Protonation sites of organic bases with several nitrogen functions: crystal structures of salts of chlordiazepoxide, dihydralazine, and phenformin

The crystal structures of 7-chloro-2-methylamino-5-phenyl-3H-1,4-benzodiazepine 4-oxide (chlordiazepoxide) hydrochloride (1), 1,4-dihydrazinophthalazine (dihydralazine) hydrosulphate trihydrate (2), and 1-(2-phenylethyl)biguanide (phenformin) hydrochloride (3) have been determined by X-ray diffraction. All have space group P21/c, and for (1): a= 13.120(5), b= 8.439(3), c= 15.070(6)Å, β= 107.81(3)°, Z= 4; for (2)a= 6.966(3), b= 11.099(4), c= 19.005(5)Å, β= 104.72(3)°, Z= 4; and for (3)a= 14.947(5), b= 9.396(3), c= 20.345(7)Å, β= 116.73(3), Z= 8. In (1) and (2) protonation occurs at a ring nitrogen atom, leading to amidinium systems. The second proton in (2) is attached to a terminal hydrazine nitrogen. The two independent cations in (3) have the same tautomeric form RHN·C(NH2)NC(NH2)2. The structure of (1) was determined by direct methods, those of (2) and (3) by the heavy-atom method. The structures were refined to R 0.059, 0.076, and 0.082 for 2 967, 2 015, and 4 672 observed intensities.