4,4′,6,6′-Tetrabromo-2,2′-(2,8-diazonia-5-azanona-1,8-diene-1,9-diyl)diphenolate

In the zwitterionic title compound, C18H17Br4N3O2, the two salicylaldimine groups form a dihedral angle of 51.94 (2)° and the dihedral angle between the aromatic ring planes is 51.14 (2)°. One of the C atoms adjacent to the aza N atom is disordered over two positions; the site-occupancy factors are 0.51 (1) and 0.49 (1). There are two strong intramolecular N—H⋯O hydrogen bonds in the molecule.

In the zwitterionic title compound, C 18 H 17 Br 4 N 3 O 2 , the two salicylaldimine groups form a dihedral angle of 51.94 (2) and the dihedral angle between the aromatic ring planes is 51.14 (2) . One of the C atoms adjacent to the aza N atom is disordered over two positions; the site-occupancy factors are 0.51 (1) and 0.49 (1). There are two strong intramolecular N-HÁ Á ÁO hydrogen bonds in the molecule.

Related literature
For general background on the use of Schiff bases in metal complexes, see: Vigato et al. (2007).
The molecular structure of (I) is illustrated in Fig. 1. The two pendant moieties in a cis conformation attach to the ends of the C-C-N-C-C backbone. The N2 atom exhibits tetrahedral sp 3 hybridization, whereas the two amide N atoms display planar sp 2 hybridization. There is no H atom attached to O1 and O2 atoms. Instead these H atoms are attached to the N1 and N3 atoms. The double-bonds C7-N1 (1.295 (6) Å) and C12-N3 (1.296 (6) Å) show the typical character of Schiff base. The dihedral angle between the salicylaldimine groups is 51.94 (2)°. The crystal structure of (I) is stabilized by intramolecular N-H···O hydrogen bonding. The C10 atom is disorder over two positions with the site-occupancy factors of 0.51 (1) and 0.49 (1). The larger than normal range of thermal motion is mostly due to the difference between the disordered group and the other atoms which are not disordered.

S3. Refinement
All H atoms except the N attached H1A and H3A which refined freely were placed in geometrically idealized positions and constrained to ride on their parent atoms (C-H = 0.93%A, 0.97%A; N-H = 0.86 Å; and U iso (H) values equal to 1.2 U eq C.  Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 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 (Å 2 )
x y z U iso */U eq Occ. (