Di-μ-acetato-bis­[(2-acetyl­pyridine thio­semicarbazonato)zinc(II)]

The title compound, [Zn₂(C₂H₃O₂)₂(C₈H₉N₄S)₂], is a centrosymmetric dinuclear mol­ecule with two acetate bridging ligands in a syn–syn arrangement. The Zn^II atom is five-coordinated in a trigonal–bipyramidal configuration by three thio­semicarbazone atoms (two N and one S) and by an O atom from each of the two acetate groups.

S1. Comment

Metal complexes of Schiff bases synthesized by the condensation of 2-acetylpyridine and thiosemicarbazides, semicarbazides and other amines (Nomiya et al., 2001; West et al., 1993; Wang et al., 2004) have received much attention owing to their antimicrobial, cytotoxic and antioxidant activities (Reddy et al., 1999; Tarafder et al., 2001). However, only a few studies of the synthesis, spectroscopic characterization and antimicrobial activities of such compounds with the Schiff base derived from 2-acetylpyridine and thiosemicarbazide have been reported to date (Kasuga et al., 2003; Kovala-Demertzi et al., 2001).

Zinc(II) complexes with thiosemicarbazone ligands have been reported to have antitumour activities and to exhibit effects in in vitro cell proliferation and differentiation. However, few studies of the antimicrobial activities of zinc(II) complexes have been reported to date (Bermejo et al., 1997; Offiong & Martelli, 1993). Divalent zinc(II) complexes are influenced significantly by the reaction conditions, such as the solvent, pH, stoichiometry and reaction temperature (Ferrari et al., 1992; Casas et al., 2000). Furthermore, d¹⁰ metal polynuclear complexes, including those containing zinc, have been found to be thermally stable and to possess photoluminescence properties, a feature that has contributed immensely to the search for new materials (Weidenbruch et al., 1989; Kunkely & Vogler, 1990; Bertoncello et al., 1992; Wang et al., 2003; Sang & Xu, 2005). As far as we are aware, no crystal structure of a dinuclear Zn^II complex of 2-acetylpyridine thiosemicarbazone has been published to date. Here, we report the synthesis and crystal structure of the title complex, (I).

Complex (I) is an acetate-bridged dinuclear Zn^II compound (Fig. 1) which has inversion symmetry. The coordination geometry around Zn is a trigonal bipyramid, based on geometric parameter calculations: τ = (β-α)/60 gives τ = 0.55, taking O1—Zn1—N2 [121.35 (16)°] as β and O2—Zn1—N1 [88.35 (14)°] as α (Addison et al., 1984). The calculated τ value and the geometry of the complex are in agreement with those of dinuclear zinc(II) acetate complexes with similar thiosemicarbazone derivatives reported earlier (Garcia et al., 2002; Bresolin et al., 1997). Compound (I) (Fig. 1), which crystallizes as a centrosymmetric dinuclear molecule with the two acetate bridging ligands in a syn–syn arrangement, is five-coordinate, with both Zn atoms coordinated by three thiosemicarbazone atoms and by an O atom of each of the two acetate groups. The Zn···Zn distance of 3.749 (16) Å is long enough to rule out any metal–metal bonding.

As in other 2-pyridylthiosemicarbazones (Garcia et al., 2002; Bermejo et al., 2004), the Zn—N_im, Zn—N_py and Zn—S bond lengths in (I) (Table 1) increase in that order. The Zn—O bond distances are very similar [Zn—O1 = 2.015 (4) Å and Zn—O2 = 2.011 (3) Å], showing the non-staggered nature of the bridging acetate ion (Ainscough et al., 1987). The Zn1—S1 bond [2.3257 (16) Å] is much longer than the other bonds, indicating that the Zn—S bond is weaker compared with the others; this is in agreement with bond distances reported for other complexes of zinc(II) with similar thiosemicarbazones (Bresolin et al., 1997). The bridging acetate groups are nearly linear and show bent coordination modes with the metal atoms [O1—C9—02 = 126.1 (5)°, Zn1—O2—C9 = 125.1 (3)° and Zn—O1—C9 = 132.0 (3)°], which is very similar to a dinclear zinc thiosemicarbazone reported previously (Garcia et al., 2002)

The N2—Zn1—N1 (N2A—Zn1A—N1A) bond angle [75.59 (16)°] of the five-membered chelate ring is much smaller than 90°, as a result of the strain created by the five-membered chelate rings Zn1/N1/C5/C6/N2 and Zn1A/N1A/C5A/C6A/N2A (You & Zhu, 2005). The C6═N2 bond length [1.292 (5) Å] conforms to the normal value of 1.32 Å for a double bond, while the C8—N3 bond length [1.337 (6) Å] conforms to the normal value of 1.37 Å for a single bond (Allen et al., 1987). As one can observe, the Zn—N bond distances involving azomethine N atoms (N2 and N2A) and pyridyl N atoms (N1 and N1A) are almost the same length, at 2.128 (4) and 2.125 (3) Å, respectively, which suggests a charge delocalization over the entire ligand. This is considered important in thiosemicarbazones, especially those containing an aryl group (Palenik et al., 1974; Campbell, 1975).

In the crystal structure of (I) (Fig. 2), intermolecular hydrogen-bond contacts N4—H4B···O2ⁱ [3.070 (5) Å] and N4—H4A···N3ⁱⁱ [3.138 (6) Å] are observed [Table 2; symmetry code: (i) x − 1, y, z; (ii) −x, 1 − y, −z]. [Please check added symmetry codes] There are fewer intermolecular hydrogen bonds in (I) than in other complexes of 2-acetylpyridine thiosemicarbazones because of the absence of solvate molecules. The distances and angle for the interaction with the coordinated O atom are comparable with the N—H.·O intermolecular attraction in a dinuclear acetate-bridged zinc complex with a similar thiosemicarbazone (Garcia et al., 2002), but without the N4—H4A···N3ⁱⁱ interaction observed in the present case. The molecules of (I) are stacked along the a axis (Fig. 2) and are linked by short intermolecular hydrogen bonding between O2 and N3.

S2. Experimental

The 2-acetylpyridine thiosemicarbazone (APytsc) Schiff base was prepared according to the method of Offiong & Martelli (1993). Single crystals of the title complex suitable for X-ray diffraction study were obtained by the reaction of Zn(CH₃COO)₂·4H₂O with APytsc in a 1:1 molar ratio in an aqueous acetonitrile (1:3) solution [Volume? Temperature? Stirred for how long?], followed by slow evaporation of the solvents at room temperature over a period of two weeks.

S3. Refinement

H atoms attached to C atoms were placed in calculated positions, with aromatic C—H = 0.93 Å and methyl C—H = 0.96 Å, and were allowed to ride on their parent atoms. Methyl groups were allowed to rotate around the C—C axis. All H atoms were assigned U_iso(H) values of XU_eq(parent), with X = 1.2 for aromatic and water H atoms, and X = 1.5 for methyl H atoms.

Computing details

Data collection: SMART (Bruker, 2002); cell refinement: SMART; data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXTL (Bruker, 2002); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The molecular structure of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been ommitted for clarity. Atoms with the suffix A are at the symmetry position (−x, 1 − y, −z).
	Fig. 2. The packing of (I) in the crystal structure. Dashed lines indicate hydrogen bonds. Atoms with the suffix A are at the symmetry position (−x, 1 − y, −z).

Di-µ-acetato-bis[(2-acetylpyridine thiosemicarbazonato)zinc(II)]

Crystal data

[Zn2(C8H9N4S)2(C2H3O2)2]	Z = 1
Mr = 635.33	F(000) = 324
Triclinic, P1	Dx = 1.736 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 7.3690 (16) Å	Cell parameters from 2125 reflections
b = 8.4128 (18) Å	θ = 0–25°
c = 10.716 (2) Å	µ = 2.19 mm^−1
α = 76.124 (4)°	T = 293 K
β = 88.754 (4)°	Block, colourless
γ = 70.758 (4)°	0.20 × 0.14 × 0.08 mm
V = 607.7 (2) Å^3

Data collection

Bruker APEX area-detector diffractometer	2093 independent reflections
Radiation source: fine-focus sealed tube	1603 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.055
ϕ and ω scans	θmax = 25.0°, θmin = 2.7°
Absorption correction: multi-scan (SADABS; Bruker, 2002)	h = −8→8
Tmin = 0.699, Tmax = 0.839	k = −10→9
3048 measured reflections	l = −10→12

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.052	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.091	H-atom parameters constrained
S = 0.99	w = 1/[σ^2(Fo^2) + (0.0035P)^2] where P = (Fo^2 + 2Fc^2)/3
2093 reflections	(Δ/σ)max < 0.001
165 parameters	Δρmax = 0.49 e Å^−3
0 restraints	Δρmin = −0.44 e Å^−3

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt)etc.and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F,and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
O1	0.4760 (5)	0.7354 (5)	0.4881 (4)	0.0659 (12)
C1	0.9206 (8)	0.2227 (7)	0.3671 (6)	0.0578 (16)
H1	0.9220	0.2556	0.4439	0.069*
C2	1.0887 (8)	0.1198 (8)	0.3304 (7)	0.0682 (19)
H2	1.2019	0.0807	0.3824	0.082*
C3	1.0869 (9)	0.0758 (8)	0.2164 (7)	0.072 (2)
H3	1.2001	0.0081	0.1888	0.086*
C4	0.9177 (8)	0.1315 (7)	0.1422 (6)	0.0621 (18)
H4	0.9149	0.1017	0.0643	0.075*
C5	0.7523 (7)	0.2323 (6)	0.1850 (5)	0.0396 (13)
C6	0.5623 (7)	0.2895 (6)	0.1171 (5)	0.0409 (13)
C7	0.5349 (7)	0.2258 (7)	0.0036 (6)	0.0587 (17)
H7A	0.4017	0.2382	−0.0082	0.088*
H7B	0.6123	0.1057	0.0172	0.088*
H7C	0.5729	0.2925	−0.0718	0.088*
C8	0.1143 (7)	0.5355 (7)	0.1832 (5)	0.0439 (14)
C9	0.5713 (7)	0.7371 (7)	0.3892 (5)	0.0409 (13)
C10	0.6384 (8)	0.8888 (7)	0.3438 (7)	0.070 (2)
H10A	0.7762	0.8510	0.3554	0.105*
H10B	0.5825	0.9731	0.3926	0.105*
H10C	0.5998	0.9402	0.2542	0.105*
N1	0.7556 (6)	0.2772 (5)	0.2968 (4)	0.0430 (11)
N2	0.4236 (6)	0.3905 (5)	0.1671 (4)	0.0379 (10)
N3	0.2415 (6)	0.4486 (5)	0.1122 (4)	0.0394 (11)
N4	−0.0684 (6)	0.5958 (5)	0.1371 (4)	0.0563 (13)
H4A	−0.0978	0.5777	0.0658	0.068*
H4B	−0.1571	0.6530	0.1787	0.068*
O2	0.6090 (5)	0.6285 (5)	0.3259 (4)	0.0551 (11)
S1	0.1573 (2)	0.5806 (2)	0.32577 (16)	0.0627 (5)
Zn1	0.48893 (8)	0.44225 (8)	0.34260 (6)	0.0397 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.070 (3)	0.066 (3)	0.047 (3)	−0.008 (2)	0.018 (2)	−0.007 (2)
C1	0.050 (4)	0.073 (4)	0.048 (4)	−0.013 (3)	−0.008 (3)	−0.020 (3)
C2	0.044 (4)	0.078 (5)	0.070 (5)	−0.003 (3)	−0.006 (4)	−0.020 (4)
C3	0.051 (4)	0.080 (5)	0.080 (5)	−0.004 (4)	0.009 (4)	−0.033 (4)
C4	0.051 (4)	0.076 (4)	0.064 (5)	−0.017 (3)	0.008 (4)	−0.032 (4)
C5	0.039 (3)	0.039 (3)	0.043 (4)	−0.014 (3)	0.010 (3)	−0.012 (3)
C6	0.050 (3)	0.041 (3)	0.038 (3)	−0.022 (3)	0.013 (3)	−0.014 (3)
C7	0.056 (4)	0.070 (4)	0.060 (4)	−0.022 (3)	0.010 (3)	−0.034 (3)
C8	0.036 (3)	0.056 (3)	0.046 (4)	−0.022 (3)	0.007 (3)	−0.014 (3)
C9	0.028 (3)	0.047 (3)	0.040 (4)	−0.005 (3)	0.003 (3)	−0.007 (3)
C10	0.060 (4)	0.064 (4)	0.095 (6)	−0.027 (3)	0.022 (4)	−0.030 (4)
N1	0.047 (3)	0.045 (3)	0.040 (3)	−0.016 (2)	0.004 (2)	−0.015 (2)
N2	0.040 (3)	0.048 (3)	0.036 (3)	−0.023 (2)	0.008 (2)	−0.018 (2)
N3	0.035 (2)	0.054 (3)	0.036 (3)	−0.016 (2)	0.005 (2)	−0.021 (2)
N4	0.043 (3)	0.082 (3)	0.051 (3)	−0.016 (3)	0.006 (3)	−0.036 (3)
O2	0.057 (2)	0.065 (3)	0.066 (3)	−0.033 (2)	0.027 (2)	−0.041 (2)
S1	0.0484 (9)	0.0912 (12)	0.0538 (11)	−0.0114 (9)	0.0032 (8)	−0.0446 (10)
Zn1	0.0454 (4)	0.0472 (4)	0.0336 (4)	−0.0212 (3)	0.0060 (3)	−0.0154 (3)

Geometric parameters (Å, º)

O1—C9	1.259 (6)	C7—H7C	0.9600
O1—Zn1^i	2.014 (4)	C8—N4	1.331 (6)
C1—N1	1.327 (6)	C8—N3	1.333 (6)
C1—C2	1.369 (7)	C8—S1	1.719 (6)
C1—H1	0.9300	C9—O2	1.222 (5)
C2—C3	1.360 (8)	C9—C10	1.489 (7)
C2—H2	0.9300	C10—H10A	0.9600
C3—C4	1.373 (8)	C10—H10B	0.9600
C3—H3	0.9300	C10—H10C	0.9600
C4—C5	1.377 (6)	N1—Zn1	2.125 (4)
C4—H4	0.9300	N2—N3	1.361 (5)
C5—N1	1.343 (6)	N2—Zn1	2.128 (4)
C5—C6	1.468 (7)	N4—H4A	0.8600
C6—N2	1.294 (5)	N4—H4B	0.8600
C6—C7	1.485 (7)	O2—Zn1	2.010 (3)
C7—H7A	0.9600	S1—Zn1	2.3247 (16)
C7—H7B	0.9600	Zn1—O1^i	2.014 (4)
C9—O1—Zn1^i	132.1 (3)	O1—C9—C10	116.4 (5)
N1—C1—C2	122.2 (6)	C9—C10—H10A	109.5
N1—C1—H1	118.9	C9—C10—H10B	109.5
C2—C1—H1	118.9	H10A—C10—H10B	109.5
C3—C2—C1	118.6 (6)	C9—C10—H10C	109.5
C3—C2—H2	120.7	H10A—C10—H10C	109.5
C1—C2—H2	120.7	H10B—C10—H10C	109.5
C2—C3—C4	120.0 (6)	C1—N1—C5	119.4 (5)
C2—C3—H3	120.0	C1—N1—Zn1	125.2 (4)
C4—C3—H3	120.0	C5—N1—Zn1	115.4 (3)
C3—C4—C5	118.9 (6)	C6—N2—N3	119.7 (4)
C3—C4—H4	120.6	C6—N2—Zn1	117.6 (4)
C5—C4—H4	120.6	N3—N2—Zn1	122.5 (3)
N1—C5—C4	120.9 (5)	C8—N3—N2	111.7 (4)
N1—C5—C6	115.8 (4)	C8—N4—H4A	120.0
C4—C5—C6	123.2 (5)	C8—N4—H4B	120.0
N2—C6—C5	115.2 (5)	H4A—N4—H4B	120.0
N2—C6—C7	123.8 (5)	C9—O2—Zn1	125.3 (3)
C5—C6—C7	120.9 (4)	C8—S1—Zn1	96.67 (18)
C6—C7—H7A	109.5	O2—Zn1—O1^i	118.95 (17)
C6—C7—H7B	109.5	O2—Zn1—N1	88.41 (14)
H7A—C7—H7B	109.5	O1^i—Zn1—N1	86.60 (15)
C6—C7—H7C	109.5	O2—Zn1—N2	115.90 (16)
H7A—C7—H7C	109.5	O1^i—Zn1—N2	121.36 (16)
H7B—C7—H7C	109.5	N1—Zn1—N2	75.63 (16)
N4—C8—N3	115.7 (5)	O2—Zn1—S1	106.67 (11)
N4—C8—S1	116.2 (4)	O1^i—Zn1—S1	101.36 (12)
N3—C8—S1	128.1 (4)	N1—Zn1—S1	156.09 (13)
O2—C9—O1	126.0 (5)	N2—Zn1—S1	81.04 (11)
O2—C9—C10	117.6 (5)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N4—H4B···O2^ii	0.86	2.34	3.073 (5)	144
N4—H4A···N3^iii	0.86	2.29	3.138 (6)	168

Symmetry codes: (ii) x−1, y, z; (iii) −x, −y+1, −z.