Crystal structure of bis-{2-[5-(3,4,5-tri-meth-oxyphenyl)-4H-1,2,4-triazol-3-yl]pyridine}palladium(II) bis-(tri-fluoro-acetate) tri-fluoro-acetic acid disolvate.

The new palladium(II) complex, [Pd(C16H16N4O3)2](CF3COO)2·2CF3COOH, crystallizes in the triclinic space group P with the asymmetric unit containing half the cation (PdII site symmetry Ci ), one tri-fluoro-actetate anion and one co-crystallized tri-fluoro-acetic acid mol-ecule. Two neutral chelating 2-[5-(3,4,5-tri-meth-oxy-phen-yl)-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 Šfor one of the C atoms). The planar configuration is supported by two intra-molecular 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 tri-fluoro-acetic acid-tri-fluoro-acetate anion pairs. Apart from classical N/O-H⋯O hydrogen-bonding inter-actions, weak C-H⋯F/N/O contacts consolidate the three-dimensional architecture. Both tri-fluoro-acetic 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.

Crystal structure and Hirshfeld-surface analysis of di-aqua-bis-(5-methyl-1H-1,2,4-triazole-3-carboxyl-ato)copper(II).

The title compound, [Cu(HL)2(H2O)2] or [Cu(C4H4N3O2)2(H2O)2], is a mononuclear octa-hedral CuII complex based on 5-methyl-1H-1,2,4-triazole-3-carb-oxy-lic acid (H2 L). [Cu(HL)2(H2O)2] was synthesized by reaction of H2 L with copper(II) nitrate hexa-hydrate (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 octa-hedral geometry provided by two bidentate HL - anions in the equatorial plane and two water mol-ecules 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%) inter-actions.

Synthesis and crystal structure of N1,N2-di-methyl-ethane-dihydrazide.

The title compound, N 1,N 2-di-methyl-ethane-dihydrazide, C4H10N4O2, was obtained by the methyl-ation of oxalyl dihydrazide protected with phthalimide. The mol-ecule 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 supra-molecular network via C-H⋯O, N-H⋯O and N-H⋯N hydrogen bonds.

Chemistry in Ukraine.

In this special issue, we highlight recent advances in chemical research by scientists in Ukraine, as well as by their compatriots and collaborators outside the country. Besides spotlighting their contributions, we see our task in fostering global partnerships and multi-, inter-, and trans-disciplinary collaborations, including much-needed co-funded projects and initiatives. The three decades of the renewed Ukraine independence have seen rather limited integration of Ukrainian (chemical) science into global research communities.[1] At the same time, the recent surge of collaborative science initiatives between European Union (EU) and Ukraine echoes the unfolding steps towards Ukraine's full research participation to the Horizon Europe Program. This recently implemented step opens enormous possibilities for Ukrainian researchers to apply for diverse EU research grants. Moreover, a number of journal special issues and collections were launched to highlight Ukrainian chemistry (i. e., by Chemistry of Heterocyclic Compounds[2] and ChemistrySelect[3] ). Other scientific initiatives include 'European Chemistry School for Ukrainians'[4] and 'Kharkiv Chemical Seminar'[5] as voluntary projects aimed at engaging Ukrainian scientists into European and international chemical research.

Solvent- and functional-group-assisted tautomerism of 3-alkyl substituted 5-(2-pyridyl)-1,2,4-triazoles in DMSO-water.

The tautomerism of a series of 5-alkyl substituted 3-(2-pyridyl)-1,2,4-triazoles in DMSO-d6-containing water has been investigated by 1H, 13C and 15N NMR spectroscopy. The populations of the three possible regioisomers in the tautomeric equilibrium (A [3-alkyl-5-(2-pyridyl)-1H], B [5-alkyl-3-(2-pyridyl)-1H] and C [5-alkyl-3-(2-pyridyl)-4H]) were determined. Isomers A (17-40%) and B (54-79%) are the major components and their ratio is insensitive to the substitution pattern, except for the unsubstituted and the methoxymethyl substituted derivatives. The isomer C (3-5%) has been fully characterised for the first time by NMR spectroscopy. Activation energies of tautomerisation (14.74-16.78 kcal mol-1) were determined by EXSY experiments, which also supported the involvement of water in the tautomerisation. Substituent effects on the 15N chemical shifts are relatively small. The DFT study of the tautomerism in DMSO-water showed that both A/B and B/C interconversions are assisted by the pyridine substituent and catalysed by solvent molecules. The NH-A/NH-B tautomerisation takes place via a relayed quadruple proton transfer mediated by three water molecules in the hydrogen-bonded cyclic substructure of a triazole·4H2O complex. The equilibrium B ⇄ C involves three steps: NH-B transfer to the pyridyl nitrogen mediated by a water molecule in a 1 : 1 cyclic complex, rotamerisation to bring the pyridinium NH close to N4 of the triazole catalysed by complexation to a DMSO molecule and transfer of the NH from the pyridinium donor to the N4 acceptor via a 1 : 1 complex with a bridging water molecule. This mechanism of 1,3-prototropic shift in triazoles is unprecedented in the literature.

Synthesis and crystal structure of a new copper(II) complex based on 5-ethyl-3-(pyridin-2-yl)-1,2,4-triazole.

The title compound, bis-[µ-3-ethyl-5-(pyridin-2-yl)-1H-1,2,4-triazol-1-ido]bis[acetato-(di-methyl-formamide)-copper(II)], [Cu2(C9H9N4)2(C2H3O2)2(C3H7NO)2] or [Cu2(L Et)2(OAc)2(dmf)2], is a triazolate complex, which contains two 3-(2-pyrid-yl)-5-ethyl-triazolates (L Et)- 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 nitro-gen atoms of the deprotonated bridging 3-(2-pyrid-yl)-5-ethyl-triazolate unit, oxygen atoms of the OAc- group and dmf mol-ecule. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into chains running along the c-axis direction.

Cooperative Spin Crossover above Room Temperature in the Iron(II) Cyanoborohydride-Pyrazine Complex.

Hysteretic spin crossover in coordination complexes of 3d-metal ions represents one of the most spectacular phenomena of molecular bistability. In this paper we describe a self-assembly of pyrazine (pz) and Fe(BH3CN)2 that afforded the new 2D coordination polymer [Fe(pz)2(BH3CN)2]∞. It undergoes an abrupt, hysteretic spin crossover (SCO) with a T1/2 of 338 K (heating) and 326 K (cooling) according to magnetic susceptibility measurements. Mössbauer spectroscopy revealed a complete transition between the low-spin (LS) and the high-spin (HS) states of the iron centers. This LS-to-HS transition induced an increase of the unit cell volume by 10.6%. Meanwhile, a modulation of multiple [C-Hδ+···Hδ--B] dihydrogen bonds stimulates a contraction in direction c (2.2%). The simplicity of the synthesis, mild temperatures of transition, a pronounced thermochromism, stability upon thermal cycling, a striking volume expansion upon SCO, and an easy processability to composite films make this new complex an attractive material for switchable components of diverse applications.

Synthesis and crystal structure of hydrated µ-oxa-lato-bis-{bis-[3-methyl-5-(pyridin-2-yl)-1H-1,2,4-triazole]iron(II)} bis-(toluene-sulfonate) 2.75-hydrate.

In the title compound [Fe2(C2O4)(C8H8N4)4](CH3C6H4SO3)2·2.75H2O, the two FeII ions have a highly distorted octa-hedral 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.

Expanding the chemical space of 3(5)-functionalized 1,2,4-triazoles.

An efficient approach to the gram-scale synthesis of 3(5)-substituted, 1,3- and 1,5-disubstituted 1,2,4-triazole-derived building blocks is described. The key synthetic precursors - 1,2,4-triazole-3(5)-carboxylates (20 examples, 35-89% yield) were prepared from readily available acyl hydrazides and ethyl 2-ethoxy-2-iminoacetate hydrochloride. Further transformations were performed following the convergent synthetic strategy and allowed the preparation of 1,3- and 1,5-disubstituted 1,2,4-triazole-derived esters (16 examples, 25-75% yield), 3(5)-substituted, 1,3- and 1,5-disubstituted carboxylate salts (18 examples, 78-93% yield), amides (5 examples, 82-93% yield), nitriles (5 examples, 30-85% yield), hydrazides (6 examples, 84-89% yield), and hydroxamic acids (3 examples, 73-78% yield). Considering wide applications of the 1,2,4-triazole motif in medicinal chemistry, these compounds are valuable building blocks for lead-oriented synthesis; they have also great potential for coordination chemistry. Supplementary Information: The online version contains supplementary material available at 10.1007/s10593-022-03064-z.

Synthesis of α-substituted 2-(1H-1,2,4-triazol-3-yl)acetates and 5-amino-2,4-dihydro-3H-pyrazol-3-ones via the Pinner strategy.

A series of 2-(1H-1,2,4-triazol-3-yl)acetates, as well as 4-mono- and 4,4-disubstituted 5-amino-2,4-dihydro-3H-pyrazol-3-ones (including spirocyclic derivatives) have been synthesized using the Pinner reaction strategy. α-Mono- and α,α-disubstituted ethyl cyanoacetates were converted into the corresponding carboxyimidate salts that served as the key intermediates. Their further reaction with formylhydrazide or hydrazine hydrate provided triazolylacetates or aminopyrazolones (including spirocyclic derivatives), depending on the structure of the starting Pinner salt and the nature of the nucleophile. The scope and limitations of the developed synthetic method have been established.

An investigation of two copper(ii) complexes with a triazole derivative as a ligand: magnetic and catalytic properties.

Two new copper(ii) complexes [Cu2(L)2(OAc)2(H2O)2] (1) (L = 3-methyl-5-pyridin-2-yl-1,2,4-triazole) and [CuL2] (2) were prerared and thoroughly studied. The complexes are able to selectively catalyze the oxidation of styrene towards benzaldehyde and of cyclohexane to KA oil. The 2D coordination polymer 1 showed an antiferromagnetic behaviour attributed to the intrachain magnetic coupling.

N'-(2-Hy-droxy-benzyl-idene)-2-(hy-droxy-imino)-propano-hydrazide.

The mol-ecule of the title compound, C(10)H(11)N(3)O(3), adopts an all-trans conformation and is approxomately planar, the largest deviation from the least-squares plane through all non-H atoms being 0.261 (1) Å. An intra-molecular O-H⋯N hydrogen bond occurs. In the crystal, the mol-ecules are packed into layers lying parallel to the ab plane by π-stacking inter-actions between the benzene ring of one molecule and the C-N bond of the oxime group of another molecule; the shortest inter-molecular C⋯C separation within the layer is 3.412 (1) Å. The layers are connected by O-H⋯O and N-H⋯O hydrogen bonds.