Journal Information
Journal ID (publisher-id): chemical
Title: Journal of the Korean Chemical Society
Translated Title (ko): 대한화학회지
ISSN (print): 1017-2548
ISSN (electronic): 2234-8530
Publisher: Korean Chemical Society대한화학회
The transition metal(II) polyaza macrocyclic complexes with the axial ligands have attracted considerable interest due to their importance as models for metalloenzyme active sites1−4 and as selective complexing agents for metal ions.5−7 The structures and chemical properties of such compounds are affected by various factors, such as the type and synthetic difference of the axial ligands. For example, the complexes [Zn(L)(NCS)]NCS and [Zn(L)(H2O)]Cl·INT·3H2O (L=3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,01.18,07.12]docosane, INT=isonicotinate) show that the zinc atoms are coordinated to the four secondary amines of macrocycle and to the nitrogen and oxygen atoms of the coordinated cyanate and water molecules,8,9 which reveal a five coordinate square pyramidal environment. However, the crystal structures of [Zn(L1)]X2 (L1=2,5,9,12-tetramethyl-1,4,8,11-tetraazacyclo tetradecane; X=H2O, N3−, NCS−) have an axially elongated octahedral geometry with two axial ligands and adopt the trans-III conformation.10,11 The different molecular topologies in these complexes may be due to the different coordination modes of anions.
In order to better understand some aspects of zinc(II) complexes of tetraaza macrocycle with axial ligands, we report the syntheses, crystal structures and chemical properties of the zinc(II) complexes [Zn(L)(H2O)2]⋅2NO2 and [Zn(L)(NO3)2] (L=3,14-dimethyl-2,6,13,17-tetraaza tricyclo[14,4,01.18,07.12]docosane).
EXPERIMENTAL▼
Materials and Physical Measurements
All chemicals used in syntheses were of reagent grade and were used without further purification. The macrocycle 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,01.18,07.12] docosane (L) was prepared according to the literature method.12 IR spectra were recorded with a Perkin-Elmer Paragon 1000 FT-IR spectrophotometer (Perkin-Elmer, Waltham, MA, USA) using KBr pellets. DSC and TGA (Mettler Toledo, Lausanne, Switzerland) were performed under flowing nitrogen at a heating rate of 10 °C min-1 using an SDT 2960 Thermogravimetric Analyzer. Elemental analyses (C, H, N) were performed on a Perkin-Elmer CHN analyzer.
Synthesis of [Zn(L)(H2O)2]⋅2NO2 (1)
ZnCl2 (136 mg, 1.0 mmol) and KNO2(170 mg, 2.0 mmol) were added to a methanol solution (20 mL) of L (336 mg, 1.0 mmol). The mixture was heated to reflux for 1 h and then cooled to room temperature. The solution was filtered and left at room temperature until colorless crystal formed. The product was recrystallized from a hot H2O/CH3CN (1:1 v/v, 20 mL) mixture. Yield: 65%. Calc. (found) for C20H44N6O6Zn: C, 45.33 (45.26); H, 8.37 (8.48); N, 15.86 (15.75)%. IR (KBr, cm−1): ν(NH) 3158, νas (O2N) 1445, νs (O2N) 1058, cm−1.
Synthesis of [Zn(L)(NO3)2] (2)
This compound was synthesized as colorless crystals by a reaction similar to that of 1, except for the use of KNO3 instead of KNO2. The product was recrystallized from a hot H2O/CH3CN (1:1 v/v, 20 mL) mixture. Yield: 65%. Calc. (found) for C20H44N6O6Zn: C, 45.33 (45.26); H, 8.37 (8.48); N, 15.86 (15.75)%. IR (KBr, cm-1): ν(NH) 3166, νs(O3N) 1356 cm-1.
Crystallography
Single crystal X-ray diffraction measurement for compound was carried out on a Bruker APEX II CCD diffractometer using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å). Intensity data were measured at 100(2) K by ω-2θ technique. Accurate cell parameters and an orientation matrix were determined by the least-squares fit of 25 reflections. The intensity data were corrected for Lorentz and polarization effects. An empirical absorption correction was applied with the SADABS program.13 The structure was solved by direct methods14 and the least-squares refinement of the structure was performed by the SHELXL-97 program.15 For 1, all atoms except all hydrogen atoms were refined anisotropically. For 2, all atoms except all hydrogen atoms and 15 atoms (N2, N3, N4, N5, O2, O3, O4, O6, C6, C8, C10, C11, C14, C18, C20) were refined anisotropically. The hydrogen atoms were placed in calculated positions allowing them to ride on their parent C atoms with Uiso(H) = 1.2Ueq (C or N). The crystallographic data, conditions used for the intensity collection, and some features of the structure refinement are listed in Table 1. Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Center, CCDC Nos. 1032374 for compound 1 and 1032375 for compound 2. Copies of this information may be obtained free of charge from the Director, CCDC, 12 Union Road, Cambridge, CB2, 1EZ, UK (fax: +44-1223-336033; e-mail: deposit@ccdc.cam.uk or http://www.ccdc.cam.ac.uk).
Table1.
Crystallographic data
aR1 = || Fo |−| Fc ||/Σ| Fo |.
bwR2 = [Σ[w(Fo2-Fc2)2]/Σ[w(Fo2)2]]1/2.
RESULTS AND DISCUSSION▼
The macrocyclic ligand skeleton of the present compounds adopts the most stable trans-III (R,R,S,S) configuration with two chair six-membered and two gauche five-membered chelate rings. The N-Zn-N angles of the six-membered chelate rings for the complexes are larger than those of the five-membered chelate rings.
An ORTEP drawing16 of [Zn(L)(H2O)2]⋅2NO2 (1) with the atomic numbering scheme is shown in Fig. 1. Selected bond lengths and angles are listed in Table 2. The title compound consists of a [Zn(L)(H2O)2]2+ cation and two nitrite anions. The coordination environment around Zn atom shows an axially elongated octahedron with four secondary amines of the macrocycle and two water molecules at the axial position. An inversion center exists on the central Zn atom. The Zn-N bond distances are 2.087(3) and 2.118(3) Å, which are similar to those found in Zn(O2CoCH3)([14] aneN4)(ClO4) (2.088(3) and 2.111(3) Å).17 The Zn-Ow bond distance is 2.331(3) Å, which is comparable to that observed for trans-[Zn(L)(H2O)2]Cl2 (2.338(3) Å).18 The axial Zn-Ow linkage is not perpendicular to ZnN4 plane as the Ow-Zn-N angles range from 85.83(12) to 94.17(12)°. Interestingly, the water molecules are hydrogen bonded to the nitrite anions [Ow-HOw1···O(2)#3 2.826(6) Å, 167(6)°; Ow-HOw2···O(1)#3 2.759(6) Å, 171(6)°; symmetry code #3: x, y, z+1 (Fig. 1 and Table 3).
Figure1.
An ORTEP drawing (30% probability ellipsoids) of [Zn(L)(H2O)2]⋅2NO2 (1) with the atomic numbering scheme. The hydrogen bonds are shown as dashed lines.
Table2.
Selected bond distances (Å) and angles (°) for [Zn(L)(H2O)2]⋅2NO2 (1)
Symmetry codes: (#1) −x+1, −y+1, −z+1 (#2) −x+1, −y+1, −z.
Table3.
Hydrogen bonding parameters (Å, °) for [Zn(L)(H2O)2]⋅2NO2 (1)
| D-H···A | D-H (Å) | H···A (Å) | D···A (Å) | D-H···A (°) |
|---|---|---|---|---|
| Ow-HOw1···O(2)#3 | 0.84(7) | 2.00(7) | 2.826(6) | 167(6) |
| Ow-HOw2···O(1)#3 | 0.81(6) | 1.96(6) | 2.759(6) | 171(6) |
Symmetry codes: (#3) x, y, z+1.
An ORTEP drawing16 of [Zn(L)(NO3)2] (2) with the atomic numbering scheme is shown in Fig. 2. Selected bond distances and angles are listed in Table 4. The zinc(II) ion is coordinated by four nitrogen atoms of the macrocyclic ligand and two oxygen atoms of the nitrate ligand in a six-coordinated octahedral geometry. The average Zn-N (secondary amines) distance of 2.097(4) Å is very similar to that found for 1 and shorter than the axial Zn-O(1) and Zn-O(4) distances of 2.299(4) and 2.306(4) Å, giving an axially elongated octahedral geometry. Also, the axial Zn-O(1) and Zn-O(4) linkages are not perpendicular to the ZnN4 plane with N-Zn-O(1) and N-Zn-O(4) angles of 83.30(17) and 97.06(18)°, respectively. The Zn-O(1)-N(5) and Zn-O(4)-N(6) angles related to the nitrate ligand are 133.1(3) and 134.4(4)°. Interestingly, the secondary amines of the macrocycle are also hydrogen bonded to the oxygen atoms of the nitrate groups [N(1)-H(1)···O(3)#1 2.997(6) Å, 152.1°; N(2)-H(2)···O(2) 2.998(7) Å, 152.4°; N(3)-H(3)···O(6)#2 3.020(6) Å, 150.2°; N(4)-H(4)···O(5) 2.970(6) Å, 149.7°], to form the one-dimensional hydrogen-bonded infinite chain (Fig. 3 and Table 5).
Figure2.
An ORTEP drawing (30% probability ellipsoids) of [Zn(L)(NO3)2] (2) with the atomic numbering scheme. The hydrogen bonds are shown as dashed lines.
Table4.
Selected bond distances (Å) and angles (°) for [Zn(L) (NO3)2] (2)
Table5.
Hydrogen bonding parameters (Å, °) for [Zn(L)(NO3)2] (2)
Symmetry code: (#1) x+1, y, z (#2) x−1, y, z.
The IR spectra of the complexes 1 and 2 show bands at 3158 and 3166 cm-1, corresponding to the ν(NH) of the coordinated secondary amines of the macrocycle. For 1, the bands at 1445 and 1058 cm-1 are assigned to the νas(O2N) and νs(O2N) of the nitrite group. For 2, the strong band at 1356 cm-1 is assigned to the νs(O3N), which indicates the coordination of the oxygen atom between NO3− and Zn(II) atom. The TGA diagrams of 1 and 2 further support the structure determined by X-ray diffraction method (Fig. 4 and Fig. 5). The compounds were heated from 25 to 1000 °C in nitrogen gas. For 1, the first weight loss is observed from 25 to 179 °C, which is due to the loss of two water molecules (observed 6.6%; calculated 6.8%). A second weight loss corresponding to the macrocycle and two nitrite ligands (observed 78.2%; calculated 77.8%) is found in the temperature range 242-581 °C. A final weigh loss is observed above 581 °C corresponding to the black residue of ZnO (observed 15.2%; calculated 15.4%). For 2, the first weight loss is observed from 251 to 546 °C, which is due to the loss of the macrocycle and two nitrate ligands (observed 84.7%; calculated 84.5%). Further weigh loss is observed at 546-1000 °C and yields a black residue of ZnO (observed 15.3%, calculated 15.5%). The formation of ZnO accompanies the decomposition of the macrocycle ligand in the zinc(II) complex.19
CONCLUSION▼
The crystal structures of the compounds 1 and 2 show a distorted octahedral coordination geometry around the zinc(II) ion, with four secondary amines and two oxygen atoms of the two water and two nitrate ligands at the axial position. The secondary amines of the compound 2 are also hydrogen bonded to the oxygen atoms of the nitrate groups, to form the one-dimensional hydrogen-bonded infinite chain. The TGA behaviors of the complexes are significantly affected by the nature of the tetraaza macrocycle and the axial ligands.