Comment

In recent years, N-functionalized 1,4,7-triazacyclononanes (tacn) have attracted attention, since they afford versatile and efficient ligands. Some metal complexes involving such ligands have potential applications: the modeling of enzymes (Wainwright, 1997), radiotherapeutic agents and time-resolved luminescence labels (Charbonnière et al., 2001). Derivatives of tacn with pendant pyridines (Tamura et al., 2000), anilines (Fallis et al., 2000), imidazoles, pyrazoles (Di Vaira et al., 2000), etc. have been reported. However, the crystal structures of derivatives of tacn with benzimidazole have not yet been reported.

Here we report the crystal structure of one such complex, viz. [1-(benzimidazol-2-ylmethyl)-1,4,7-triazacyclononane]chlorocopper(II) perchlorate, (I), which has potential pharmaceutical application as an SOD (superoxide dismutase) mimic. In this complex, the copper atom is located at the center of a distorted trigonal bipyramid of five coordinating atoms (four N atoms and one chlorine atom). N2 and N4 are located in the axial positions, and N1, N3, Cl2 are in the equatorial plane. The N2-Cu1-N4 angle is 164.01 (9)°; the three axial-equatorial angles N2-Cu1-N1, N2-Cu1-N3, and N2-Cu1-Cl2 are 83.55 (8), 83.43 (9) and 94.26 (7)°, respectively. In the equatorial plane, the angles N1-Cu1-Cl2, Cl2-Cu1-N3 and N3-Cu1-N1 are 153.09 (6), 123.14 (6) and 83.37 (8)°, respectively. The copper atom is located 0.0670 (2) Å below the least-squares plane defined by N1, N3 and Cl2.

The distance Cu1-Cl2 is 2.2828 (9) Å. Of the four Cu-N bonds, the shortest is that to the pendant nitrogen, N4 [1.964 (2) Å], whereas the average distance for the three bonds to the triazacyclononane-N atoms is 2.103 (6) Å. This value compares well with the corresponding value of 2.080 (1) Å in the related imidazole compound (Di Vaira et al., 2000).

The crystal structure of the title complex is stabilized by hydrogen bonds of the type N-HO(perchlorate) and N-HCl, where Cl belongs to a neighboring cation (Table 1).

Figure 1 View of the title complex, showing the labeling of the non-H atoms and 30% probability ellipsoids. H atoms have been omitted.

Figure 2 A view of the crystal packing along the a axis. Hydrogen bonds are shown as dashed lines.

Experimental

1,4,7-Triazacyclononane (tacn) was prepared by a modified literature method (Koyama & Yoshino, 1972), while 2-chloromethylbenzimidazole (cbz) was prepared according to the method of Rousek (1991). The title compound was synthesized as follows: to a methanol solution of tacn (0.05 mol) and cbz (0.05 mol) was added a methanol solution of Cu(ClO₄)₂·6H₂O (0.05 mmol), with stirring at reflux. The mixture was stirred continuously for 5 h, and then cooled and filtered. Slow evaporation of the solution give a blue crystalline compound. Crystals suitable for X-ray analysis were obtained by diffusion of diethyl ether into an acetonitrile solution over a period of three days.

Crystal data

[CuCl(C14H21N5)]ClO4 Mr = 457.80 Monoclinic, P21/n a = 10.336 (1) Å b = 13.428 (1) Å c = 13.051 (1) Å = 99.56 (2)° V = 1786.2 (3) Å3 Z = 4 Dx = 1.702 Mg m-3 Mo K radiation Cell parameters from 3169 reflections = 2.2-25.1° = 1.55 mm-1 T = 293 (2) K Block, blue 0.3 × 0.2 × 0.2 mm

Data collection

Bruker APEX CCD area-detector diffractometer and scans Absorption correction: multi-scan (SADABS; Bruker, 2000) Tmin = 0.696,  Tmax = 0.733 9413 measured reflections 3334 independent reflections 2636 reflections with I> 2(I) Rint = 0.056 max = 25.5° h = -11 12 k = -13 16 l = -14 15

Refinement

Refinement on F2 R[F2> 2(F2)] = 0.036 wR(F2) = 0.069 S = 1.09 3334 reflections 235 parameters H-atom parameters constrained w = 1/[2(Fo2) + (0.02P)2] where P = (Fo2 + 2Fc2)/3 (/)max < 0.001 max = 0.39 e Å-3 min = -0.38 e Å-3

Table 1 Hydrogen-bonding geometry (Å, °) D-HA D-H HA DA D-HA N2-H2CCl2i 0.91 2.49 3.361 (2) 160 N3-H3CO2 0.91 2.25 3.058 (3) 148 N5-H5CO2ii 0.86 2.29 3.009 (3) 141 N5-H5CCl2iii 0.86 2.73 3.331 (2) 128 Symmetry codes: (i) -x,-y,-z; (ii) ; (iii) 1-x,-y,-z.

All H atoms were placed geometrically and refined with a riding model. C-H values were set to 0.97 and 0.93 Å for atoms C1-C7 and C10-C13, respectively; N-H = 0.91 Å for N2 and N3, and 0.86 Å for N5. U_iso was constrained to be 1.2U_eq of the carrier atom.

Data collection: SMART (Bruker, 2000); cell refinement: SMART; data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXTL (Bruker, 2000); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.