The crystal structure of (E)-amino(2-(4-methylbenzylidene)hydrazineyl)methaniminium 4-methylbenzoate, C₉H₁₃N₄ ⁺ C₈H₇O₂ ⁻

Source of material

Two gram (0.0181 mol) aminoguanidine hydrochloride salt in a 100 mL round-bottom flask is dissolved in a mixture of purified water (15 mL) and methanol (15 mL), and 2.346 mL (0.0199 mol) of 4-methylbenzaldehyde is added. After mixing in a magnetic stirrer at room conditions for 24 h, it is neutralized with equivalent 0.72 g (1 eq) NaOH. In order for the precipitation to occur well, it is kept in the refrigerator for 30–45 min, the precipitated material is filtered with a crucible, washed with distilled water (3 × 5 mL) and dried under vacuum. After waiting for one day, crystallization is done in ethanol and water (EtOH/H₂O). To purify the substance, it is kept in the refrigerator for 24 h. The crystalline material formed is filtered, washed in cold ethanol, then dried in a vacuum oven (yield: 94%).

Experimental details

The H atoms of the NH and NH₂ groups were located from a difference- Fourier map and refined freely [N2—HN2 = 0.90(2), N3—HN3 = 0.91(2), N3—HN4 = 0.88(2), N4—HN5 = 0.89(2) and N4—HN6 = 0.92(2) Å]. All C-bound H atoms were positioned geometrically and refined using a riding model, with C—H = 0.93 and 0.96 Å, for aryl and methyl H-atoms, respectively. The U _iso(H) were allowed at 1.5U _eq(C_methyl) or 1.2U _eq(C_non-methyl).

Comment

During the 1960s, Wyeth laboratories, Inc., Philadelphia, produced a series of benzylidene aminoguanidines during the search for new and improved antihyperten-sive medicines. In 1969, one of the chemicals in this class, E-2,6-dichlorobenzylidene aminoguanidine acetate, was found as a new, strong hypotensive agent [6].

The title salt is composed of one cation and one anion in the asymmetric unit. The cations and the anions of the title salt are nearly co-planar: the maximum deviations from the mean plane of the non–H atoms are −0.592(1) Å for O2, 0.328(2) Å for N3 and 0.250(2) Å for N4, respectively.

The cation group is stabilized by the N—H ⃛ N hydrogen bond [N3—HN4/N1: HN4/N1 = 2.33(2) Å, N3 ⃛ N1 = 2.677(4) Å with angle at HN4 = 103.9(16)^∘], forming a S(5) ring [7].

In the cation, the C—N bond distances are N3—C9 = 1.331(2) Å and N4—C9 = 1.312(2) Å. The C=N bond distance is N1—C8 = 1.273(2) and N2—C9 = 1.334(2) Å. The N—N bond distance of 1.3852(19) Å is shorter than a single bond and indicating significant delocalization along the NNC(NH₂)N moiety. All bond length and bond angles in the title salt can be compared with those of the related compounds which are 2-((2,6-dichlorophenyl)methylene)hydrazinecarboxamide acetate (CSD refcode HIVYOB: orthorhombic space group: Pbca (61), a = 13.389(5), b = 11.007(6), c = 17.342(5) Å, Z = 4) [8] and N’’-[(2,6-dichlorophenyl)methylidene] carbonohydrazonic diamide (Form I (CSD refcode SOMZOM): monoclinic space group: P2₁/c (14), a = 16.3082(4) Å, b = 8.2933(3) Å, c = 7.4489(3) Å, β = 98.201(3)^∘, Z = 4; Form II (SOMRUK): triclinic space group: P 1 ‾ (2), a = 7.9018(3) Å, b = 10.8460(7) Å, c = 12.9559(8) Å, α = 78.313(5)^∘, β = 72.515(4)^∘, γ = 83.119(4)^∘, Z = 4) [9].

In the crystal, the cations and anions of the title salt which are co-planar are linked by N—H ⃛ O hydrogen bonds N2—HN2/O1: HN2/O1 = 2.52(2) Å, N2/O1 = 3.219(4) Å with angle at HN2 = 134.4(18) Å, N2—HN2/O2: HN2/O2 = 2.12(2) Å, N2/O2 = 3.001(4) Å with angle at HN2 = 166(2)^∘ and N4—HN5/O1: HN5/O1 = 1.85(2) Å, N4/O1 = 2.722(4) Å with angle at HN5 = 167(2)^∘], forming the R 1 2 (6) and R 1 2 (4) ring motifs. Furthermore the cations and anions are connected by the N—H ⃛ O [N3—HN3/O2: HN3/O2 = 2.17(2) Å, N3/O2 = 2.972(4) Å with angle at HN3 = 147.6(19)^∘, N3—HN4/O2: HN4/O2 = 2.44(2) Å, N3/O2 = 3.115(4) Å with angle at HN4 = 134.2(18)^∘ and N4—HN6/O2: HN6/O2 = 2.10(2) Å, N4/O2 = 2.948(4) Å with angle at HN6 = 152(2)^∘], C—H ⃛ O [C4—H4/O1: H4/O1 = 2.56 Å, C4/O1 = 3.322(4) Å with angle at H4 = 140^∘] and very weak π-π stacking interactions [Cg1(C2—C7)⃛Cg2(C11—C16) ⁱ  = 3.916(4) Å, angle = 7.45(9)^∘ and slippage = 1.320 Å; Cg2(C11—C16) ⃛ Cg1(C2—C7) ⁱ  = 3.916(4) Å, angle = 7.45(9)^∘ and slippage = 1.78 Å for symmetry operation (i): 1 − x, 1 − y, 1 − z], generating the molecular layers paralel to the (100) plane.