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One-Dimensional Copper(II) Complexes Containing Only ... They represent the first examples of metal azido complexes containing only single end-on azid...
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One-Dimensional Copper(II) Complexes Containing Only Single End-On Azido Bridges: Crystal Structures and Magnetic Properties En-Qing Gao,†,‡ Yan-Feng Yue,† Shi-Qiang Bai,† Zheng He,† and Chun-Hua Yan*,†

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 3 1119-1124

State Key Lab of Rare Earth Materials Chemistry and Applications & PKU-HKU Joint Lab in Rare Earth Materials and Bioinorganic Chemistry, Peking University, Beijing 100871, China, and Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, Shanghai 200062, China Received November 6, 2004;

Revised Manuscript Received January 2, 2005

ABSTRACT: Two one-dimensional (1D) azido-bridged coordination polymers of formula [Cu(L1)(µ-1,1-N3)(N3)]n (1) and [Cu(L2)(µ-1,1-N3)(N3)]n (2) have been synthesized and structurally characterized, and their magnetic properties have been studied, where L1 and L2 are the bidentate Schiff bases obtained from the condensation of 2-pyridylaldehyde with aniline and p-chloroaniline, respectively. Both compounds consist of 1D uniform chains in which the Cu(II) ions with a distorted square pyramidal geometry are interlinked by single end-on azido bridges in the asymmetric basal-apical fashion, and the chains are interlinked by weak C-H‚‚‚N hydrogen bonds into two-dimensional (2D) layers. They represent the first examples of metal azido complexes containing only single end-on azido bridges. Temperature- and field-dependent magnetic analyses reveal that weak antiferromagnetic interactions are mediated by the single asymmetric bridges, with the exchange parameters being -2.2 and -3.7 cm-1 for 1 and 2, respectively. Introduction The design and magnetism of polynuclear molecules and coordination polymers with particular structures are currently attracting intense attention for understanding the fundamental science of magnetic interactions and magnetostructural correlations in molecular systems and for developing new functional moleculebased materials.1,2 In this context, the exceptional abilities of the azide anion as a versatile bridge to link two or more metal centers in different modes and as a good mediator to transmit different magnetic interactions, together with the remarkable diversities of the metal azido systems in polymeric dimensionality, topology, and bulk magnetic property, have evoked considerable interest.1-3 The azido ion can link two or more metal ions in the µ-1,1 (end-on, EO), µ-1,3 (end-to-end, EE), µ-1,1,3, or still other modes, yielding various polynuclear and one- (1D), two- (2D), or three-dimensional (3D) species of different topologies, depending on the metal ion and the coligand used.3-6 The magnetic exchange mediated via an azido bridge can be ferro- (F) or antiferromagnetic (AF), depending on the bridging mode and bonding parameters. It has been widely stated that the exchange is generally ferromagnetic in nature for the EO mode, and antiferromagnetic for the EE mode,3-9 although an increasing number of exceptions have been reported recently.10,11 For copper(II) systems, the exchange is strongly dependent upon the coordination geometries of the metal ion and the azido bridge. For instance, the azido bridge between two square pyramidal Cu(II) ions may assume a basal-basal or a * To whom correspondence should be addressed. Fax: +86-1062754179. E-mail: [email protected]. † Peking University. ‡ East China Normal University.

basal-apical disposition, which should affect the magnetic exchange.12-18 The versatile features of metal-azido systems in coordination chemistry and magnetochemistry may lead to novel topologies and properties that are difficult to achieve with other bridging ligands, but the versatility also presents great challenges in the design of materials with specific structures and properties. With our present state of knowledge, it seems impossible to predict a priori the bridging mode or topology with a specific ligand. Nevertheless, neutral bidentate coligands and Mn(II) tend to form 1D complexes with alternating double EO and double EE azido bridges, as found for 2,2′-bipy,5b a series of five 2-pyridylaldehyde Schiff bases,7a and some other ligands with two nitrogen donors.5c,d,12 Only three exceptions have been reported, where 2D Mn(II) complexes with double EO and single EE azido bridges were formed.7b,13a On the other hand, the structures of the Cu(II)-azido systems with bidentate coligands are much more diverse and more sensitive to the coligands used, and various mononuclear, binuclear, and polymeric 1D complexes with different azido bridging modes have been obtained, not only due to the coordination diversity of the azido ion, but also due to the coordination flexibility of the Cu(II) ion. In continuation of our previous work on Mn(II)-azido systems with bidentate Schiff bases, we conducted the investigation on the Cu(II) systems, in hopes of obtaining novel azido-bridged topologies. The EO azido bridge tends to coexist with another one or two azido bridges (EO or EE) or other bridging groups, such as carboxylato, diazine, etc.19,20 The occurrence of the single EO azido bridge, i.e., the case that there is no other bridge between the two metal ions bridged by a single EO azido bridge, is very rare. The first compound containing such bridges is a tetraman-

10.1021/cg0496181 CCC: $30.25 © 2005 American Chemical Society Published on Web 02/25/2005

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ganese(II) complex in which macrocyclic binuclear moieties with bis(µ-alkoxo)(µ-1,1-azido) triple bridges are joined by single EO azido bridges15a (Scheme 1a). The other known compounds containing such bridges are all Cu(II) complexes: two 3D structures in which Cu(II) chains with alternating trans-oxamidato and single EO azido bridges are joined by µ-bromide or µ-1,3-azido bridges15b,c (Scheme 1b), two 1D Cu(II) coordination polymers with alternating single EO and single EE azido bridges12,15d (Scheme 1c), and a 1D Cu(II) coordination polymer containing single EO bridges and two different kinds of double EO bridges12 (Scheme 1d). All these compounds contain at least another type of bridge to form the whole structures, and the species containing only single EO bridges are still lacking. In the present paper, we report, for the first time, the syntheses, crystal structures, and magnetic properties of two 1D compounds that contain only single EO azido bridges. The complexes are of the formula [Cu(L1)(µ1,1-N3)(N3)]n (1) and [Cu(L2)(µ-1,1-N3)(N3)]n (2), where L1 and L2 are the bidentate Schiff bases obtained from the condensation of 2-pyridylaldehyde with aniline and p-chloroaniline, respectively. Experimental Section Materials and Physical Measurements. All the starting chemicals were of A. R. grade and used as received. The Schiff bases were prepared according to the literature methods for analogous compounds.21 Elemental analyses (C, H, N) were performed on an Elementar Vario EL analyzer. IR spectra were recorded on a Nicolet Magna-IR 750 spectrometer equipped with a Nic-Plan microscope. Variable-temperature magnetic susceptibilities were measured on an Oxford MagLab 2000 magnetometer. Diamagnetic corrections were made with Pascal’s constants for all constituent atoms.22 Caution! Although not encountered in our experiments, azido complexes of metal ions are potentially explosive. Only a small amount of the materials should be prepared, and it should be handled with care. [Cu(L1)(µ-1,1-N3)(N3)]n (1). A mixture solution of L1 (0.50 mmol) and sodium azide (1.0 mmol) in 5 mL of methanol was added into a side of a H-shaped tube, and a methanolic solution (5 mL) of copper(II) perchlorate hexahydrate (0.5 mmol) was added into the other side. Then methanol was carefully added to both sides until the bridge of the tube was full. The tube was sealed and was left to stand at room temperature. Slow diffusion between the two solutions yielded dark green crystals within about 1 week. Yield, 31.2%. Anal. Calcd. for C12H10CuN8: C, 43.70; H, 3.06; N, 33.98. Found: C, 43.71; H, 3.19; N, 34.04%. Main IR bands (cm-1): 2059vs, 2033s, 1597m, 1488m, 1446m, 1338m, 1155m, 1023m, 929w, 780m, 743w, 695m.

Gao et al. Table 1. Summary of Crystallographic Data for the Complexes formula formula weight crystal system space group a, Å b, Å c, Å β, deg V, Å3 Z Dc, g/cm3 µ(Mo-KR), mm-1 T, K θ range, deg reflns measured unique reflns/Rint R1 [I > 2σ(I)] wR2 (all data) GOF on F2 Fmax/Fmin, e Å-3

1

2

C12H10CuN8 329.82 monoclinic P21/c 9.6735(3) 19.5436(5) 7.0889(2) 94.4613(11) 1336.13(7) 4 1.640 1.641 293(2) 3.56-27.48 24677 3002 /0.1077 0.0385 0.0782 0.957 0.316/-0.358

C12H9CuN8Cl 364.26 orthorhombic Pccn 18.4371(3) 21.3954(4) 7.2088(1) 2843.65(8) 8 1.702 1.733 293(2) 3.45-27.48 41528 3228/0.0778 0.0358 0.0856 1.017 0.385/-0.331

[Cu(L2)(µ-1,1-N3)(N3)]n (2). The complex was prepared by a procedure similar to that for 1, using L2 instead of L1. Yield, 41.6%. Anal. Calcd. for C12H9ClCuN8: C, 39.57; H, 2.49; N, 30.76. Found: C, 39.43; H, 2.63; N, 30.78%. Main IR bands (cm-1): 2055vs, 2033s, 1595m, 1485m, 1443w, 1341m, 1091m, 1009m, 920w, 835m, 773m, 704m. X-ray Crystallographic Study. Diffraction intensity data for single crystals of 1 and 2 were collected at room temperature on a Nonius Kappa CCD area detector equipped with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å). Empirical absorption corrections were applied using the Sortav program.23 The structure was 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.24 Hydrogen atoms were placed at calculated positions and refined isotropically using the riding model. Pertinent crystallographic data and structure refinement parameters are summarized in Table 1. The powder XRD patterns of the bulk samples of 1 and 2 were measured on a Rigaku D/MAX-2000 diffractometer using graphite-monochromated Cu KR radiation (λ ) 1.5418 Å). The measured patterns are in good agreement with those calculated from the single-crystal data (see Supporting Information).

Results and Discussion IR Spectra. The IR spectra of the two complexes are quite similar. In the 2000-2100 cm-1 region expected for the νas(N3) absorption, the occurrence of two sharp and strong bands at about 2055 and 2033 cm-1 indicates the presence of two different azido groups.4c,18a The medium band at ca. 1340 cm-1 is assignable to the azido symmetric νs(N3) stretching mode. The ν(CdN) absorption characteristic of the Schiff base ligands occurs at ca. 1590 cm-1 as a medium band. Description of the Structures. The structure of 1 consists of zigzag uniform chains in each of which neighboring Cu(II) chromophores are related by a c glide in the P21/c space group and linked by single azido bridges in the EO mode. A perspective view of the chain structure is depicted in Figure 1, and selected bond lengths and angles are listed in Table 2. In the complex, each Cu(II) ion is placed in a distorted square pyramidal environment, which is completed by two nitrogens from the bidentate L1 ligand and two azido ions at the basal positions, and a third azido ion at the apical position. The basal Cu-N distances (av.

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Figure 1. A perspective view of the chain structure of 1 with the atom labeling scheme. The thermal ellipsoids were drawn at the 30% possibility level. Symmetry codes: A, x, -y + 3/2, z + 1/2; B, x, -y + 3/2, z - 1/2; C, x, y, z + 1. Table 2. Selected Bond Lengths (Å) and Angles (°) for the Complexesa Cu(1)-N(1) Cu(1)-N(2) Cu(1)-N(3) Cu(1)-N(6) Cu(1)-N(6A) N(3)-N(4) N(4)-N(5) N(6)-N(7) N(7)-N(8) N(1)-Cu(1)-N(6) N(1)-Cu(1)-N(6A) N(6)-Cu(1)-N(6A) N(2)-Cu(1)-N(3) N(2)-Cu(1)-N(6) N(2)-Cu(1)-N(1) N(2)-Cu(1)-N(6A) N(3)-Cu(1)-N(6) N(3)-Cu(1)-N(1) N(3)-Cu(1)-N(6A) Cu(1)-N(6)-Cu(1B) N(7)-N(6)-Cu(1) N(7)-N(6)-Cu(1B) N(4)-N(3)-Cu(1) N(5)-N(4)-N(3) N(8)-N(7)-N(6)

1

2

2.034(2) 2.045(2) 1.957(2) 1.961(2) 2.416(2) 1.194(3) 1.148(3) 1.206(3) 1.154(3) 150.36(9) 90.95(8) 117.67(9) 169.48(10) 93.47(9) 80.36(9) 85.71(8) 96.66(11) 92.13(10) 87.06(10) 113.6(1) 127.40(19) 117.11(17) 124.0(2) 176.0(3) 175.8(3)

2.031(2) 2.032(2) 1.940(2) 1.951(2) 2.598(2) 1.195(3) 1.147(3) 1.196(3) 1.154(3) 154.49(9) 84.70(8) 118.54(10) 167.47(9) 91.96(9) 80.23(8) 84.70(8) 99.23(10) 91.79(10) 87.37(9) 107.01(10) 132.71(19) 112.48(16) 123.7(2) 176.1(3) 174.5(3)

a Symmetry codes: A, x, -y + 3/2, z + 1/2; B, x, -y + 3/2, z 1/2 for 1; A, -x + 1/2, y, z + 1/2; B, -x + 1/2, y, z - 1/2 for 2.

2.04 Å) for the L1 ligand is somewhat longer than the basal Cu-N(azido) distances (av. 1.96 Å), while the apical Cu-N distance (2.416 Å) is significantly longer than the basal distances, indicating a rather weak axial coordinative interaction. The derivations of the four basal nitrogen donors from the mean basal plane are -0.312(1), 0.307(1), 0.278(1), and -0.272(1) Å for N1, N2, N3, and N6, respectively, and the Cu atom is 0.210(1) Å out of the plane toward the apex. The diagonal basal N-Cu-N angles [150.36(9) and 169.5(1)°] and the basal-apical N6-Cu-N6A angle [117.67(9)°] are significantly deviated from the ideal values. These deviations result in a large distortion of the square pyramidal geometry toward trigonal bipyrimidal. The distortion parameter τ, defined as |β - R|/60 by Addison et al.,25 is 0.317, where β and R are the two diagonal basal bond angles. There are two different types of azido ions in the compound, one as a terminal ligand in the basal position

Figure 2. A perspective view down the a axis showing the layer formed via hydrogen bonds in 1. Hydrogen atoms except those involved in hydrogen bonding have been omitted for clarity. Symmetry code D: -x + 1, y - 1/2, -z + 3/2.

and the other, in the end-on mode, as the only bridge between metal ions. Both types of azido ions are quasilinear with the N-N-N angles being ca. 176° and exhibit asymmetric N-N bond lengths with the bonds involving the donor atoms being relatively long. The Cu-N-Cu bridging angle is 113.6(1)°, and the Cu‚‚‚Cu distance is 3.670 Å. The EO bridge assumes an basalapical disposition with asymmetric Cu-N distances, i.e., the same nitrogen atom of the bridge resides on the apical position of one copper but in the basal plane of the neighboring copper, with the apical Cu-N distance being significantly longer than the basal one (Table 2). Such a disposition is typical of the single EO azido bridges in the three complexes reported previously.12,15 The singly bridged Cu(II) chains run along the c direction, and there exist interchain C-H‚‚‚N hydrogen bonds between the azomethine CH groups of the Schiff bases and the uncoordinated terminal nitrogens of the nonbridging azido ligands (C6-H‚‚‚N5D, where D: -x + 1, y - 1/2, -z + 3/2) between neighboring chains (Figure 2), the relevant parameters being 2.53 Å for the H‚‚‚N distance, 3.367(4) Å for the C‚‚‚N distance, and 149.9° for the C-H‚‚‚N angle. The weak hydrogen bonds interlink the neighboring chains into thick layers parallel to the [100] plane, and the shortest interchain Cu‚ ‚‚Cu distance within a layer is 9.31 Å [Cu1‚‚‚Cu1 (1 x, 1 - y, 1 - z)]. The layers are stacked down the a direction without indications of hydrogen bonding or π-π interactions, and the shortest interlayer Cu‚‚‚Cu distance is 9.67 Å [Cu1‚‚‚Cu1 (1 + x, 1 + y, 1 + z)]. Although compound 2 crystallized in a space group (Pccn) different from that of 1, it consists of 1D chains that are isostructural to those in 1 (Figure 3), the neighboring Cu(II) ions in each chain being also related by a c glide. The basal Cu-N distances show no significant differences from those of 1 (Table 2), but the asymmetry of the EO azido bridging fragment is more significant, with the apical Cu-N distance being as long as 2.598(2) Å. This is indicative of a very weak axial coordination. The derivations of the basal donors from the mean basal plane are slightly smaller ((0.28 and (0.25 Å), and the Cu atom is 0.136(1) Å out of the plane toward the apex. The parameter describing the distortion of the square pyramidal geometry toward trigonal bipyrimidal is τ ) 0.217, smaller than that for 1. In the azido-bridging moiety, the Cu-N-Cu angle [107.0(1)°]

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Figure 3. A perspective view of the chain structure of 2 with the atom labeling scheme. The thermal ellipsoids were drawn at the 30% possibility level. Symmetry codes: A, -x + 1/2, y, z + 1/2; B, -x + 1/2, y, z - 1/2; C, x, y, z + 1.

Figure 5. χ and χT versus T plots for complexes 1 (top) and 2 (bottom). The solid lines represent the best fit of the experimental data. Figure 4. A perspective view down the b axis showing the layer formed via hydrogen bonds in 2. Hydrogen atoms except those involved in hydrogen bonding have been omitted for clarity. Symmetry code D: x - 1/2, -y + 1, -z + 1/2.

is smaller than that of 1, but the Cu‚‚‚Cu distance (3.677 Å) is essentially identical, as a result of the compensation between the longer Cu-N distance and the smaller Cu-N-Cu angle. The packing pattern of the chains in 2 also resembles that in 1: the chains run along the c direction, and are interlinked by weak C-H‚‚‚N hydrogen bonds into supramolecular layers, with the azomethine C-H groups of the Schiff bases as hydrogen donors (Figure 4). However, the hydrogen acceptors in 2 are the uncoordinated terminal nitrogens of the bridging azido ligands, instead of the nonbridging ones in 1. The C6‚‚‚N8D (D: x - 1/2, -y + 1, -z + 1/2) distance is 3.377(4) Å, and the H‚‚‚N distance and the C-H‚‚‚N angle are 2.50 Å and 157.5°, respectively. The shortest interchain Cu‚‚‚ Cu distance within a layer is 9.16 Å [Cu1‚‚‚Cu1 (-x, -y + 1, -z + 1)]. The layers are parallel to the [010] plane and stacked down the b direction without indications of hydrogen bonding or π-π interactions, and the shortest interlayer Cu‚‚‚Cu distance is 7.59 Å [Cu1‚‚‚ Cu1 (-x + 1/2, -y + 1/2, z)]. Magnetic Properties. The magnetic susceptibilities (χ) of the two complexes were measured in the 3-300 K temperature range and are shown as χ and χT versus T plots in Figure 5. The temperature dependence of the reciprocal susceptibilities for 1 and 2 obeys the CurieWeiss law with C ) 0.41 emu mol-1 K, θ ) -3.8 K, and

Figure 6. Magnetization curves for complexes 1 (O) and 2 (4) at 1.8 K. The solid lines represent the curve predicted by the Brillouin function with S ) 1/2 and g ) 2.04.

C ) 0.43 emu mol-1 K, θ ) -6.7 K, respectively. The negative θ values indicate that an antiferromagnetic interaction is operative between neighboring Cu(II) ions. The C values correspond to the spin-only value expected for an uncoupled Cu(II) ion with g ) 2.08 and 2.12, respectively. These are consistent with the experimental χT values of 0.41 and 0.42 emu mol-1 K at 300 K for 1 and 2, respectively. Upon cooling of the sample, the χ values increase monotonically, and the χT products decrease first slowly and then quickly to 0.21 and 0.15

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Table 3. Structural and Magnetic Parameters for the Single EO Bridges in Cu(II) Complexes complexa

Cu-N (Å)b

Cu-N-Cu (°)

Cu‚‚‚Cu (Å)

τc

J (cm-1)

[Cu2(µ-oxen)(µ-1,1-N3)2(Br)]n [Cu4(µ-oxen)2(µ-1,1-N3)2(µ-1,3-N3)]n(ClO4)n

1.98, 1.95 (bb) 1.98, 1.98 (bb) 2.41, 1.95 (ba) 2.28, 2.01 (ba) 2.34, 1.99 (ba) 2.30, 1.97 (ba) 2.42, 1.96 (ba) 2.60, 1.95 (ba)

112.5 111.8 97.3 130.0 116.6 110.9 113.6 107.1

3.27 3.27 3.28 3.88 3.69 3.52 3.67 3.68

0.05, 0.08 0.015 0.19 0.02, 0.10 0.21, 0.10 0.21, 0.28 0.32 0.22

-85.7 d d -11.5 14.1 d -2.2 -3.7

[Cu2(hppz)2(N3)2(µ-1,1-N3)(µ-1,3-N3)]n [Cu2(L)2(N3)2(µ-1,1-N3)(µ-1,3-N3)]n [Cu2(Me-L)(µ-1,1-N3)4]n [Cu(L1)(N3)(µ-1,1-N3)]n, 1 [Cu(L2)(N3)(µ-1,1-N3)]n, 2

ref 15b 15c 15d 12 12 this work this work

a H oxen ) N,N′-bis(2-aminoethyl)oxamide, hppz ) homopiperazine, L ) 2-(pyrazol-1-ylmethyl)pyridine, Me-L ) 2-(3-methylpyrazol2 1-ylmethyl)pyridine. b The letters in the parenthesis indicate the disposition modes of the single azido bridges between metal ions: bb ) basal-basal disposition, ba ) basal-apical disposition. c The distortion parameter of the coordination geometry around the Cu atom.25 d Not reported.

emu mol-1 K at 3 K for 1 and 2, respectively, confirming the antiferromagnetic interactions. The antiferromagnetic interactions in the complexes are also supported by the field-dependent magnetizations measured at 1.8 K (Figure 6). As the field is increased from 0 to 6 T, the magnetization values of 1 and 2 increase much more slowly than those predicted by the Brillouin function for noninteracting Cu(II) systems. The magnetization values at the field of 6 T are 0.84 and 0.57 Nβ, respectively, significantly lower than the expected saturation values. Moreover, the magnetization value of 2 is significantly lower than that of 1, supporting that the antiferromagnetic interaction in 2 is stronger than that in 1. According to the structural data, the antiferromagnetic interactions should be attributed to intrachain superexchange mediated via the EO bridges. To simulate the experimental magnetic behavior, we used the following numerical expression for uniform antiferromagnetic chains of S ) 1/2:26

χM )

0.25 + 0.074975x + 0.075235x2 Ng2β2 kT 1 + 0.9931x + 0.172135x2 + 0.757825x3 (1)

with x ) |J|/kT, and J is the coupling parameter based on the isotropic spin Hamiltonian H ) -JΣSiSi+1. The least-squares fits of the experimental data to the above expression led to J ) -2.2 cm-1 with g ) 2.04 for 1, and J ) -3.7 cm-1 with g ) 2.08 for 2. The J parameters confirm that weak antiferromagnetic interactions are mediated by the single EO azido bridges in 1 and 2. These rather weak magnetic interactions are consistent with the structural data and can be justified by considering the geometry around the copper atoms and the disposition of the bridging azido ion between neighboring Cu(II) ions.1 The singly occupied orbital around the square pyramidal Cu(II) ion is mainly of dx2-y2 type lying in the basal plane, with a small contribution from dz2 due to the distortion of the coordination geometry. Consequently, the spin density of one Cu(II) ion is effectively delocalized toward the azido nitrogen atom that resides in the basal plane of the Cu(II) ion, but the delocalization of the spin density of the neighboring Cu(II) ion toward the same nitrogen atom is poor because the nitrogen atom occupies the apical position of the second Cu(II) ion with a longer distance. Therefore, the overlap between the magnetic orbitals of the two Cu(II) ions is rather small, and the resulting magnetic exchange is predicted to be rather weak. This

situation contrasts with that for the EO azido bridge that adopts a symmetric basal-basal disposition. It has been established that the symmetric EO azido bridge, which usually occurs in pair or coexists with other bridges, mediates medium-to-strong ferromagnetic interactions for small Cu-N-Cu bridging angles or antiferromagnetic interactions for larger bridging angles.8,9 The critical angle is 104° according to empirical analyses,19a and 108° according to a density functional study.27 No theoretical investigation has been performed on the magnetic interaction mediated by the asymmetrical basal-apical EO azido bridge. As has been mentioned, the occurrence of the single EO ion as the only bridge between two metal ions is very rare. The structural and magnetic information of the known Cu(II) complexes containing such bridges is summarized in Table 3. The Cu(II) ions in these complexes assume the pseudo-square pyramidal geometry. The single EO azido bridge in [Cu2(µ-trans-oxen)(µ-1,1-N3)2(Br)]n [H2oxen ) N,N′-bis(2-aminoethyl)oxamide] adopts a quasi-symmetric basal-basal disposition between metal ions and mediates a relatively strong antiferromagnetic interaction,15b as expected for a bridging angle larger than the critical angle (see above). Both symmetric and asymmetric single EO azido bridges are present in [Cu4(µ-trans-oxen)2(µ-1,1-N3)2(µ1,3-N3)]n(ClO4)n,15c in which the interactions mediated by these bridges were not quantified, but the overall antiferromagnetic interaction between the binuclear Cu(oxen)Cu units has been mainly attributed to the symmetric bridges. On the other hand, the single EO azido bridges in the other complexes adopt the asymmetric basal-apical disposition and mediate relatively weak magnetic interactions, antiferromagnetic or ferromagnetic. As can been seen from Table 3, the dependence of the interaction upon the Cu-N-Cu bridging angle established for the symmetric EO azido bridge is invalid for the asymmetric one, and it is impossible to establish any general magnetostructural correlation with these limited experimental data. This situation is similar to that for the double EO bridge, which consists of two asymmetric basal-apical EO azido ions,12-14 as has been summarized by us recently.12 Conclusions While our previous work suggested bidentate Schiff base coligands derived from 2-pyridylaldehyde and aniline derivatives form 1D Mn(II) complexes with alternating double EO-double EE azido bridges, the present paper shows that the L1 and L2 Schiff bases

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form 1D copper(II) coordination polymers with single azido bridges. The complexes represent the first compounds that contain only single azido bridges in the EO mode. The single bridge assumes an asymmetric basalapical disposition between metal ions and mediates a weak antiferromagnetic interaction. This contribution exemplifies the remarkable diversity of Cu(II)-azido systems, and we believe that there are still great potentials in finding novel Cu(II)-azido structures with new coligands. Acknowledgment. We are thankful for the financial support of NSFC (20201009, 20490210, 20221101, and 20423005) and the Foundation of Science and Technology Development of Shanghai (03ZR14024).

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(11)

(12) (13)

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Supporting Information Available: Crystallographic data in CIF format and XRD patterns in PDF format for the crystal structures. This material is available free of charge via the Internet at http://pubs.acs.org. (15)

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