Binuclear copper(II) complexes of functionalized 1,2,4-triazoles: Synthesis,structure, and magnetic properties

Copper(II) coordination compounds with 3-(pyridin-2-yl)-5-(2-salicylideniminophenyl)-1H-1,2,4-triazole and 1,3-bis(5-(pyridin-2-yl)-1,2,4-triazole-3-yl)propane have been synthesized. The complexes have been studied by elemental and thermal analysis, IR and electron spectroscopy, electron paramagnetic resonance (EPR), and magnetochemistry. According to X-ray diffraction data, the complexes have binuclear structures in which metal cations are bonded via the nitrogen atoms of two bridging triazole rings.     

Spin crossover in iron(II) complexes of 3,5-di(2-pyridyl)-1,2,4-triazoles and 3,5-di(2-pyridyl)-1,2,4-triazolates

The iron coordination chemistry of 3,5-di(2-pyridyl)-1,2,4-triazoles and 3,5-di(2-pyridyl)-1,2,4-triazolates is reviewed. This includes both mononuclear and dinuclear complexes, and both iron(II) and iron(III) oxidation states. The main focus is on the synthesis, structure and magnetic properties of these complexes.     

Acid — Base properties of 3(5)-azido-1,2,4-triazoles

The pK_a and values of a series of 3(5)-azido-1,2,4-triazoles are correlated with the _I and _C constants according to the equation pK =_II + _CC + pK_o. The high _I values in both cases are due to the closeness of the substituent to the reaction center. The _C/_I ratio attests to different contributions of the inductive and mesomeric effects of a substituent during transmission of its effect from the 5-position to the N₁ and N₄ heteroatoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1288–1291, September, 1974.     

Zinc complexes with 3-Pyridinyl-5-(2-salicylideneiminophenyl)-1H-1,2,4-triazoles

New coordination compounds of zinc with 3-(pyridine-2-yl)-5-(2-salicylideneiminophenyl)-1H-1,2,4-triazole (H₂L¹) and 3-(pyridine-4-yl)-5-(2-salicylideneiminophenyl)-1H-1,2,4-triazole (H₂L²) are obtained. According to X-ray diffraction data, binuclear zinc complexes with L¹, namely, [Zn₂L₂¹]. 0.5EtOH and [Zn₂L₂¹] · 2C₄H₈O₂ · 2H₂O obtained in different solvents, are structurally related molecular complexes. The product of the reaction with H₂L² is the {[ZnL²(Py)] · CHCl₃} _n coordination polymer. The 1,2,4-triazoles under study and the complexes on their basis luminesce in solutions with emission maxima ranging from 412 to 503 nm. These coordination compounds in the solid state emit in the green range of the spectrum (λ_max = 496 and 485 nm).     

Cu(I) and Fe(II) complexes with N,N-dimethylthioformamide and Fe(II) complexes with N,N-dimethylformamide

The synthesis of the following Cu(I) and Fe(II) complexes with N,N-dimethylthioformamide (DMTF) and N,N-dimethylformamide (DMF) are described: Cu(DMTF)₄ClO₄, Cu(DMTF)₂Cl, Cu(DMTF)₂Br, Cu(DMTF)₂I, Fe(DMTF)₆(ClO₄)₂, Fe(DMTF)₂Cl₂, Fe(DMTF)₂Br₂, Fe(DMTF)₂I₂, Fe(DMF)₆(ClO₄)₂, Fe(DMF)₂Cl₂, Fe(DMF)Br₂ and Fe(DMF)₃I₂. Electronic absorption spectra, IR spectra, magnetic susceptibilities of the solids and in solution as well as conductivities have been measured of these compounds in order to obtain information on the nature of the interaction between the cations and the ligands, the coordination in the crystalline state, in solution and the dissociation of these compounds in the respective solvents.     

The coordination chemistry of Zn(II), Cd(II) and Hg(II) complexes with 1,2,4-triazole derivatives

This perspective illustrates the coordination features of complexes constructed by 1,2,4-triazole derivatives and transition metal ions which belong to Group IIB, namely Zn(II), Cd(II) and Hg(II), demonstrates their behaviors in thermal stabilities, gas or liquid adsorption, fluorescence and nonlinear optical properties and also discusses the relation between their properties and crystal structures. Various 1,2,4-triazole derivatives containing versatile donor sites for coordination can be obtained through introducing different substituent groups to C3, N4 and C5 positions, thus offering rich coordination modes. The structures of these complexes rely on their triazole ligands, as well as mixed ligands, metal ions, anions and synthetic conditions. Obviously, the diversity in structure induces the controllability of properties, since the properties are influenced by several factors, which is significant for the applications of potential multifunctional materials.     

New antifungal 1,2,4-triazoles with difluoro(heteroaryl)methyl moiety

New 1,2,4-triazoles (1) having a difluoro(heteroaryl)methyl moiety were designed and synthesized via 1-aryl-2,2-difluoro-2-(heteroaryl)ethanones (2), which were prepared by two routes starting from the reaction of ethyl 2,2-difluoro(heteroaryl)acetate with phenyllithiums (Route A) and from the reaction of chlorodifluoro(heteroaryl)methane with benzaldehydes (Route B). The compounds 1 except for 1g show antifungal activities against yeasts and filamentous fungi in vitro, especially (+)-1f have equal or superior activities compared to those of itraconazole.     

Preparation and surface photoelectric properties of Fe(II/III) complexes

Four Fe(II/III) supramolecules, {[Fe(Hpdc)₂(H₂O)₂]·2H₂O} (1), [Fe(HImbc)₂(H₂O)₂] (2), [Fe(phen)₂(CN)₂]·CH₃CH₂OH·2H₂O (3), K[Fe(tp)₂]·SO₄ (4) (H₂pdc = 2,5-Pyridinedicarboxylic acid, H₂Imbc = 4,5-Imidazoledicarboxylic acid, phen = 1,10-phenanthroline, tp⁻ = poly(pyrazolyl)borate), were synthesized by hydrothermal and room temperature stirring methods. They were characterized by single crystal X-ray diffraction, surface photovoltage spectroscopy (SPS), field-induced surface photovoltage spectroscopy (FISPS), electron paramagnetic resonance (EPR), UV–Vis absorption spectra (UV–Vis), infrared spectra (IR) and element analysis. The structural analyses indicate that complex (1) is a supramolecule with 2D structure connected by hydrogen bonds. Complex (2) is a supramolecule with hydrogen-bonded 3D structure. Complexes (3) and (4) are both 1D supramolecules connected by hydrogen bonds. The electronic state of central metal Fe(II) ions in complexes (1) and (2) is d⁶ with FeN₂O₄ coordination mode, lying in weaker distorted octahedral field. The electronic state of Fe(II) ion in complex (3) is d⁶ with Fe(CN)₂N₄ mode in the strong distorted octahedral field. The electronic state of Fe(III) ion in complex (4) is d⁵ with FeN₆ mode, lying in the strong octahedral field. The micro-environment of Fe(II/III) ions in the four complexes is further investigated by EPR. The SPS of four complexes all exhibit photovoltage responses in the range of 300–700 nm. This indicates that they all possess certain photoelectric conversion capability. The effects of component, structure, type of ligands of the complexes, valence state and coordination micro-environment of the central metal ions on the SPS were discussed. Furthermore, the SPS and UV–Vis absorption spectra were interrelated.     

Comparative study on the photophysical properties between carbene-based Fe (II) and Ru (II) complexes

The comparative study on the photophysical properties between cheap metal Fe (II) complexes and noble metal Ru (II) complexes with identical ligand coordination is performed by the combination of density functional theory (DFT) and time-dependent density functional theory (TDDFT) to evaluate the potential alternative applications of Fe (II) complexes. RuBIP (BIP = 2,6-bis (imidazol-2- ylidene)pyridine) is theoretically established that the radiative lifetime of the second lowest triplet state is more consistence with experimental value. However, FeBIP retains nonluminous because of low-lying ³MC originated from weak d orbital splitting. FeBIPC (FeBIP with carboxylic acid groups) has twice longer lifetime than its parent complex FeBIP due to the great decrease of the energy gap between ³MLCT and ³MC. What's more, the lifetimes of Fe (II) complexes detected in the experiments are more accessible to nonradiative decay lifetimes of ³MC. The carboxylic acid groups are beneficial for the improvement of luminescent possibility and controllability of Fe (II) complexes, while there is still a huge challenge for effective material replacement comparing with Ru (II) complexes.     

The nature of spin-state transitions in Fe(II) complexes

The nature of the spin-state transition for three complexes of Fe(II), namely [Fe(phy)₂] (ClO₄)₂, [Fe(phy)₂] (BF₄)₂ and [Fe(bts)₂(NCS)₂] (where phy = 1,10-phenantroline-2-carbaldehyde phenyihydrazone and bts = 2.2′-bi-5-methyl-2-thiazoline) has been investigated by differential scanning calorimetry. For [Fe(phy)₂] (ClO₄)₂ and [Fe(phy)₂] (BF₄)₂, the spin transition is essentially of first order with ΔH = 15.7 ± 1. ΔS = 64 ± 4 and ΔH = 24.2 = 1kJ/mole. ΔS = 86 ± 5 J mol^?1 K^?1, respectively. For [Fe(bts)₂(NCS)₂] the DSC studies do not suggest a first-order transition. The observations conform to the conclusions drawn from previous studies. The relevance of ΔH and ΔS derived from ln K versus l/T plots is discussed.     

Reaction of 3(5) -diazo-1,2,4-triazoles with nitroalkane anions

The 1,2,4-triazolylhydrazones of the corresponding nitro aldehydes were obtained by the reaction of the anions of nitromethane, nitroethane, and 1-nitropropane with diazo-1,2,4-triazoles. 2-Nitropropane, 1,1-dinitroethane, 1,1-dinitropropane, and trinitromethane form 1,2,4-triazolylazonitro compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 713–717, May, 1972.     

Mass spectra of 1,2,4-triazoles—II: Alkyl 1,2,4-triazoles

The mass spectra of monomethyl 1,2,4-triazoles contain fragment ions produced by specific cleavage of the heterocyclic ring. A major fragmentation from many molecular ions involves the elimination of HCN, but loss of N₂ is either very small or completely absent. No N or H scrambling occurs within the triazole ring system, as evidenced by labelling studies. The loss of a hydrogen atom from the molecular ions of 3-alkyl-1,2,4-triazoles (alkyl ? C₂H₅) originates from hydrogens attached to the β carbon and nitrogen atoms.     

Energetic quaternary salts containing bi(1,2,4-triazoles)

New energetic salts (2, 3, 9, 10, and 11) were synthesized via the protonation of 4,4'-bi(1,2,4-triazole) or N-4-(1,2,4-triazole)-N-3-(4-methyl-1,2,4-triazole)amine with nitric acid or perchloric acid or 5-nitro-tetrazole. The structures of 4,4'-bi(1,2,4-triazolium) nitrate (2), N,N-dimethyl-N'-(5-methyl-tetrazole)methanimidamide (8), and N-4-(1,2,4-triazole)-N-3-(4-methyl-1,2,4-triazolium)amine perchlorate (10) were confirmed by a single-crystal X-ray analysis. The physical properties and heats of combustion of the new ionic salts were measured, and the heats of formation were also determined.     

Nitroimines: II. Structure of Nitroamino-1,2,4-triazoles

According to the X-ray diffraction data, compounds formerly known as 3(5)-nitroamino-1,2,4-triazoles are in fact N-nitroimines rather than primary N-nitroamines. Their chemical properties and UV and NMR spectra indicate their nitroimine structure in solution as well.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 6, 2005, pp. 928–933.Original Russian Text Copyright © 2005 by Astakhov, Vasil’ev, Molokeev, Revenko, Stepanov.     

Tuning the spin-transition properties of pyrene-decorated 2,6-bispyrazolylpyridine based Fe(II) complexes

Two 2,6-bispyrazolylpyridine ligands (bpp) were functionalized with pyrene moieties through linkers of different lengths. In the ligand 2,6-di(1H-pyrazol-1-yl)-4-(pyren-1-yl)pyridine (L1) the pyrene group is directly connected to the bpp moiety via a C-C single bond, while in the ligand 4-(2,6-di(1H-pyrazol-1-yl)pyridin-4-yl)benzyl-4-(pyren-1-yl)butanoate (L2) it is separated by a benzyl ester group involving a flexible butanoic chain. Subsequent complexation of Fe(II) salts revealed dramatic the influence of the nature of the pyrene substitution on the spin-transition behaviour of the resulting complexes. Thus, compound [Fe(L1)(2)](ClO(4))(2) (1) is blocked in its high spin state due to constraints caused by a strong intermolecular π-π stacking in its structure. On the other hand, the flexible chain of ligand L2 in compounds [Fe(L2)(2)](ClO(4))(2) (2) and [Fe(L2)(2)](BF(4))(2)·CH(3)CN·H(2)O (3) prevents structural constraints allowing for reversible spin transitions. Temperature-dependent studies of the photophysical properties of compound 3 do not reveal any obvious correlation between the fluorescence of the pyrene group and the spin state of the spin transition core.     

The thermodynamic characteristics of formation of nickel(II) complexes with L-tyrosine in aqueous-ethanolic solvents

Acid dissociation constants of L-tyrosine (H₂Tyr) and the constants of complex formation between L-tyrosine and nickel(II) ions in water-ethanol mixtures were determined potentiometrically. The Gibbs energies of transfer of tyrosine, HTyr⁻ tyrosinate anion, and [NiHTyr]⁺ complex from water into binary solvents were calculated. An increase in the stability constants of the [NiHTyr]⁺ and [Ni(HTyr)₂] complexes in solvents with a high content of ethanol was caused by weakening of the solvation of amino ligand donor groups.