Akira Kawase

Molecular Structure of Bis(1-(2-pyridyl)-3-(4-bromophenyl)-5-phenylformazanato)zinc(II).

To date, no structure has been reported for any metal formazan chelete, despite their considerable importance as analytical reagents. The authors have already determined the crystal structure of 1-(2-pyridyl)-3-(4bromophenyl)-5-phenylformazan (PBF).2 In this paper we report on the structure of bis[(1-(2-pyridyl)-3-(4bromophenyl)-5-phenylformazanato]zinc(II). This Zn complex was prepared as described previously. A deep dark-red crystal (0.4X0.2X0.2 mm3) was obtained from a dioxane solution. The crystal and experimental data are given in Table 1. The data were corrected for Lorentz, polarization and absorption effects (an empirical absorption correction based on a scan, ,u=33.6 cm, transmission factors from 0.626 to 0.998). The structure was solved by direct methods and successive Fourier synthesis. Hydrogen atoms were added at the calculated positions. The refinement was carried out by a full-matrix least squares method with anisotropic temperature factors for the non-H-atoms. The positional and thermal parameters of the H-atoms were fixed. The final atomic coordinates and the selected bond distances and angles are given in Tables 2 and 3. The molecular structure is shown in Fig, 1. Two PBF ligands coordinate to the Zn ion in a mer configuration. This complex exhibits a two-fold symmetry with the Zn-atom located on the two-fold axis, as shown in Fig. 1. Each PBF ligand is essentially planar, except for that of the phenyl group (C13 C18). The tridentate ligand coordinates via the pyridyl nitrogen and the two azo nitrogens (N1, N4), resulting in two fivemembered chelate rings, respectively. The arrangement around the Zn atom is shown in Fig. 2. The coordination geometry is that of a slightly distorted octahedron. This deviation is probably due to steric factors. The dihedral angle between the plane for the N1, N4 and N5 atoms and that of the Nl*, N4* and N5* atoms is 88.5°.