Dichloridobis[2-(2-chloro­ethyl)-1,2,3,4-tetra­hydro­pyrazino[1,2-a]benzimidazole-κN]cobalt(II)

Zhong Zhang; Yao Zhao; Zhi-Rong Geng; Zhi-Lin Wang

doi:10.1107/S1600536808018011

. 2008 Jun 19;64(Pt 7):m942–m943. doi: 10.1107/S1600536808018011

Dichloridobis[2-(2-chloroethyl)-1,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole-κN]cobalt(II)

Zhong Zhang ^a, Yao Zhao ^a, Zhi-Rong Geng ^a, Zhi-Lin Wang ^a,^*

PMCID: PMC2961898 PMID: 21202795

Abstract

In the title compound, [CoCl₂(C₁₂H₁₄ClN₃)₂], the central Co^II ion lies on a twofold rotation axis and adopts a distorted tetrahedral coordination geometry defined by two N atoms from two 2-(2-chloroethyl)-1,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole ligands and two chloride anions. The Cl atom located in the side chain of the ligand is involved in intermolecular C—H⋯Cl hydrogen bonding, which links neutral complex units into a one-dimensional right-handed helical chain running along a crystallographic 4₁ axis. Such hydrogen-bonded helical chains are connected to each other to form a homochiral three-dimensional supramolecular network. One C atom of the 2-chloroethyl chain is disordered over two positions, with site-occupancy factors of 0.52 and 0.48.

Related literature

For related literature, see: Balamurugan et al. (2004 ▶); Matrick & Day (1961 ▶); Parker et al. (2004 ▶); Sundberg et al. (1977 ▶).

Experimental

Crystal data

[CoCl₂(C₁₂H₁₄ClN₃)₂]
M _r = 601.25
Tetragonal,
a = 9.5706 (8) Å
c = 29.911 (4) Å
V = 2739.7 (5) Å³
Z = 4
Mo Kα radiation
μ = 1.04 mm⁻¹
T = 293 (2) K
0.32 × 0.21 × 0.18 mm

Data collection

Bruker SMART APEX CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2000 ▶) T _min = 0.763, T _max = 0.829
14573 measured reflections
2703 independent reflections
2219 reflections with I > 2σ(I)
R _int = 0.061

Refinement

R[F ² > 2σ(F ²)] = 0.055
wR(F ²) = 0.131
S = 1.01
2703 reflections
169 parameters
2 restraints
H-atom parameters constrained
Δρ_max = 0.54 e Å⁻³
Δρ_min = −0.80 e Å⁻³
Absolute structure: Flack (1983 ▶), 1274 Friedel pairs
Flack parameter: 0.07 (5)

Data collection: SMART (Bruker, 2000 ▶); cell refinement: SAINT (Bruker, 2000 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg, 1998 ▶) and ORTEP-3 (Farrugia, 1997 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808018011/om2235sup1.cif

e-64-0m942-sup1.cif^{(17.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808018011/om2235Isup2.hkl

e-64-0m942-Isup2.hkl^{(132.8KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected geometric parameters (Å, °).

Co1—N2	2.026 (4)
Co1—Cl2	2.2423 (13)

Open in a new tab

N2ⁱ—Co1—N2	103.8 (2)
N2—Co1—Cl2	109.08 (12)
Cl2—Co1—Cl2ⁱ	110.64 (7)

Open in a new tab

Symmetry code: (i) Inline graphic .

Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1A⋯Cl1ⁱⁱ	0.97	2.87	3.812 (5)	164
C5—H5⋯Cl2ⁱⁱⁱ	0.93	2.79	3.709 (5)	171

Open in a new tab

Symmetry codes: (ii) Inline graphic ; (iii) .

Acknowledgments

This project was supported by the Nature Science Foundation of China (grant No. 20475026).

supplementary crystallographic information

Comment

Nitrogen mustards that contain a reactive N,N-bis-(2-chloroethyl)amine group are widely used as alkylating agents in cancer chemotherapy. However, these nitrogen mustards exhibit high chemical reactivity and usually show no selectivity of DNA alkylation. Recently, it has been proved that complexation of macrocyclic nitrogen mustards with metals may be an effective strategy in the design of hypoxia-selective antitumor prodrugs (Parker et al., 2004). As part of our work, some metal complexes of a monofunctional mustard, 2-(2-chloroethyl)-l,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole (L), were prepared in order to evaluate their antitumor and antimalarial activities. Here, we report the crystal structure of a novel Co(II) mustard complex.

As depicted in Fig. 1, the complete complex molecule is generated by a twofold symmetry operation, with the Co^II ion located on the rotation axis. The distorted tetrahedral coordination sphere around the Co^II center consists of two benzimidazole N atoms from two L ligands and two chloride anions. The Co—N distance of 2.026 (4) Å and Co—Cl length of 2.2423 (13) Å (Table 1) are comparable to those reported in the literature (Sundberg et al., 1977).

In the crystal packing, intermolecular C—H···Cl hydrogen bonding play a key role. Fig. 2 illustrates that adjacent neutral complex units are connected by C1—H1A···Cl1 interactions into a one-dimensional right-handed helical architecture running along a crystallographic 4₁ screw axis in the c direction. Five complex fragments form a helix turn with a long pitch of 29.911 (4) Å. The shortest intrachain Co—Co distance is 10.072 Å. Further C—H···Cl hydrogen bond linkages (Table 2) extend such one-dimensional helical chains into a homochiral three-dimensional hydrogen-bonded network (Balamurugan et al., 2004).

Experimental

The ligand 2-(2-chloroethyl)-l,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole was synthesized according to a literature method (Matrick & Day, 1961).

The title compound was prepared by adding a methanol solution (10 ml) of CoCl₂.6H₂O (1 mmol) into a methanol solution (10 ml) of 2-(2-chloroethyl)-l,2,3,4-tetrahydropyrazino[1,2-a]benzimidazole (2 mmol). The resulting mixture was refluxed for two hours and filtered after cooling to room temperature. Blue single crystals of the title compound suitable for X-ray diffraction analysis were obtained by slow diffusion of diethyl ether into the filtrate. Elemental analysis found: C 47.80; H 4.60; N 14.03%; calculated for C₂₄H₂₈Cl₄CoN₆: C 47.94; H 4.69; N 13.98%.