Proton-transfer compounds featuring the unusual 4-arsonoanilinium cation from the reaction of (4-aminophenyl)arsonic acid with strong organic acids

The crystal structures of the 1:1 proton-transfer compounds of (4-aminophenyl)arsonic acid (p-arsanilic acid) with the strong organic acids, 2,4,6-trinitrophenol (picric acid), 3,5-dinitrosalicylic acid, (3-carboxy-4-hydroxy)benzenesulfonic acid (5-sulfosalicylic acid) and toluene-4-sulfonic acid have been determined at 200 K and their hydrogen–bonding patterns examined. The compounds are, respectively, anhydrous 4-arsonoanilinium 2,4,6-trinitrophenolate (1), the hydrate 4-arsonoanilinium 2-carboxy-4,6-dinitrophenolate monohydrate (2), the hydrate 4-arsonoanilinium (3-carboxy-4-hydroxy)benzenesulfonate monohydrate (3) and the partial solvate 4-arsonoanilinium toluene-4-sulfonate 0.8 hydrate (4). The asymmetric unit of2, a phenolate, comprises two independent but conformationally similar cation-anion pairs and two water molecules of solvation, and in all compounds, extensive inter-species hydrogen–bonding interactions involving arsono O–H···O and anilinium N–H···O hydrogen–bonds generate three-dimensional supramolecular structures. In the cases of1and2, the acceptors include phenolate and nitro O-atom acceptors, with3and4, additionally, sulfonate O-atom acceptors, and with the hydrates2–4, the water molecules of solvation. A feature of the hydrogen–bonding in3is the presence of primary chains extending along (010) through centrosymmetric cyclicR22(8) motifs together with conjoined cyclicR34(12) motifs, which include the water molecule of solvation. The primary hydrogen–bonding in the substructure of4involves homomolecular cation–cation arsono O–H···O interactions forming columns down the crystallographic four-fold axis of the unit cell.

Intermolecular interactions of proton transfer compounds: synthesis, crystal structure and Hirshfeld surface analysis

Three new proton transfer compounds, [2-ammonio-5-methylcarboxybenzene perchlorate (1), (C8H10NO2+·ClO4−), 4-(ammoniomethyl)carboxybenzene nitrate (2), (C8H10NO2+·NO3−), and 4-(ammoniomethyl)carboxybenzene perchlorate (3), (C8H10NO2+·ClO4−)], have been synthesized, their IR modes of vibrations have been assigned and their crystal structures studied by means of single-crystal X-ray diffraction. Their asymmetric units consist of one cation and one anion for both compounds (1) and (2). However, the crystal structure of compound (3) is based on a pair of cations and a pair of anions in its asymmetric unit. The three-dimensional Hirshfeld surface analysis and the two-dimensional fingerprint maps revealed that the three structures are dominated by H...O/O...H and H...H contacts. The strongest hydrogen-bonding interactions are associated with O—H...O and N—H...O constituting the highest fraction of approximately 50%, followed by those of the H...H type contributing 20%. Other close contacts are also present, including weak C...H/H...C contacts (with about 10%).

Novel fluorescent probes based on intramolecular charge- and proton-transfer compounds

Excited-state intramolecular proton-transfer (ESIPT) compounds and intramolecular charge-transfer (ICT) compounds have attracted attention due to their interesting and even unique emission properties. The intense and environment-sensitive emission showed by some members of the two families has been exploited in fluorescent probes for various forms of environmental sensing. In this paper, we summarize our recent study on the utilization of novel ESIPT and ICT compounds with intense emission as fluorescent probes after an introduction to the ESIPT and/or ICT processes and related photophysics mechanism.

Proton-transfer compounds with 4-amino-N-(4,6-dimethylpyrimidin-2-yl)benzenesulfonamide (sulfamethazine): the structures and hydrogen bonding in the salts with 5-nitrosalicylic acid and picric acid

The structures of the anhydrous proton-transfer compounds of the sulfa drug sulfamethazine with 5-nitrosalicylic acid and picric acid, namely 2-(4-aminobenzenesulfonamido)-4,6-dimethylpyrimidinium 2-hydroxy-5-nitrobenzoate, C12H15N4O2S+·C7H4NO4−, (I), and 2-(4-aminobenzenesulfonamido)-4,6-dimethylpyrimidinium 2,4,6-trinitrophenolate, C12H15N4O2S+·C6H2N3O7−, (II), respectively, have been determined. In the asymmetric unit of (I), there are two independent but conformationally similar cation–anion heterodimer pairs which are formed through duplex intermolecular N+—H...Ocarboxylateand N—H...Ocarboxylatehydrogen-bond pairs, giving a cyclic motif [graph setR22(8)]. These heterodimers form separate and different non-associated substructures through aniline N—H...O hydrogen bonds, one one-dimensional, involving carboxylate O-atom acceptors, the other two-dimensional, involving both carboxylate and hydroxy O-atom acceptors. The overall two-dimensional structure is stabilized by π–π interactions between the pyrimidinium ring and the 5-nitrosalicylate ring in both heterodimers [minimum ring-centroid separation = 3.4580 (8) Å]. For picrate (II), the cation–anion interaction involves a slightly asymmetric chelating N—H...OR21(6) hydrogen-bonding association with the phenolate O atom, together with peripheral conjointR12(6) interactions between the same N—H groups and O atoms of theortho-related nitro groups. An inter-unit amine N—H...Osulfonehydrogen bond gives one-dimensional chains which extend alongaand inter-associate through π–π interactions between the pyrimidinium rings [centroid–centroid separation = 3.4752 (9) Å]. The two structures reported here now bring to a total of four the crystallographically characterized examples of proton-transfer salts of sulfamethazine with strong organic acids.