Synthesis and Characterization of Two Binuclear Macrocyclic Zinc(II) Complexes by Anion Exchange①

OU Gung-Chun HUANG Zhong-Wen PAN Ze-Yi ZHOU Dong-Li YUAN Xin-You (Deprtment of Biology nd Chemistry, Hunn University of Science nd Engineering, Yongzhou, Hunn 425199, Chin)

b (Key Laboratory of Functional Organometallic Materials of Hunan Province College, Hengyang Normal University, Hengyang, Hunan 421008, China)

1 INTRODUCTION

The synthesis and characterization of heteronuclear metal complexes are a subject of much attention not only because of their unique physicochemical properties and functions, but also of their potential applications in the fields of metalloenzymes, electronic, magnetic and redox nature[1-7].Recently, an extensive exploration of coordination polymers consisting of ion exchange attracted particular interest from chemists, and many smart materials have been reported[8–12].

In our previous report, a few binuclear complexes[ML][VO3]2[13], [ML]2[V6O17][14], [NiL]3[V16O38(H2O)][13]and [NiL]5[V34O82][15]were obtained from the reactions of [ML](ClO4)2(L = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, M = Ni,Cu) with NH4VO3by anion exchange, and other binuclear complexes such as [ML]2[H2Mo5P2O23][16]and [NiL][Ni(CN)4][17,18]were given by other anions instead of ClO4-. The ClO4-anion of [ML](ClO4)2was easily substituted to form binuclear complexes by anion exchange. As a continuance of our research on the constructions of binuclear functional coordination polymers, two complexes {[ZnL(VO3)2]·0.33H2O}n(1) and [ZnL(H2O)2][Ni(CN)4] (2) were obtained when [ZnL](ClO4)2was reacted with NH4VO3and [Ni(CN)4]2-by anion exchange, respecttively. Complex 1 displays a three-dimensional structure constructed through the con-nections of [VO3]nn–chains with [ZnL]2+, generating one-dimensional channels. The monomers of[ZnL(H2O)2]2+and [Ni(CN)4]2-are connected through the intermolecular hydrogen bonds to form a two-dimensional sheet in 2.

2 EXPERIMENTAL

The macrocyclic ligand and its Zn(II) complexes were prepared according to the literature method[19–21]. All the other chemicals were commercially sourced and used without further purification. Elemental analyses were determined using an Elementar Vario EL elemental analyzer. IR spectra were recorded in the 4000～400 cm-1region using KBr pellets and a Bruker EQUINOX 55 spectrometer. TG analyses were performed on a Perkin-Elmer TGS-2 instrument in flowing air at a heating rate of 10 ℃·min-1. XRD data were recorded in a Bruker D8 ADVANCE X-ray powder diffractometer(Cu Kα, λ = 1.5418 ?).

2. 1 Synthesis of {[ZnL(VO3)2]·0.33H2O}n 1

An aqueous solution (20 mL) of NH4VO3(0.117 g,1 mmol) was layered with an acetonitrile solution(20 mL) of ZnL(ClO4)2(0.185 g, 0.33 mmol).Several weeks later, colorless block-shaped crystals of 1 were obtained in ～20% yield. Anal. found: C,34.62; H, 6.59; N, 10.23%. Calcd. for C16H36.67N4ZnO6.33V2: C, 34.70; H, 6.67; N, 10.12%.IR (KBr, cm–1): 934(v V=O), 909&795(v V–O).

2. 2 Synthesis of [ZnL(H2O)2][Ni(CN)4] 2

Similar to the synthesis of compound 1, using K2[Ni(CN)4] (0.079 g, 0.33 mmol) instead of NH4VO3gave 0.049 g (27%) of colorless blockshaped crystals of 2. Anal. found: C, 43.69; H, 7.49;N, 20.33%. Calcd. for C20H40N8ZnO2Ni: C, 43.78; H,7.34; N, 20.42%. IR (KBr, cm–1): 2133 (v CN).

2. 3 Structure determination

Single-crystal data for 1 and 2 were collected on a Bruker Smart 1000 CCD diffractometer with Mo-Kα radiation (λ = 0.71073 ?). Empirical absorption corrections were applied by using the SADABS program[22]. Both structures were studied using direct methods, which yielded the positions of all non-hydrogen atoms. These were refined first isotropically and then anisotropically. All the hydrogen atoms (expect those of nitrogen atoms and water molecules) were placed in the calculated positions with fixed isotropic thermal parameters and included in structure factor calculations in the final stage of full-matrix least-squares refinement. The hydrogen atoms of macrocyclic nitrogen atoms were located in difference Fourier map and refined isotropically, and hydrogen atoms of water molecule in 1 were not added as they were located in a special position. All calculations were performed using the SHELXTL system of computer programs[23]. For 1, O1W water molecule is disordered over two symmetry related sites with 50% occupancy. The crystallographic data for 1 and 2 are summarized in Table 1. Selected bond lengths and bond angles are listed in Table 2.Hydrogen bond parameters for 2 are given in Table 3.

3 RESULTS AND DISCUSSION

3. 1 Description of the structures

X-ray crystal structural analysis reveals that compound 1 contains one [ZnL]2+, two [VO3]-and one-third water (Fig. 1). Each Zn(II) atom lies on an inversion center and is coordinated with four macrocyclic nitrogen atoms in the equatorial plane and two oxygen atoms of [VO3]-anions in the axial positions. The average Zn-N distance of 2.110(4) ? is close to the Zn-O distance of 2.104(3) ?. The vanadium center in [VO4] tetrahedron is coordinated with two bridging oxygen atoms (Ob) and two terminal oxygen atoms (Ot), and the V-Obbond distances (1.786(3) and 1.815(3) ?) are longer than the V-Otdistances (1.618(3) and 1.644(3) ?) (Table 2).The [VO4] tetrahedra are connected through sharing μ2-oxygen atoms to form one-dimensional left- and right-handed helical chains of [VO3]nn-, similar to those previously reported[24], and each helical chain is further connected with adjacent helical chain with opposite chirality by macrocyclic complexes of[ZnL]2+, forming a central symmetrical three-dimensional framework with one-dimensional channel along the c-axis (Figs. 2 and 3). The channels are filled with water molecules. The pore size is 8.4? ×8.4? (measured by the C··C distances) along the c axis. The pores are filled with guest water molecules,and the solvent accessible volume of 1 was estimated by PLATON[25]to be 12.7% (702.7 ?–3)of the total crystal volume.

Table 1. Crystal Data and Structure Refinement for 1 and 2

Symmetry codes: A: 5/3-x, 1/3-y, 1/3-z; B: 2/3-y, -2/3+x-y, 1/3+z; D: -x, 1-y, 2-z

Table 3. Hydrogen Bond Parameters (?, °) for 2

Fig. 1. Molecular structure of 1 (H atoms and water molecule are omitted for clarity).Symmetry codes for the generated atoms: A (5/3-x, 1/3-y, 1/3-z), B (2/3-y, -2/3+x-y, 1/3+z), C (1+y, 1-x+y, -z)

Fig. 2. 1D zigzag chain of [VO3]nn- in 1

Fig. 3. 3D structure with 1D channels along the c-axis (The macrocyclic ligand L and the guest water molecules are omitted for clarity) and the left- and right-handed helical chain of [VO3]nn- in 1

Compound 2 contains one [ZnL]2+cation, one[Ni(CN)4]2-anion and two coordinated water molecules (Fig. 4). In 2, each Zn(II) atom lies on an inversion center, and is coordinated with four macrocyclic nitrogen atoms in the equatorial plane and two oxygen atoms of two water molecules in the axial positions. The Zn-N distances (2.086(3)～2.115(3) ?) are shorter than the Zn-O distances(2.308(3) ?), reflecting Jahn-Teller distortion. The monomers of [ZnL(H2O)2]2+are connected through the O–H··N (2.776(5) and 2.791(5) ?, Table 3)intermolecular hydrogen bonds between the two oxygen atoms of coordinated water and four nitrogen atoms of surrounding four [Ni(CN)4]2-anions,generating a two-dimensional hydrogen-bonded sheet (Fig. 5).

Fig. 4. Molecular structure of 2 (H atoms and water molecule are omitted for clarity).Symmetry codes for the generated atoms: D (-x, 1-y, 2-z), E (-x, 2-y, 2-z)

Fig. 5. Side view of two-dimensional hydrogen-bonded sheet in 2

3. 2 XRD and TG

The simulated and experimental XRPD patterns of compounds 1 and 2 are shown in Fig. 6. Their peak positions are in good agreement with each other, indicating the phase purity of the products.The thermogravimetric analyses were carried out in flowing air at a heating rate of 10 ℃·min-1in the temperature range of 25～800 ℃ for complex 1, as shown in Fig. 7. The TG curve of 1 shows that the observed weight loss (1.1%) is consistent with the calculated value (1.1%) below 250 ℃. The framework is stable up to about 300 ℃, and then begins to decompose upon further heating.

Fig. 6. XRPD patterns of complexes 1 and 2

Fig. 7. TG curve of complex 1

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