High and low spin mononuclear and dinuclear iron(II) complexes of 4-amino and 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazoles

The first dinuclear iron(II) complexes of any 4-substituted 3,5-di(2-pyridyl)-4H-1,2,4-triazole ligands, [Fe(II)2(adpt)2(H2O)1.5(CH3CN)2.5](BF4)4 and [Fe(II)2(pldpt)2(H2O)2(CH3CN)2](BF4)4, are presented [where adpt is 4-amino-3,5-di(2-pyridyl)-4H-1,2,4-triazole and pldpt is 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole]. Both dinuclear complexes feature doubly triazole bridged iron(II) centers that are found to be [high spin-high spin] at all temperatures, 4-300 K, and to exhibit weak antiferromagnetic coupling. In the analogous monometallic complexes, [Fe(II)(Rdpt)2(X)2](n+), the spin state of the iron(II) center was controlled by appropriate selection of the axial ligands X. Specifically, both of the chloride complexes, [Fe(II)(adpt)2(Cl)2] x 2 MeOH and [Fe(II)(pldpt)2(Cl)2] x 2 MeOH x H2O, were found to be high spin whereas the pyridine adduct [Fe(II)(adpt)2(py)2](BF4)2 was low spin. Attempts to prepare [Fe(II)(pldpt)2(py)2](BF4)2 and the dinuclear analogues [Fe(II)2(Rdpt)2(py)4](BF4)4 failed, illustrating the significant challenges faced in attempts to develop control over the nature of the product obtained from reactions of iron(II) and these bis-bidentate ligands.     

Synthesis,crystal structure,and properties of copper(II) and manganese(II) complexes with azide and 3,4-di(2′-pyridyl)-1,2,5-oxadiazole

Two transition metal complexes with azide and 3,4-di(2′-pyridyl)-1,2,5-oxadiazole (dpo), [Cu₂(dpo)₂(N₃)₄] (1), and [Mn(dpo)₂(N₃)₂] (2), have been synthesized and characterized by single-crystal X-ray diffraction. The Cu(II) complex is binuclear with double end-on (EO) azido bridges, in which each Cu(II) ion assumes a distorted square pyramidal geometry, and each EO azido bridge adopts a quasi-symmetric fashion. In contrast, the Mn(II) complex is mononuclear, in which the Mn(II) ion is ligated by two dpo ligands and two terminal azide ions, with a distorted octahedron geometry. Magnetic studies on the Cu(II) complex revealed that the double EO azido bridge mediates ferromagnetic coupling with J=12.8 cm⁻¹.     

Iron(II) spin crossover complexes with branched long alkyl chain

The bzimpy iron(II) complexes, 1-3, containing branched long alkyl chains were synthesized and characterized in detail. The temperature-dependant magnetic susceptibility of 1 showed gradual spin crossover behavior from low spin to high spin state, while 2 retained only low spin state in the same condition. Interestingly, 3 displayed an abrupt spin transition in temperature range from T_1/2↑ = 236 K to T_1/2↓ = 230 K with the thermal hysteresis loop about 6 K. The differential scanning calorimetric analysis of 3 revealed two species of liquid crystal phase transitions at 236 K and 351 K, respectively.     

The magnetic and structural elucidation of 3,5-bis(2-pyridyl)-1,2,4-triazolate-bridged dinuclear iron(II) spin crossover compounds

Variable temperature magnetic susceptibility, Mössbauer spectroscopic and X-ray crystallographic studies are described on two structurally similar families of dinuclear iron(II) spin crossover (SCO) complexes of formula [Fe(NCX)(py)]₂(μ-L)₂, where L is either a 3,5-bis(2-pyridyl)-pyrazolate bridging ligand, bpypz⁻, examples of which have been earlier reported by Kaizaki and coworkers, or a corresponding 3,5-bis(2-pyridyl)-1,2,4-triazolate, bpytz⁻. Compounds synthesised were [Fe(NCS)(py)]₂(μ-bpypz)₂ (1), [Fe(NCSe)(py)]₂(μ-bpypz)₂ (2), [Fe(NCS)(py)]₂(μ-bpytz)₂ (3), [Fe(NCSe)(py)]₂(μ-bpytz)₂ (4), [Fe(NCBH₃)(py)]₂(μ-bpytz)₂ (5). The crystal and molecular structures of 1 and 3 are very similar in their HS–HS forms (HS = high spin d⁶). In contrast to reported SCO behaviour for precipitated samples of 1, also repeated here, crystals of 1 show only HS–HS behaviour with no spin crossover transition. Complex 3 likewise displays HS–HS magnetism, with very weak antiferromagnetic coupling. Compound 5 displays a well resolved two-step, full spin transition from HS–HS to LS–LS states while compound 2 shows a one step transition. The Mössbauer data for 2 and 5 show unusual features at low temperatures.     

Synthesis,Crystal Structures,and Magnetic Properties of Three New Iron Complexes Derived from 3,5‐Bis(pyridin‐2‐yl)‐1,2,4‐triazole

Two new iron(III) complexes and one iron(II) complex have been synthesized from the solvothermal reactions of FeCl₃·6H₂O with 3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole (Hbpt) in methanol or acetonitrile. KSCN acted as the reducing agent in the synthesis of iron(II) complex of 3 . [FeCl₃(Hbpt)(H₂O)]·H₂O ( 1 ) crystallizes in the triclinic space group with a = 7.475(1), b = 9.468(2), c = 12.309(2) Å, α = 73.880(2), β = 74.746(2), γ = 81.849(2)°, V = 805.2(2) ų, Z = 2. [Fe₂(bpt)₂Cl₄] ( 2 ): orthorhombic space group Pnnm with a = 9.895(2), b = 10.632(2), c = 13.195(2) Å, V = 1388.1(4) ų, Z = 2. [Fe₂(bpt)₂(MeOH)₂Cl₂] ( 3 ): orthorhombic space group Pbca with a = 14.4204(16), b = 9.8737(11), c = 19.792(2) Å, V = 2818.1(5) ų, Z = 4. 1 features the first structurally characterized metal complex of the neutral Hbpt ligand in which the Hbpt ligand adopts an unprecedented zwitterionic form. 2 shows a neutral dinuclear iron(III) complex and the [Fe₂(bpt)₂]⁴⁺ unit is ideally planar. The two iron(III) ions separated by a distance of 4.408(2) Å are doubly triazolate‐bridged. Each dimeric unit is connected with six other dimeric ones via the bifurcated C‐H···Cl hydrogen bonds, these connections extend the dimeric moieties into a three‐dimensional molecular architecture. 3 is a neutral centrosymmetric dinuclear Fe^II complex, in which intermolecular moderate O‐H···N hydrogen bonding interactions between the methanol molecules and 4‐position nitrogen atoms of the triazolato groups extend the dinuclear species into a two‐dimensional supramolecular architecture of (4,4) topology. Magnetic studies indicate there exists an antiferromagnetic spin coupling in Fe^III₂ and Fe^II₂ units via the double triazolate bridges in 2 and 3 .     

Syntheses,crystal structures,and spectral characterization of an asymmetrically substituted 1,2,4-triazole and its iron(II) complex

One new asymmetrically substituted 1,2,4-triazole, 4-amino-3-(p-bromophenyl)-5-(2-pyridyl)-1,2,4-triazole (L), and its iron(II) complex, trans-[FeL₂(NCS)₂] (1), have been synthesized and characterized by elemental analyses, FT-IR, ¹H NMR, ESI mass spectra, and single-crystal X-ray crystallography. Crystallographic studies revealed that 1 contains a distorted octahedral [FeN₆] core with two trans NCS^?. Each L adopts a chelating bidentate coordination via N of pyridyl and one N of the triazole ring. Magnetic susceptibility measurements indicated that 1 remained in a high-spin state between 1.8 and 300?K.     

Spin-Crossover Iron(II) Compounds with Pendent Tetraphenylethylene Group

Two iron(II) compounds with the general formula of [Fe(phen-TPE)₂(NCX)₂] ⋅ Y (phen-TPE=3-(tetraphenylethylene)-1,10-phenanthroline; X=S and Y=2DMF for 1 ⋅ 2DMF ; X=Se and Y=DMF for 2 ⋅ DMF ) were synthesized and characterized by single-crystal X-ray crystallography and magnetic measurements. Both compounds exhibited thermal-induced complete one-step spin-crossover (SCO) behavior with the critical transition temperatures of 210 K and 260 K for 1 ⋅ 2DMF and 2 ⋅ DMF , respectively. The SCO behavior of these two isomorphic compounds depended significantly on robust intermolecular π⋅⋅⋅π interactions, NCX⁻ groups and solvent molecules.     

Syntheses,crystal structures,and spectral properties of Mn(II) and Co(II) complexes with 3-(p-chlorophenyl)- 4-(p-methylphenyl)-5-(2-pyridyl)-1,2,4-triazole

Two new complexes, trans-[MnL₂(NCS)₂] (1) and trans-[CoL₂(H₂O)(EtOH)](ClO₄)₂?·?H₂O (2) with asymmetrical triaryltriazole ligands [L?=?3-(p-chlorophenyl)-4-(p-methylphenyl)-5-(2-pyridyl)-1,2,4-triazole], have been synthesized and characterized by elemental analysis, FT-IR, ESI-MS, and single-crystal X-ray diffraction. In the complexes each L adopts a chelating bidentate mode via the nitrogen of pyridyl and triazole. Both complexes have a similar distorted octahedral core with two NCS^? ions in the trans position in 1, while one H₂O and one EtOH are present in the axial sites in 2.     

Spin Crossover Studies on Bis{hydro-tris(1,2,4-triazolyl)borato}iron(II)

The spin-crossover behavior of bis{hydro-tris(1,2,4-triazolyl)borato}iron(II) is investigated in bulk and as a magnetically diluted sample in the solid state and in solution as a function of temperature by magnetic susceptibility measurements and differential scanning calorimetry. In aqueous solution the low-spin to high-spin transition is shown in turn to decrease the longitudinal relaxation time T₁ of water protons with increasing temperature. The solid-state magnetically diluted samples were prepared by cocrystallization with the isostructural zinc complex.     

Influence of CF3 Substituents on the Spin Crossover Behavior of Iron(II) Coordination Polymers with Schiff Base-like Ligands

A Schiff base-like ligand bearing CF₃ substituents was synthesized and converted to iron(II) coordination polymers [{FeL(L_ax)}_n] using five different bridging ligands L_ax. The structure of the coordination polymers was investigated using powder X-ray diffraction and single-crystal X-ray diffraction in the case of [{FeL(bipy)}_n]. The later revealed an untypical ABAB pattern of alternating equatorial ligands rotated by 180° with regard to each other along the chain. The temperature-dependent magnetic behavior was investigated with a SQUID magnetometer and the spin states at room temperature were confirmed by ⁵⁷Fe-Mössbauer spectroscopy. Three out of five coordination polymers show spin crossover behavior in the temperature range between 50 and 400 K with different kind of curve progressions (abrupt, gradual, step-wise). The other two coordination polymers are either fully highspin or fully low spin.     

Synthesis,crystal structure and fungicidal activity of 1-(4-chlorophenyl)-2-(5-((3,5-dimethyl-1H-pyrazol-1-yl)methyl)-4-phenyl-4H-1,2,4-triazol-3-ylthio)ethanone

A novel bis-heterocyclic compound was synthesized and characterized. The crystal structure of the title compound (C₂₂H₂₀ClN₅OS, Mr = 437.94) has been determined by single-crystal X-ray diffraction. The crystal is of triclinic, space group P-1 with a = 8.646 (2), b = 9.148 (3), c = 14.540 (4) Å, α = 94.422 (4), β = 98.500 (4), γ = 102.823 (4)°, V = 1101.8 (5) Å³, Z = 2, F(000) = 312, Dc = 1.320 g/cm³, μ = 0.2900 mm^?1, the final R ₁ = 0.041000 and wR ₂ = 0.1160 for 2675 observed reflections with I > 2σ(I). A total of 5623 reflections were collected, of which 3866 were independent (R _int = 0.019000). The fungicidal activity of title compound was determined, the results showed the title compound displayed moderate fungicidal activity against G. zeae Petch, Phytophthora infestans (Mont.) de Bary, Botryosphaeria berengeriana f. sp. piricola (Nose) koganezawa et Sakuma, Fusarium oxysporum f.sp. cucumerinum, and Cercospora arachidicola.     

1－（取代异噁唑基）－1，2，4．三唑和1－（取代嘧啶基）－1，2，4－三唑的合成及生物活性

合成了１５个新的１－（取代异噁唑基）－１，２，４－三唑和１－（取代嘧啶基）－１，２，４－三唑化合物，经元素分析、ＩＲ、１ＨＮＭＲ和ＭＳ证实其结构，并对其代表化合物进行了抑菌及植物生长调节活性的初步观察     

Spin State in (Porphinato)iron(III) Complex. A Spin‐Crossover Complex with Two Magnetically Distinct Sites

The results of low temperature X‐ray determination, Mössbauer and magnetic measurement of spin‐crossover (isothiocyanato)(porphinato)iron(III) hemipyridine are reported. The features in 77 K Mössbauer spectrum include two doublets, one with a quadrupole splitting (ΔE_Q) of 1.961 mm s^?1 (low‐spin site) and the other with ΔE_Q = 0.792 mm s^?1 (high‐spin site). As the temperature of the sample is increased to 300 K, the signal intensity of the high‐spin site grows to 92% at the expense of the low‐spin signal. The variable‐temperature magnetic susceptibility data also support that the tetraphenyl complex is a spin‐crossover complex.     

Synthesis,crystal structure,Hirshfeld surfaces,and spectral properties of Cu(II) and Co(II) complexes with 3-phenoxymethyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole

A new asymmetrical substituted triazole, 3-phenoxymethyl-4-phenyl-5-(2-pyridyl)-1,2,4-triazole (L) and its complexes, cis-[Cu₂ L ₂Cl₄]·2CH₃CN (1) and trans-[CoL ₂Cl₂]·2H₂O·2CH₃CN (2), have been synthesized and characterized by IR, single-crystal X-ray diffraction, thermogravimetric analyses and Hirshfeld surfaces. In the structure, two L are mainly stabilized by an intermolecular C–H?N hydrogen bond. In 1 (or 2), each L involves a doubly-bidentate (or chelating bidentate) coordination mode through one pyridine and two nitrogens (or one) of triazole, respectively. Complex 1 has a distorted trigonal bipyramidal [CuN₃Cl₂] core with two cis Cl^? while 2 shows a distorted octahedron [CoN₄Cl₂] with two trans Cl^?. We also prepared molecular Hirshfeld surface and fingerprint plot for L, 1 and 2, which revealed the influence of different metals on coordinate of L.     

Relevance of supramolecular interactions, texture and lattice occupancy in the designer iron(II) spin crossover complexes

New Fe^II complexes of formula [Fe(3-Br-phen)₂(NCS)₂]·Solvent (Solvent=0.5 CH₃OH (1), 2 CH₂Cl₂ (2), desolvation of 2 (3), 0.5 CH₃COCH₃ (4) and 0 (5)) have been synthesized. ⁵⁷Fe Mössbauer and magnetic investigation reveal unique features atypical of classic [Fe(phen)₂(NCS)₂] polymorphs. Complex 1, prepared by precipitation in MeOH, undergoes upon cooling below room temperature an incomplete and gradual thermally induced spin conversion, while 4 prepared by an extraction method remains mostly in the low-spin state. The non solvated compounds 3 and 5, display a more abrupt spin crossover on cooling around T_1/2=175 K and T_1/2=198 K, respectively. Defects/soft lattice inclusion due to different methods of material synthesis, extent of aging, reaction medium and associated solvent molecules have enormous influence on the particle size and magnetic properties of these complexes. Scanning electron micrographs helps to establish a logical relationship among methods employed for synthesis, texture of materials and their effect on magnetic properties. The crystal structure of 2 determined in the monoclinic space group P2/c (100 K) reveals a mononuclear complex consisting of a distorted FeN₆ octahedron in the low-spin state, constructed from two 3-bromo-1, 10-phenanthroline and two isothiocyanato anions in cis position. Intermolecular interactions between mononuclear units of the S?Br, S?C(H) and π-π type afford a 2D supramolecular network. DFT calculations for the single molecule 2 reveals an energy difference between high-spin and low-spin isomers of 7 kJ/mol suggesting a slight destabilization of the low-spin state compared to [Fe(phen)₂(NCS)₂]. Normal co-ordinate analysis was also carried out for 3 and compared with experimental temperature dependent Raman spectra for 5.     

Synthesis,Magnetic Properties and X‐ray Structure Analysis of a 1‐D Chain Iron(II) Spin Crossover Complex with wide Hysteresis

The reaction of [FeL(MeOH)₂] (L being a tetradentate [N₂O₂]^2? coordinating Schiff base like ligand [([3,3′]‐[1,2‐phenylenebis(iminomethylidyne)]bis(2,4‐pentane‐dionato)(2‐)N,N′,O²,O²′], MeOH = methanol) with 4,4′‐bipyridine (bipy) results in the formation of a new iron(II ) spin crossover coordination polymer of the formula [FeL(bipy)] ( 1 ). T‐dependent susceptibility measurements revealed an abrupt HS ? LS spin transition with an approximately 18 K‐wide thermal hysteresis loop (T_1/2↑ = 237 K and T_1/2↓ = 219 K). The isolation of crystals suitable for X‐ray structure analysis allowed the determination of the motive of the molecule structure of the first 1‐D chain compound with hysteresis in the HS form at 250 K. Despite the low qualtity of the data, we were able to obtain some insight into the interplay of covalent and elastic interactions that are both responsible for the high cooperative interactions during the spin transition in this compound.     

Dinuclear Fe(III) complexes with spin crossover

Abstract  A series of dinuclear Fe(III) complexes was synthesized in which the Schiff-base blocking ligand L⁵ coordinates each of the centers which are linked by a bidentate, bipyridine-type ligand. For these systems, [L⁵Fe^III{bridge}Fe^IIIL⁵](BPh₄)₂, thermally induced spin crossover is observed. The corollary of the systems is that the spin crossover interferes with the magnetic exchange interaction. The overlap of the energy bands of the LL and HH reference states (L, low-spin; H, high-spin) causes the exchange interaction to act against the spin crossover (leading to incompleteness or gradual behavior). Graphical abstract