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1.  Bis(2,2′-bipyridine)[1,9-bis(diphenylphos­phanyl)-1,2,3,4,6,7,8,9-octahydropyrim­ido[1,2-a]pyrimidin-5-ium]ruthenium(II) hexa­fluorido­phosphate dibromide di­chloro­methane disolvate monohydrate 
In the cation of the title complex, [Ru(C31H32N3P2)(C10H8N2)2](PF6)(Br)2·2CH2Cl2·H2O, the ruthenium ion is coordinated in a distorted octa­hedral geometry by two 2,2′-bi­pyridine (bpy) ligands and a chelating cationic N-di­phenyl­phosphino-1,3,4,6,7,8-hexa­hydro-2-pyrimido[1,2-a]pyrimidine [(PPh2)2-hpp] ligand. The tricationic charge of the complex is balanced by two bromide and one hexa­fluorido­phosphate counter-anions. The compound crystallized with two mol­ecules of di­chloro­methane (one of which is equally disordered about a Cl atom) and a water mol­ecule. In the crystal, one of the Br anions bridges two water mol­ecules via O—H⋯Br hydrogen bonds, forming a centrosymmetric diamond-shaped R 4 2(8) motif. The cation and anions and the solvent mol­ecules are linked via C—H⋯F, C—H⋯Br, C—H⋯Cl and C—H⋯O hydrogen bonds, forming a three-dimensional network.
PMCID: PMC3884983  PMID: 24454158
2.  2-Oxo-1,2-dihydro­pyrimidin-3-ium di-μ-chlorido-bis­{dichloridobis[pyrimidin-2(1H)-one-κN 3]cuprate(II)} dihydrate 
The asymmetric unit of the title compound, (C4H5N2O)2[Cu2Cl6(C4H4N2O)2]·2H2O, consists of one cation, one half of a centrosymmetric dianion and one water mol­ecule. The centrosymmetric dianion formed by dimerization in the crystal structure has neutral pyrimidin-2-one ligands coordinated to each copper(II) centre through Cu—N bonds. The Cu atoms each have a distorted trigonal bipyramidal geometry, with the N atom of the pyrimidin-2-one ligand in an axial position, and dimerize by sharing two equatorial Cl atoms. N—H⋯Cl, O—H⋯Cl and N—H⋯O hydrogen bonds connect the anions, cations and water mol­ecules, forming a three-dimensional network.
PMCID: PMC2961836  PMID: 21202780
3.  Bis(2,4,6-tri­amino­pyrimidin-1-ium) sulfate penta­hydrate 
The asymmetric unit of the title salt, 2C4H8N5 +·SO4 2−·5H2O, contains four 2,4,6-tri­amino­pyrimidinium (TAPH+) cations, two sulfate anions and ten lattice water mol­ecules. Each two of the four TAPH+ cations form dimers via N—H⋯N hydrogen bonds between the amino groups and the unprotonated pyrimidine N atoms [graph-set motif R 2 2(8)]. The (TAPH+)2 dimers, in turn, form slightly offset infinite π–π stacks parallel to [010], with centroid–centroid distances between pyrimidine rings of 3.5128 (15) and 3.6288 (16) Å. Other amino H atoms, as well as the pyrimidinium N—H groups, are hydrogen-bonded to sulfate and lattice water O atoms. The SO4 2− anions and water mol­ecules are inter­connected with each other via O—H⋯O hydrogen bonds. The combination of hydrogen-bonding inter­actions and π–π stacking leads to the formation of a three-dimensional network with alternating columns of TAPH+ cations and channels filled with sulfate anions and water mol­ecules. One of the sulfate anions shows a minor disorder by a ca 37° rotation around one of the S—O bonds [occupancy ratio of the two sets of sites 0.927 (3):0.073 (3)]. One water mol­ecule is disordered over two mutually exclusive positions with an occupancy ratio of 0.64 (7):0.36 (7).
PMCID: PMC3793762  PMID: 24109349
4.  2-Amino-3-carb­oxy­pyrazin-1-ium perchlorate bis­(2-amino­pyrazin-1-ium-3-carboxyl­ate) monohydrate 
The asymmetric unit of the title compound, C5H6N3O2 +·ClO4 −·2C5H5N3O2·H2O, comprises two symmetry-independent zwitterions, one cation, one perchlorate anion and one water mol­ecule. In the crystal, the three different types of organic entities are linked by N—H⋯O and N—H⋯N hydrogen bonds, forming undulating sheets parallel to (1-10). These sheets are in turn connected by O—H⋯N and O—H⋯O hydrogen bonds involving perchlorate anions and water mol­ecules, forming a three-dimensional network. Intra­molecular N—H⋯O and weak inter­molecular C—H⋯O hydrogen bonds are also present.
PMCID: PMC3379306  PMID: 22719504
5.  1-{[4′-(1H-1,2,4-Triazol-2-ium-1-ylmeth­yl)biphenyl-4-yl]meth­yl}-1H-1,2,4-triazol-2-ium bis­(3-carb­oxy-5-iodo­benzoate)–5-iodo­benzene-3,5-dicarb­oxy­lic acid–water (1/2/2) 
The neutral carb­oxy­lic acid mol­ecule and the carboxyl­ate anion in the title compound, C18H18N6 2+·2C8H4IO4 −·2C8H5IO4·2H2O, are both nearly planar (r.m.s. deviations = 0.034 and 0.045 Å, respectively). In the cation, the mid-point of the C—C bond linking the two benzene rings lies on a center of inversion, and the triazole ring is approximately perpendicular to the adjacent benzene ring [dihedral angle = 83.2 (3)°]. In the crystal, the cations, anions, carb­oxy­lic acid and lattice water mol­ecules are linked by N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds, generating a ribbon running along [1-10]. The crystal studied was a non-merohedral twin with the components in a 51.2 (1):48.8 (1) ratio.
PMCID: PMC3344494  PMID: 22590256
6.  2-Amino-4-methyl-6-oxo-3,6-dihydro­pyrimidin-1-ium perchlorate–2-amino-6-methyl­pyrimidin-4(1H)-one–water (1/1/1) 
In the title compound, C5H8N3O+·ClO4 −·C5H7N3O·H2O, each perchlorate anion is paired with a protonated cationic 2-amino-6-methyl­pyrimidin-4(1H)-one and another non-protonated entity of the same organic pyrimidinone. The crystal structure is stabilized by N—H⋯Oorg, N—H⋯Owater, N—H⋯OClO4, O—H⋯OClO4, N—H⋯N and C—H⋯OClO4 hydrogen bonds between the anions, organic entities and water mol­ecules. Inter­molecular π–π stacking inter­actions between neighbouring organic rings are observed with a face-to-face distance of 3.776 (2) Å, and O—H⋯O hydrogen bonds link the perchlorate anions and the water mol­ecules into chains along the b-axis direction. The perchlorate anion and the inter­stitial water mol­ecule are disordered over two mutually incompatible positions with a common occupancy ratio of 0.678 (16):0.322 (16).
PMCID: PMC3200758  PMID: 22065517
7.  Adenin-1-ium hydrogen isophthalate di­methyl­formamide monosolvate 
In the title proton-transfer organic salt, C5H6.3N5 +·C8H4.7O4 −·C3H7NO, the adeninium moiety is protonated at the N atom in the 1-position of the 6-amino-7H-purin-1-ium (adeninium) cation. In the solid state, the second acidic proton of isophthalic acid is partially transferred to the imidazole N atom of the adeninium cation [refined O—H versus N—H ratio = 0.70 (11):0.30 (11)]. Through the partially transferred proton, the adeninium cation is strongly hydrogen bonded (N—H⋯O/O—H⋯N) to the isophthalate anion. This strong inter­action is assisted by another N—H⋯O hydrogen bond originating from the adeninium NH2 group towards the isophthalate keto O atom, with an R 2 2(8) graph-set motif. This arrangement is linked via N—H⋯O hydrogen bonds to the O atoms of the carboxyl­ate group of an isophthalate anion. Together, these hydrogen bonds lead to the formation criss-cross zigzag isophthalate⋯adeninium chains lying parallel to (501) and (50-1). The adeninium cations and the isophthalate anions are arranged in infinite π stacks that extend along the c-axis direction [inter­planar distance = 3.305 (3) Å]. Mol­ecules are inclined with respect to this direction and within the stacks they are offset by ca. half a mol­ecule each. Combination of the N—H⋯O and O—H⋯N hydrogen bonds with the π–π inter­actions forms infinitely stacked isophthalate⋯adeninium chains, thus leading to a two-dimensional supra­molecular structure with parallel inter­digitating layers formed by the π stacked isophthalate⋯adeninium chains. The DMF mol­ecules of crystallization are bonded to the adeninium cations through strong N—H⋯O hydrogen bonds and project into the lattice space in between the anions and cations. There are also C—H⋯O hydrogen bonds present which, combined with the other inter­actions, form a three-dimensional network. The crystal under investigation was found to be split and was handled as if non-merohedrally twinned.
PMCID: PMC3998323  PMID: 24764884
8.  Bis(2-amino-4-methyl­pyrimidin-3-ium) trans-diaqua­bis­(pyrazine-2,3-di­car­boxylato)cobaltate(II) hexa­hydrate 
In the crystal structure of the mononuclear title compound, (C5H8N3)2[Co(C6H2N2O4)2(H2O)2]·6H2O or (ampymH)2[Co(pyzdc)2(H2O)2]·6H2O (ampym = 2-amino-4-methyl pyrimidine, pyzdcH2 = pyrazine-2,3-dicarb­oxy­lic acid), the CoII ion is hexa­coordinated by two (pyzdc)2− groups in the equatorial plane and two water mol­ecules in axial positions, giving an N2CoO4 bound set. The (pyzdc)2− anion acts as a bidentate ligand through one carboxyl­ate group O atom and pyrazine ring N atom. There are diverse N—H⋯ O and O—H⋯O and O—H⋯N hydrogen-bonding inter­actions, which lead to the formation of a three-dimensional supra­molecular architecture. Off-set or slipped π–π stacking inter­actions are also observed between adjacent pyrimidine rings with face-to-face distances of 3.6337 (9) Å.
PMCID: PMC2983271  PMID: 21587454
9.  Bis(7-amino-1,2,4-triazolo[1,5-a]pyrimidin-4-ium) bis­(oxalato-κ2 O 1,O 2)cuprate(II) dihydrate 
The structure of the title ionic compound, (C5H6N5)2[Cu(C2O4)2]·2H2O, consists of a centrosymmetric copper(II) oxalate dianion, two monoprotonated mol­ecules of the adenine analog 7-amino-1,2,4-triazolo[1,5-a]pyrimidine (7atp) and two water mol­ecules of crystallization. The CuII ion, located on an inversion center, exhibits a sligthly distorted square-planar coordination geometry, in which two oxalate anions bind in a bidentate fashion. The triazolopyrimidine ligand is protonated at the N atom in position 4, instead of its most basic N atom in position 3. This fact may be explained by the network stability, which is provided through the formation of a two-dimensional wave-like network parallel to (50) by N—H⋯O, O—H⋯N and O—H⋯O hydrogen bonds. These nets are further connected via C—H⋯O inter­actions.
PMCID: PMC3246957  PMID: 22219777
10.  Diaqua­bis{[1-hydr­oxy-2-(1H-imidazol-3-ium-1-yl)ethane-1,1-di­yl]bis­(hydrogen phospho­nato)}manganese(II) 
In the title compound, [Mn(C5H9N2O7P2)2(H2O)2], the MnII atom (site symmetry ) is coordinated by four phos­pho­n­ate O atoms from a pair of partially deprotonated 1-hydr­oxy-2-(imidazol-3-yl)ethane-1,1-bis­phophonic acid ligands (imhedpH3 −) and two water mol­ecules, resulting in a slightly distorted trans-MnO6 octa­hedral geometry for the metal ion. In the ligands, the imidazole units are protonated and two of the hydr­oxy O atoms of the phospho­nate groups are deprotonated and chelate the MnII, thus forming the neutral mol­ecule of the title compound. The two protonated O atoms within the phospho­nate groups of one imhedpH3 − ligand act as hydrogen-bond acceptors for a bifurcated hydrogen bond originating from the coordinated water mol­ecule. The phospho­nate units of neigboring mol­ecules are connected with their equivalents in neighboring mol­ecules via two types of inversion-symmetric hydrogen-bonding arrangements with four and two strong O—H⋯O hydrogen bonds, respectively. The two inter­actions connect mol­ecules into infinite chains along [111] and [110], in combination forming a tightly hydrogen-bonded three-dimensional supra­molecular network. This network is further stabilized by additional hydrogen bonds between the protonated imidazole units and one of the coordinated P—O O atoms and by additional O—H⋯O hydrogen bonds between the water mol­ecules and the P=O O atoms of neigboring mol­ecules.
PMCID: PMC2972148  PMID: 21578704
11.  Poly[hydrazin-1-ium [diaqua­bis­(μ4-pyridazine-3,6-dicarboxyl­ato)trilithate] monohydrate] 
The structure of the title compound, {(N2H5)[Li3(C6H2N2O4)2(H2O)2]·H2O}n, is composed of mol­ecular dimers, each built up of two symmetry-related LiI ions with distorted trigonal–bipyramidal coordinations bridged by two deprotonated ligand mol­ecules via their N,O-bonding sites. Doubly solvated LiI ions with a distorted tetra­hedral geometry link adjacent dimers, forming a polymer generated by bridging bidentate carboxyl­ato O atoms to LiI ions in adjacent dimers, forming anionic layers parallel to the ac plane with monoprotonated hydrazinium cations and crystal water mol­ecules positioned between them. The layers are held together by an extended system of hydrogen bonds in which the hydrazinium cations and coordinated and crystal water mol­ecules act as donors and carboxyl­ate O atoms act as acceptors.
PMCID: PMC3343883  PMID: 22589851
12.  2,9-Dimethyl-1,10-phenanthrolin-1-ium (6-carb­oxy-4-hy­droxy­pyridine-2-carboxyl­ato-κ3 O 2,N,O 6)(4-hy­droxy­pyridine-2,6-dicarboxyl­ato-κ3 O 2,N,O 6)nickelate(II) 2.35-hydrate: a proton-transfer compound 
The title proton-transfer compound, (C14H13N2)[Ni(C7H3NO5)(C7H4NO5)]·2.35H2O, consists of an [Ni(hypydc)(hypydcH)]− anion, a dmpH+ cation and 2.35 uncoordinated water mol­ecules (where hypydcH2 = 4-hy­droxy­pyridine-2,6-dicarb­oxy­lic acid and dmp = 2,9-dimethyl-1,10-phenanthroline). The NiII atom is coordinated by two N atoms and four O atoms from the carboxyl­ate groups of the (hypydc)2− and (hypydcH)− ligands, forming a distorted octa­hedral environment. In the anion, the two pyridine rings are inclined to one another by 89.24 (10)°. In the crystal, cations are linked via O—H⋯O hydrogen bonds forming dimers, graph-set [R 2 2(16)], centered about inversion centers. These dimers are further linked by other cation O—H⋯O hydrogen bonds, graph-set [R 6 6(42)], forming a two-dimensional network in (011). Additional inter­molecular O—H⋯O, N—H⋯O, N—H⋯N, and weak C—H⋯O hydrogen bonds, and π–π inter­actions [shortest centroid–centroid distance = 3.5442 (14) Å], connect the two dimensional networks, forming a three-dimensional arrangement. The H atoms of one of the methyl groups are disordered over two sites with equal occupancy.
PMCID: PMC3008066  PMID: 21588502
13.  Crystal structure of 4-amino-5-fluoro-2-oxo-2,3-di­hydro­pyrimidin-1-ium 3-hy­droxy­pyridine-2-carboxyl­ate 
The protonated N atom and 2-amine group of the 5-fluoro­cytosinium (5FC) cation inter­act with the 3-hy­droxy­picolinate (3HAP) anion through a pair of nearly-parallel N—H⋯O hydrogen bonds, forming a robust (8) ring motif. The ions are further linked by N—H⋯N, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, leading to supra­molecular wave-like sheets and the crystal structure is further stabilized by C—H⋯π inter­actions, generating a three-dimensional architecture.
The asymmetric unit of the title salt, C4H5FN3O+·C6H4NO3 −, contains one 4-amino-5-fluoro-2-oxo-2,3-di­hydro­pyrimidin-1-ium (5-fluoro­cytosinium, 5FC) cation and a 3-hy­droxy­picolinate (3HAP) anion. The 4-amino-5-fluoro-2-oxo-2,3-di­hydro­pyrimidine mol­ecule is protonated at one of the pyrimidine N atoms. The typical intra­molecular N—H⋯F and O—H⋯O S(5) and S(6) hydrogen-bond ring motifs are observed in the cations and anions. The protonated N atom and 2-amine group of the 5FC cation inter­act with the 3HPA anion through a pair of nearly parallel N—H⋯O hydrogen bonds, forming a robust R 2 2(8) ring motif. The ions are further linked by N—H⋯N, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds, generating R 2 2(7), R 3 3(12) and R 6 5(18) ring motifs, respectively, leading to supra­molecular wave-like sheets parallel to (010). The crystal structure is further stabilized by C—H⋯π inter­actions, generating a three-dimensional architecture.
PMCID: PMC4257234  PMID: 25484736
crystal structure; anti­fungal drug; 5-fluorocytosine; hydrogen bonding; supra­molecular structure; hydrogen-bond ring motifs; crystal structure
14.  2-Trifluoro­methyl-1H-benzimidazol-3-ium tetra­fluoro­borate–2-trifluoro­methyl-1H-benzimidazole–water (1/1/1) 
The asymmetric unit of the title compound, C8H6F3N2 +·BF4 −·C8H5F3N2·H2O, consists of two 2-trifluoro­methyl­benzimidazole mol­ecules, each of which is protonated on a 50% basis, one tetra­fluoro­borate anion and a water mol­ecule. The two 2-trifluoromethylbenzimidazole mol­ecules thus exist as half-neutral half-cation entities. They are linked by N—H⋯N hydrogen bonds involving the half-occupancy hydrogens in each mol­ecule. The F atoms of one of the trifluoro­methyl groups are disordered over two sets of sites [in a 0.518 (14):0.482 (14) ratio], as are the F atoms of the tetra­fluoroborate anion [0.507 (14):0.493 (14) ratio]. The water mol­ecule is linked to one of the 2-trifluoro­methyl­benzimidazole mol­ecules via an N—H⋯O hydrogen bond.
PMCID: PMC3344031  PMID: 22589940
15.  Bis{3-amino-1-carbamo­thioyl-5-[(2-{[(5-methyl-1H-imidazol-3-ium-4-yl)meth­yl]sulfan­yl}eth­yl)amino]-1H-1,2,4-triazol-4-ium} hexa­chloridobismuthate(III) nitrate dihydrate 
The asymmetric unit of the title hydrated salt, (C10H18N8S2)2[BiCl6]NO3·2H2O, contains two independent 3-amino-1-carbamo­thioyl-5-[(2-{[(5-methyl-1H-imidazol-3-ium-4-yl)meth­yl]sulfan­yl}eth­yl)amino]-1H-1,2,4-triazol-4-ium cations, one hexa­chloridobismuthate anion, one nitrate anion and two solvent water mol­ecules. The dihedral angles between the imidazole and triazole rings in the cations are 44.7 (3) and 89.4 (3)°. The BiIII ion is coordinated by six chloride ligands in a slightly distorted octa­hedral geometry. In each cation, an intra­molecular N—H⋯S hydrogen bond is observed. In the crystal, N—H⋯Cl, N—H⋯S, N—H⋯O, O—H⋯Cl, O—H⋯S and O—H⋯O hydrogen bonds connect the components into a three-dimensional network. In addtion, π–π stacking inter­actions between inversion-related triazole rings are observed, with a centroid–centroid distance of 3.322 (3) Å
PMCID: PMC3772431  PMID: 24046574
16.  Bis(5-amino-4-amino­carbonyl-1H-imid­azol-3-ium) (5-amino-4-amino­carbonyl-1H-imidazol-3-ium-κO)-di-μ-chlorido-hepta­chlorido-dibismuth(III) mono­hydrate 
The title compound, (C4H7N4O)2[Bi2Cl9(C4H7N4O)]·H2O, was prepared by the reaction of bis­muth trichloride and 5-amino-1H-imidazole-4-carboxamide in a dilute HCl medium. The asymmetric unit contains two 5-amino-4-amino­carbonyl-1H-imidazol-3-ium cations, one edge-shared non-centrosymmetric biocta­hedral [Bi2C19(C4H7N4O)]2− dianion and a water mol­ecule. In the dianion, the planar 5-amino-4-amino­carbonyl-1H-imidazol-3-ium ligand occupies an equatorial site and is inclined at an angle of 75.7 (2)° to the Bi2(μ-C1)2 plane. The salt forms a three-dimensional network arising from hydrogen bonds between cations, anions and water mol­ecules.
PMCID: PMC2961098  PMID: 21202193
17.  3,4,7,8-Tetra­methyl-1,10-phenanthrolin-1-ium nitrate monohydrate 
In the crystal of the title compound, C16H17N2 +·NO3 −·H2O, the tetra­methyl-1,10-phenanthrolinium cations, nitrate anions and lattice water mol­ecules are all located on a mirror plane with the methyl H atoms of the cation equally disordered over two sites about the mirror plane. The cation, anion and water mol­ecule are linked by O—H⋯O and N—H⋯O hydrogen bonds into a sheet parallel to the bc plane. π–π stacking between phenanthroline ring systems is observed in the crystal structure, the centroid–centroid distance being 3.4745 (6) Å.
PMCID: PMC3379486  PMID: 22719684
18.  Bis[8-ethyl-5-oxo-2-(piperazin-4-ium-1-yl)-5,8-dihydro­pyrido[2,3-d]pyrimidine-6-carb­oxy­lic acid] 2,5-dicarb­oxy­benzene-1,4-di­carboxyl­ate octa­hydrate 
The asymmetric unit of the title compound, 2C14H18N5O3 +·C10H5O8 2−·8H2O, contains one [H2ppa]+cation, one half of an [H2btec]2− anion (H4btec = 1,2,4,5-benzene­tetra­carb­oxy­lic acid and Hppa = 8-ethyl-5-oxo-2-piperazin-1-yl-5,8-dihydro­pyrido[2,3-d]pyrimidine-6-carb­oxy­lic acid) that is completed by inversion symmetry and four water mol­ecules. In the crystal, the mol­ecules are connected by inter­molecular hydrogen-bonding inter­actions and π–π stacking between the benzene rings of the [H2btec]2− anion and the pyrimidine rings of the [H2ppa]+ cation [centroid–centroid distance = 3.597 (3) Å], generating a three-dimensional supra­molecular structure.
PMCID: PMC3099930  PMID: 21754029
19.  9-Amino­acridin-10-ium 4-amino­benzo­ate dihydrate 
The asymmetric unit of the title hydrated salt, C13H11N2 +·C7H6NO2 −·2H2O, consists of two independent 9-amino­acridinium cations, two 4-amino­benzoate anions and four water mol­ecules. Both 9-amino­acridinium cations are essentially planar, with maximum deviations of 0.034 (1) and 0.025 (2) Å, and are protonated at the pyridine N atoms. The 4-amino­benzoate anions are approximately planar, with dihedral angles of 9.16 (19) and 5.4 (2)° between the benzene ring and the carboxyl­ate group. In the crystal, the two independent anions are connected by N—H⋯O hydrogen bonds, forming a layer parallel to (100). The layers are connected through the cations by N—H⋯N and N—H⋯O hydrogen bonds. The water mol­ecules, which form O—H⋯O hydrogen-bonded chains along the b-axis direction, connect the anions and the cations by O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds. The crystal structure also features π–π inter­actions [centroid–centroid distances = 3.6343 (9)–3.8366 (10) Å] and a C—H⋯π inter­action.
PMCID: PMC4051093  PMID: 24940241
20.  Bis(5-amino-3-carb­oxy-1H-1,2,4-triazol-4-ium) dihydrogenphosphate nitrate 5-amino-1H-1,2,4-triazol-4-ium-3-carboxyl­ate 
In the title compound, 2C3H5N4O2 +·H2PO4 −·NO3 −·C3H4N4O2, three independent 5-amino-1H-1,2,4-triazol-3-carb­oxy­lic acid moieties are observed. Two are in the form of cations, while the third is in the zwitterionic form. The triazole rings in the two cations are almost coplanar, making an angle of 4.11 (7)°. Layers parallel to the (20-1) plane, resulting from hydrogen bonding of the organic mol­ecules and the nitrate anions, are linked via H2PO4 − infinite zigzag chains running parallel to the c axis. The crystal studied was an inversion twin, with refined components of 0.33 (7) and 0.67 (7).
PMCID: PMC3344471  PMID: 22590233
21.  5-Amino-3-carb­oxy-1H-1,2,4-triazol-4-ium nitrate monohydrate 
The two-dimensional crystal packing of the title compound, C3H5N4O2 +·NO2 −·H2O, results from the stacking of well separated layers (i.e. with nothing between the layers) parallel to the (-113) plane in which adjacent cations adopt a head-to-head arrangement such that two –COOH groups are linked via two water mol­ecules (the water O atom behaves simultaneously as donor and acceptor of hydrogen bonds) and two –NH2 groups are linked through two nitrate anions. This arrangement leads to alternating hydro­philic and hydro­phobic zones in which O—H⋯O and N—H⋯O hydrogen bonds, respectively, are observed.
PMCID: PMC3344063  PMID: 22589972
22.  2,6-Diamino-4-oxo-3,4-dihydropyrim­idin-1-ium chloride dihydrate 
In the crystal structure of the title compound, C4H7N4O+·Cl−·2H2O, adjacent cations are connected to one another through N—H⋯O hydrogen bonds, forming infinite chains along the b axis. These chains are further hydrogen bonded to the chloride anions and water mol­ecules, resulting in a three-dimensional network. The pyrimidine rings of adjacent mol­ecules are arranged in an anti­parallel manner above each other with centroid–centroid distances of 3.435 (1) Å, indicative of π–π inter­actions.
PMCID: PMC3007964  PMID: 21588646
23.  2-{(E)-[1-(2-Hydroxy­ethyl)-3,3-dimethyl-3H-indol-1-ium-2-yl]vin­yl}-6-hydroxy­meth­yl-4-nitro­phenolate dihydrate 
The title merocyanine-type mol­ecule, C21H22N2O5·2H2O, crystallizes in a zwitterionic form and has an E configuration at the styryl C=C bond. The styryl part of the mol­ecule and the indolium ring are slightly twisted and form a dihedral angle of 13.4 (1)°. The 1.274 (3) Å C—O bond length in the phenolate fragment is the longest among similar mol­ecules. Hydrogen bonds between solvent water mol­ecules, two hydroxyl groups and the phenolate O atom dictate the packing arrangement of mol­ecules in the crystal and join the mol­ecules into a two-dimensional polymeric network which propagates parallel to (001). Four water mol­ecules and four hydr­oxy groups form a centrosymmetric homodromic cyclic motif of O—H⋯O hydrogen bonds. Another cyclic centrosymmetric motif is generated by four water mol­ecules and two phenolate O atoms.
PMCID: PMC2977230  PMID: 21583596
24.  catena-Poly[2-methyl-1H-imidazol-3-ium [(aqua­chloridocadmate)-di-μ-chlorido]] 
The asymmetric unit of the title compound, {(C4H7N2)[CdCl3(H2O)]}n, contains one 1-methyl-1H-imidazol-3-ium cation, one CdII atom, three Cl atoms and one water mol­ecule. Adjacent Cd ions are inter­connected alternately by paired Cl− bridges to generate an infinite one-dimensional coordination chain along the b axis. In the chain, the crystallographically unique CdII atom, with a distorted octa­hedral geometry, is coordinated by five Cl− ions and one water mol­ecule. Intra-chain O—H⋯Cl hydrogen bonding and N—H⋯Cl hydrogen bonding between the cations and the anionic chains consolidate the crystal packing.
PMCID: PMC3246997  PMID: 22219817
25.  5-Amino-1H-1,2,4-triazol-4-ium-3-carboxyl­ate hemihydrate 
The asymmetric unit of the title compound, C3H4N4O2·0.5H2O, comprises two whole mol­ecules of 5-amino-1H-1,2,4-triazole-3-carb­oxy­lic acid in its zwitterionic form (proton transfer occurs from the carb­oxy­lic acid group to the N hetero­atom at position 1), plus one water mol­ecule of crystallization. The organic moieties are disposed into supra­molecular layers linked by N—H⋯O and N—H⋯N hydrogen bonds parallel to the bc plane. Additional O—H⋯O and N—H⋯O hydrogen bonds involving the water mol­ecules and the organic mol­ecules lead to the formation of double-deck supra­molecular arrangements which are inter­connected along the a axis via π–π stacking [centroid–centroid distance = 3.507 (3) Å].
PMCID: PMC3213518  PMID: 22091097

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