Crystal Structures and Hirshfeld Surface Analysis of Two Inner Salts of 3-carboxy-2-(quinolinium-1-ylmethyl)propanoate, and 3-(3-carbamoylpyridinium-1-yl)-2-(carboxymethyl)propanoate

Abstract Two crystalline inner salts 3-carboxy-2-(quinolinium-1-ylmethyl)propanoate dihydrate (1), and 3-(3-carbamoylpyridinium-1-yl)-2-(carboxymethyl)propanoate (2) were featured by the X-ray diffraction analysis, IR, mp, and elemental analysis. Salt 1 crystallizes in the triclinic, space group P-1, with a = 7.8315(8) Å, b = 11.1063(12) Å, c = 11.3763(14) Å, α = 67.5800(10)º, β = 82.295(2)º, γ = 80.970(2)º,V = 900.38(17) ų, Z = 2. Salt 2 adopts the monoclinic, space group P2(1)/n, with a = 8.4782(8) Å, b = 7.7825(7) Å, c = 16.8649(17) Å, β = 97.999(2)º, V = 1101.95(18) ų, Z = 4. Both salts comprise the extensive O-H···O H-bonds as well as other non-covalent associates. The percentage contribution of the significant non-covalent contacts were calculated via the Hirshfeld surface analysis. The hetero supramolecular synthons R₂¹(6), R₂²(10), R₂²(12), R₂²(13), R₂²(14), R₂²(16), R₂²(22), R₃³(9), R₄²(8), R₄³(10), and R₅⁵(17) were established at the both salts. Most of the synthons were not found repeatedly, yet the R₂²(10) was established at the both cases. The role of these non-covalent interactions in the crystal structure extension is ascertained. These weak interactions combined together, both salts exhibited the 3D framework structures.