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The unit cell of the title compound, [Ni(C16H10ClN6)2]·2CH3OH, consists of a neutral complex and two methanol molecules. In the complex, the two tridentate 2-(3-(4-chlorophenyl)-1H-1,2,4-triazol-5-yl)-6-(1H-pyrazol-1-yl)pyridine ligands coordinate to the central NiII ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudooctahedral coordination sphere. Neighbouring tapered molecules are linked through weak C—H(pz)...π(ph) interactions into monoperiodic chains, which are further linked through weak C—H...N/C interactions into diperiodic layers. The intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative contributions of the contacts to the crystal packing to be H...H 32.8%, C...H/H...C 27.5%, N...H/H...N 15.1%, and Cl...H/H...Cl 14.0%. The average Ni—N bond distance is 2.095 Å. Energy framework analysis at the HF/3–21 G theory level was performed to quantify the interaction energies in the crystal structure.

The reaction of cadmium iodide with 3-aminopyrazole (3-apz) in ethanolic solution leads to tautomerization of the ligand and the formation of crystals of the title compound, catena-poly[[diiodidocadmium(II)]-bis(μ-3-amino-1H-pyrazole)-κ2N2:N3;κ2N3:N2], [CdI2(C3H5N3)2]n or [CdI2(3-apz)2]n. Its asymmetric unit consists of a half of a Cd2+ cation, an iodide anion and a 3-apz molecule. The Cd2+ cations are coordinated by two iodide anions and two 3-apz ligands, generating trans-CdN4I2 octahedra, which are linked into chains by pairs of the bridging ligands. In the crystal, the ligand molecules and iodide anions of neighboring chains are linked through interchain hydrogen bonds into a di-periodic network. The intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative quantitative contributions of the weak intermolecular contacts.

The synthetic availability of molecular water oxidation catalysts containing high-valent ions of 3d metals in the active site is a prerequisite to enabling photo- and electrochemical water splitting on a large scale. Herein, the synthesis and crystal structure of diammonium {μ-1,3,4,7,8,10,12,13,16,17,19,22-dodecaazatetracyclo[8.8.4.13,17.18,12]tetracosane-5,6,14,15,20,21-hexaonato}ferrate(IV) acetic acid trisolvate, (NH4)2[FeIV(C12H12N12O6)]·3CH3COOH or (NH4)2[FeIV(L–6H)]·3CH3COOH is reported. The FeIV ion is encapsulated by the macropolycyclic ligand, which can be described as a dodeca-aza-quadricyclic cage with two capping triazacyclohexane fragments making three five- and six six-membered alternating chelate rings with the central FeIV ion. The local coordination environment of FeIV is formed by six deprotonated hydrazide nitrogen atoms, which stabilize the unusual oxidation state. The FeIV ion lies on a twofold rotation axis (multiplicity 4, Wyckoff letter e) of the space group C2/c. Its coordination geometry is intermediate between a trigonal prism (distortion angle φ = 0°) and an antiprism (φ = 60°) with φ = 31.1°. The Fe—N bond lengths lie in the range 1.9376 (13)–1.9617 (13) Å, as expected for tetravalent iron. Structure analysis revealed that three acetic acid molecules additionally co-crystallize per one iron(IV) complex, and one of them is positionally disordered over four positions. In the crystal structure, the ammonium cations, complex dianions and acetic acid molecules are interconnected by an intricate system of hydrogen bonds, mainly via the oxamide oxygen atoms acting as acceptors.

The reaction of cadmium bromide tetrahydrate with 3-aminopyrazole (3-apz) in ethanolic solution leads to tautomerization of the ligand and the formation of crystals of the title compound, catena-poly[[dibromidocadmium(II)]-bis(μ-3-amino-1H-pyrazole)-κ2N3:N2;κ2N2:N3], [CdBr2(C3H5N3)2]n or [CdBr2(3-apz)2]n. Its asymmetric unit consists of a half of a Cd2+ cation, a bromide anion and a 3-apz molecule. The Cd2+ cations are coordinated by two bromide anions and two 3-apz ligands, generating trans-CdN4Br2 octahedra, which are linked into chains by pairs of the bridging ligands. In the crystal, the ligand molecules and bromide anions of neighboring chains are linked through interchain hydrogen bonds into a two-dimensional network. The intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative quantitative contributions of the weak intermolecular contacts.

The title compound, [FeLi2(C12H12N12O6)(H2O)4]·4H2O, consists of iron complex anions, lithium cations and water molecules. The complex anion shows a clathrochelate topology. The coordination geometry of the FeIV centre is intermediate between a trigonal prism and a trigonal antiprism. In the crystal, the complex anions are connected through two Li cations into dimers, which are connected by Li—O bonds, forming infinite chains along the b-axis direction.

The unit cell of the title compound, [Fe(C18H15N6O2)2]·2CH3OH·2CHCl3, consists of a charge-neutral complex molecule, two methanol and two chloroform molecules. In the complex, the two tridentate 2-(5-(3,4-dimethoxyphenyl)-1,2,4-triazol-3-yl)-6-(pyrazol-1-yl)pyridine ligands coordinate to the central FeII ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octahedral coordination sphere. Neighbouring tapered molecules are linked through weak C—H(pz)...π(ph) interactions into one-dimensional chains, which are joined into two-dimensional layers through weak C—H...N/C/O interactions. Furthermore, the layers stack in a three-dimensional network linked by weak interlayer C—H...π interactions of the methoxy and phenyl groups. The intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative contributions of the contacts to the crystal packing to be H...H 32.0%, H...C/C...H 26.3%, H...N/N...H 13.8%, and H...O/O...H 7.5%. The average Fe—N bond distance is 2.185 Å, indicating the high-spin state of the FeII ion. Energy framework analysis at the HF/3–21 G theory level was performed to quantify the interaction energies in the crystal structure.

As a result of the high symmetry of the Aea2 structure, the asymmetric unit of the title compound, [FeII(C18H15N6)2]·2MeOH, consists of half of a charge-neutral complex molecule and a discrete methanol molecule. The planar anionic tridentate ligand 2-[5-(3,4-dimethylphenyl)-4H-1,2,4-triazol-3-ato]-6-(1H-pyrazol-1-yl)pyridine coordinates the FeII ion meridionally through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octahedral coordination sphere of the central ion. The average Fe—N bond distance is 1.955 Å, indicating a low-spin state of the FeII ion. Neighbouring cone-shaped molecules, nested into each other, are linked through double weak C—H(pz)...π(ph') interactions into mono-periodic columns, which are further linked through weak C—H...N′/C′ interactions into di-periodic layers. No interactions shorter than the sum of the van der Waals radii of the neighbouring layers are observed. Energy framework analysis at the B3LYP/6–31 G(d,p) theory level, performed to quantify the intermolecular interaction energies, reproduces the weak interlayer interactions in contrast to the strong interaction within the layers. Intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, showing the relative contributions of the contacts to the crystal packing to be H...H 48.5%, H...C/C...H 28.9%, H...N/N...H 16.2% and C...C 2.4%.

The unit cell of the title compound, [FeII(C17H12BrN6O)2]·2MeOH, consists of a charge-neutral complex molecule and two independent molecules of methanol. In the complex molecule, the two tridentate ligand molecules 2-[5-(3-bromo-4-methoxyphenyl)-4H-1,2,4-triazol-3-yl]-6-(1H-pyrazol-1-yl)pyridine coordinate to the FeII ion through the N atoms of the pyrazole, pyridine and triazole groups, forming a pseudo-octahedral coordination sphere around the central ion. In the crystal, neighbouring asymmetric molecules are linked through weak C—H(pz)...π(ph) interactions into chains, which are then linked into layers by weak C–H...N/C interactions. Finally, the layers stack into a three-dimensional network linked by weak interlayer C—H...π interactions between the methoxy groups and the phenyl rings. The intermolecular contacts were quantified using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing the relative contributions of the contacts to the crystal packing to be H...H 34.2%, H...C/C...H 25.2%, H...Br/Br...H 13.2%, H...N/N...H 12.2% and H...O/O...H 4.0%. The average Fe—N bond distance is 1.949 Å, indicating the low-spin state of the FeII ion. Energy framework analysis at the HF/3–21 G theory level was performed to quantify the interaction energies in the crystal structure.

9-Aminoacridinium chloride N,N-dimethylformamide monosolvate, C13H11N2+Cl−·C3H7NO, crystallizes in the monoclinic space group P21/c. The salt was crystallized from N,N-dimethylformamide. The asymmetric unit consists of two C13H11N2+Cl− formula units. The 9-aminoacridinium (9-AA) molecules are protonated with the proton on the N atom of the central ring. This N atom is connected to an N,N-dimethylformamide molecule by a hydrogen bond. The H atoms of the amino groups create short contacts with two chloride ions. The 9-AA cations in adjacent layers are oriented in an antiparallel manner. The molecules are linked via a network of multidirectional π–π interactions between the 9-AA rings, and the whole lattice is additionally stabilized by electrostatic interactions between ions.

The unit cell of the title compound, [Zn(C17H18N3O4)2]·CH4O·C2H6O, contains two complex molecules related by an inversion centre, plus one methanol and one ethanol solvent molecule per complex molecule. In each complex, two deprotonated pyridine aroylhydrazone ligands {3,4,5-trimethoxy-N′-[1-(pyridin-2-yl)ethylidene]benzohydrazide} coordinate to the ZnII ion through the N atoms of the pyridine group and the ketamine, and, additionally, through the O atom of the enolate group. In the crystal, dimers are formed by π–π interactions between the planar ligand moieties, which are further connected by C...O and C...C interactions. The intermolecular interactions were investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing that the most important contributions for the crystal packing are from H...H (44.8%), H...C/C...H (22.2%), H...O/O...H (18.7%) and C...C (3.9%) interactions.

In the molecule of the title anthracene derivative, C22H17NO2, the benzene ring is inclined to the mean plane of the anthracene ring system (r.m.s. deviation = 0.024 Å) by 75.21 (9)°. In the crystal, molecules are linked by pairs of O—H...O hydrogen bonds, forming classical carboxylic acid inversion dimers with an R22(8) ring motif. The dimers are linked by C—H...π interactions, forming a supramolecular framework.

The title compound, C14H12BrNO2, was synthesized by the condensation reaction of 2,3-dihydroxybenzaldehyde and 2-bromo-3-methylaniline. It crystallizes in the centrosymmetric triclinic space group P\overline{1}. The configuration about the C=N bond is E. The dihedral angle between the planes of the 5-(2-bromo-3-methylphenyl ring and the catechol ring is 2.80 (17)°. In the crystal, O—H...O hydrogen-bond interactions consolidate the crystal packing.

In the title complex, [Cu(C18H12F6N2O4)]·0.5C6H6O2, the CuII ion has a square-planar coordination geometry, being ligated by two N and two O atoms of the tetradentate open-chain Schiff base ligand 6,6′-{(1E,1′E)-[ethane-1,2-diylbis(azanylylidene)]bis(methanylylidene)}bis[2-(trifluoromethoxy)phenol]. The crystal packing is stabilized by intramolecular O—H...O and intermolecular C—H...F, C—H...O and C—H...π hydrogen bonds. In addition, weak π–π interactions form a three-dimensional structure. Hirshfeld surface analysis and two-dimensional fingerprint plots were performed and created to analyze the intermolecular interactions present in the crystal, indicating that the most important contributions for the crystal packing are from F...H/H...F (25.7%), H...H (23.5%) and C...H/H...C (12.6%) interactions.

In the title compound, bis(2-methoxyethyl xanthato-κS)(N,N,N′,N′-tetramethylethylenediamine-κ2N,N′)zinc(II) acetone hemisolvate, [Zn(C4H7O2S2)2(C6H16N2)]·0.5C3H6O, the ZnII ion is coordinated by two N atoms of the N,N,N′,N′-tetramethylethylenediamine ligand and two S atoms from two 2-methoxyethyl xanthate ligands. The amine ligand is disordered over two orientations and was modelled with refined occupancies of 0.538 (6) and 0.462 (6). The molecular structure features two C—H...O and two C—H...S intramolecular interactions. In the crystal, molecules are linked by weak C—H...O and C—H...S hydrogen bonds, forming a three-dimensional supramolecular architecture. The molecular structure was optimized using density functional theory (DFT) at the B3LYP/6–311 G(d,p) level. The smallest HOMO–LUMO energy gap (3.19 eV) indicates the suitability of this crystal for optoelectronic applications. The molecular electrostatic potential (MEP) further identifies the positive, negative and neutral electrostatic potential regions of the molecules. Half a molecule of disordered acetone was removed with the solvent-mask procedure in OLEX2 [Dolomanov et al. (2009). J. Appl. Cryst. 42, 339–341] and this contribition is included in the formula.

The asymmetric unit of the title compound, [Fe(C13H18BN6)2], contains two half independent complex molecules. In each complex, the FeII atom is located on an inversion center and is surrounded by two scorpionate ligand butyltris(1H-pyrazol-1-yl)borate molecules that coordinate to the iron(II) ion through the N atoms of the pyrazole groups. The two independent complex molecules differ essentially in the conformation of the butyl substituents. In the crystal, the complex molecules are linked by a series of C—H...π interactions, which generate a supramolecular three-dimensional structure. At 120 K, the average Fe—N bond distance is 1.969 Å, indicating the low-spin state of the iron(II) atom, which does not change upon heating, as demonstrated by high-temperature magnetic susceptibility measurements.

The asymmetric unit of the title compound, C15H12N2O2, contains two crystallographically independent molecules in which the dihedral angles between the benzene rings in each are 13.26 (5) and 7.87 (5)°. An intramolecular O—H...N hydrogen bonds results in the formation of an S(6) ring motif. In the crystal, molecules are linked by weak C—H...O and C—H...N hydrogen bonds, forming layers parallel to (011). In addition, π–π stacking interactions with centroid–centroid distances in the range 3.693 (2)–3.931 (2) Å complete the three-dimensional network.

The title compound, C9H11NO2, was obtained as unexpected product from the reaction of (4-{2-benzyloxy-5-[(E)-(3-chloro-4-methylphenyl)diazenyl]benzylidene}-2-phenyloxazol-5(4H)-one) with 2-methoxyaniline in the presence of acetic acid as solvent. The amide group is not coplanar with the benzene ring, as shown by the C—N—C—O and C—N—C—C torsion angles of −2.5 (3) and 176.54 (19)°, respectively. Hirshfeld surface analysis and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H...H (53.9%), C...H/H...C (21.4%), O...H/H...O (21.4%) and N...H/H...N (1.7%) interactions.

The title compound, C15H15NO2, is a Schiff base that exists in the keto–enamine tautomeric form and adopts a Z configuration. The molecule is almost planar, with the two phenyl rings twisted relative to each other by 9.60 (18)°. There is an intramolecular N—H...O hydrogen bond present forming an S(6) ring motif. In the crystal, pairs of O—H...O hydrogen bonds link adjacent molecules into inversion dimers with an R22(18) ring motif. The dimers are linked by very weak π–π interactions, forming layers parallel to (\overline{2}01). Hirshfeld surface analysis, two-dimensional fingerprint plots and the molecular electrostatic potential surfaces were used to analyse the intermolecular interactions, indicating that the most important contributions for the crystal packing are from H...H (55.2%), C...H/H...C (22.3%) and O...H/H...O (13.6%) interactions.

In the title compounds, 9-bromo-2,5-dimethyl-11,12-dihydro-5H-5,11-methanobenzo[g][1,2,4]triazolo[1,5-c][1,3,5]oxadiazocine, C13H13BrN4O (I), and 7-methoxy-5-methyl-2-(pyridin-4-yl)-11,12-dihydro-5H-5,11-methanobenzo[g][1,2,4]triazolo[1,5-c][1,3,5]oxadiazocine, C18H17N5O2 (II), the triazole ring is inclined to the benzene ring by 85.15 (9) and 76.98 (5)° in compounds I and II, respectively. In II, the pyridine ring is almost coplanar with the triazole ring, having a dihedral angle of 4.19 (8)°. In the crystal of I, pairs of N—H...N hydrogen bonds link the molecules to form inversion dimers with an R22(8) ring motif. The dimers are linked by C—H...π and C—Br...π interactions forming layers parallel to the bc plane. In the crystal of II, molecules are linked by N—H...N and C—H...O hydrogen bonds forming chains propagating along the b-axis direction. The intermolecular interactions were investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots, and the molecular electrostatic potential surface was also analysed. The Hirshfeld surface analysis of I suggests that the most significant contributions to the crystal packing are H...H (42.4%) and O...H/H...O (17.9%) contacts. For compound II, the H...H (48.5%), C...H/H...C (19.6%) and N...H/H...N (16.9%) interactions are the most important contributions.

In the complex cation of the title compound, [Fe(C27H41N10O3)](PF6)2, the tripodal tris{4-[1-(2-methoxyethyl)imidazol-2-yl]-3-azabut-3-enyl}amine ligand is coordinated to an FeII ion through the nitrogen atoms of three imidazole and three imino groups. The Fe atom exhibits a distorted octahedral geometry. In the crystal, l and d antipodes are arranged in layers in the bc plane. Weak C...F and C—H...F/O contacts exist between the ligands of the complex cation and the PF6− anions, generating a three-dimensional network. At 120 K, the FeII ion is in a low-spin state, with an average Fe—N bond distance of 1.970 (2) Å. On heating, the FeII ion converts to the high-spin state, as demonstrated by magnetic susceptibility measurements.

The title compound, C14H12ClNO3, is a Schiff base that exists in the keto–enamine tautomeric form and adopts a Z configuration. In the crystal, the dihedral angle between the planes of the benzene rings is 5.34 (15)°. The roughly planar geometry of the molecule is stabilized by a strong intramolecular N—H...O hydrogen bond. In the crystal, pairs of centrosymmetrically related molecules are linked by O—H...O hydrogen bonds, forming R22(10) rings. Besides this, the molecules form stacks along the [001] direction with C—H...π and C—H...Cl contacts between the stacks. The intermolecular interactions in the crystal were analysed using Hirshfeld surfaces. The most significant contribution to the crystal packing is from H...H contacts (30.8%).

In the title complex, (6,6′-{(1E,1′E)-[ethane-1,2-diylbis(azanylylidene)]bis(methanylylidene)}bis[2-(trifluoromethoxy)phenol]-κ4O,N,N′,O′)nickel(II), [Ni(C18H12F6N2O4)], the nickel(II) ion has a square-planar coordination sphere, being ligated by two N and two O atoms of the Schiff base ligand 6,6′-{(1E,1′E)-[ethane-1,2-diylbis(azanylylidene)]bis(methanylylidene)}bis[2-(trifluoromethoxy)phenol] (L). Inversion-related molecules are linked by a short Ni...Ni interaction of 3.2945 (6) Å forming a dimer. In the crystal, the dimers stack up the a axis, with a closest Ni...Ni separation of ca 3.791 Å. There are no other significant intermolecular interactions present. However, the Hirshfeld surface analysis and the two-dimensional fingerprint plots indicate that the packing is dominated by H...F/F...H, H...H, O...H/H...O and C...H/H...C contacts.

High-valent iron compounds do not form spontaneously under ambient conditions and those that are synthetically available are rarely stable. Here, the authors synthesize stable iron(IV) hexahydrazide clathrochelate complexes in aqueous media via a metal-templated reaction accompanied by aerobic oxidation.

In the cation of the title compound, C7H12ClN2Se+·Cl−, the ethylene groups and the Se–Cl fragment adopt a cis configuration with a C—Se—Cl angle of 96.09 (6)°. In the crystal, intermolecular N—H...Cl hydrogen bonds link two cations and two chlorine anions into centrosymmetric clusters. π–π interactions between the pyrazole rings [centroid–centroid distance of 3.530 (2) Å] link these clusters into columns along [001] with short intermolecular Se...Cl− contacts of 2.995 (1) Å.

The asymmetric unit of the title compound, [Cu(CHO2)Cl(C5H8N2)3]2·[CuCl2(C5H8N2)2] or 2[A]·[B], contains one A molecule and one half-molecule of B, located on a centre of inversion. The CuII environments in A and B are different. In A, the CuII atom is coordinated by three N atoms from three 3,5-dimethyl-1H-pyrazole (L) ligands, one O atom from a formate ligand and a chloride anion in an axial position [Cu—Cl = 2.4275 (7) Å] in a distorted tetragonal–pyramidal geometry. The CuII atom in B is coordinated by two N atoms from two L ligands and two chloride anions [Cu—Cl = 2.2524 (6) Å] in a distorted square-planar geometry. In the crystal, intermolecular N—H...O hydrogen bonds link molecules A into centrosymmetric dimers. Intermolecular N—H...Cl hydrogen bonds further link these dimers with the B molecules, forming chains propagating in [101].

In the title compound, [Ho(C6H12Cl3N3O2P)3(C18H15OP)], the HoIII ion is surrounded by six O atoms from the three bidentate N-[bis(dimethylamino)phosphinoyl]-2,2,2-trichloroacetamido ligands (L−) and by one O atom from the triphenylphosphine oxide ligand, with the formation of a distorted monocapped octahedron. In one ligand L−, the trichloromethyl group is rotationally disordered between two orientations in a 1:1 ratio, while two dimethylamino groups in another ligand L− are disordered between two conformations, each with the same 1:1 ratio.

The title compound, {[Cu(C10H14N4Se)2(H2O)](BF4)2·2C18H15PO·H2O}n, has a polymeric structure where each CuII ion adopts a square-pyramidal coordination constituted by four N atoms of pyrazole moieties in the equatorial plane and an axial O atom of a water molecule. A pair of bis(3,5-dimethyl-1H-pyrazol-4-yl) selenide ligands bridges the CuII centres into a chain extending along the c axis. The water molecules, anions and triphenylphosphine oxide molecules are involved in intermolecular hydrogen bonding, which links the chains into a three-dimensional network.

In the title compound, {[Cu(C10H14N4Se)2(H2O)]Cl2·H2O}n, the CuII ion, lying on a twofold rotation axis, has a square-pyramidal geometry constituted by four N atoms of pyrazolyl groups in the basal plane and an apical O atom of a water molecule. A pair of bis(3,5-dimethyl-1H-pyrazol-4-yl) selenide ligands bridge the Cu centers into a polymeric double-chain extending along [001]. The chloride anions are involved in intermolecular N—H...Cl and O—H...Cl hydrogen bonds, which link the chains into a three-dimensional network.

In the title compound, {[Cu(C10H14N4Se)2](ClO4)2}n, the CuII ion is located on a twofold rotation axis and has a tetragonally distorted square-planar geometry constituted by four N atoms. A pair of bis(3,5-dimethyl-1H-pyrazol-4-yl) selenide (L) ligands bridges the copper centers into a polymeric chain extending along [001]. The perchlorate anions are involved in intermolecular N—H...O hydrogen bonding, which links the chains into layers parallel to the bc plane.

The crystal structure of the title compound, K+·C3H4NO4−·H2O, consists of potassium cations, monoanions of 2-carboxyacetohydroxamic acid [namely 2-(N-hydroxycarbamoyl)acetate] and solvent water molecules. The elements of the structure are united in a three-dimensional network by numerous K...O coordinate bonds and O—H...O and N—H...O hydrogen bonds. The coordination sphere of the K+ ions may be described as a distorted double capped octahedron. Bond lengths and angles are similar to those in related compounds.

The title compound, [Cu2(C7H6N2O3)Cl2(C5H5N)4]·C3H8O, is a binuclear pyrazolate complex, in which the two CuII atoms have different coordination numbers and are connected by a bridging Cl atom. One CuII atom has a distorted square-pyramidal coordination environment formed by two pyridine N atoms, one bridging Cl atom and an N,O-chelating pyrazolate ligand. The other CuII atom adopts an octahedral geometry defined by two pyridine N atoms at the axial positions, two Cl atoms and the coordinated pyrazolate ligand in the equatorial plane. An O—H...O hydrogen bond connects the complex molecules and propan-2-ol solvent molecules into pairs. These pairs form columns along the a axis.

The title structure, C9H11N3O2, is a racemate. The chiral centre is situated at the N—C—N C atom of the imidazolidine ring. The interplanar angle between the mean planes of the pyridine and imidazolidine rings is 89.41 (5)°. The methyl group is in a trans position with respect to the pyridine N atom. In the crystal, the molecules are arranged in zigzag layers parallel to the b axis. The molecules within the layers are interconnected by strong O—H...N and weak N—H...O hydrogen bonds; the former take place between OH groups and amine N atoms and the latter between the amine N atom and the carbonyl O atom. In addition, C—H...O interactions are also present.

The molecule of the title compound, C14H12N2O4, lies across a crystallographic inversion centre situated at the mid-point of the C—C intra-annular bond. The molecule is not planar, the dihedral angle between the aromatic rings being 50.1 (1)°. The oxime group is in an E position with respect to the –OH group and forms an intramolecular O—H...N hydrogen bond. In the crystal structure, intermolecular O—H...O hydrogen bonds link molecules into chains propagating along [001]. The crystal structure is further stabilized by intermolecular stacking interactions between the rings [centroid-to-centroid distance = 3.93 (1) Å], resulting in layers parallel to the bc plane.

In the title compound, [Cu(C2H3O2)2(C5H8N2)2], the CuII atom has a distorted tetragonal–bipyramidal geometry, with the equatorial plane formed by two N atoms belonging to two 3,5-dimethyl-1H-pyrazole ligands and two O atoms from two acetate anions. The second O atoms of the acetate groups provide elongated Cu—O axial contacts, so that the acetates appear to be coordinated in a pseudo-chelate fashion. The pyrazole ligands are situated in cis positions with respect to each other. In the crystal structure, molecules are linked through intermolecular N—H...O hydrogen bonds, forming a one-dimensional chain.

The title compound, {[Co2(C15H14N4O3)2(C5H5N)4(H2O)2]ClO4·3.66H2O}n, is a one-dimensional coordination polymer, with both CoII and CoIII centres in its structure. The ligand environment surrounding CoIII is formed by two N,N-chelating pyrazole-containing ligands and two pyridine molecules in axial positions. The high-spin CoII ions, situated at crystallographic centres of inversion, exhibit a distorted octahedral coordination mode. The ClO4− anion is linked to the polymer chain via hydrogen bonds. The chains are connected by hydrogen bonds to produce a three-dimensional structure.

The title compound, [ZnCl2(C10H12N4O2)]·0.5H2O, was readily prepared by the reaction between ZnCl2 and 2-hydroxyimino-N′-[1-(2-pyridyl)ethylidene]propanohydrazide. The Zn atom has a distorted trigonal–bipyramidal geometry with two Cl atoms and one azomethine N atom in the equatorial plane and one pyridine N atom and one amide O atom in the axial positions. In the crystal structure, complex molecules are connected in pairs by N—H...Cl hydrogen bonds, formed between the amide NH of one molecule and the Cl atom of a neighboring one. Molecular pairs are connected by hydrogen bonds involving the uncoordinated water molecule, which lies on a twofold axis.

In the title compound, [Cu(C2O4)(C5H8N2)2(H2O)], the CuII atom is coordinated in a slightly distorted square-pyramidal geometry by two N atoms belonging to the two 3,5-dimethyl-1H-pyrazole ligands, two O atoms of the oxalate anion providing an O,O′-chelating coordination mode, and an O atom of the water molecule occupying the apical position. The crystal packing shows a well defined layer structure. Intra-layer connections are realised through a system of hydrogen bonds while the nature of the inter-layer interactions is completely hydrophobic, including no hydrogen-bonding interactions.