Rational Design of Mono-, Bi-, and Tetranuclear Macrocyclic Oxamido

Peking University, Beijing 100871, People's Republic of China, and National Key. Laboratory of ... donor groups for another metal ion, such as the mon...
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Rational Design of Mono-, Bi-, and Tetranuclear Macrocyclic Oxamido-Metal Complexes via Stepwise Complexation Jin-Kui Tang,† Yan Ou-Yang,† Hui-Bo Zhou,† Yi-Zhi Li,§ Dai-Zheng Liao,*,†,‡ Zong-Hui Jiang,† Shi-Ping Yan,†,| and Peng Cheng†

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 2 813-819

Department of Chemistry, Nankai University, Tianjin 300071, People’s Republic of China, State Key Laboratory of Structural Chemistry, Fujian Institute of Research on Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, People’s Republic of China, State Key Laboratory of Rare Earth Materials Chemistry and Applications, Peking University, Beijing 100871, People’s Republic of China, and National Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, People’s Republic of China Received May 28, 2004;

Revised Manuscript Received October 25, 2004

ABSTRACT: By using the macrocyclic oxamido-copper(II) complex as a building block and N3- and Cl- as auxiliary bridged groups, a binuclear complex and two tetranuclear complexes derived from the binuclear species have been prepared by stepwise synthesis and characterized. Their formulas are Cu(µ-exoO2)cyclam (1), [Cu(µ-exoO2)cyclamCu(tmen)](ClO4)2‚H2O (2), {[Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5(tmen)]2(ClO4)4, [Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5(tmen)]2(ClO4)2} (3), and [Cu(µ-exoO2)cyclamCu(µ-Cl)0.5(tmen)]2(ClO4)3 (4), where tmen ) N,N,N′N′-tetramethylethylenediamine and (exoO2)cyclam ) 1,4,8,11-tetraazacyclotradecanne-2,3-dione. The structure of complex 1 consists of the neutral copper(II) complex of the [14]N4 macrocyclic oxamido dianion, and the packing of the molecules along the b orientation results in a novel one-dimensional wavelike chain through weak coordination bonds and hydrogen bonds. The structure of complex 2 consists of binuclear cations, a weakly coordinated water molecule, and perchlorate anions, and the structures of 3 and 4 consist of tetranuclear cations derived from binuclear species through azide and chloride ligands, respectively, and perchlorate anions. Introduction The construction of solid-state architectures and crystal engineering have become rapidly developing areas of research which have implications for the rational design of functional materials.1-9 Self-assembly of suitably designed ligands with transition-metal ions allows the creation of inorganic architectures with defined geometry and special properties.10-12 However, while an accurate prediction of overall crystal structure currently is almost impossible,13 it may be achieved in the future. A rational synthetic strategy leading to metal assemblies is to utilize metal complexes having coordination ability as building blocks to react with transition metal ions.14,15 Among a number of basic building blocks employed in the design of polymetallic systems, the mononuclear Cu(II) complexes of N,N′-bis(coordinating group substituted) oxamides have been proven to be versatile ones, which have generated a rich coordination chemistry of polymetallic systems.16-19 The use of the macrocyclic oxamido-copper(II) complex as a building block has been rather limited until recently,20-22 although polymetallic complexes of macrocyclic ligands have been of great interest to supramolecular and coordination chemists for their special structures, properties, and/or functionalities.23 In the present work, by using the macrocyclic oxamido-copper(II) complex as a building block and N3* Corresponding author. Fax: +86-22-23502779. E-mail: coord@ nankai.edu.cn. † Nankai University. ‡ Fujian Institute. | Peking University. § Lanzhou University.

and Cl- as auxiliary bridged groups, we intend to assemble polymetallic systems by stepwise synthesis. The underlying principles of our design are as follows: (a) A successful strategy to design and synthesize polynuclear species is the “complex as ligand” approach, i.e., using mononuclear complexes that contain potential donor groups for another metal ion, such as the mononuclear Cu(II) complexes of N,N′-bis(coordinating group substituted) oxamides. They are well-known to be versatile ligands which can chelate as well as bridge metal ions to build polymetallic systems.16-19 One of the most outstanding characteristics of these ligands is the easy transformation of cis-trans conformations, which makes it practical to design tunable molecular materials with extended structures and desired properties. Although the flexibility can give rise to a rich variety of complexes and extended structures, it allows much less control over the final type of complex obtained.16 The macrocyclic oxamides in which the exo-cis conformation of the oxygen donors is enforced allow us to synthesize polynuclear systems in more controlled fashion via the stepwise complexation of the macrocyclic and the exo donors (Figure 1).21 The use of ancillary ligands on the metal ions avoids polymerization and leads to binuclear species instead of extended networks. (b) Meanwhile, the dinuclear species can also be used as starting materials in which the metal ions have free coordination positions. This opens up the opportunity of linking together these dinuclear species using a suitable auxiliary bridge. The azide group is such a versatile bridge, which can adopt either end-to-end and end-on coordination modes between metal ions.24-27 Our attempts along these lines resulted in the isolation and structural

10.1021/cg049828d CCC: $30.25 © 2005 American Chemical Society Published on Web 01/05/2005

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Tang et al. Table 1. Selected Bond Lengths [Å] and Angles [deg] for Cu(exoO2)cyclam (1) Cu-N(1) Cu-N(3) Cu‚‚‚O(1b) N(1)-C(1) N(1)-C(10) N(2)-C(2) N(2)-C(3) N(3)-C(5) N(3)-C(6) N(4)-C(8) N(4)-C(7) N(1)-Cu(1)-N(2) N(1)-Cu(1)-N(3) N(2)-Cu(1)-N(3) N(1)-Cu(1)-N(4) N(2)-Cu(1)-N(4) N(3)-Cu(1)-N(4) C(1)-N(1)-C(10) C(1)-N(1)-Cu(1) C(10)-N(1)-Cu(1) C(2)-N(2)-C(3)

Figure 1. Some CuII complexes that have been used as ligands (noncyclic and macrocyclic oxamides).

characterization of novel mononuclear precursor 1, its related binuclear precursor 2, and tetranuclear complexes 3 and 4 derived from 2 through azide and chloride ligands, respectively. Experimental Section General. All reagents used in the syntheses were of analytical grade and were used without further purification. The Cu(exoO2)cyclam (1) precursor was prepared according to literature methods.21 C, H, and N elemental analyses were carried out with a Perkin-Elmer analyzer model 240. IR spectra were recorded as KBr disks on a Shimadzu IR-408 infrared spectrophotometer in the 4000-600 cm-1 region. UVvis spectra in acetonitrile were recorded on a Shimadzu UV2401 PC spectrophotometer. The X-band electron paramagnetic resonance (EPR) spectra of the powdered sample were recorded on a Bruker ER 200 D-SRC esr spectrometer at room temperature. Synthesis. Caution! Although we have not encountered any problems, azido and perchlorate salts of metal complexes are potentially explosive and should be handled with care. (a) Synthesis of the Single Crystal of [Cu(µ-exoO2)cyclamCu(tmen)](ClO4)2‚H2O (2). An aqueous solution (5 cm3) of Cu(ClO4)2‚6H2O (1 mmol, 371 mg) was added to a suspension of Cu(µ-exoO2)cyclam (1 mmol, 289 mg) in 10 mL of water. To the resulting solution was added dropwise an aqueous solution (20 cm3) of tmen (1 mmol, 116 mg) with constant stirring. Dark green crystals were obtained by slow evaporation of the resulting solution at room temperature. Elemental analysis obsd (calcd): C, 27.9 (28.0); H, 5.6 (5.6); N, 12.2 (12.4)%. IR (KBr): ν(N-C-O) 1620, 1450 cm-1. (b) Synthesis of the Single Crystal of {[Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5(tmen)]2(ClO4)4, [Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5](tmen)}2(ClO4)2} (3). NaN3 (1 mmol, 65 mg) in water (20 mL) was added to an aqueous solution of Cu(µ-exoO2)cyclamCu(tmen)(ClO4)2 prepared by mixing Cu(ClO4)2‚6H2O (1 mmol, 371 mg), Cu(µ-exoO2)cyclam (1 mmol, 289 mg), and tmen (1 mmol, 116 mg) in 25 mL of water. Dark green crystals were obtained by slow evaporation of the resulting solution at room temperature. Elemental analysis obsd (calcd): C, 30.2 (29.8); H, 4.8 (5.2); N, 16.5 (16.4)%. IR (KBr): νasym(N3) 2075 cm-1, νsym(N3) 1320 cm-1; ν(N-C-O) 1620, 1450 cm-1. (c) Synthesis of the Single Crystal of [Cu(µ-exoO2)cyclamCu(µ-Cl)0.5(tmen)]2(ClO4)3 (4). NaCl (1 mmol, 58.5

1.9410(16) 2.0082(16) 2.539 1.314(3) 1.460(3) 1.311(3) 1.461(3) 1.479(3) 1.475(3) 1.478(3) 1.479(3) 83.87(7) 177.15(7) 96.06(7) 94.78(7) 161.49(8) 86.18(7) 119.01(18) 113.99(13) 125.24(15) 118.16(16)

Cu-N(2) Cu-N(4) Cu‚‚‚Cub O(1)-C(2) O(2)-C(1) C(1)-C(2) C(3)-C(4) C(4)-C(5) C(6)-C(7) C(8)-C(9) C(9)-C(10) C(3)-N(2)-Cu(1) C(2)-N(2)-Cu(1) C(6)-N(3)-Cu(1) C(8)-N(4)-C(7) C(8)-N(4)-Cu(1) C(7)-N(4)-Cu(1) O(2)-C(1)-N(1) O(2)-C(1)-C(2) N(1)-C(1)-C(2) O(1)-C(2)-N(2)

1.9544(16) 2.0300(17) 5.853 1.252(3) 1.256(2) 1.542(3) 1.514(3) 1.524(4) 1.518(3) 1.516(4) 1.524(4) 127.04(13) 113.47(13) 108.12(13) 113.00(17) 115.77(13) 106.42(13) 127.86(19) 119.05(17) 113.09(16) 127.11(19)

mg) in water (20 mL) was added to an aqueous solution of Cu(µ-exoO2)cyclamCu(tmen)(ClO4)2 prepared by mixing Cu(ClO4)2‚ 6H2O (1 mmol, 371 mg), Cu(µ-exoO2)cyclam (1 mmol, 289 mg), and tmen (1 mmol, 116 mg) in 25 mL of water. Dark green crystals were obtained by slow evaporation of the resulting solution in the presence of NaClO4 at room temperature. Elemental analysis obsd (calcd): C, 30.2 (29.9); H, 5.3 (5.0); N, 13.2 (13.3)%. IR (KBr): ν(N-C-O) 1620, 1450 cm-1. X-ray Data Collection and Structure Determination of 1-4. Determination of the unit cell and data collection were performed on a Bruker Smart 1000 (1, 2, and 4) and a Siemens SMART (3) area detector, with graphite-monochromated Mo KR radiation ()0.71073 Å) using the φ and ω scan technique. A total of 4774 reflections (2078 independent reflections Rint ) 0.0179) were collected for 1 in the range 2.40 < θ < 25.03, 5241 reflections (4522 independent reflections Rint ) 0.0475) were collected for 2 in the range 2.67 < θ < 25.03, 10602 reflections (4612 independent reflections Rint ) 0.0547) were collected for 3 in the range 1.84 < θ < 25.02, and 12134 reflections (12134 independent reflections Rint ) 0.000) were collected for 4 in the range 1.1 < θ < 27.5. Of these, 1907 reflections for 1, 2163 reflections for 2, 11598 reflections for 3, and 2510 reflections for 4 were considered observed (I > 2σ(I)) and were used in the structure refinements. Empirical absorption corrections were applied using the SADABS program. The structures were solved by the direct method and refined by the full-matrix least-squares method on F2 with anisotropic thermal parameters for all non-hydrogen atoms.32 The function minimized was ∑w(|Fo|2 - |Fc|2) where w ) 1/[σ2(Fo2) + (0.1543P)2 + 3.0815P] for 1, w ) 1/[σ2(Fo2) + (0.0800P)2]for 2, w ) 1/[σ2(Fo2) + (0.0550P)2] for 3, and w ) 1/[σ2(Fo2) + (0.0290P)2] for 4 where P ) (|Fo|2 + 2|Fc|2)/3. The hydrogen atoms of solvent molecules were not added, and the other hydrogen atoms were located geometrically and refined isotropically. Selected bond lengths and angles are presented in Tables 1-4.

Results and Discussion Description of the Structures. Crystal data for 1-4 are presented in Table 5. (a) [Cu(exoO2)cyclam] (1). The synthesis of 1 has been reported by Robertson et al.,16 but the X-ray structural results were not available. (Red crystals were obtained by slow evaporation in a water-acetone solution at room temperature.) The packing of the molecules along the c orientation results in a novel one-dimensional wavelike chain through weak coordination bonds and hydrogen bonds. The [exoO2]cyclam ligand displays two different coor-

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Table 2. Selected Bond Lengths [Å] and Angles [deg] for [Cu(µ-exoO2)Cu(tmen)](ClO4)2‚H2O (2) Cu(1)-N(2) Cu(1)-N(1) Cu(1)-N(4) Cu(1)-N(3) Cu(2)-O(1) Cu(2)-O(2) N(2)-Cu(1)-N(1) N(2)-Cu(1)-N(4) N(1)-Cu(1)-N(4) N(2)-Cu(1)-N(3) N(1)-Cu(1)-N(3) N(4)-Cu(1)-N(3)

1.934(6) 1.935(6) 1.965(7) 1.992(8) 1.922(6) 1.943(5) 85.1(3) 176.7(4) 94.3(3) 95.2(3) 179.6(3) 85.4(3)

Cu(2)-N(6) Cu(2)-N(5) O(1)-C(2) O(2)-C(1) N(1)-C(1) N(2)-C(2) O(1)-Cu(2)-O(2) O(1)-Cu(2)-N(6) O(2)-Cu(2)-N(6) O(1)-Cu(2)-N(5) O(2)-Cu(2)-N(5) N(6)-Cu(2)-N(5)

1.983(6) 2.002(6) 1.267(9) 1.264(9) 1.278(9) 1.270(9) 86.0(2) 176.3(3) 93.7(2) 93.1(2) 177.0(3) 87.0(3)

Table 3. Selected Bond Lengths [Å] and Angles [deg] for {[Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5(tmen)]2(ClO4)4, [Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5(tmen)]2(ClO4)2} (3) Cu3-O21 Cu3-N9 Cu3-N10 Cu3-N11 Cu3-N12 Cu3-O13_b Cu4-O3 Cu4-O4 Cu4-N13 Cu4-N14 Cu4-N15 O31-Cu1-N2 O31-Cu1-N3 O31-Cu1-N4 N1-Cu1-N2 N1-Cu1-N3 N1-Cu1-N4 N2-Cu1-N3 N2-Cu1-N4 N3-Cu1-N4 O31-Cu1-N1 O1-Cu2-O2 O1-Cu2-N6 O1-Cu2-N7 O2-Cu2-N5 O2-Cu2-N6 O2-Cu2-N7 N5-Cu2-N6 O1-Cu2-N5 N6-Cu2-N7 N5-Cu2-N7 O21-Cu3-N9 O21-Cu3-N10 O21-Cu3-N11

2.670(2) 1.9574(9) 1.9238(9) 1.995(2) 2.0122(19) 2.9237(19) 1.9812(8) 1.9682(9) 2.0407(9) 2.0410(9) 2.2180(13) 84.40(4) 92.79(6) 95.02(5) 84.01(3) 173.59(5) 97.40(4) 96.12(4) 178.51(4) 82.53(5) 93.60(4) 84.77(3) 164.48(4) 97.42(5) 165.52(3) 91.03(3) 99.01(4) 87.71(4) 92.62(4) 98.00(5) 95.45(4) 97.60(5) 87.81(5) 87.95(7)

Cu1-N1 Cu1-N2 Cu1-N3 Cu1-N4 Cu1-O31 Cu2-O1 Cu2-O2 Cu2-N6 Cu2-N7 Cu2-N5

1.9469(9) 1.9689(9) 2.0008(15) 1.9888(11) 2.8738(18) 1.9504(10) 1.9742(9) 2.0391(10) 2.2037(12) 2.0446(10)

O21-Cu3-N12 O13_b-Cu3-O21 N9-Cu3-N10 N9-Cu3-N11 N9-Cu3-N12 O13_b-Cu3-N9 N10-Cu3-N11 N10-Cu3-N12 O13_b-Cu3-N10 N11-Cu3-N12 O13_b-Cu3-N11 O13_b-Cu3-N12 O3-Cu4-O4 O3-Cu4-N13 O3-Cu4-N14 O3-Cu4-N15 O4-Cu4-N13 O4-Cu4-N14 O4-Cu4-N15 N13-Cu4-N14 N13-Cu4-N15 N14-Cu4-N15

89.17(8) 178.70(6) 84.41(3) 174.14(6) 97.74(7) 83.63(4) 97.72(6) 176.51(6) 92.73(4) 80.41(8) 90.80(7) 90.25(7) 84.77(3) 91.15(3) 168.68(3) 97.74(4) 161.81(3) 93.37(3) 97.88(4) 87.16(3) 100.24(4) 93.58(4)

dination sites, an inner N4 and an external O2. The first can be occupied by a copper(II) ion leading to the mononuclear complex [Cu(exoO2cyclam)] which, in a second step, can act as a bidentate chelating agent toward a second metal ion through the external O2 site. Ancillary ligands may control the nuclearity of the compound, acting either as a simple end-cap ligand to produce discrete dinuclear complexes or as a bridging ligand to give polynuclear complexes of higher nuclearity. The use of end-cap ligand tmen on the metal ions avoids polymerization and leads to binuclear species instead of trinuclear species as obtained by Robertson et al. The structure consists of the neutral copper(II) complex of the [14]N4 macrocyclic oxamido dianion. A perspective view of 1 with the atom numbering scheme is shown in Figure 2, and selected bond lengths and angles are listed in Table 1. The copper atom resides in the coordination cavity formed by the four nitrogen donors of the macrocyclic oxamide, with a distorted square-planar geometry. The deviations of donor atoms

Figure 2. ORTEP view of the binuclear complex cation in 1. Ellipsoids are at the 30% possibility level.

Figure 3. Projection of the quasi-1D wavelike chain formed via weak coordination bonds and hydrogen bonds in the crystal structure of 1 down the b axis. Table 4. Selected Bond Lengths [Å] and Angles [deg] for [Cu(µ-exoO2)cyclamCu(µ-Cl)0.5(tmen)]2(ClO4)3 (4) Cu(1)-O(1) Cu(1)-O(2) Cu(1)-N(5) Cu(1)-N(6) Cu(1)-Cl(3) Cu(2)-N(1) O(1)-Cu(1)-O(2) O(1)-Cu(1)-N(5) O(2)-Cu(1)-N(5) O(1)-Cu(1)-N(6) O(2)-Cu(1)-N(6) N(5)-Cu(1)-N(6) O(1)-Cu(1)-Cl(3) O(2)-Cu(1)-Cl(3) N(5)-Cu(1)-Cl(3) N(6)-Cu(1)-Cl(3) N(1)-Cu(2)-N(2) N(1)-Cu(2)-N(3) N(2)-Cu(2)-N(3)

1.980(4) 1.981(4) 2.014(5) 2.017(5) 2.4259(8) 1.939(5) 83.50(15) 91.22(18) 162.4(2) 167.7(2) 94.88(19) 86.7(2) 93.06(12) 93.30(13) 103.80(19) 99.24(17) 84.76(19) 172.8(2) 96.7(2)

Cu(2)-N(2) Cu(2)-N(3) Cu(2)-N(4) O(1)-C(1) O(2)-C(2)

1.940(4) 1.989(5) 2.015(5) 1.273(6) 1.271(6)

N(1)-Cu(2)-N(4) N(2)-Cu(2)-N(4) N(3)-Cu(2)-N(4) Cu(1)-Cl(3)-Cu(1)#2 O(1)-C(1)-N(1) O(1)-C(1)-C(2) N(1)-C(1)-C(2) O(2)-C(2)-N(2) O(2)-C(2)-C(1) N(2)-C(2)-C(1) C(1)-O(1)-Cu(1) C(2)-O(2)-Cu(1)

94.2(2) 169.6(2) 85.7(2) 180.0 127.5(5) 116.4(5) 116.1(5) 129.0(5) 116.3(5) 114.7(5) 110.3(3) 110.1(3)

from the N4 mean plane are 0.190 Å (N1), -0.188 Å (N2), 0.177 Å (N3), and -0.179 Å (N4), and the copper atom is 0.135 Å out of the plane. The Cu-N (amido) bond (averaged to 1.9477 Å) is shorter than the Cu-N (imine) bond (averaged to 2.0191 Å), consistent with the stronger donor ability of the deprotonated amido nitrogen compared to the imine nitrogen. In the crystal of complex 1, the neutral molecules are stacked in such a way that the one “vacant” axial coordination site of the copper atom is occupied by the oxamido oxygen (O1b) arising from an adjacent molecule, with an interatomic Cu‚‚‚O distance of 2.539 Å, indicative of weak coordination bonds. In addition, the other oxamido oxygen links to one imine nitrogen (N3)

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Figure 4. ORTEP view of the binuclear complex cation in 2. Ellipsoids are at the 30% possibility level. Table 5. Summary of Crystallographic Data for Complexes 1-4 formula Mw space group a [Å] b [Å] c [Å] R [deg] β [deg] γ [deg] V [Å3] Z Fcalc [g/cm3] µ(Mo KR) [mm-1] T [K] R1 [I > 2σ(I)] wR2 [all data]

1

2

3

4

C10H18CuN4O2 289.82 P21/n 6.8685(6) 9.6487(8) 17.8645(15) 90 95.620(2) 90 1178.23(17) 4 1.634 1.850 293(2) 0.0244 0.0820

C16H38Cl2Cu2N6O11 688.50 P1 h 7.864(6) 13.003(10) 14.611(11) 67.337(12) 83.197(15) 85.470(14) 1368.1(18) 2 1.671 1.1813 293(2) 0.0709 0.180

C64H120Cl6Cu8N30O32 2542.92 P2/n 24.383(3) 8.008(2) 27.148(3) 90 91.830(10) 90 5299.3(16) 2 1.594 1.810 298(2) 0.0139 0.0480

C32H68Cl4Cu4N12O16 1272.94 C2/c 22.845(6) 12.810(3) 18.561(5) 90 105.933(4) 90 5223(2) 4 1.619 1.884 293(2) 0.0509 0.1295

of the macrocyclic oxamide through a hydrogen bond (N3‚‚‚O2b (2.5 - x, -0.5 - y, 0.5 - z), 2.920 Å). As a result of the two types of weak intermolecular interactions, the molecules are stacked along the b axis to form a quasi-one-dimensional wavelike chain, in which copper atoms are arranged in a zigzag fashion (Figure 3). The nearest intrachain Cu‚‚‚Cu distance is 5.998 Å. (b) [Cu(µ-exoO2)cyclamCu(tmen)](ClO4)2‚H2O (2). The structure consists of homobinuclear [Cu(µ-exoO2)cyclamCu(tmen)]2+ cations, weakly coordinated water molecules, and two set perchlorate ions. A perspective view of the binuclear cation is depicted in Figure 4, and selected bond lengths and angles are listed in Table 2. Cu1 is coordinated by four nitrogen atoms of the macrocyclic organic ligand with the donor atoms deviating from their mean plane by 0.0294 Å (N1), -0.0290 Å (N2), 0.0283 Å (N3), and -0.0287 Å (N4). Cu1 is connected to Cu2 via the exo-cis oxygen atoms of the oxamido macrocyclic ligands with the Cu‚‚‚Cu separations of 5.109 Å and Cu2 assumes a square-pyramidal environment, with the two carbonyl O-atoms O(1) and O(2) of the macrocyclic oxamido ligand and the two nitrogen atoms from the tmen ligand in equatorial positions and one weakly coordinated oxygen atom belonging to a water molecule in axial position. Cu2 is displaced from the least-squares basal plane toward the apex by 0.0568 Å. Cu1 and Cu2 are displaced toward

the same side of the bridge plane between them, which is planar, by -0.0645 and -0.2124 Å, respectively. (c) {[Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5(tmen)]2(ClO4)4, [Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5(tmen)]2(ClO4)2} (3). The structure consists of two different, but similar, units [Cu(µ-exoO2)cyclamCu(µ-1,3-N3)0.5(tmen)]2(ClO4)4- (denoted as 3a) and [Cu(µ-exoO2)cyclamCu(µ1,3-N3)0.5)(tmen)]2(ClO4)2+ (denoted as 3b), and the charge neutrality is achieved because one (3a) is anionic and the other (3b) is cationic. Perspective views of the two units are depicted in Figure 5, and selected bond lengths and angles are listed in Table 3. In unit 3a, Cu1 is coordinated by four amino nitrogens of the macrocyclic organic ligand with the basal donor atoms deviating from their mean plane by 0.0600 Å (N1), -0.0601 Å (N2), 0.0599 Å(N3), and -0.0598 Å (N4), and the metal atom is displaced out of the plane by only -0.0504 Å. Two perchlorate ions reside below and above the CuN4 plane, respectively. The Cu‚‚‚O (perchlorate) distances are 2.874 Å (Cu1‚‚‚O31) and 3.486 Å (Cu1‚‚‚O14) Å. Therefore, the coordination polyhedron of the Cu1 can be described as an octahedron with significant axial elongation (4+2). Cu1 is connected to the Cu2 via the exo-cis oxygen atoms of the oxamido macrocyclic ligand with the Cu‚‚‚Cu separations of 5.195 Å, resulting in binuclear entities. These binuclear entities are linked centrosymmetrically by an azido

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Figure 5. ORTEP view of the tetranuclear unit of 3a (a) and 3b (b). Ellipsoids are at the 30% possibility level.

bridging ligand with the Cu‚‚‚Cu separation of 5.754 Å to form “dimer-of-dimers” tetranuclear cations. The coordination sphere of the Cu(2) is completed by two nitrogen atoms from the tmen ligand in the basal plane to form a square pyramid with apical elongation. Cu(2) is displaced from the least-squares basal plane toward the apex by 0.2597 Å, and deviations of the basal donors from this plane are only -0.0068 Å (O1), 0.0069 Å (O2), 0.0064 Å (N5), and -0.0065 Å (N6). The main difference between units 3a and 3b is that one oxygen atom (O21) of the one and only associated perchlorate anion is weakly interacting with Cu3 and is positioned in the remaining apical site at a distance of 2.670 Å in unit 3b, while two oxygen atoms from the two associated perchlorate anions are positioned in the apical sites above and below Cu(1) in unit 3a. (d) [Cu(µ-exoO2)cyclamCu(µ-Cl)(tmen)]2(ClO4)3 (4). Complex 4 is nearly isostructural to 3. Selected bond distances and angles are listed in Table 4. The structure (Figure 6) consists of centrosymmetric [Cu(µ-exoO2)cyclamCu(µ-Cl)0.5(tmen)]2 tetranuclear cations separated by perchlorate anions. The terminal copper(II)

Figure 6. ORTEP view of the tetranuclear complex cation in 4. Ellipsoids are at the 30% possibility level.

atom Cu(2) is coordinated by four amino nitrogens of the macrocyclic organic ligand with the basal donor atoms deviating from their mean plane by 0.1539 Å (N1), 0.1518 Å (N2), -0.1456 Å (N3), and 0.1477 Å (N4), and the metal atom is displaced out of the plane by

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-0.0268 Å. The closest contact between Cu2 and the oxygen of perchlorate in the same molecule is 2.914 Å (Cu2‚‚‚O4). Cu(2) is connected to the Cu(1) via the exocis oxygen atoms of the oxamido macrocyclic ligand with the Cu‚‚‚Cu separations of 5.176 Å, resulting in binuclear entities. Different from the situation in 1, these binuclear entities are linked centrosymmetrically by a chloride anion, instead of an azido bridging ligand with the Cu‚‚‚Cu separation of 4.852 Å to form dimer-ofdimers tetranuclear cations. The coordination sphere of the Cu(1) is completed by two nitrogen atoms from the tmen ligand in the basal plane to form a square pyramid with apical elongation. As far as the dinuclear entity is concerned, the replacement of the axially weakly bound water molecule by potentially bridging ligands allowed the rational preparation of dimers and one- and two-dimensional polymers. The use of N3- and Cl- as auxiliary bridged groups resulted in dimers. The weak interaction between the copper atoms and the oxygen atoms of the perchlorates may prevent constructing an alternating oxamido-azide (chloride) one-dimensional chain. Characterizations. The IR spectrum of complex 1 shows a sharp band at ca. 2075 cm-1 and a very weak band at ca. 1320 cm-1, corresponding to νasym(N3) and νsym(N3) stretching vibrations, and suggests the presence of the asymmetric µ-1,3-N3 bridging mode in the complex.28 The IR spectra of complexes 1-3 show two strong bands at ca. 1620 and ca. 1450 cm-1, attributed to the ν(N-C-O) stretching bands, which are characteristic of the bridging oxamido group.17 The appearance of a strong and broad band occurring at ca. 1100 cm-1 in the spectra indicates the presence of perchlorate anions.29 The electronic absorption spectra of the four complexes in acetonitrile below 400 nm are dominated by intense bands due to intraligand and charge-transfer transitions in the Cu(II) chromophore.22a In the 400900 nm region, they exhibit a broad band: A relatively stronger band centered at 507 nm was observed for 1 and can be attributed to the d-d transitions of Cu(II) in an environment close to square planar.17 The corresponding d-d bands for 2-4 are obscured by the strong charge-transfer bands due to the Cu(II) chromophore. The X-band powder ESR spectrum of 1 is axial with g| > g⊥ > 2.02, typical of a copper(II) (d9) ion in axial symmetry with the unpaired electron present in the dx2-y2 orbital.30 The X-band powder ESR spectra of 2-4 at room temperature are very similar and exhibit only a broad and asymmetrical band centered at g ) 2.10, indicating a magnetic exchange interaction between the metal ions; however, signals at half field are not distinct.31 Conclusion The rational design of mono-, bi-, and tetranuclear macrocyclic oxamidato-metal complexes via stepwise complexation has been reported in this paper. The [exoO2]cyclam ligand displays two different coordination sites, an inner N4 and an external O2. The first can be occupied by a copper(II) ion leading to the mononuclear complex [Cu(exoO2cyclam)] which, in a second step, can act as a bidentate chelating agent toward a second metal ion through the external O2 site and result in discrete dinuclear complex [Cu(µ-exoO2)cyclamCu(tmen)](ClO4)2‚

Tang et al.

H2O in the presence of ancillary ligand tmen. Meanwhile, in the dinuclear entity, the replacement of the axially weakly bound water molecule by potentially bridging ligands (N3-, Cl-) allowed the rational preparation of dimers of the binuclear entity. The weak interaction between the copper atoms and the oxygen atoms of the perchlorates may prevent constructing an alternating oxamido-azide (chloride) one-dimensional chain. The packing of the molecules in complex 1 along the b orientation results in a novel one-dimensional wavelike chain through weak coordination bonds and hydrogen bonds. Acknowledgment. This work was supported by the Natural Science Foundation of China (Nos. 20331010, 50172021, and 90101028). We are thankful to Professor George M. Sheldrick of Gottingen University in Germany for providing the SHELX-97 program. References (1) (a) Zaworotko, M. J. Angew. Chem., Int. Ed. 2000, 39, 30523054. (b) Losier, P.; Zaworotko, M. J. Angew. Chem., Int. Ed. Engl. 1996, 35, 2779-2782. (c) Subramanian, S.; Zaworotko, M. J. Angew. Chem., Int. Ed. Engl. 1995, 34, 2127-2129. (2) (a) Braga, D.; Grepioni, F.; Orpen, A. G. Crystal Engineering: From Molecules and Crystals to Materials; NATO Science Series; Kluwer Academic: Dordrecht, The Netherlands, 1999. (b) Braga, D.; Grepioni, F.; Desiraju, G. R. Chem. Rev. 1998, 98, 1375-1406. (3) The Crystal as a Supramolecular Entity; Desiraju, G. R., Ed.; Wiley: New York, 1995. (4) (a) Gardner, G. B.; Venkataraman, D.; Moore, J. S.; Lees, S. Nature 1995, 374, 792-795. (b) Fujita, M.; Oguro, D.; Milyazawa, M.; Oka, H.; Yamaguchi, K.; Ogura, K. Nature 1995, 378, 469-471. (5) (a) Keller, S. W. Angew. Chem., Int. Ed. Engl. 1997, 36, 247248. (b) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311-2327. (6) Van Veggel, F. C. M.; Verboom, W.; Reinhoudt, D. N. Chem. Rev. 1994, 94, 279-299. (7) (a) Mayr, A.; Mao, L. F. Inorg. Chem. 1998, 37, 5776-5780. (b) Hirsch, K. A.; Wilson, S. R.; Moore, J. S. Inorg. Chem. 1997, 36, 2960-2968. (8) (a) Fujita, M.; Kwon, Y. J.; Sasaki, O.; Yamaguchi, K.; Ogura, K. J. Am. Chem. Soc. 1995, 117, 7287-7288. (b) Fujita, M.; Kwon, Y. J.; Washizu, S.; Ogura, K. J. Am. Chem. Soc. 1994, 116, 1151-1152. (9) (a) Price, D. J.; Tripp, S.; Powell, A. K.; Wood, P. T. Chem.s Eur. J. 2001, 7, 200-208. (b) Power, K. N.; Hennigar, T. L.; Zaworotko, M. J. Chem. Commun. 1998, 595-596. (c) Blake, A. J.; Champness, N. R.; Khlobystov, A. N.; Lemenovskii, D. A.; Li, W.-S.; Schro¨der, M. Chem. Commun. 1997, 2027-2028. (10) (a) Lehn, J. M. Supramolecular Chemistry: Concepts and Perspectives; VCH: Weinheim, 1995. (b) Yaghi, O. M. In Access in Nanoporous Materials; Pinnavania, T. L., Thorpe, M. F., Eds.; Plenum: New York, 1995; p 111. (11) (a) Sato, O.; Iyoda, T.; Fujishima, A.; Hashimoto, K. Science 1996, 271, 49-51. (b) Choi, H. J.; Suh, M. P. J. Am. Chem. Soc. 1998, 120, 10622-10628. (12) (a) Batten, S. R.; Robson, R. Angew. Chem., Int. Ed. 1998, 37, 1460-1494. (b) Hagraman, P. J.; Hagraman, D.; Zubieta. J. Angew. Chem., Int. Ed. 1999, 38, 2638-2684. (c) Blake, A. J.; Champness, N. R.; Hubberstey, P.; Li, W.-S.; Withersby, M. A.; Schro¨der, M. Coord. Chem. Rev. 1999, 183, 117-138. (13) Desiraju, G. R. Angew. Chem., Int. Ed. Engl. 1995, 34, 2311-2327. (14) Rochon, F. D.; Melanson, R.; Andruh, M. Inorg. Chem. 1996, 35, 6086-6092. (15) (a) Baxter, P. N. W.; Lehn, J. M.; Fischer, J.; Youinou, M. T. Angew. Chem., Int. Ed. Engl. 1994, 33, 2284-2287. (b) Hanan, G. S.; Arana, C. R.; Lehn, J. M.; Fenske, D. Angew. Chem., Int. Ed. Engl. 1995, 34, 1122-1124.

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