Contrasting the supra­molecular structures in the isomeric pair 5-bromo-3-nitro­salicyl­aldehyde phenyl­hydrazone and 3-bromo-5-nitro­salicyl­aldehyde phenyl­hydrazone

Isomeric 5-bromo-3-nitro­salicyl­aldehyde phenyl­hydrazone and 3-bromo-5-nitro­salicyl­aldehyde phenyl­hydrazone, C₁₃H₁₀BrN₃O₃, both crystallize with two mol­ecules in the asymmetric unit. In both isomers, an intra­molecular O—H...N hydrogen bond links the hy­droxy group and the imine N atom. In the 5-bromo-3-nitro isomer, there are two independent N—H...O hydrogen-bonded chains, each mol­ecule in the asymmetric unit forming its own chain. These chains are then linked to form a three-dimensional framework by a combination of weak C—H...O, C—H...Br, C—H...π and π–π stacking inter­actions. In the 3-bromo-5-nitro isomer, N—H...O hydrogen bonds link the independent mol­ecules alternately into a zigzag chain, which is reinforced by a weak C—H...O inter­action. Individual chains are linked by a C—H...Br inter­action and a three-dimensional framework is generated by π–π stacking inter­actions.

Substituted 4-alk­oxy-7-Cl-quinolines exhibiting [pi]-[pi] stacking

The mol­ecules of 4-all­yloxy-7-chloro­quinoline, C₁₂H₁₀ClNO, (I), 7-chloro-4-meth­oxy­quinoline, C₁₀H₈ClNO, (II), and 7-chloro-4-eth­oxy­quinoline, C₁₁H₁₀ClNO, (III), are all planar. In all three structures, [pi]-[pi] inter­actions between the quinoline ring systems are generated by unit-cell translations along the a axes, irrespective of space group. These structures are the first reported for 4-alk­oxy­quinolines.

Three 2-(methysulfanyl)­nicotinamides

The mol­ecular conformations of three N-alkyl-2-(methyl­sulfan­yl)nicotinamide derivatives, namely N-cyclo­hexyl-2-(methyl­sulfan­yl)nicotinamide, C₁₃H₁₈N₂OS, (I), N-isopropyl-2-(methyl­sulfan­yl)nicotinamide, C₁₀H₁₄N₂OS, (II), in which there are two mol­ecules in the asymmetric unit which were chosen to form a hydrogen-bonded pair, and N-(2-hy­droxy­eth­yl)-2-(methyl­sulfan­yl)nicotinamide dihydrate, C₉H₁₂N₂O₂S·2H₂O, (III), are compared with those of four unsubstituted N-alkyl­nicotinamide compounds. The substituted com­pounds show a higher degree of torsion of the pyridine ring with respect to the amide group than do the unsubstituted compounds, with dihedral angles in the range 40-60° for the former and 20-35° for the latter. In (I) and (II), the supra­molecular structure is defined by amide-N to carbonyl-O chains. In (III), the nicotinamide mol­ecules are linked by hydrogen bonds to two water mol­ecules resulting in two linked chains of rings which form the three-dimensional network.

Five N'-benzyl­idene-N-methyl­pyrazine-2-carbohydrazides

The compounds N'-benzyl­idene-N-methyl­pyrazine-2-carbohydrazide, C₁₃H₁₂N₄O, (IIa), N'-(2-meth­oxy­benzyl­idene)-N-methyl­pyrazine-2-carbohydrazide, C₁₄H₁₄N₄O₂, (IIb), N'-(4-cyano­benzyl­idene)-N-methyl­pyrazine-2-carbohydrazide dihydrate, C₁₄H₁₁N₅O·2H₂O, (IIc), N-methyl-N'-(2-nitro­benzyl­idene)­pyrazine-2-carbohydrazide, C₁₃H₁₁N₅O₃, (IId), and N-methyl-N'-(4-nitro­benzyl­idene)­pyrazine-2-carbohydrazide, C₁₃H₁₁N₅O₃, (IIe), have dihedral angles between the pyrazine rings and the benzene rings in the range 55-78°. These methyl­ated pyrazine-2-carbohydrazides have supra­molecular structures which are formed by weak C-H...O/N hydrogen bonds, with the exception of (IIc) which is hydrated. There are [pi]-[pi] stacking inter­actions in all five compounds. Three of these structures are compared with their nonmethyl­ated counterparts, which have dihedral angles between the pyrazine rings and the benzene rings in the range 0-6°.

Comparison of the structure of (E)-2-(2-benzylidenehydrazinylidene)quin­oxaline with those of its chloro- and bromobenzylidene analogues

The structures of (E)-2-(2-(phenylidene)hydrazinyl)quinoxaline and six Cl and Br derivatives have similar supramolecular structures involving an N-H...N hydrogen bond and [pi]-[pi] stacking interactions.