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The structures of the title compounds 2-hydroxy-N′-methylacetohydrazide, 1, and 2-hydroxy-N-methylacetohydrazide, 2, both C3H8N2O2, as regioisomers differ in the position of the methyl group relative to the N atoms in 2-hydroxy-acetohydrazide. In the structure of 1, the 2-hydroxy-acetohydrazide core [OH—C—C(=O)—NH—NH] is almost planar and the methyl group is rotated relative to this plane. As opposed to 1, in the structure of 2 all non-hydrogen atoms lie in the same plane. The hydroxyl and carbonyl groups in structures 1 and 2 are in trans and cis positions, respectively. The methyl amino group and carbonyl group are in the cis position relative to the C—N bond in structure 1, while the amino group and carbonyl group are in the trans position relative to the C—N bond in stucture 2. In the crystal, molecules of 1 are linked by N—H...O and O—H...N intermolecular hydrogen bonds, forming layers parallel to the ab crystallographic plane. A Hirshfeld surface analysis showed that the H...H contacts dominate the crystal packing with a contribution of 55.3%. The contribution of the H...O/O...H interaction is somewhat smaller, amounting to 30.8%. In the crystal, as a result of the intermolecular O—H...O hydrogen bonds, molecules of 2 form dimers, which are linked by N—H...O hydrogen bonds and a three-dimensional supramolecular network The major contributors to the Hirshfeld surface are H...H (58.5%) and H...O/O...H contacts (31.7%).

The title compound, bis[μ-2,2′-(4H-1,2,4-triazole-3,5-diyl)diacetato]bis[diaquacopper(II)] dihydrate, [Cu2(C6H5N3O4)2(H2O)4]·2H2O, is a dinuclear octahedral CuII triazole-based complex. The central copper atoms are hexa-coordinated by two nitrogen atoms in the equatorial positions, two equatorial oxygen atoms of two carboxylate substituents in position 3 and 5 of the 1,2,4-triazole ring, and two axial oxygen atoms of two water molecules. Two additional solvent water molecules are linked to the title molecule by O—H...N and O...H—O hydrogen bonds. The crystal structure is built up from the parallel packing of discrete supramolecular chains running along the a-axis direction. Hirshfeld surface analysis suggests that the most important contributions to the surface contacts are from H...O/O...H (53.5%), H...H (28.1%), O...O (6.3%) and H...C/C...H (6.2%) interactions. The crystal studied was twinned by a twofold rotation around [100].

This study presents the synthesis, characterization and Hirshfeld surface analysis of the title mononuclear complex, [PdCl2(C12H14N4)]·C3H7NO. The compound crystalizes in the P21/c space group of the monoclinic system. The asymmetric unit contains one neutral complex Pd(HLc-Pe)Cl2 [HLc-Pe is 2-(3-cyclopentyl-1,2,4-triazol-5-yl)pyridine] and one molecule of DMF as a solvate. The Pd atom has a square-planar coordination. In the crystal, molecules are linked by intermolecular N—H...O and C—H...N hydrogen bonds, forming layers parallel to the bc plane. A Hirshfeld surface analysis showed that the H...H contacts dominate the crystal packing with a contribution of 41.4%. The contribution of the N...H/H...N and H...O/O...H interactions is somewhat smaller, amounting to 12.4% and 5%, respectively.

In the title complex, [U(C10H7N3O3)O2(CH3OH)]n, the UVI cation has a typical pentagonal–bipyramidal environment with the equatorial plane defined by one N and two O atoms of one doubly deprotonated 2-[5-(2-hydroxyphenyl)-1H-1,2,4-triazol-3-yl]acetic acid ligand, a carboxylate O atom of the symmetry-related ligand and the O atom of the methanol molecule [U—N/Oeq 2.256 (4)–2.504 (5) Å]. The axial positions are occupied by two oxide O atoms. The equatorial atoms are almost coplanar, with the largest deviation from the mean plane being 0.121 Å for one of the O atoms. The benzene and triazole rings of the tetradentate chelating–bridging ligand are twisted by approximately 21.6 (2)° with respect to each other. The carboxylate group of the ligand bridges two uranyl cations, forming a neutral zigzag chain reinforced by a strong O—H...O hydrogen bond. In the crystal, adjacent chains are linked into two-dimensional sheets parallel to the ac plane by C/N—H...N/O hydrogen bonding and π–π interactions. Further weak C—H...O contacts consolidate the three-dimensional supramolecular architecture. In the solid state, the compound shows a broad medium intensity LMCT transition centred around 463 nm, which is responsible for its red colour.

The new palladium(II) complex, [Pd(C16H16N4O3)2](CF3COO)2·2CF3COOH, crystallizes in the triclinic space group P\overline{1} with the asymmetric unit containing half the cation (PdII site symmetry Ci), one trifluoroactetate anion and one co-crystallized trifluoroacetic acid molecule. Two neutral chelating 2-[5-(3,4,5-trimethoxyphenyl)-4H-1,2,4-triazol-3-yl]pyridine ligands coordinate to the PdII ion through the triazole-N and pyridine-N atoms in a distorted trans-PdN4 square-planar configuration [Pd—N 1.991 (2), 2.037 (2) Å; cis N—Pd—N 79.65 (8), 100.35 (8)°]. The complex cation is quite planar, except for the methoxo groups (δ = 0.117 Å for one of the C atoms). The planar configuration is supported by two intramolecular C—H...N hydrogen bonds. In the crystal, the π–π-stacked cations are arranged in sheets parallel to the ab plane that are flanked on both sides by the trifluoroacetic acid–trifluoroacetate anion pairs. Apart from classical N/O—H...O hydrogen-bonding interactions, weak C—H...F/N/O contacts consolidate the three-dimensional architecture. Both trifluoroacetic moieties were found to be disordered over two resolvable positions with a refined occupancy ratio of 0.587 (1):0.413 (17) and 0.530 (6):0.470 (6) for the protonated and deprotonated forms, respectively.

The asymmetric unit of the title compound, catena-poly[[[aquabis(pyridine-κN)cadmium(II)]-μ2-4,4′-(1H-1,2,4-triazole-3,5-diyl)dibenzoato-κ4O,O′:O′′,O′′′] 4.5-hydrate], {[Cd(C16H9N3O4)(C5H5N)2(H2O)]·4.5H2O}n or {[Cd(bct)(py)2(H2O)]·4.5H2O}n (I), consists of a Cd2+ cation coordinated to one bct2– carboxylate dianion, two molecules of pyridine and a water molecule as well as four and a half water molecules of crystallization. The metal ion in I possesses a pentagonal–bipyramidal environment with the four O atoms of the two bidentately coordinated carboxylate groups and the N atom of a pyridine molecule forming the O4N equatorial plane, while the N atom of another pyridine ligand and the O atom of the water molecule occupy the axial positions. The bct2– bridging ligand connects two metal ions via its carboxylic groups, resulting in the formation of a parallel linear polymeric chain running along the [1\overline{1}1] direction. The coordinated water molecule of one chain forms a strong O—H...O hydrogen bond with the carboxylate O atom of a neighboring chain, leading to the formation of double chains with a closest distance of 5.425 (7) Å between the cadmium ions belonging to different chains. Aromatic π–π stacking interactions between the benzene fragments of the anions as well as between the coordinated pyridine molecules belonging to different chains results in the formation of sheets oriented parallel to the (\overline{1}01) plane. As a result of hydrogen-bonding interactions involving the water molecules of crystallization, the sheets are joined together in a three-dimensional network.

The title compound, N1,N2-dimethylethanedihydrazide, C4H10N4O2, was obtained by the methylation of oxalyl dihydrazide protected with phthalimide. The molecule is essentially non-planar with a dihedral angle between the two planar hydrazide fragments of 86.5 (2)°. This geometry contributes to the formation of a multi-contact three-dimensional supramolecular network via C—H...O, N—H...O and N—H...N hydrogen bonds.

The title compound, [Cu(HL)2(H2O)2] or [Cu(C4H4N3O2)2(H2O)2], is a mononuclear octahedral CuII complex based on 5-methyl-1H-1,2,4-triazole-3-carboxylic acid (H2L). [Cu(HL)2(H2O)2] was synthesized by reaction of H2L with copper(II) nitrate hexahydrate (2:1 stoichiometric ratio) in water under ambient conditions to produce clear light-blue crystals. The central Cu atom exhibits an N2O4 coordination environment in an elongated octahedral geometry provided by two bidentate HL− anions in the equatorial plane and two water molecules in the axial positions. Hirshfeld surface analysis revealed that the most important contributions to the surface contacts are from H...O/O...H (33.1%), H...H (29.5%) and H...N/N...H (19.3%) interactions.

The title compound, bis[μ-3-ethyl-5-(pyridin-2-yl)-1H-1,2,4-triazol-1-ido]bis[acetato(dimethylformamide)copper(II)], [Cu2(C9H9N4)2(C2H3O2)2(C3H7NO)2] or [Cu2(LEt)2(OAc)2(dmf)2], is a triazolate complex, which contains two 3-(2-pyridyl)-5-ethyl-triazolates (LEt)− in bidentate-bridged coordination modes. Both copper atoms are involved in the formation of a planar six-membered metallocycle Cu–[N—N]2–Cu. The inversion center of the complex is located at the mid-point of the Cu...Cu vector. Each CuII atom has a distorted trigonal–bipyramidal environment formed by the three nitrogen atoms of the deprotonated bridging 3-(2-pyridyl)-5-ethyl-triazolate unit, oxygen atoms of the OAc− group and dmf molecule. In the crystal, C—H...O hydrogen bonds link the molecules into chains running along the c-axis direction.

In the title compound [Fe2(C2O4)(C8H8N4)4](CH3C6H4SO3)2·2.75H2O, the two FeII ions have a highly distorted octahedral FeN4O2 environment formed by two bidentate triazole-based chelating ligands and a bis-bidentate oxalate bridging anion that connects the metal ions. Stabilization within the crystal structure is provided via a system of O—H...O and N—H...O hydrogen bonding, which determines the formation of a two-dimensional architecture along the a-axis direction.