found in the nature of each precursor: (i) The influence of metal center. For example, in the formation of 3-D compounds 1 and 2, the greatest influence is the existence of Jahn–Teller effect of the Cu(II) ion. Via elongated Cu-X bonds, CuX2 units form a 2-D gridlike layer when they react with bridging 1,4-btzb. As another example, the reason why Cd(SCN)2 in 3 and 4 is 1-D while Co(SCN)2 and Ni(SCN)2 in 5-7 are mononuclear is that the Cd-S bond length is longer than the Co-S and Ni-S ones (Cd, period V; Co and Ni, period IV). (ii) The influence of flexibility of 1-ditetrazole ligands. Observing carefully the investigated compounds, one might find that 1-ditetrazoles exhibit different shapes in different complexes. In compounds 1-4, 1-ditetrazoles are Z-shaped, while in compounds 5-7, they are V-shaped. For Z-shaped 1-ditetrazole, two tetrazole rings are parallel to each other (dihedral angle ) zero), whereas for V-shaped 1-ditetrazole, they are perpendicular to each other (dihedral angle ) 95.6° for 5 and 6 and 80.6° for 7) (see Scheme 1). The Z-shaped 1-ditetrazoles commonly extend inorganic units into a 2-D or 3-D network, while the V-shaped one tends

3117 3108 3110 3118 3146 3141 3165 3121 3120 3146 3155

Z-shape Z-shape Z-shape Z-shape V-shape V-shape Z-shape Z-shape Z-shape V-shape V-shape

ref 16 this this this this this 16 13 this this 13

work work work work work work work

to link the inorganic units to form a 1-D chain. Four reported M-1-ditetrazole complexes, [Fe(1,4-btzb)3] · (PF6)2 (3-D, Zshaped), [Fe(1,2-btze)3] · (BF4)2 (1-D, V-shaped), [Cu(1,2btze)3] · (ClO4)2 (1-D, V-shaped), and [Fe(1,2-btzp)3] · (ClO4)2 (1-D, V-shaped), also support this conclusion. By the way, both free 1,4-btzb and free 1,2-btze are Z-shaped.13,16 The flexibility of some organic ligands like 1-ditetrazole is more interesting, and in the future, much attention will be paid to them to design and construct new coordination architectures. (iii) The influence of counteranions. As stated in the literature, the role that the counteranion plays in the course of crystal growth is very important (besides the basic fact of balancing the systemic charge).27 On the one hand, counteranions like X- or SCN- in complexes 1-4 can act as the bridges, linking the M(II) centers into 1-D chained or 2-D layered SBUs. On the other hand, counteranions like ClO4-, BF4-, or PF6- act as guest species in the reported complexes, templating the host to form a porous network. Of course, the coordination capability to the metal of the counteranion determines its existing mode in the complex. According to the title and the reported compounds, the order of coordination capability can be given: SCN- > Cl- > 1-ditetrazole > ClO4-, BF4-, PF6-. It is the lower coordination capability that makes ClO4-, BF4-, or PF6- exist usually in the form of guest molecules in complexes with 1-ditetrazole. The formation of different networks of 3-D [Fe(1,4btzb)3] · (PF6)2 and 1-D [Fe(1,2-btze)3] · (BF4)2 is ascribed to the size of the guest molecules. Subsequently as the next work in our group, the counteranions may be extended to all kinds of carboxylates. IR and TG Analysis. In ref 16, Grunert et al. gave the attribution in detail of each IR peak in 1,4-bztb, based on which all the peaks of the compounds can be better assigned. It deserves noting that the sharp peak appearing in the range of 3100–3200 cm- is typically characteristic for the 1-tetrazole ligand, which should be attributed to the aromatic C-H stretching vibration. As shown in Table 3, the peaks of ν(C-H) are at 3117 cm- for free 1,4-btzb and 3121 cm- for free 1,2btze, but for complexes, some shifts generally occur. Sometimes the shift is small (20 cm-1). The small shift as in compounds 1-4 indicates that the shape of the 1-tetrazole ligand in the complexes is similar to that of the free ligand, namely, Z-shaped, whereas the large shift as in compounds 5-8 indicates that the organic ligand’s shape in the complexes transforms from Z to V.

1540 Crystal Growth & Design, Vol. 8, No. 5, 2008

Compound 9 is really an exception, and the peak is at 3165 cm-1, moving 48 cm-, although 1,4-btzb shows a Z-shape. The TG analyses show that the compounds possess good thermal stability; the temperatures for the onset of decomposition are near 200 °C. Reference 16 reported the TG analysis of complex 9, but no attribution in detail was given. The weight loss (found, ca. 50%) at 250 °C should correspond to the loss of 1,4-btzb. But the calculated result of complete loss of 1,4btzb is ca. 62%. Obviously, 1,4-btzb was decomposed, perhaps yielding the N3- anion existing in the form of Fe(N3)3 (calcd 49%). Complex 5 shows a similar result. As shown in Figure S5 (Supporting Information), the mass loss at 220 °C (found, ca. 55%) is assigned to the partial loss of 1,4-btzb, producing Ni(N3)2 (calcd 54%). Conclusion In sum, the described reactions between inorganic salts and 1-ditetrazoles produced seven new coordination polymers exhibiting three topologies. The nature of each precursor, as well as the distortion and period of the metal center, the coordination capability and size of counteranion, and the flexibility of 1-ditetrazole are considered as the factors determining the structures of products. Based on the position of ν(C-H)aromatic from IR, the shape of 1-ditetrazole in the complex can be identified to be Z- or V-shaped. Acknowledgment. Thanks for financial support are due to the “Fonds zur Förderung der Wissenschaftlichen Forschung in Österreich” (Project 19335-N17) and to the “Hochschuljubiläumstiftung der Stadt Wien” (Project H-01684/2007). We kindly thank the Eurasia-Pacific Uninet (EPU) for providing a six-month scholarship for Dr. Jie-Hui Yu, as well as the Austrian Academic Exchange Service (ÖAD) for their highly appreciated support. Supporting Information Available: Figures showing the SBUs and network structure of 2, the network structures of 3 and 4, the chain structure of 6, and the TG curve of 5. This material is available free of charge via the Internet at http://pubs.acs.org.

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