Synthesis and Characterization of Compartmental Macrocyclic Binuclear Copper(II) Complex with Bidentate Perchlorato Ligand

Results and Discussion

General Properties. The pale green perchlorato complex 1 is insoluble in cold solvents like methanol, acetone, and dimethylformamide, but has poor solubility in acetonitrile, dimethylsulfoxide, hot dimethylformamide, hot methanol, and hot acetone. In hot methanol, the air-stable moistureinsensitive complex 1 has lower value than molar conductance for 1:1 electrolytes. Thus, it seems that an anion coordination might exist in hot methanol.8 Such result is in general agreement with the expectation from the spectral data and the crystal structure of complex 1.

The electronic absorption spectrum of complex 1 shows different absorption bands of the dinuclear Cu(II)-chloro complex,5a indicating the different coordination environments for Cu(II) centers. The broad absorption band near 546 nm can be assigned to the spin-allowed d-d electronic transition of Cu(II) (3d9). This show the band arising from 2Eg→ 2T2g (Oh) transition, which exhibits the characteristic feature of Jahn-Teller effects of Cu(II) ions.9 The formation of dinuclear Cu(II) complex was inferable from elemental analysis, molar conductance and electronic absorption spectrum of the complex 1 as well as is evidenced by characteristic IR absorption bands and FAB mass spectrum. The IR spectrum of the perchlorato complex 1 displays the characteristic bands of coordinated perchlorate anion at 1150, 1110, 1085, and 641 cm−1.10 The significant ions observed in the FAB mass spectrum of complex 1 include [Cu(H[20]-DCHDC)]+ and [Cu2([20]-DCHDC)(ClO4)]+ at m/z 546 and 707, respectively.

Description of Crystal Structures. Pale green crystals of the complex 1, [Cu2([20]-DCHDC)(μ-O2ClO2)2]·1.6CH3CN·0.4CH3OH suitable for X-ray diffraction study were obtained by recrystallization from warm acetonitrile:CH3OH (1:1) solution. The structure of complex 1 with the atomic numbering scheme is shown in Figure 1. The summary of the crystal data, experimental details and refinement results for complex 1 is listed in Table 1. Selected bond lengths and angles relevant to the coordination geometry for crystals of complex 1 are listed in Table 2.

Table 1.Crystallographic Data and Structure Refinement for Complex 1

Table 2.Symmetry code: a−x, 1−y, −z.

The X-ray analysis reveals that 1 is compartmental macrocyclic dinuclear copper(II) complex bridged by two bidentate perchlorato ligand, which is located on a crystallographic inversion center (Figure 1(a)). Therefore, the asymmetric unit of 1 consists of one copper(II) ion, a half of [20]-DCHDC2− macrocyclic ligand, one perchlorato ligand, four-fifths of an acetonitrile molecule and one-fifth of an methanol molecule.

In crystal structure of 1, each copper(II) ion is six-coordinate, being bound to two oxygen and two imine nitrogen donors from each of the two N2O2 compartments of macrocyclic [20]-DCHDC2− ligand. The coordination sphere is completed by two oxygen atoms from two different perchlorato ligands. The copper(II) coordination in 1 can be described as a distorted octahedral geometry, where each of the two N2O2 compartments of macrocyclic [20]-DCHDC2− ligand satisfies four basal positions. The basal Cu-ligand bond distances are very close falling in the range 1.886(3)-1.900(2) Å, which are similar with those of chloro cupric complex with the [20]-DCHDC macrocyclic ligand.5a The remaining apical positions of the copper(II) center are occupied by two perchlorato ligands with somewhat longer contacts [Cu1-O2 2.586(2) Å and Cu1A-O3 2.660(2) Å] owing to the Jahn- Teller effect in d9 electronic configuration. The largest distortion from the regular octahedral geometry is occurred in the angle of O3-Cu1-O2i of 168.15(10) Å (Figure 1(a)), which may be due to the fact that the perchlorato ligands bridge between two neighboring Cu(II) ions in the end-toend (μ-1,3-O2-ClO2) configuration

Two Cu(II) centers in 1 are bridged by the two phenoxo oxygen atoms of [20]-DCHDC2− and two μ1,3-perchlorato ligands with the separation distance of 2.8786(9) Å, slightly longer than the sum of van der Waals radius of Cu atoms (2.86 Å).11 Thus, two Cu(II) ions accommodated within compartmental macrocyclic ligand are quadruply bridged by a bis(μ-phenoxo)-bis(μ-perchlorato) moiety, in which two perchlorato ligands exhibit the classical syn-syn bridging mode. To the best of our knowledge, complex 1 represents the first structurally characterized example of a macrocyclic dinuclear perchlorato Cu(II) complex containing two bridging perchlorate ligands.

Figure 1.(a) Crystal structure of complex 1 with the asymmetric atom-labeling scheme. (b) Perspective views of the unit cell with hydrogen bonds shown as dashed lines along the a-axis. All hydrogens, disordered atoms and solvent molecules are omitted for clarity. [Symmetry codes: i) −x, 1−y, −z.].

As shown in Figure 1(b) and Table 3, there are many nonclassic intermolecular C-H···O hydrogen bonds [average distance of H···O = 3.427(7) Å] in crystal packing structure of complex 1. The compartmental macrocyclic dinuclear copper(II) complexes, [Cu2([20]-DCHDC)(μ-O2ClO2)2], are cross-linked by intermolecular hydrogen bonds, resulting in the pseudo 3D framework with channel cavity. Disordered solvent molecules (acetonitrile and methanol) are accommodated in the channel cavity

In summary, the compartmental macrocyclic dinuclear Cu(II)-perchlorato complex was prepared by the anion exchange exchange of its chloride salt and fully characterized by element analysis, conductance, electronic and IR spectra as well as FAB-MS method. Its crystal structure determined by X-ray crystallography reveals the two distorted octahedral copper(II) centers are quadruply bridged by the two phenoxide oxygen atoms of [20]-DCHDC macrocyclic ligand as well as two μ1,3-perchlorato ligands. Furthermore, complex 1 exhibits the pseudo-3D supramolecular network generated by the C-H···O hydrogen bonds.

Table 3.Symmetry codes: ax+1, y, z; b− x, y+1/2, − z+1/2; cx+1, − y+1/2, z+1/2.

 

Experimental

General Methods. All chemicals were commercial analytical reagents and were used without further purification. Solvents used for electrochemical and spectroscopic studies were purified by standard procedures. 2,6-Diformyl-p-cresol (DFPC) was prepared with high yields by an improved oxidation method using active manganese(IV) dioxide. The two square pyramidal copper complex bridged by the two phenoxide oxygen atoms, [Cu2([20]-DCHDC)Cl2]·6H2O was synthesized in our laboratory as described earlier.5a

Measurements. Microanalyses of C, H, and N were carried out using LECO CHN-900 analyzer. Conductance measurements of the complexes were performed in CH3OH at 25 ± 1 ℃ using an ORION 162 conductivity temperature meter. IR spectra were recorded with a Bruker FSS66 FT-IR spectrometer. FAB-MS spectra were obtained on a JEOL JMS-700 Mass Spectrometer using argon (6 kV, 10 mA) as the FAB gas. The accelerating voltage was 10 kV and glycerol was used as the matrix. The mass spectrometer was operated in positive ion mode and mass spectra were calibrated by Alkali-CsI positive.

Synthesis of [Cu2([20]-DCHDC)(μ-O2Cl-O2)2]·1.6CH3CN·0.4CH3OH (1). To an aqueous solution (50 mL) of [Cu2([20]-DCHDC)Cl2]·6H2O (0.6986 g, 1 mmol), a saturated aqueous sodium perchlorate solution (15 mL) was added dropwise with stirring. The resulting mixture was refluxed for 2 h, and then pale green precipitate that formed was collected by filtration, thoroughly washed with water, and dried in vacuo. Yield 72%. Pale green crystals of the complex 1 suitable for X-ray diffraction study were obtained by recrystallization of from warm acetonitrile:CH3OH (1:1) solution. Anal. Calcd (Found) % for Cu2(C30H34N4O2)(ClO4)2(CH3CN)1.6(CH3OH)0.4: C, 45.49 (45.59); H, 4.59 (4.37); N, 8.84 (8.51). IR (KBr pellet, cm−1) 3310, 3024, 2927, 2859, 1627, 1550, 1448, 1382, 1313, 1240, 1150, 1110, 1085, 862, 769, 641, 502. λM (methanol): 108 ohm−1cm2mol−1.

X-ray Crystallography of Complex. The single crystal was attached to glass fibers and mounted on a Bruker SMART diffractometer equipped with a graphite-monochromated Mo Kα (λ= 0.71073 Å) radiation, and a CCD detector; 50 frames of two-dimensional diffraction images were collected and processed to obtain the cell parameters and orientation matrix. All data collections were performed at 173 K. Decay was monitored by 50 standard data frames measured at the beginning and end of data collection. The program SAINTPLUS12 was used for integration of the diffraction profiles. All of the calculations for the structure determination were carried out using the SHELXTL package.13 All nonhydrogen atoms were refined anisotropically and all hydrogen atoms were placed in idealized positions and refined isotropically in a riding manner along with the their respective parent atoms. In complex 1, four carbon atoms (C8, C10, C11, and C13) of cyclohexane moiety were disordered over two sites with site occupancy factor of 0.50. Moreover, lattice solvent molecules (acetonitrile and methanol molecules) were found to occupy two independent positions, which are too close to each other to be fully occupied at the same time. Accordingly, the SOFs of both molecules were refined with their sum fixed at 1, which resulted in the site occupancy factors of 0.80 for acetonitrile and 0.20 for methanol. The summary of the crystal data, experimental details and refinement results for complex 1 is listed in Table 1.

Crystallographic data for the structures reported here have been deposited with CCDC (Deposition No. CCDC-295088 for 1). These data can be obtained free of charge via http:// www.ccdc.cam.ac.uk/conts/retrieving.html or from CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, E-mail: deposit @ccdc.cam.ac.uk (or FIZ, D-76344, Eggenstein-Leopoldshafen, Germany, E-mail: crysdata@fiz-karlsruhe.de).