Crystal structures of pure 3-(4-bromo-2-chlorophenyl)-1-(pyridin-4-yl)benzo[4,5]imidazo[1,2-d][1,2,4]triazin-4(3H)-one and contaminated with 3-(4-bromophenyl)-1-(pyridin-4-yl)benzo[4,5]imidazo[1,2-d][1,2,4]triazin-4(3H)-one

The side product of the cyclocondensation reaction between ethyl benzimidazole-2-carboxylate and the nitrile imine of the corresponding hydrazonyl chloride, C20H11BrClN5O, crystallized in two crystal forms. Form (1) is a co-crystal of the target compound (without any chlorine substituent) and a side product containing a Cl atom in position 2 of the bromophenyl group, C20H12BrN5O·0.143C20H11BrClN5O. (2) contains the pure side product. The slightly different conformation of the ring systems leads to a different packing of (1) and (2), but both crystal structures are dominated by π–π interactions.

The side product of the cyclocondensation reaction between ethyl benzimidazole-2-carboxylate and the nitrile imine of the corresponding hydrazonyl chloride, C 20 H 11 BrClN 5 O, crystallized in two crystal forms. Form (1) is a cocrystal of the target compound (without any chlorine substituent) and a side product containing a Cl atom in position 2 of the bromophenyl group, C 20 H 12 BrN 5 OÁ0.143C 20 H 11 BrClN 5 O.
(2) contains the pure side product. The slightly different conformation of the ring systems leads to a different packing of (1) and (2), but both crystal structures are dominated byinteractions.

Structural commentary
During crystallization of the product from a bi-solvent mixture of n-heptane and EtAc, two types of crystals were obtained. The biggest and highest quality blocks among them, (1) ISSN 2056-9890 ( Fig. 1), were obtained as a co-crystal of the target compound and a side product containing a chlorine atom in position 2 of the bromophenyl group. The chlorine atom in it is attached to the bromophenyl group as a side product obtained during preparation of the starting material, namely hydrazonoyl chloride, via chlorination of the corresponding hydrazone. The quantitative ratio between the side:target product is 1:7. The second type of crystals, (2), nice column-like crystals, turned out to contain the pure side product (Fig. 2). Furthermore, crystals of (2) contain two independent molecules (A and B) in the asymmetric unit. Their geometry is almost identical but different from (1) (see Table 1). The r.m.s. fit of all nonhydrogen atoms from molecule A onto B is 0.116 Å . The fused 13-membered ring system in (1) and (2) is nearly planar with an r.m.s. deviation of 0.025 Å in (1) and an r.m.s. deviation of 0.100 Å for molecule A and 0.089 Å for molecule B of (2).

Database survey
Two similar structures have been published previously (Abu Thaher et al., 2016a,b). All crystal structures show the typical interaction of the fused 13-membered ring system. The angles between the least-squares planes through the pyridine ring and the 13-membered ring vary from 50.38 (17) to 79.98 (7) , probably depending on the molecular packing, while the angles between the substituted phenyl ring and the 13-membered ring range from 43.13 (15) to 78.64 (9) depending on the size of the substituent. The crystal structure of (2) with the atom labelling. Displacement ellipsoids drawn at the 50% probability level. The two independent molecules are labelled with suffixes A and B. Table 1 Torsion angles ( ).

Figure 1
The crystal structure of (1), with the atom labelling and displacement ellipsoids drawn at the 50% probability level. The Cl atom has a siteoccupation factor of only 1/8. phenyl)-4-pyridinecarbohydrazonoyl chlorideÁHCl was added slowly in a portion-wise manner; in parallel 0.5 ml of Et 3 N was added dropwise. The reaction was stirred overnight (about 12 h); the reaction mixture was filtered and concentrated under vacuum. The solid residue was purified by column chromatography (SiO 2 , heptane:ethyl acetate; 2:1, then 1:1). Suitable crystals for X-ray were obtained by slow evaporation of heptane/ethyl acetate (1:1).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Hydrogen atoms attached to carbons were placed at calculated positions with C-H = 0.95 Å (aromatic) or 0.98-0.99 Å (Csp 3 atom). All H atoms were refined in the riding-model approximation with isotropic displacement parameters (set at 1.2-1.5 times of the U eq of the parent atom). The s.o.f. for the chlorine atom in (1) was initially refined and then fixed at 0.125.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq