Supramolecular association in proton-transfer adducts containing benzamidinium cations. III. Three molecular salts of 3-methoxy-, 4-methoxy- and 3,4,5-trimethoxybenzoates with benzamidine

Abstract

Three molecular salts, benzamidinium 3-methoxybenzoate, C7H9N2(+)·C8H7O3(-), (I), benzamidinium 4-methoxybenzoate, C7H9N2(+)·C8H7O3(-), (II), and benzamidinium 3,4,5-trimethoxybenzoate monohydrate, C7H9N2(+)·C10H11O5(-)·H2O, (III), were formed from the proton-transfer reactions of 3-methoxy, 4-methoxy- and 3,4,5-trimethoxybenzoic acids with benzamidine (benzenecarboximidamide, benzam). Monoclinic salts (I) and (II) have a 1:1 ratio of cation to anion. In monoclinic salt (III), two cation-anion pairs and two water molecules constitute the asymmetric unit. In all three molecular salts, the amidinium fragments and the carboxylate groups are completely delocalized, and the delocalization favours the aggregation of the molecular components into nonplanar dimers with an R(2)(2)(8) graph-set motif by N(+)-H···O(-) (±) charge-assisted hydrogen bonding (CAHB). Of the three molecular salts, (I) and (II) show similar conformations of the anionic components and exhibit bidimensional isostructurality, which consists of alternating R(2)(2)(8) and R(6)(4)(16) rings resulting in a corrugated sheet propagated parallel to the crystallographic ab plane. In molecular salt (III), the R(2)(2)(8) synthon is retained but the supramolecular structure is different, due to the presence of three bulky methoxy substituents and a water molecule. The structures reported here further demonstrate the robustness of R(2)(2)(8) hydrogen-bonded synthons having the benzamidinium cation as a building block, whereas N(+)-H···O(-) hydrogen bonds external to the salt bridge contribute to the overall structure organization.

Proton-transfer salts of diphenylphosphinic acid with substituted 2-aminopyridine: crystal structure, spectroscopic and DFT studies

“…The presence of hydrogen bonds between proton donors and acceptors plays an important role with respect to the formation and stability of 1:1 or 2:1 proton-transfer salts (Smith & Wermuth, 2010a,b, 2011, 2013c, 2014Smith et al, 2007Smith et al, , 2008Subha et al, 2022). Various organic bases can receive a proton and become protonated cations, examples being pyrazine (Lengyel et al, 2019), piperazine (Ding et al, 2014;Muslim et al, 2021;Subha et al, 2022), imidazole (Massey et al, 2016;Khan et al, 2021), indole (Ma et al, 2018), quinoline (Belombe et al, 2011;Li et al, 2012;Khan et al, 2022), 1,2,4-triazole and other azoles (Luo et al, 2011;Massey et al, 2012;Tucker et al, 2015;Singh et al, 2021), hydrazine (Smith et al, 2009), benzamidine (Portalone, 2010(Portalone, , 2014Irrera et al, 2012), sulfamethazine (Padrela et al, 2019), guanidine (Smith et al, 2007;Ghasemi et al, 2019), adenine (Sedghiniya et al, 2019) and amines (Rosokha et al, 2006;Zhang & Zhu, 2007;Ding et al, 2012Ding et al, , 2013Smith & Wermuth, 2013a, 2016Shmukler et al, 2019;El-Dissouky et al, 2020).…”

Occurence of Charge-Assisted Hydrogen Bonding in Bis-amidine Complexes Generating Macrocycles

“…This peculiar interaction named “salt bridge” or charge-assisted hydrogen bonding (CAHB) can strongly connect different building blocks and lead to the formation of exciting supramolecular architectures. In a recent work on amidinium-carboxylate interaction, published by Portalone, the contact between the simple benzeneamidinium and some methoxy-substituted benzoates were investigated. The single crystal X-ray molecular structures revealed short distances in the CAHB N +1/2 -H---O –1/2 units between N +1/2 and O –1/2 [in the range 2.751(3)–2.850(2) Å] similar to the N to O distances measured in classic N–H---O or O–H---N units (e.g., d N–O = 2.731–2.794 and 2.706–2.771 Å in the supramolecular cyclic dimer and trimers dioximes, respectively or d N–O = 2.6–3.0 Å in proteins).…”