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In the title compound, C6H10N3O2+·C4H5O6−·0.5HCl·C4H6O6·2H2O, histidine exists, in the zwitterionic form, as a cation with a protonated amino group, a protonated ring N atom and a deprotonated carboxyl­ic acid group. The tartaric acid mol­ecules exist as a semi-tartrate anion and a neutral tartaric acid mol­ecule. The chloride ion sits on a special position. The structure is stabilized by a number of O—H⋯O, N—H⋯O and O—H⋯Cl hydrogen bonds, in addition to van der Waals interactions. Water mol­ecules are also found to mediate O—H⋯O hydrogen-bonded interactions among amino acid and tartaric acid mol­ecules. In the crystal structure, the histidinium cation exists in an open conformation I, which is sterically the most favourable; the imidazole group is trans to the carboxyl group and gauche to the amino N atom.

In the title compound, C6H7N2O+ center dot C2O2F3-, the carboxamide group is twisted by 16.3 (8) degrees from the pyridine ring plane. The protonated cations are linked to the anions by N-H center dot center dot center dot O hydrogen bonds to form a distorted lamellar structure.

In the title compound, C7H8NO2+center dot C2F3O2-, the carboxyl plane of the cation is twisted out of the plane of the aromatic ring. The cations form C(8) chains through `head- to- tail' N-H center dot center dot center dot O hydrogen-bonding interactions. These chains form a sheet-like structures, separated by an interlayer distance of 3.388 (2) angstrom. Furthermore, cations and anions form R-4(2)(8) and R-4(4)(24) ring motifs through N-H center dot center dot center dot O and O-H center dot center dot center dot O hydrogen bonds.

In the title compound, 2C6H7N2O+·2C4H5O6−·1.25H2O, the carboxamide planes of the cations are twisted relative to the pyridine rings. The crystal structure is stabilized by an intricate three-dimensional network of N—H⋯O and O—H⋯O hydrogen bonds. Inter­estingly, the anions and water mol­ecules form extensive ring motifs through O—H⋯O hydrogen bonds, and the cations are incorporated into these rings.

The asymmetric unit of the title compound, C8H22N2 2+·2C7H6NO2 −·2.25H2O, consists of half each of two centrosymmetric tetramethylbutane-1,4-diammonium cations, two p-aminobenzoate anions and 2.25 solvent water molecules. As a characteristic feature of 4-aminocarboxylic acid, twisting of the carboxylate group from the aromatic plane is observed in the p-aminobenzoate anions. Other noteworthy features are the `head-to-tail' chain and the formation of dimers through N—H...O and O—H...O hydrogen bonds involving amino groups, carboxylate groups and water molecules. Futhermore, an intricate three-dimensional hydrogen-bonding network involving N—H...O and O—H...O is observed.

In the title compound, C6H6NO2+.C2HO4-, the cations and anions are situated on a mirror plane. The crystal structure involves two-dimensional lamellar sheets formed by cations and anions linked through N-(HO)-O-... and O-(HO)-O-... hydrogen bonds. These sheets are separated by a distance of 3.024 (1) angstrom.

In the title mol­ecule, C26H23Cl2NO3S, the tetra­hydro­pyridine ring adopts a half-chair conformation. Intra­molecular O—H⋯O hydrogen bonding generates an S(6) ring motif. Inter­­molecular N—H⋯Cl, C—H⋯Cl and C—H⋯S hydrogen bonding generates primary graph-set motifs C(8), C(11) and C(6), respectively. No significant π–π inter­actions exist in the crystal structure.

The title compound, (C8H10NO)2[CuCl4], crystallizes with one 4-acetyl­anilinium cation and one half of a tetra­chloro­cuprate(II) anion in the asymmetric unit as the anion lies about a mirror plane with the Cu atom and two Cl− ligands lying in the mirror plane. The geometry around the copper(II) ion is that of a discrete flattened tetra­hedron. The cations are connected through N—H⋯O hydrogen bonds leading to a lamellar structure parallel to the ab plane. These sheets are also connected through the anions by N—H⋯Cl hydrogen bonds, leading to a three-dimensional hydrogen-bonded network.

The title compound, (C8H22N2)[CuCl4], is composed of one N,N,N′,N′-tetra­methyl­butane-1,4-diammonium cation and a tetra­chloro­cuprate(II) anion. The anion is mononuclear and has a flattened tetra­hedral geometry. In the cation, the dimethyl­amino substituents are trans with respect to the central C—C bond of the butane. In the crystal structure, the anions and cations are linked by N—H⋯Cl hydrogen bonds, forming chains along the a axis.

In the title compound, C15H17NO2, the six-membered cyclo­hexene ring has an envelope conformation. The structure is stabilized by O—H⋯N hydrogen bonds and weak van der Waals inter­actions. There are no C—H⋯π or π–π inter­actions between the two ring systems; however, there is an inter­molecular C—H⋯O hydrogen bond.

In the title compound, C20H24, the central cyclo­hexene ring is in a distorted half-chair conformation. The crystal structure is stabilized by weak van der Waals inter­actions.

In the title compound, C22H20, the central cyclo­hexene ring is in a slightly distorted half-chair conformation and the structure is stabilized by C—H⋯π inter­actions.

In the title compound, C35H34N2O2, the isoxazolidine ring adopts a twisted conformation and the piperidine ring is in a half-chair conformation. Weak C—H⋯π inter­actions are observed in the crystal structure.

In the title compound, C19H28BrNO3, which crystallizes with two mol­ecules in the asymmetric unit, the six-membered cyclo­hexa­none ring exists in a sightly distorted chair conformation. The bromo and methoxy­ethoxy groups are oriented axially, whereas the phenyl group and tert-butyl adopt equatorial positions. The crystal structure is stabilized by O—H⋯O inter­molecular hydrogen bonds.

In the title compound, C14H18BrNO2, the six-membered cyclo­hexa­none ring has a sightly distorted chair conformation. The oximino function in the compound assumes an E configuration, with the hydroxyl group anti to the substitutents on the tertiary C atom. Of the other three substituents, the bromo and eth­oxy groups are axial and the phenyl group is equatorial. Inversion-related mol­ecules form O—H⋯N hydrogen-bonded dimers.

In the title compound, C15H20O3, the cyclo­hexane ring adopts a chair conformation. The crystal structure is stabilized by O—H⋯O hydrogen bonds in addition to van der Waals inter­actions. An inter­molecular C—H⋯π inter­action is also observed.

In the title compound, C6H6NO2+·NH4+·SO42−·NH3SO3, 3-carboxy­pyridinium ions form N—H⋯O hydrogen-bonded chains along the b axis. Ammonium and sulfate ions and sulfamic acid mol­ecules form a two-dimensional network of hydrogen bonds parallel to (001). This leads to the formation of alternate hydro­philic and hydro­phobic layers.

The title compound, C17H17N5OS, adopts the configurations Z around the imine C=N bond and E around the C(O)—NH bond. The configurations are stabilized by two intra­molecular N—H⋯N hydrogen bonds. In the crystal structure, mol­ecules are linked together by N—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title compound, C5H12NO2+·C2F3O2−, the valine mol­ecule is in a cationic state, with a protonated amino group and an uncharged carboxylic acid group. The trifluoro­acetic acid mol­ecule is deprotonated and it displays rotational disorder. Inversion-related valinium residues are linked by N—H⋯O hydrogen bonds into a dimer. The dimers and the trifluoro­acetate anions are alternately connected by O—H⋯O and N—H⋯O hydrogen bonds to form a layer parallel to the ab plane.

In the title mol­ecule, C31H28N2O2, the piperidinone ring adopts the usual twist-boat conformation. The aryl rings at positions 2 and 3 are axial and those at positions 5 and 6 are equatorial. In the crystal structure, there are no hydrogen bonds nor are there any significant π⋯π stacking inter­actions and, apart from two weak C—H⋯π(arene) inter­actions, mol­ecules are separated by normal van der Waals distances.

In the title compound, C5H6N+·C4H5O6−, the pyridine mol­ecule exists as a cation and the tartaric acid mol­ecule as a semi-tartrate anion. The semi-tartrate anions are linked by O—H⋯O hydrogen bonds to form hollow columns running parallel to the a axis. The pyridinium cations, trapped in the columns, are linked to the semi-tartrate anions via strong N—H⋯O hydrogen bonds.

In the title compound, C6H16N4O2 +·C2F3O2 −, the amino acid exists as a zwitterionic argininium cation, with positively charged amino and guanidinium groups and a negatively charged carboxylate group. The trifluoroacetic acid molecule is deprotonated. The stoichiometry between the argininium ion and the trifluoroacetate anion is 1:1. The aggregation of argininium cations and trifluoroacetate anions is strikingly similar to those observed in the 1:2 stoichiometric analogue.

In the title mol­ecular structure, C12H18N4OS2+·2C6H2N3O7−, the thia­zolium ring bearing the hydr­oxyethyl side chain is disordered over two sites about the methyl­ene bridge. In the minor occupancy component, the dihedral angles are quite different from the range observed in related structures. In the crystal structure, the thia­minium cation and one of the picrate anions form a centrosymmetric hydrogen-bonded cluster. Both anions form `anionic holes' with the thia­minium cation.

In the title compound, C30H24N2O·0.5C4H8O2, the piperidone ring adopts the chair conformation and all the phenyl rings are equatorially oriented. The ethyl acetate molecule is present as a space filler and does not participate in the hydrogen-bonding network. The crystal structure is stabilized through C—H...N and C—H...O hydrogen bonds. No significant C—H...π and π–π interactions are observed.

In the title compound, C9H11NO2·C7H6O2, the amino acid mol­ecule exists as a zwitterion and the carboxylic acid mol­ecule is in an unionized state. There is a strong O—H⋯O inter­molecular hydrogen bond between the phenyl­alanine and benzoic acid mol­ecules, and these mol­ecular pairs form hydrogen-bonded double layers.

In the title compound, C29H22Cl2N2O2, the piperidinone ring adopts its usual twist–boat conformation. The crystal packing is stabilized by a three-dimensional network of C—H⋯O hydrogen bonds involving the nitroso and carbonyl O atoms. No significant C—H⋯π, π–π and Cl⋯Cl inter­actions are observed but there are weak Cl⋯Cl interactions.

The asymmetric unit of the title compound, C9H11NO2·C9H12NO2+·C3H3O4−, consists of two phenyl­alanine mol­ecules, one as a zwitterion (P) and the other as a cation (P+), in addition to a malonate anion (Mal−). The phenyl­alaninium and phenyl­alanine mol­ecules are linked by a very short syn–syn carbox­yl–carboxyl­ate (–COO−⋯HOOC–) hydrogen bond [O⋯O = 2.429 (4) A]. The Mal− anion is stabilized by a strong intra­molecular O—H⋯O hydrogen bond. The aggregation of P and P+ is mediated through Mal−, leading to an infinite double chain along the c axis.

In the title compound, C9H12NO2+·C2Cl3O2−, the amino acid mol­ecule exists in the cationic form with a positively charged amino group and an uncharged carboxyl­ic acid group. The tri­chloro­acetic acid mol­ecule exists in the anionic state. The phenyl­alaninium cations and the tri­chloro­acetate anions form hydrogen-bonded double chains, linked together by N—H⋯O and O—H⋯O hydrogen bonds, extending along the c axis.

In the title compound, C4H10NO3+·C2Cl3O2−, (I), the amino acid mol­ecule exists in the cationic form, with a positively charged amino group and an uncharged carboxylic acid group. The tri­chloro­acetic acid mol­ecule exists in the anionic state. The threoninium cations and the tri­chloro­acetate anions form hydrogen-bonded double layers, linked together by a network of N—H⋯O and O—H⋯O hydrogen bonds and extended along the b axis. These double layers have no hydrogen-bonded interactions between them. No classic head-to-tail hydrogen bonds are observed in (I).

In the title compound, [UO2(C15H9O2)2(C17H18O)] or [UO2(DBM)2(DBA)], where DBM is di­benzoyl methanate and DBA is di­benzyl­acetone, the UVI atom is coordinated by seven O atoms in a distorted pentagonal–bipyramidal geometry. The di­phenyl­propane-1,3-dionate system acts as a chelating ligand and coordinates through both of its ketonate O atoms, while the DBA ligand coordinates through the O atom. The average U—O distances for U—O(uranyl) [1.742 (2) A], U—O(diketonate) [2.349 (2) A] and U—O(DBA) [2.406 (2) A] are within normal ranges. The DBA mol­ecule retains its trans–trans geometry in the structure.

In the title compound, 2C5H11NO2·C4H6O4, the dl-valine mol­ecule exists in the zwitterionic form and the neutral succinic acid mol­ecule lies across an inversion center. There are no direct hydrogen-bonding interactions between succinic acid mol­ecules. Valine and succinic acid mol­ecules form alternating columns parallel to the c axis and are interlinked through characteristic hydrogen bonds to form a three-dimensional network.

In the title compound, C21H22N2O3, the geometry of the heterodiene (N=C—C=C) indicates the presence of a resonance effect across the C—C bond. The heterodiene prefers the s-trans configuration. The mol­ecules aggregate as double layers parallel to the (101) plane. Consecutive layers, labelled ABAB…, are inversely related to one another.

In the title compound, C4H10NO3+·C4H3O4−, the threonine mol­ecule exists as a cation and the maleic acid mol­ecule exists in the mono-ionized state. In the semi-maleate ion, there is an intramolecular O—H⋯O hydrogen bond. The mol­ecules aggregate into infinite parallel layers which extend in the (0\overline 22) plane. These layers have no hydrogen-bonded interactions between them, only van der Waals interactions. The semi-maleate ion is essentially planar. The structure is stabilized by O—H⋯O and N—H⋯O hydrogen bonds, in addition to weak C—H⋯O interactions. No classical head-to-tail hydrogen bonds are observed.

The asymmetric unit of the title compound, C20H21NO3, contains two crystallographically independent mol­ecules, approximately related by a local twofold axis. These two mol­ecules differ from each other in the orientation of the ethyl group. In both mol­ecules, the piperidone ring adopts a slightly distorted chair conformation, with the phenyl rings and carbethoxy group attached equatorially. The crystal packing is characterized by C—H⋯π and C—H⋯O interactions.

In the title mol­ecule, C25H25NO, the piperidone ring adopts a slightly distorted chair conformation. The two methyl­phenyl rings are oriented differently with reference to the central piperidone plane. The crystal packing is characterized by C—H⋯π and C—H⋯O interactions. It can be concluded that the stable conformation is the same in the solid state as in solution.

The thia­zine ring in the title compound, C14H19NO5S, adopts a slightly distorted chair conformation. The substituents, viz. the ethoxy­carbonyl and methoxy­phenyl groups, are located cis to one another. In the crystal structure, the inversion-related mol­ecules exist as C—H⋯O hydrogen-bonded dimers, and these are linked by N—H⋯O and C—H⋯O interactions to form layers parallel to the ac plane.

In the title compound, C20H18O3, the benzoyl and phenyl groups lie on opposite sides of the di­hydro­furan ring. The di­hydro­furan ring adopts a conformation intermediate between an envelope and a half-chair. The crystal packing is characterized by van der Waals forces and C—H⋯O interactions.

In the title complex, catena-poly­[[[dicadmium(II)]-μ-dl-alanine-di-μ-chloro] monohydrate], {[CdCl2(C3H7NO2)]·H2O}n, the dl-alanine mol­ecules exist in the zwitterionic form. The Cd atoms lie on inversion centers and are coordinated by four Cl atoms and two carboxyl O atoms, forming a distorted octahedral environment. These octahedra are linked through Cl—Cl edges and are bridged by the carboxyl groups of the alanine residues, forming a one-dimensional polymer chain that extends along [100].

In the title compound, [Co(C3H7NO2)2(H2O)4](NO3)2, the CoII atom lies on a crystallographic inversion centre and the asymmetric unit comprises the anion and one-half cation. CoII is coordinated by six O atoms, two from alanine mol­ecules and four from water mol­ecules, forming an octahedron with minimal distortion. The O atoms of the nitrate group do not coordinate to cobalt but participate in hydrogen bonding.

In the title compound, [UO2(C15H11O2)2(C18H15OP)] or [UO2(DBM)2(Ph3PO)], where DBM is di­benzoyl methanate, the UVI atom is coordinated by seven O atoms in a distorted pentagonal–bipyramidal geometry. The di­phenyl­propane-1,3-dionate system acts as a chelating ligand and coordinates through both of its ketonate O atoms and the tri­phenyl phosphine oxide ligand coordinates through the O atom. The U—O distances range from 1.759 (4) to 2.385 (4) A.

In the title compound, C9H12NO2+·C2Cl3O2−·H2O, the phenyl­alanine mol­ecule exists as a cation with a positively charged amino group and a neutral carboxyl­ic acid group. The tri­chloro­acetic acid mol­ecule is deprotonated as an anion and forms N—H⋯O hydrogen bonds with the phenylalanin­ium cations. Water mol­ecules also mediate interactions with amino acid and tri­chloro­acetate ions through O—H⋯O hydrogen bonds. The aggregation pattern observed in the title salt has striking similarities with those observed in l-phenyl­alanine l-phenyl­alaninium formate and l-phenyl­alanine l-phenyl­alaninium perchlorate.

In the title adduct, C9H11NO2·C4H4O4, the amino acid mol­ecules exist as zwitterions and the fumaric acid mol­ecules exist in the unionized state, a feature uncommon in similar crystal structures. The asymmetric unit is composed of two mol­ecules of each species. The fumaric acid mol­ecules are related to each other through a pseudo-inversion centre and are essentially planar. The phenyl­alanine and fumaric acid mol­ecules form hydrogen-bonded double layers, linked together by hydrogen bonds and extending along [001]. These double layers are flanked, on either side, by the hydro­phobic side chains of phenyl­alanine, leading to alternating hydro­philic and hydro­phobic zones.

In the title compound, C6H14NO2+.C2HO4-, the leucine molecule exists in the cationic form, with a protonated amino group and an uncharged carboxylic acid group. Oxalic acid exists in the mono-ionized state. Pseudo-inversion centres relate the leucinium cations and semi-oxalate anions. The leucinium and semi-oxalate ions form hydrogen-bonded, double-layered chains, extending parallel to the b axis. The leucinium cations are arranged in these double layers on opposite sides leading to alternating hydrophobic and hydrophilic layers.

In the title compound, C5H11NO2.0.5C(4)H(4)O(4), the valine molecule exists as a zwitterion and the fumaric acid molecule in the unionized state, forming an adduct, a feature uncommon in similar crystal structures. The fumaric acid molecule has a centre of symmetry and is planar with a trans configuration about the central C=C bond. The fumaric acid molecules have no hydrogen-bonded interactions among themselves and only mediate interactions between DL-valine layers, leading to a three-dimensional network of molecules.

In the title compound, C5H6N+·C2HO4−·C2H2O4·2H2O, the pyridine mol­ecule exists as a cation and the oxalic acid mol­ecules as an oxalate(1−) ion and a neutral oxalic acid. The structure is stabilized by O—H⋯O and N—H⋯O hydrogen bonds in addition to carbonyl–carbonyl O⋯C short contacts and van der Waals interactions. The water mol­ecules are also found to mediate interactions between oxalate ions and oxalic acid mol­ecules through a number of O—H⋯O hydrogen bonds. Pairs of pyridinium cations related by a center of inversion are surrounded by semi-oxalate anions and oxalic acid mol­ecules, and the complex may be described as an inclusion compound.

In the crystal structure of the title compound, Cl3CCOOH or C2HCl3O2, mol­ecules form centrosymmetric pairs leading to centrosymmetric dimers through strong O—H⋯O hydrogen bonds. In the absence of other strong intermolecular interactions, the Cl⋯O [3.029 (1) A] and Cl⋯Cl [3.612 (1) A] interactions presumably play an important role in the stabilization of the crystal structure.