4-Bromo-N 2,N 2,N 6,N 6-tetraethylpyridine-2,6-dicarboxamide

The title compound, C15H22BrN3O2, consists of a pyridine ring with a bromine atom in the para position and two diethylamide groups in the ortho positions of the ring. Despite the positions of the three substituents on the pyridine ring, the molecule does not exhibit either local or crystallographic twofold symmetry as the two diethylamido units exhibit significantly different Npy—C—C—Nam torsion angles of 46.3 (4) and 62.7 (4)° (py is pyridine and am is amine). Intermolecular C—H⋯O interactions support the packing.

The title compound, C 15 H 22 BrN 3 O 2 , consists of a pyridine ring with a bromine atom in the para position and two diethylamide groups in the ortho positions of the ring. Despite the positions of the three substituents on the pyridine ring, the molecule does not exhibit either local or crystallographic twofold symmetry as the two diethylamido units exhibit significantly different N py -C-C-N am torsion angles of 46.3 (4) and 62.7 (4) (py is pyridine and am is amine). Intermolecular C-HÁ Á ÁO interactions support the packing.

Comment
The title compound, shown in Figure 1 and Scheme 1, is often utillized as the chelating and sensitizing moiety in ligands for lanthanide ion luminescent complexes, such as in (tert-butoxycarbonyl) alanine methyl ester, the structure of which has been reported (Muller et al., 2003) or in a N,N,N',N'-tetraethylpyridine-2,6,dicarboxamide-based ligand (Renaud et al., 1997. It has also been used as an intermediate to ligands capable of coordinating lanthanide ions (de Bettencourt-Dias et al., 2006) and as such was isolated in our research group. It consists of a pyridine ring with a bromide in position 4 and diethylamide groups in positions 2 and 5. This molecule is devoid of crystallographic symmetry and the asymmetric unit comprises one molecule. While at first impression the amide groups seem to be related by a twofold axis, closer inspection shows that they are different. This is evidenced by the torsion angles between the groups and the pyridine ring. The torsion angle for the atoms N1-C1-C7-N2 is 62.7 (4)° and the torsion angle for N1-C5-C6-N3 is 46.3 (4)°. The observed difference between the two ethyl groups might be a consequence of the C-H···O hydrogen bond interactions in which they are involved and which help support the packing structure, shown in Figure 2. Despite the presence of the pyridine rings and of the bromine atoms, π-π, C-Br···π or C-H···Br interactions are not observed.

Experimental
The title compound was synthesized as follows. PBr 5 was obtained by slowly adding 8 ml of PBr 3 to 3.5 ml of Br 2 in 20 ml hexanes at 0 °C. After one hour, the hexanes were decanted and 5 g of chelidamic acid were added. The mixture was heated for six hours (85-90 °C.) The acid bromide which formed in this step was then extracted with chloroform and used without further purification in the next step.

Refinement
Hydrogen atoms were positioned geometrically using a riding model with C-H = 0.95, 0.99 and 0.98 Å for aromatic CH and aliphatic CH 2 and CH 3 H atoms, respectively, and U iso (H)=1.2-1.5 U eq (C).
supplementary materials sup-2 Figures Fig. 1. Molecular structure of the title compound, with atom numbering (except H atoms) and 50% probability displacement ellipsoids for non-H atoms.