Transition metal complexes with ­thiosemicarbazide-based ligands. XLIII. Chlorobis(3-methylisothiosemicarbazide-κ²N¹,N⁴)zinc(II) chloride

In the title compound, [ZnCl(C₂H₇N₃S)₂]Cl, the Zn^II ion is five-coordinated in a distorted trigonal–bipyramidal arrangement, with the hydrazine N atoms located in the apical positions. The structure is stabilized by N—H...Cl hydrogen bonds, which involve both the Cl atoms and all the hydrogen donors, except for one of the two thio­amide N atoms. A comparison of the geometry of thio­semicarbazide and S-­methyl­iso­thio­semicarbazide complexes with Zn^II, Cu^II and Ni^II shows the pronounced influence of the hydrogen-bond network on the coordination geometry of Zn^II compounds.

S1. Comment

A number of complexes of transition metals and thiosemicarbazide-based ligands have found application in medicine, technology and analytical chemistry (Casas et al., 2001). In recent years, interest in the crystal engineering of metal complexes has stimulated investigation of the means of engagement of thiosemicarbazide (TSC)-based metal complexes in supramolecular structures (Burrows et al., 1997; Allen et al., 1999). The relatively rigid structure of metal-TSC chelate rings and the capacity of the ligand for hydrogen bonding make these molecules potentially important for the stabilization of supramolecular structures. In its complexes, TSC behaves as a chelating bidentate ligand coordinated through the terminal hydrazine N atom and the S atom. Upon methylation of the S atom, the manner of coordination of TSC changes, involving the thioamide N atom instead of S (Bogdanović et al., 2001).

A comparison of the previously reported structures of the Ni^II (Obadović et al., 1997; Bourosh et al., 1987) and Cu^II (Gerbeleu et al., 1987) complexes with S-methylisothiosemicarbazide (ITSC) and the corresponding TSC analogues (Campbell, 1975) shows that, in both types of compounds, the geometry of the coordination polyhedron is similar. In order to investigate the influence of a different coordination mode on the geometry of the coordination polyhedron in the absence of ligand field-stabilization energy, and also the packing characteristics of the corresponding compound, we have determined the crystal structure of the title complex, [Zn(ITSC)₂Cl₂], (I). \sch

To date, the crystal structures of two Zn^II complexes with TSC have been reported, namely tetrahedral [Zn(TSC)Cl₂] (Cavalca et al., 1960) and octahedral [Zn(TSC)₃Cl₂] (Nardelli & Chierici, 1960). Since a different coordination mode of the ITSC ligand changes the arrangement of potential hydrogen-bond donors, it is expected that these changes will be reflected in the number and disposition of hydrogen bonds in the crystal structure.

The crystal structure of (I) consists of monomeric units comprising [Zn(ITSC)₂Cl]⁺ and Cl^- ions. The coordination geometry around the metal ion can be described as a distorted trigonal-bipyramidal (τ = 0.72; Addison et al., 1984), with two thioamide Natoms and a Cl atom in the equatorial sites and two hydrazine N atoms in the apical positions (Fig. 1). The differences between the Zn—N(hydrazine) and Zn—N(thioamide) bond lengths are more pronounced in this complex [0.234 (8) and 0.253 (8) Å] than in the previously reported Ni^II and Cu^II complexes with S-methylisothiosemicarbazide, where this difference ranges from 0.05–0.09 Å. Nonequivalence of the M—N1 and M—N4 bond lengths can be explained in terms of the different hybridization of the corresponding N atoms. In (I), this effect is strengthened, probably as a consequence of the different degree of contribution of the p orbitals in the equatorial and apical bonds of a trigonal-bipyramid (Cotton & Wilkinson, 1967).

The packing of the molecules in (I) is determined by relatively strong N—H···Cl hydrogen bonds (Ferari Belicchi et al., 1992) (distance and angle ranges are 2.38–2.64 Å and 152–174°, respectively). The repeating pairs of molecules, connected by hydrogen bonds, form zigzag chains along the b axis [the symmetry codes of the interacting pairs are: (x, y, z) and (-x, y + 1/2, 1/2 - z), and (1/2 - x, -y, z + 1/2) and (x + 1/2, 1/2 - y, -z)]. The cross-linking of these chains via N—H···Cl hydrogen bonds builds a complex three-dimensional net. Intermolecular hydrogen bonds which involve only cations can be described in graph-set notation (Etter, 1991; Bernstein et al., 1995) as C(4) [Cl1, H2A, N1A, Zn1] (for molecules inside the chain) and C(5) [Cl1, H3, N2, N1, Zn1] (for molecules between the chains) (Fig. 2). The same pair of motifs is present in the structurally similar compound [Zn(TzHy)₂Cl]Cl [TzHy is (2-thiazolin-2-yl)hydrazine; Bernalte-Garcia et al., 1997]. In both molecules, chemically equivalent types of atoms are arranged in the same way, forming the trigonal bipyramid.

It is interesting to note that, irrespective of the mole ratio of the reactants, the same bis(ligand) complex was obtained, while the reactions of ZnCl₂ and TSC yield two different structures, tetrahedral (mono) and octahedral (tris). It is difficult to determine the main factor which favours trigonal-bipyramidal coordination upon methylation of the S atom, bearing in mind that the steric requirements of both ligands are approximately the same and that the Zn^II ion has a preference for forming tetrahedral and octahedral structures. However, it should be noticed that the bite angles of thiosemicarbazide and S-methylisothiosemicarbazide are more in accordance with trigonal-bipyramidal (where the chelate ring spans axial and equatorial positions) and octahedral symmetry than the tetrahedral arrangements.

One of the factors that we would like to stress is the different arrangement of the hydrogen bonds as a result of the different coordination mode. Considering the small bite angle of the TSC ligand, it is expected that bis-tetrahedral structures of this ligand will be rather distorted. In the case of the tetrahedral complex [Zn(TSC)₂(NO₃)₂] (Tong et al., 2000), due to the presence of the nitrate group as a counter-ion, complementary hydrogen interactions are formed between the donor pair of cations i.e. the hydrazine and thioamide N atoms of TSC moiety, and the nitrate O atoms as an acceptor pair. These interactions play an important role in the stabilization of [Zn(TSC)₂(NO₃)₂]. In the presence of a counter-ion with one donor site, stabilization through complementary hydrogen bonds is not possible. In mono-Zn(TSC)Cl₂ (Reference?), a different kind of tetrahedral structure is formed. Since only one molecule of the TSC ligand and two Cl atoms are involved in the formation of this complex, its tetrahedral geometry is less distorted. The positions of the H atoms in mono-Zn(TSC)Cl₂ have not not been reported so we cannot analyze the role of the hydrogen bonds in the stabilization of this complex.

In contrast with TSC complexes, the coordination of ISTC through the hydrazine and thioamide N atoms reduces the ability of the latter atom to form a hydrogen bond. This may be the reason why, in (I), the pair of hydrazine N atoms plays a major role in the stabilization of the structure. One of the thioamide N atoms (N4A) forms an intramolecular hydrogen bond with the Cl^- anion, while the other one (N4) is the only hydrogen-bond donor which is not involved in the hydrogen-bonding net. The closest acceptor, the coordinated Cl atom, is at a distance of 3.01 Å from atom H4(N4)(-x - 1, y - 1/2, 1/2 - z). This contact could be categorized as a long intermolecular contact, since it exceeds the sum of the van der Waals radii for H and Cl atoms (Aullon et al., 1998).

S2. Experimental

White monocrystals of complex (I) were obtained by the reaction of EtOH solutions of stoichiometric amounts of Zn(OAc)₂·2H₂O and S-methylisothiosemicarbazide hydrogen iodide, and an excess of LiCl₂.

S3. Refinement

H atoms were positioned geometrically at distances of 0.96, 0.90 and 0.86 Å from their parent C, Nsp³ and Nsp² atoms, respectively, and their isotropic displacement parameters were fixed at 1.5 and 1.2 times the equivalent isotropic displacement parameter of their parent C and N atoms, respectively.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1988); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: WinGX (Farrugia, 1999) and PLATON (Spek, 1999).

Figures

	Fig. 1. The molecular geometry and atom-labelling scheme for (I) with 50% probability displacement ellipsoids.
	Fig. 2. The crystal structure of (I) viewed down the a axis, showing the formation of hydrogen-bonded zigzag chains. The S(CH3) group has been omitted for the sake of clarity.

(I)

Crystal data

[Zn(C2H7N3S)2Cl]Cl	Dx = 1.765 Mg m^−3
Mr = 346.6	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P212121	Cell parameters from 25 reflections
a = 9.402 (2) Å	θ = 12.8–17.4°
b = 10.121 (3) Å	µ = 2.59 mm^−1
c = 13.710 (3) Å	T = 293 K
V = 1304.6 (6) Å^3	Cube, white
Z = 4	0.24 × 0.23 × 0.22 mm
F(000) = 704

Data collection

Enraf-Nonius CAD-4 diffractometer	θmax = 30.0°, θmin = 2.5°
ω/2θ scans	h = −13→13
4392 measured reflections	k = 0→14
3730 independent reflections	l = 0→19
1913 reflections with I > 2σ(I)	3 standard reflections every 60 min
Rint = 0.095	intensity decay: 3.1%

Refinement

Refinement on F^2	H-atom parameters constrained
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0311P)^2] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.065	(Δ/σ)max < 0.001
wR(F^2) = 0.124	Δρmax = 0.63 e Å^−3
S = 0.98	Δρmin = −0.63 e Å^−3
3730 reflections	Absolute structure: Flack (1983); 1561 Friedel pairs
136 parameters	Absolute structure parameter: 0.00 (3)
0 restraints

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.

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

	x	y	z	Uiso*/Ueq
Zn1	−0.47341 (9)	0.05028 (9)	0.18476 (6)	0.0271 (2)
Cl2	−0.6464 (2)	−0.2407 (2)	0.00274 (14)	0.0350 (5)
Cl1	−0.2997 (2)	−0.0478 (3)	0.27754 (14)	0.0428 (5)
S5	−0.3392 (3)	0.3251 (2)	−0.06148 (17)	0.0533 (7)
S5A	−0.9001 (2)	−0.0853 (3)	0.30246 (19)	0.0603 (8)
N1A	−0.5795 (6)	0.1589 (5)	0.3075 (5)	0.0317 (15)
H1A	−0.5211	0.1648	0.3593	0.038*
H2A	−0.6044	0.2409	0.2888	0.038*
N1	−0.3901 (6)	−0.0309 (6)	0.0454 (4)	0.0318 (15)
H1	−0.3144	−0.0832	0.0565	0.038*
H2	−0.4575	−0.0786	0.0148	0.038*
N2A	−0.7008 (7)	0.0836 (7)	0.3306 (4)	0.0429 (19)
H3A	−0.7514	0.1015	0.3812	0.051*
N4A	−0.6539 (6)	−0.0504 (6)	0.2006 (4)	0.0288 (13)
H4A	−0.6763	−0.1136	0.1617	0.035*
N2	−0.3510 (7)	0.0786 (6)	−0.0113 (4)	0.0339 (16)
H3	−0.3054	0.0687	−0.0652	0.041*
N4	−0.4465 (7)	0.2119 (6)	0.1043 (4)	0.0327 (17)
H4	−0.4741	0.2879	0.1249	0.039*
C3	−0.3868 (8)	0.1993 (7)	0.0211 (5)	0.0276 (18)
C3A	−0.7351 (8)	−0.0169 (8)	0.2713 (5)	0.031 (2)
C6A	−0.9100 (9)	−0.2271 (7)	0.2271 (6)	0.059 (3)
H7A	−0.9982	−0.2722	0.2389	0.089*
H6A	−0.8321	−0.2851	0.2418	0.089*
H5A	−0.9051	−0.2009	0.1599	0.089*
C6	−0.4660 (11)	0.4497 (9)	−0.0355 (6)	0.073 (3)
H7	−0.4494	0.5246	−0.0770	0.110*
H5	−0.4574	0.4761	0.0315	0.110*
H6	−0.5600	0.4160	−0.0470	0.110*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn1	0.0301 (4)	0.0274 (4)	0.0236 (4)	−0.0014 (5)	0.0034 (4)	0.0023 (5)
Cl2	0.0416 (12)	0.0316 (10)	0.0319 (10)	−0.0055 (10)	−0.0091 (10)	−0.0007 (9)
Cl1	0.0499 (13)	0.0415 (12)	0.0370 (11)	0.0050 (13)	−0.0206 (9)	−0.0001 (12)
S5	0.0642 (17)	0.0463 (14)	0.0494 (14)	0.0109 (14)	0.0268 (13)	0.0209 (12)
S5A	0.0338 (12)	0.0766 (19)	0.0705 (17)	−0.0203 (13)	0.0231 (13)	−0.0226 (16)
N1A	0.040 (4)	0.027 (3)	0.028 (3)	−0.007 (3)	−0.001 (3)	−0.003 (3)
N1	0.034 (4)	0.024 (4)	0.037 (4)	−0.001 (3)	0.004 (3)	0.000 (3)
N2A	0.040 (4)	0.058 (5)	0.030 (4)	−0.014 (4)	0.020 (3)	−0.021 (4)
N4A	0.031 (3)	0.027 (3)	0.028 (3)	0.001 (3)	0.006 (3)	−0.005 (3)
N2	0.044 (4)	0.035 (4)	0.023 (3)	0.005 (4)	0.011 (3)	0.005 (3)
N4	0.049 (5)	0.025 (3)	0.024 (3)	−0.002 (3)	0.015 (3)	−0.001 (3)
C3	0.028 (4)	0.027 (4)	0.028 (4)	−0.002 (4)	−0.000 (4)	0.009 (3)
C3A	0.030 (4)	0.034 (5)	0.028 (4)	−0.000 (4)	−0.004 (4)	0.000 (4)
C6A	0.065 (7)	0.039 (6)	0.073 (7)	−0.025 (5)	−0.003 (6)	0.003 (5)
C6	0.109 (8)	0.055 (6)	0.057 (6)	0.036 (8)	0.030 (6)	0.019 (6)

Geometric parameters (Å, º)

Zn1—N4	1.989 (6)	N2A—C3A	1.342 (9)
Zn1—N4A	1.991 (6)	N2A—H3A	0.8600
Zn1—N1	2.223 (5)	N4A—C3A	1.279 (8)
Zn1—N1A	2.244 (6)	N4A—H4A	0.8600
Zn1—Cl1	2.296 (2)	N2—C3	1.343 (9)
S5—C3	1.761 (8)	N2—H3	0.8600
S5—C6	1.772 (9)	N4—C3	1.278 (8)
S5A—C3A	1.752 (8)	N4—H4	0.8600
S5A—C6A	1.771 (8)	C6A—H7A	0.9600
N1A—N2A	1.407 (7)	C6A—H6A	0.9600
N1A—H1A	0.9000	C6A—H5A	0.9600
N1A—H2A	0.9000	C6—H7	0.9600
N1—N2	1.403 (8)	C6—H5	0.9600
N1—H1	0.9000	C6—H6	0.9600
N1—H2	0.9000
N4—Zn1—N4A	126.2 (2)	C3A—N4A—Zn1	117.1 (5)
N4—Zn1—N1	77.4 (2)	C3A—N4A—H4A	121.4
N4A—Zn1—N1	101.8 (2)	Zn1—N4A—H4A	121.4
N4—Zn1—N1A	94.0 (2)	C3—N2—N1	118.0 (6)
N4A—Zn1—N1A	77.9 (2)	C3—N2—H3	121.0
N1—Zn1—N1A	169.3 (2)	N1—N2—H3	121.0
N4—Zn1—Cl1	124.9 (2)	C3—N4—Zn1	118.0 (5)
N4A—Zn1—Cl1	108.9 (2)	C3—N4—H4	121.0
N1—Zn1—Cl1	93.8 (2)	Zn1—N4—H4	121.0
N1A—Zn1—Cl1	96.5 (2)	N4—C3—N2	119.7 (7)
C3—S5—C6	102.4 (4)	N4—C3—S5	127.8 (6)
C3A—S5A—C6A	103.0 (4)	N2—C3—S5	112.4 (6)
N2A—N1A—Zn1	105.3 (4)	N4A—C3A—N2A	121.1 (7)
N2A—N1A—H1A	110.7	N4A—C3A—S5A	127.5 (6)
Zn1—N1A—H1A	110.7	N2A—C3A—S5A	111.4 (6)
N2A—N1A—H2A	110.7	S5A—C6A—H7A	109.5
Zn1—N1A—H2A	110.7	S5A—C6A—H6A	109.5
H1A—N1A—H2A	108.8	H7A—C6A—H6A	109.5
N2—N1—Zn1	106.1 (4)	S5A—C6A—H5A	109.5
N2—N1—H1	110.5	H7A—C6A—H5A	109.5
Zn1—N1—H1	110.5	H6A—C6A—H5A	109.5
N2—N1—H2	110.5	S5—C6—H7	109.5
Zn1—N1—H2	110.5	S5—C6—H5	109.5
H1—N1—H2	108.7	H7—C6—H5	109.5
C3A—N2A—N1A	117.9 (6)	S5—C6—H6	109.5
C3A—N2A—H3A	121.0	H7—C6—H6	109.5
N1A—N2A—H3A	121.0	H5—C6—H6	109.5

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N4A—H4A···Cl2	0.86	2.55	3.328 (6)	152
N2—H3···Cl1^i	0.86	2.38	3.238 (6)	174
N2A—H3A···Cl2^ii	0.86	2.38	3.188 (7)	156
N1—H1···Cl2^iii	0.90	2.52	3.321 (6)	149
N1A—H2A···Cl1^iv	0.90	2.49	3.385 (6)	172
N1—H2···Cl2	0.90	2.42	3.265 (6)	156
N1A—H1A···Cl2^iv	0.90	2.64	3.509 (6)	162

Symmetry codes: (i) −x−1/2, −y, z−1/2; (ii) −x−3/2, −y, z+1/2; (iii) x+1/2, −y−1/2, −z; (iv) −x−1, y+1/2, −z+1/2.