Synthesis and Structure of [Zn(PASC)2](ClO4)2·H2O

Yu Qing, Bao Xiaoge, Zhu Ligang, Bian Hedong, Liang Hong
(College of Chemistry and Chemical Engineering, Guangxi Normal University, Guilin 541004, China)

Received May 6, 2006;Supported by The Science Foundation of Guangxi and The Youth Science Foundation of Guangxi and The Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of MOE.

Abstract The complex [Zn(PASC)2](ClO4)2·H2O (PASC = pyridine-2-carbaldehyde semicarbazone, C7H8N4O) has been synthesized and characterized structurally. It crystallizes in the triclinic system, space group P¨© with a = 1.0064(2) nm, b = 1.1236(2) nm, c = 1.2252(2) nm, a = 113.017(6)o, b = 110.058(7)o, g = 93.780(6)o, V = 1.1653(3) nm3, wR2 = 0.1115 and Z = 2. The diffraction data (I>2s (I)) is 4677. The zinc ion has a distorted octahedron configuration with one carbonyl O atom, two imino N atoms and two pyridyl N atoms.

Thiosemicarbazones and their metal complexes are of considerable interest because of their potential pharmacological properties[1], and a wide variation in their modes of bonding and stereochemistry[2] whereas their semicarbazone analogs have been received much less attention[3]. However, semicarbazones are reported to possess versatile structural features and very good antifungal and antibacterial properties. Three structural isomers (E-, E‘- and Z-forms) are reported[4], and they can coordinate to the metal either as a neutral ligand or as a deprotonated ligand through the NNO atoms[4-5]. In our continuing studies[6-7], the title complex of the Schiff base (PASC) that are synthesized from the condensation of pyridine-2-carbaldehyde and semicarbazone had been reported[8].

    1.1 Materials and physical measurements
    All reagents were of analytical grade from commercial sources and were used without any further purification. The PASC was prepared according to the reference[8]. Elemental analyses for C, H and N atoms were carried out on a Model 2400 IIPerkin-Elmer elemental analyzer. The infrared spectrum was taken on a Perkin-Elmer Spectrum One FT-IR Spectrometer in the 4000–400 cm-1 region by using KBr pellets. The diffraction data were collected on a Bruker SMART CCD diffractometer using graphite monochromated MoKa radiation (l= 0.071073 nm).
    1.2 Preparation of [Zn(PASC)2](ClO4)2·H2O
    Single crystals of the title complex suitable for X-ray crystallographic analysis were obtained by solvothermal treatment of Zn(ClO4)2·6H2O (0.0744 g, 0.2 mmol) and the Schiff base ligand (0.0328 g, 0.2 mmol), methanol (0.2 mL) and ethanol (1.0 mL). The mixture was placed in a thick Pyrex tube (ca 20 cm long), then cooled with liquid N2, and air evacuated. The sealed tube was heated at 353K for two days to yield colorless crystals. Anal.calcd.(found) for C14H18Cl2N8O11Zn: C, 27.54 (27.48); H, 2.95 (2.98); N, 18.36 (18.28)%. IR (KBr, cm-1): 3436(s), 1662(ms), 1633(ms), 1474(m), 1108(s), 774(w), 627(m).
    1.3 Crystal structure determination and refinement
    Suitable crystals of the title complex (colorless, dimensions 0.26 mm ¡Á 0.24 mm ¡Á 0.20 mm) was used for the structure determination. Data collection at 293(2) K was carried out with a Bruker SMART CCD instrument using MoKa radiation. The structures were solved by direct methods in SHELXS-97[9] and refined by full-matrix least-squares, based on F2, using SHELXL-97[10]. All non-hydrogen atoms were assigned anisotropic thermal parameters. The coordinates of the hydrogen atoms were obtained from difference Fourier maps and refined with a common isotropic thermal parameter. For the title complex, convergence was reached at a final R1 = 0.0387 [for I > 2s(I)], wR2 = 0.1115 (for all data), with allowance for the thermal anisotropy for all non-hydrogen atoms. Details of data collection and processing are given in Table 1.Fig.1 ORTEP projection of [Zn(PASC)2]2+

Table 1 Crystal data and structure analysis parameter of the complex

Complex [Zn(PASC)2](ClO4)2·H2O V (nm3) 1.1653(3)
Crystal size (mm3) 0.26 ¡Á 0.24 ¡Á 0.20 Z 2
Empirical formula C14H18Cl2N8O11Zn Dc (g/cm3) 1.740
Temperature (K) 293(2) F (000) 620
Wavelength (nm) 0.071073 Scan mode w-2q
Formula weight 610.63 range for data collection (¡ã) 2.02-26.42
Crystal system triclinic Absorption coefficient(mm-1) 1.356
Space group P¨© Reflections collected 6734
a (nm) 1.0064(2) Independent reflections 4677
b (nm) 1.1236(2) Goodness-of-fit 1.044
c (nm) 1.2252(2) R [I > 2s (I)] 0.0387
a(¡ã) 113.017(6) wR2 0.1115
b(¡ã) 110.058(7) Maximum diff. peak (e/nm3) 489
g(¡ã) 93.780(6) Minimum diff. peak (e/nm3) -361

Fig.2 The 2-D network structure by hydrogen bonds of the title complex

Table 2 Selected bond lengths (nm) and bond angles (¡ã) of the complex

Bonds Aengths Bonds Lengths
Zn(1)-N(1) 0.2189(2) Zn(1)-N(6) 0.2079(2)
Zn(1)-N(2) 0.2070(2) Zn(1)-O(1) 0.2160(2)
Zn(1)-N(5) 0.2151(3) Zn(1)-O(2) 0.2176(2)
Bonds Angles Bonds Angles
N(2)-Zn(1)-N(6) 176.17(9) N(5)-Zn(1)-O(2) 149.22(9)
N(2)-Zn(1)-N(5) 106.09(9) O(1)-Zn(1)-O(2) 92.48(9)
N(6)-Zn(1)-N(5) 75.85(9) N(2)-Zn(1)-N(1) 75.54(9)
N(2)-Zn(1)-O(1) 74.32(9) N(6)-Zn(1)-N(1) 101.06(9)
N(6)-Zn(1)-O(1) 109.01(9) N(5)-Zn(1)-N(1) 96.04(9)
N(5)-Zn(1)-O(1) 93.73(9) O(1)-Zn(1)-N(1) 149.82(9)
N(2)-Zn(1)-O(2) 104.61(8) O(2)-Zn(1)-N(1) 93.55(9)
N(6)-Zn(1)-O(2) 73.62(9)
    The structure of the title complex consists of discrete [Zn(PASC)2]2+ cations, perchlorate counter-ions and water molecules.Figure 1 shows the ORTEP projection of [Zn(PASC)2]2+,and selected bond lengths and bond angles are listed in Table 2. The two neutral semicarbazone ligands are planar, and each set of the coordinating carbonyl O, imino N and pyridyl N atoms occupies a meridional plane of the octahedron around the Zn atom. The Zn1/O1/C7/N3/N2/C6/C1/N1 (mean deviation from plane = 0.04795 nm) and Zn1/O2/C14/N7/N6/C13/C8/N5 (mean deviation from plane = 0.00239 nm) planes are nearly perpendicular to each other (dihedral angle 81.2o). The perchlorate counter-ion is not involved in coordination, a feature that is also observed in bis{1-[(E)-2-pyridinylmethylidene] semicarbazide} cobalt(II) diperchlorate monohydrate[11]. .One perchlorate anion is much disordered, with the oxygen atoms occupying eight sites. The pyridine-2-carbaldehyde semicarbazone ligands possess an E configuration with respect to the azomethine double bond, which is different from bis(2-formylpyridine semicabazonato)nickel(II) [11].
    The Zn-N and Zn-O coordination distance are comparable with those reported for other zinc(II) complexes with 2-acetylpyridinesemicarbazone or 2,6-diacetylpyridine bis(semicarbazone) [2]. The C=O bond lengths [C(7) – O(1) = 0.1234(4) nm and C(14) – O(2) = 0.1240(3) nm] are close to those reported by Liang et al [6]. The distortions from ideal octahedral coordination of the zinc(II) are seen in the chelate bite angles, which are less than 90o. The supramolecular architecture is stabilized by an extensive 2-D network (Fig.2, Table 3) of hydrogen bonds (N-H···O) involving the cations, counter-ions and water molecules.

    Table 3
    Hydrogen-bonding geometry (nm, ¡ã) for the title complex
D-H···A ARU d(D-H)/nm d(H···A)/nm d(D···A)/nm ¡Ï(DHA)/¡ã
N(3)-H(3A)···O(8) 2555.03 0.086 0.209 0.29033 158
N(4)-H(4A)···O(6) 1445.02 0.086 0.254 0.31438 128
N(4)-H(4A)···O(5) 2555.02 0.086 0.254 0.32236 137
N(4)-H(4B)···O(7) 2555.03 0.086 0.222 0.30672 168
N(7)-H(7A)···O(9) 2566.03 0.086 0.199 0.28256 164
N(8)-H(8A)···O(5) 2565.02 0.086 0.257 0.33081 144
N(8)-H(8B)···O(10) 2566.03 0.086 0.224 0.30600 159

ARU-code: 2555. = -x, -y, -z; 1445. = -1+x, -1+y, z; 2566. = -x, 1-y, 1-z; 2565. = -x, 1-y, -z.