Charge-assisted Hydrogen Bonds Research Articles

Semiconducting Organic Assemblies Prepared from Tetraphenylethylene Tetracarboxylic Acid and Bis(pyridine)s via Charge-Assisted Hydrogen Bonding

Principles of crystal engineering have been applied toward the construction of supramolecular assemblies between an acid-functionalized tetraphenylethylene derivative and three different bis(pyridine)s [4,4'-bis(pyridyl)ethylene, 4,4'-bis(pyridyl)ethane, and 4,4'-bipyridine]. Each assembly was structurally characterized, and charge transfer interactions within each sample were visually apparent. Quantum chemical calculations were used to determine crystal band structure and band gap magnitude, and electrical properties of the materials were measured using conducting probe atomic force microscopy (CP-AFM). The crystals displayed charge-carrier capability, and the magnitude of semiconductivity varied systematically as a function of conjugation in the bis(pyridine) component. Crystals incorporating 4,4'-bis(pyridyl)ethylene and 4,4'-bipyridine displayed conductivities comparable to those of established organic semiconductors (μ(eff) = 0.38 and 1.7 × 10(-2) cm(2)/V·s, respectively).

Does electron density in bond critical point reflect the formal charge distribution in H-bridges? The case of charge-assisted hydrogen bonds (CAHBs)

The charge-assisted hydrogen bond (CAHB) was investigated for a set of H-bridges of N–H⋯Cl type. The properties of these bonds, i.e. interaction energy and electron density measured in a specific point of the bond, were represented as functions of H⋯Cl distance. It appears that the energy of interaction is very strongly affected by formal charges, which may be explained by the presence of efficient interaction between formal ions. Surprisingly, the electron density measured in the H-bond critical point is totally independent of the formal charges. For the given H⋯Cl distance the ρ BCP value is the same, no matter whether neutral molecules or oppositely charged ions interact with each other.

Synthesis and redox properties of triarylmethane dyecation salts of anions [M6O19]2−(M = Mo, W)

Four salts have been isolated combining the triarylmethane dye cations pararosaniline (PR(+)) and crystal violet (CV(+)) with the hexametalates [M(6)O(19)](2-) (M = Mo, W). A new hexatungstic acid H(2)[W(6)O(19)]·4dma (dma = dimethylacetamide) was isolated and is a useful synthon for hexatungstate salts. Single-crystal X-ray diffraction confirmed the presence of PR(+) and [Mo(6)O(19)](2-) ions in [PR](2)[Mo(6)O(19)]·6dmf (dmf = dimethylformamide). A number of charge-assisted hydrogen bonds N-H···O exist between the cation -NH(2) functions and the anion oxygen atoms. Comparative cyclic voltammetry of salts [A]Cl (A = PR, CV), [Bu(4)N](2)[M(6)O(19)](2-) and A(2)[M(6)O(19)] was established in MeCN and Me(2)SO solutions and of solids in contact with the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [emim][tfsa]. In the molecular solvents, the reversible potential for the process [Mo(6)O(19)](2-/3-) is less negative than the first reduction processes of the dye cations. In contrast, that for [W(6)O(19)](2-/3-) is more negative. Spectro-electrochemistry and bulk electrolysis experiments reveal significantly different pathways in the two cases. In contrast, in the [emim][tfsa] medium, a positive shift in reduction potential of at least 400 mV is seen for the anion processes but relatively little change for the dye cation processes. This means that initial reduction of the anions always precedes that of the dyes, providing significant simplification of the complex voltammetric data. Chemically modified electrodes can be used in the ionic liquid because of slow dissolution kinetics. However, reduced anion salts dissolve rapidly, allowing dissolved phase electrochemistry to be examined. The electrochemistries of the oxidized salts A(2)[M(6)O(19)] are essentially those of the individual ions, although low level interaction of A(+) with reduced anions [M(6)O(19)](3-,4-) is evident. The work establishes protocols for synthesis and handling of intensely absorbing and relatively insoluble salts which can now be applied to systems containing more complex polyoxometalate anions.

The dicyclohexylamine salt of RG108 (N-phthalyl-L-tryptophan), a potential epigenetic modulator

The dicyclo­hexyl­amine salt of RG108 (N-phthalyl-l-tryptophan) co-crystallizes with a water mol­ecule and a disordered mol­ecule of dimethyl­formamide (DMF), viz. dicyclo­hexyl­aminium (S)-2-(1,3-dioxoisoindolin-2-yl)-3-(1H-indol-3-yl)propanoate dimethyl­formamide solvate monohydrate, C12H24N+·C19H13N2O4 −·C3H7NO·H2O. The conformation of the deprotonated compound is constrained by charge-assisted strong hydrogen bonds with the dicyclo­hexyl­aminium ion and a dense hydrogen-bond network involving co-crystallized solvent mol­ecules. The dihedral angle between the fused ring systems in the anion is 58.35 (4)°.

Photothermal studies of the room temperature photo-induced spin state change in the Fe(III)(salten)(mepepy) complex

The complex [Fe(III)(salten)(mepepy)]BPh 4 (salten = 4-azaheptamethylene-1,7-bis(salicylideneiminate; mepepy = 1-(pyridin-4-yl)-2-(N-methylpyrrol-2-yl)-ethene; BPh 4 = tetraphenyl borate) has been investigated to determine the volume and enthalpy changes associated with the room temperature photo-induced spin crossover. Here we report the photophysical properties of the trans to cis isomerization of the mepepy ligand as well as the spin crossover of the Fe(III)(salten)(mepepy) complex in acetonitrile:water mixtures using photoacoustic calorimetry (PAC). The PAC studies indicate that the trans to cis transition of the mepepy ligand occurs faster than the ∼20 ns response time of the acoustic detector and gives rise to a negligible volume change (0.7 ± 0.3 mL mol −1) and an enthalpy change of 33 ± 10 kcal mol −1. These results are consistent with the loss of a charge assisted hydrogen bond between a water molecule and the pyridyl ring of the mepepy upon photoisomerization. In the case of Fe(III)(salten)(mepepy) photoexcitation, PAC results indicate that the high-spin to low-spin transition, also occurring in ≲ 20 ns, gives rise to small volume and enthalpy changes (0.9 mL mol −1 and 4 kcal mol −1). Analysis of the results indicate that the observed thermodynamics are related to a distortion of the Fe(II)(salten)(mepepy) complex associated with the cleavage of an Fe ⋯ N bond upon spin conversion.

Iron, copper and zinc ammonium-1-hydroxyalkylidene-diphosphonates with zero-, one- and two-dimensional covalent metal–ligand structures extended into three-dimensional supramolecular networks by charge-assisted hydrogen-bonding

Hydrothermal synthesis with MCl 2 (M = Fe, Cu, and Zn) and disodium 5-ammonium-1-hydroxypentylidene-1,1-bisphosphonate, (Na +) 2[ +H 3N(CH 2) 4C(OH)(PO 3 2−)(PO 3H −)] (Na 2HAC 5OHP 2) or sodium 3-ammonium-1-hydroxypropylidene-1,1-bisphosphonate hydrate, Na +[ +H 3N(CH 2) 2C(OH)(PO 3H –)(PO 3H –)]·H 2O (NaH 2PAM·H 2O) the sodium salt of pamidronic acid, H 3PAM) yielded the one-dimensional (1D) iron, molecular copper and two-dimensional (2D) zinc compounds 1D-{[Fe(μ 3-η 5-HAC 5OHP 2)]·H 2O}, 1, [Cu(η 2-H 2AC 5OHP 2) 2], 2, 2D-{[Zn 2(μ 5-η 7-AC 5OHP 2)Cl], 3, and 2D-{[Zn(μ 2-η 3-H 2PAM) 2], 4, respectively. The bisphosphonate ligand bridges (μ n ) between 2– 5 metal atoms and uses 2– 7 oxygen donor atoms towards metal coordination (η n ). The zwitterionic nature of the now bis- or tetrakis-deprotonated ammonium–bisphosphonate is retained in the metal complexes. From the reaction of NiCl 2 and Na 2HAC 5OHP 2 the zwitterionic 5-ammonium-1-hydroxypentylidene-1-phosphonic acid, +H 3N(CH 2) 4CH(OH)PO 3H −, 5 was obtained as a product of the ligand P–C bond hydrolysis. Adjacent strands, molecules or layers in 1– 4, respectively are organized through the Coulomb attraction between the positive ammonium group and the negative phosphonate groups, supported by hydrogen-bonding. Each protic H atom on the C–OH, NH 3 + and –PO 3H − group is involved in charge-assisted hydrogen-bonding. The ammonium-pentylidene groups act as hydrophobic separators between the hydrophilic units with the polar M{C(OH)(PO 3) 2} and {NH 3} units. Bond valence sum calculations support the Fe(II) oxidation state in 1, which was experimentally determined from a quantitative polarographic Fe(II)/Fe(III) speciation analysis as well as a temperature variable magnetic study.

Supramolecular association in proton-transfer adducts containing benzamidinium cations. I. Four molecular salts with uracil derivatives

Four organic salts, namely benzamidinidium orotate (2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylate) hemihydrate, C(7)H(9)N(2)(+).C(5)H(3)N(2)O(4)(-).0.5H(2)O (BenzamH(+).Or(-)), (I), benzamidinium isoorotate (2,4-dioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate) trihydrate, C(7)H(9)N(2)(+).C(5)H(3)N(2)O(4)(-).3H(2)O (BenzamH(+).Isor(-)), (II), benzamidinium diliturate (5-nitro-2,6-dioxo-1,2,3,6-tetrahydropyrimidin-4-olate) dihydrate, C(7)H(9)N(2)(+).C(4)H(2)N(3)O(5)(-).2H(2)O (BenzamH(+).Dil(-)), (III), and benzamidinium 5-nitrouracilate (5-nitro-2,4-dioxo-1,2,3,4-tetrahydropyrimidin-1-ide), C(7)H(9)N(2)(+).C(4)H(2)N(3)O(4)(-) (BenzamH(+).Nit(-)), (IV), have been synthesized by a reaction between benzamidine (benzenecarboximidamide or Benzam) and the appropriate carboxylic acid. Proton transfer occurs to the benzamidine imino N atom. In all four acid-base adducts, the asymmetric unit consists of one tautomeric aminooxo anion (Or(-), Isor(-), Dil(-) and Nit(-)) and one monoprotonated benzamidinium cation (BenzamH(+)), plus one-half (which lies across a twofold axis), three and two solvent water molecules in (I), (II) and (III), respectively. Due to the presence of protonated benzamidine, these acid-base complexes form supramolecular synthons characterized by N(+)-H...O(-) and N(+)-H...N(-) (+/-)-charge-assisted hydrogen bonds (CAHB).

Constructor graph description of the hydrogen-bonding supramolecular assembly in two ionic compounds: 2-(pyrazol-1-yl)ethylammonium chloride and diaquadichloridobis(2-hydroxyethylammonium)cobalt(II) dichloride

Covalent bond tables are used to generate hydrogen-bond pattern designator symbols for the crystallographically characterized title compounds. 2-(Pyrazol-1-yl)ethylammonium chloride, C(5)H(10)N(3)(+).Cl(-), (I), has three unique, strong, charge-assisted hydrogen bonds of the types N-H...Cl and N-H...N that form unary through ternary levels of graph-set interactions. Diaquadichloridobis(2-hydroxyethylammonium)cobalt(II) dichloride, [CoCl(2)(C(2)H(8)NO)(2)(H(2)O)(2)]Cl(2), (II), forms five unique charge-assisted hydrogen bonds of the types O-H...Cl and N-H...Cl. These form graph-set patterns up to the quinary level. The Co complex in (II) resides at a crystallographic inversion center; thus the number of hydrogen bonds to consider doubles due to their G-equivalence, and the handling of such a case is demonstrated.

Solid-state synthesis of head-to-tail photodimers from supramolecular assemblies directed by charge-assisted hydrogen bonds

A supramolecular approach based on the self-assembly of a hydrogen bonding switch with unsaturated pyridyl compounds is exploited in order to drive the topochemical synthesis of head-to-tail photodimers via charge-assisted hydrogen bonds.

Synthesis and Structure−Activity Relationships of Cyanoguanidine-Type and Structurally Related Histamine H4 Receptor Agonists

Recently, we identified high-affinity human histamine H3 (hH3R) and H4 receptor (hH4R) ligands among a series of NG-acylated imidazolylpropylguanidines, which were originally designed as histamine H2 receptor (H2R) agonists. Aiming at selectivity for hH4R, the acylguanidine group was replaced with related moieties. Within a series of cyanoguanidines, 2-cyano-1-[4-(1H-imidazol-4-yl)butyl]-3-[(2-phenylthio)ethyl]guanidine (UR-PI376, 67) was identified as the most potent hH4R agonist (pEC50 = 7.47, alpha = 0.93) showing negligible hH1R and hH2R activities and significant selectivity over the hH3R (pKB = 6.00, alpha = -0.28), as determined in steady-state GTPase assays using membrane preparations of hH(x)R-expressing Sf9 cells. In contrast to previously described selective H4R agonists, this compound and other 3-substituted derivatives are devoid of agonistic activity at the other HR subtypes. Modeling of the binding mode of 67 suggests that the cyanoguanidine moiety forms charge-assisted hydrogen bonds not only with the conserved Asp-94 but also with the hH4R-specific Arg-341 residue. 2-Carbamoyl-1-[2-(1H-imidazol-4-yl)ethyl]-3-(3-phenylpropyl)guanidine (UR-PI97, 88) was unexpectedly identified as a highly potent and selective hH3R inverse agonist (pKB = 8.42, >300-fold selectivity over the other HR subtypes).

Coulombic interactions, hydrogen bonding and supramolecular chirality in pyridinium trifluoromethanesulfonate

The title compound, C5H6N+.CF3SO3-, was serendipitously crystallized in the chiral space group P4(3)2(1)2. The component entities associate into hydrogen-bonded helical chains, which propagate along the a and b axes of the crystal, with an alternating disposition of the cations and anions along the chain. N-H...O charge-assisted hydrogen bonds, from each pyridinium cation to two adjacent trifluoromethanesulfonate anions and from every anion to two different cations, direct the formation of the supramolecular chiral arrays. The crystal packing exhibits nonconventional C-H...O and C-H...F hydrogen bonds between the components. The observed structure demonstrates induction of supramolecular chirality by a combination of Coulombic attractions and intermolecular hydrogen bonds.

NH4][(CH3)2NH2]2[Ta(C2O4)4]·2H2O: the first (oxalato)tantalate(V) complex structurally characterized

The compound [NH4][(CH3)2NH2]2[Ta(C2O4)4]·2H2O has been synthesized and characterized by elemental and TG/DTA analyses, IR spectroscopy and by the single-crystal X-ray diffraction study. The structure comprises the [Ta(C2O4)4]3− anion, NH4 + and [(CH3)2NH2]+ cations and crystallization water molecules. The Ta atom is octacoordinated by oxygen atoms from four bidentate oxalate groups forming a coordination polyhedron close to the triangular dodecahedron. The charge-assisted hydrogen bonds from both cations connect the [Ta(C2O4)4]3− anions into a three-dimensional framework. The synthesis and properties of [NH4][(CH3)2NH2]2[Ta(C2O4)4]·2H2O, the first structurally characterized compound with the tetra(oxalato)tantalate(V) anion, is reported.

Metal-Organic Frameworks with Direct Transition Metal-Sulfonate Interactions and Charge-Assisted Hydrogen Bonds

Seven compounds with framework structures made of divalent metal-imidazole (Im) complexes (M(II) = Co, Ni, and Mn) linked by 1,5-napthalenedisulfonate (1,5nds) were synthesized and structurally characterized. Five of these compounds, Mn(Im)(4)(1,5nds) (two forms), Co(Im)(4)(1,5nds) (two forms), and Ni(Im)(4)(1,5nds), contain direct sulfonate-metal coordination and represent the first such compounds with open d-shell transition metals without Jahn-Teller distortion. The two disulfonate ligands in these octahedrally coordinated metal centers are found in both trans- and cis-geometries and link the centers into chains. The chains are held together by charge-assisted hydrogen bonds between sulfonate and imidazole ligands from different chains. The remaining two compounds, Co(Im)(6)(1,5nds) x 2 H(2)O and Ni(Im)(6)(1,5nds) x 2 H(2)O, exhibit only charge-assisted hydrogen bonds between the octahedral M(Im)(6)(2+) cations and the disulfonate anions.

Crystal Structure Analysis and in Silico pKa Calculations Suggest Strong pKa Shifts of Ligands as Driving Force for High‐Affinity Binding to TGT

A novel ligand series is presented to inhibit tRNA-guanine transglycosylase (TGT), a protein with a significant role in the pathogenicity mechanism of Shigella flexneri, the causative agent of Shigellosis. The enzyme exchanges guanine in the wobble position of tRNA(Asn,Asp,His,Tyr) against a modified base. To prevent the base-exchange reaction, several series of inhibitors have already been designed, synthesized, and tested. One aim of previous studies was to address a hydrophobic pocket with different side chains attached to the parent skeletons. Disappointingly, no significant increase in binding affinity could be observed that could be explained by the disruption of a conserved water cluster. The ligand series examined in this study are based on the known scaffold lin-benzoguanine. Different side chains were introduced leading to 2-amino-lin-benzoguanines, which address a different pocket of the protein and avoid disruption of the water cluster. With the introduction of an amino group in the 2-position, a dramatic increase in binding affinity can be experienced. To explain this significant gain in binding affinity, Poisson-Boltzmann calculations were performed to explore pK(a) changes of ligand functional groups upon protein binding, they can differ significantly on going from aqueous solution to protein environment. For all complexes, a permanent protonation of the newly designed ligands is suggested, leading to a charge-assisted hydrogen bond in the protein-ligand complex. This increased strength in hydrogen bonding takes beneficial effect on binding affinity of the ligands, resulting in low-nanomolar binders. Crystal structures and docking emphasize the importance of the newly created charge-assisted hydrogen bond. A detailed analysis of the crystal structures in complex with substituted 2-amino-lin-benzoguanines indicate pronounced disorder of the attached side chains addressing the ribose 33 binding pocket. Docking suggests multiple orientations of these side chains. Obviously, an entropic advantage of the residual mobility experienced by these ligands in the bound state is beneficial and reveals an overall improved protein binding.

Molecular tectonics: design of 2-D networks by simultaneous use of charge-assisted hydrogen and coordination bonds

Using a combination of charge-assisted H- and coordination-bonds, a tetra component system composed of a dicationic and a dianionic organic tecton, Ag(+) cation and XF(6)(-) (X= P, As, Sb) anion behaves as planned and leads to the formation of 2-D isostructural networks for which the energetic contributions of the two recognition events dominate the construction process.

Experimental charge density in an oxidized trinuclear iron complex using 15 K synchrotron and 100 K conventional single-crystal X-ray diffraction

The experimental electron density distribution in a crystal consisting of the simplest conceivable trinuclear carboxylate-bridged iron-mu3-oxo dianion with two alpha-picolinium cations has been determined using both synchrotron (15 K) and conventional (100 K) X-ray diffraction data. The constituent trinuclear oxo-centered molecule consists of six mu2-bridging formate groups between the iron pairs, while the axial ligand for all iron atoms is another formate group. The compound {[FeO(HCOO)5(HCOO)3]2-.H2O.2(alpha-CH3NC5H5)}, (1) crystallizes in the monoclinic space group P2(1)/m with charge assisted hydrogen bonds linking the alpha-picolinium cations to the trinuclear groups. The chemical bonding in the weakly asymmetric Fe3O-core of 1 has been examined through the use of the quantum theory of atoms in molecules, and in combination with experimental d-orbital populations, a significant electron sharing is observed between the Fe atoms and the central oxygen. The central oxygen exhibits clear sp2 hybridization, and the iron atoms have valence shell charge concentrations in all metal-ligand bond directions. The relative bond strengths are evaluated based upon the charge density distribution and found to be in accordance with the geometrical results. Integrated group charges follow expectations from formal chemical valences.

Tetra-chloro-(bis-(3,5-dimethylpyrazolyl)methane)gold(III) chloride: An HIV-1 reverse transcriptase and protease inhibitor

The title compound ([3,5-Me(2)bpzaH(2)][AuCl(4)]Cl, 1) (Me(2)bpza=bis(3,5-dimethylpyrazolyl)acetic acid), was prepared by reacting H[AuCl(4)] with 3,5-Me(2)bpza; and spectroscopically and structurally characterized. In the solid state structure of 1, the pyrazolyl ligand is doubly protonated to form two strong charge assisted hydrogen bonds of the type N(+)Hcdots, three dots, centeredCl(-) with the single chloride anion whilst the [AuCl(4)](-) anion remains discrete. The anti-HIV-1 activity of 1 was determined by a colorimetric direct enzyme reverse transcriptase (RT) assay and a fluorogenic protease (PR) assay. Compound 1 significantly (p<0.05) inhibited RT over a concentration range of 5-250muM and inhibited HIV-1 protease at 100muM. Compound 1 inhibited two very important HIV-1 enzymes (RT and PR) in direct enzyme assays and therefore warrants further evaluation.

H-Bonded Complexes of Aniline with HF/F−and Anilide with HF in Terms of Symmetry-Adapted Perturbation, Atoms in Molecules, and Natural Bond Orbitals Theories

The hydrogen-bonded isoelectronic complexes of aniline with HF/F- and an ionic form of aniline with HF were investigated by use of computational methods: Symmetry-Adapted Perturbation Theory (SAPT), Atoms in Molecules (AIM), and Natural Bond Orbitals (NBO) approaches. All computations were based on structural models previously generated at the B3LYP/6-311+(d,p) level. The differences between neutral (Ph-NH2...HF)and anionic (Ph-NH2...F- and Ph-NH-...HF) complexes were clearly outlined. The discussed charged complexes serve as Lewis acids and base, HF and F-, respectively. It was found that electrostatic and induction energy terms, obtained as a result of the SAPT method, are most dependent on the type of H-bonding (i.e.,charged or neutral). The electrostatic term is the most distinctive between the neutral and charge-assisted hydrogen bonds in the investigated two-body systems, whereas the latter is more significant in the case of weaker interactions (larger H...B distances). Application of Principal Component Analysis (PCA) to energy components obtained from the SAPT procedure indicated that all of them are relatively well intercorrelated.The above-mentioned terms together with the exchange energy terms are the most important contributions ofthe main principal component, which describes 95% of the total variance. Comparison of AIM parameters in bond critical points for modeled H-bond systems shows a good agreement with those from equilibrium complexes, both experimental and calculated ones. It was found that charged H-bonded complexes exhibit larger fluctuation of electron density and its Laplacian in bond critical points, in line with SAPT analysis. NBO results confirmed the effect of the strength of interaction on property changes both in the region of H-bonding and outside of it. The latter, more distant consequences follow the Bent-Walsh rule for all studied complexes.

A Series of Guest-Defined Metal-Complex/Disulfonate Frameworks of Hydrogen-Bonded [Co(en)2(ox)]+and 2,6-Naphtalenedisulfonate

A new series of soft-host frameworks assembled by charge-assisted hydrogen bonds between a cationic metal complex (MC) and an anionic disulfonate specifically (Co(en)2(ox)) + and 2,6-naphthalenedisulfonate (NDS), is synthesized and structurally characterized. The five new compounds have a general formula (MC)2(NDS) ·n(guest) where guests are H2O, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), p-nitrophenol (pnp), and 4-dimethylaminopyridine (dmapy). All five structures are of the pillared-layer type where the layers are constructed of MC cations held together by a multitude of hydrogen bonds, both direct and indirect via sulfonate groups. The organic residues of the disulfonate serve as pillars. The structures of the layers and the orientations of the pillars adjust to the specifics of the guest molecules, and, as a result, four different patterns are observed. Compared to the recently reported analogous compounds with (Co(NH3)6) 3+ , these compounds have larger interpillar galleries because of the lower charge of the complex. The same effect was observed in a similar series with (Co(en)2(ox)) + complexes but linked with 4,4'- biphenyldisulfonate. The factors that influence the frameworks such as the charge of the metal complex and the guest molecules are discussed.

Solid state structural studies of saccharin salts with some heterocyclic bases

Five saccharin salts with heterocyclic bases 1,2-bis(4-pyridyl)ethane, 1; trans-1,2-bis(4-pyridyl)ethylene, 2; piperazine, 3; 1,4-dimethylpiperazine, 4 and 2,2′-dipyridylamine, 5 have been synthesized and characterized by single crystal X-ray diffraction. The crystal structures reveal that in all the salts, the hydrogen atom has been transferred from saccharin nitrogen to the base nitrogen and sustained through charge-assisted hydrogen bonds. In salts 1–3, N+–H donor forms N+–H⋯O hydrogen bonds with the carbonyl oxygen of saccharinate, whereas it forms N+–H⋯N− in 4 and intramolecular N+–H⋯N in 5. Salts 2 and 3 also form weak N+–H⋯N−hydrogen bonds. Only in salt3, the SO2 moiety is involved in conventional hydrogen bonding.