Nanoparticles of iron(II) spin-crossover

We report the synthesis of spin crossover 69 nm spherical nanoparticles of [Fe(NH(2)-trz)(3)](Br)(2).3H(2)O.0.03(surfactant) (NH(2)trz = 4-amino-1,2,4-triazole, surfactant = Lauropal), prepared by the reverse micelle technique, which exhibit at room temperature a thermal hysteresis characterized by magnetic, diffuse reflectivity and Raman studies.     

Chemical/Physical pressure tunable spin-transition temperature and hysteresis in a two-step spin crossover porous coordination framework

A two-dimensional (2D) square-grid type porous coordination polymer [Fe(bdpt)(2)]·guest (1·g, Hbdpt = 3-(5-bromo-2-pyridyl)-5-(4-pyridyl)-1,2,4-triazole) with isolated small cavities was designed and constructed as a spin-crossover (SCO) material based on octahedral Fe(II)N(6) units and an all-nitrogen ligand. Three guest-inclusion forms were successfully prepared for 1·g (1·EtOH for g = ethanol, 1·MeOH for g = methanol, 1 for g = Null), in which the guest molecules interact with the framework as hydrogen-bonding donors. Magnetic susceptibility measurements showed that 1·g exhibited two-step SCO behavior with different transition temperatures (1·EtOH < 1·MeOH < 1) and hysteresis widths (1·EtOH > 1·MeOH > 1 ≈ 0). Such guest modulation of two-step spin crossover temperature and hysteresis without changing two-step state in a porous coordination framework is unprecedented. X-ray single-crystal structural analyses revealed that all two-step SCO processes were accompanied with interesting symmetry-breaking phase transitions from space group of P2(1)/n for all high-spin Fe(II), to P1? for ordered half high-spin and half low-spin Fe(II), and back to P2(1)/n for all low-spin Fe(II) again by lowering temperature. The different SCO behaviors of 1·g were elucidated by the steric mechanism and guest-host hydrogen-bonding interactions. The SCO behavior of 1·g can be also controlled by external physical pressure.     

Cooperative spin crossover and order-disorder phenomena in a mononuclear compound [Fe(DAPP)(abpt)](ClO(4))(2) [DAPP = [bis(3-aminopropyl)(2-pyridylmethyl)amine], abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole

The synthesis and detailed characterization of the new spin crossover mononuclear complex [Fe(II)(DAPP)(abpt)](ClO(4))(2), where DAPP = [bis(3-aminopropyl)(2-pyridylmethyl)amine] and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, are reported. Variable-temperature magnetic susceptibility measurements and M?ssbauer spectroscopy have revealed the occurrence of an abrupt spin transition with a hysteresis loop. The hysteresis width derived from magnetic susceptibility measurements is 10 K, the transition being centered at T(c) downward arrow = 171 K for decreasing and T(c) upward arrow = 181 K for increasing temperatures. The crystal structure was resolved in the high-spin (293 and 183 K) and low-spin (123 K) states. Both spin-state structures belong to the monoclinic space group P2(1)/n (Z = 4). The thermal spin transition is accompanied by the shortening of the mean Fe-N distances by 0.177 A. The two main structural characteristics of [Fe(DAPP)(abpt)](ClO(4))(2) are a branched network of intermolecular links in the crystal lattice and the occurrence of two types of order-disorder transitions (in the DAPP ligand and in the perchlorate anions) accompanying the thermal spin change. These features are discussed relative to the magnetic properties of the complex. The electronic structure calculations show that the structural disorder in the DAPP ligand modulates the energy gap between the HS and LS states. In line with previous studies, the order-disorder phenomena and the spin transition in [Fe(DAPP)(abpt)](ClO(4))(2) are found to be interrelated.     

The High-spin↔Low-spin Equilibrium of Iron(Ⅱ) Complexes with Schiff Base Ligand:Optical,Magnetic and Spectroscopic Properties

Spin transition compounds are of great interest because of their potential application in molecular based electronic devices such as optical memoty and switch, display and data record^[1]. The occurrence of iron(Ⅱ) spin crossover systems depends on the ligand field strength. Iron(Ⅱ) spin crossover compounds mainly have sixfold nitrogen coordination and the range of lODq is very narrow:10Dq^HS≈11500-12500 cm^-1 and 10Dq^LS≈19000-21000 cm^-1[2]. The sensitivity of the spin state to small perturbations suggests that new coordination complexes exhibiting spin transition phenomena could be designed through a fine tuning of the ligands surrounding the metal. The derivatives of 1,2,4-triazole have been found to generate an intermediate ligand field force and the iron(Ⅱ) compounds containing such ligands which yielded spin-crossover materials exhibiting cooperative behavior have been reported recently^[3]. In this paper we present two new iron(Ⅱ) compounds FeL₃(ClO₄)₂·2H₂O (1) and FeL₃(BF₄)₂·3H₂O (2),where L is the Schiff base ligand derived from 4-amino-l,2,4-triazole and benzaldehyde. The compounds appear as white (HS) powders at room temperature and the color changes to pink (LS) upon decreasing the temperature to liquid nitrogen. 1 and 2 are investigated by the optical setup (520 nm, 293-77 K), ⁵⁷Fe Mössbauer Spectroscopy (293-77 K) and magnetic susceptibility (293-4 K). The HS→LS and LS→HS transitions were observed at Tc↓=135 K (1) and 169 K (2), and Tc↑=150 K (1) and 180 K (2), respectively. The thermal hysteresis is found to be 15 K and 11 K for 1 and 2. The area fractions are calculated to be 57% for 1 and 43% for 2. Variable temperature magnetic susceptibility data were fitted to magnetic susceptibility equations derived from domain model, two level Ising-type model and regular solution model. The calculated variations of enthalpy and entropy of the compounds fall within the limits ΔH≈8.1-10.9 kJ·mol^-1 and ΔS≈47-61 J·K^-1·mol^-1 found for mononuclear iron(Ⅱ) spin transition compounds from calorimetric measurements. The cooperativity parameter y determines the occurrence of hysteresis.     

Spectroscopic identification of some derivatives of 3,4-diamino-4H-1,2,4-triazole and 3-Hydrazino-4H-1,2,4-triazole

Spectroscopic methods (ir, ¹H- and ¹³C-nmr, ms and uv) have been used for the structural elucidation and identification of different isomeric 1,2,4-triazole derivatives, obtained by cyclisation reactions from appropriate diaminoguanidines. The four compounds 3,4-diamino-4H-1,2,4-triazole, 3-hydrazino-4H-1,2,4-triazole, 3-amino-4-(2,6-dichlorobenzylideneamino)-4H-1,2,4-triazole and 3-(2,6-dichlorobenzylidenehydrazino)-4H-1,2,4-triazole, were chosen as representative structures to illustrate the general spectroscopic properties for 3,4-diamino- and 3-hydrazino-substituted 4H-1,2,4-triazoles and the corresponding hydrazones, with different substituents in the 5-position of the triazole ring (alkyl-, aralkyl-, mercapto-, hydroxy- and amino-groups). Nmr and uv spectroscopy were found to be the best methods for confirmation of the different series of hydrazones, while ir and nmr were found to be suitable for the structural elucidation of compounds in the series of 3,4-diamino- and 3-hydrazino-4H-1,2,4-triazoles, respectively.     

新型"分子合金"类Fe(II)配合物的合成和自旋转换性能

合成了Fe[(Htrz)~9~/~4(NH~2trz)~3~/~4](BF~4)~2.H~2O(1)和Fe[(Htrz)~3~/~2(NH~2trz)](BF~4).3H~2O(2)两个"分子合金"类自旋转换配合物。其变温光谱表明,它们在室温附近具有自旋转换行为,同时还伴有热致变色及滞后现象。     

New iron(II) spin crossover coordination polymers [Fe(μ-atrz)3]X2·2H2O (X = ClO4¯, BF4¯) and [Fe(μ-atrz)(μ-pyz)(NCS)2]·4H2O with an interesting solvent effect

A potential bridging triazole-based ligand, atrz (trans-4,4'-azo-1,2,4-triazole), is chosen to serve as building sticks and incorporated with a spin crossover metal center to form a metal organic framework. Coordination polymers of iron(II) with the formula [Fe(μ-atrz)(3)]X(2)·2H(2)O (where X = ClO(4)(-) (1·2H(2)O) and BF(4)(-) (2·2H(2)O)) in a 3D framework and [Fe(μ-atrz)(μ-pyz)(NCS)(2)]·4H(2)O (3·4H(2)O) in a 2D layer structure were synthesized and structurally characterized. The magnetic measurements of 1·2H(2)O and 2·2H(2)O reveal spin transitions near room temperature; that of 3 exhibits an abrupt spin transition at ~200 K with a wide thermal hysteresis, and the spin transition behavior of these polymers are apparently correlated with the water content of the sample. Crystal structures have been determined both at high spin and at low spin states for 1·2H(2)O, 2·2H(2)O, and 3·4H(2)O. Each iron(II) center in 1·2H(2)O and 2·2H(2)O is octahedrally coordinated with six μ-atrz ligands, which in turn links the other Fe center forming a strong three-dimensional (3D) network; counteranion and water molecules are located in the voids of the lattice. The FeN(6) octahedron of 3·4H(2)O is formed with two atrz, two pyrazine (pyz) ligands, and two NCS(-) ligands, where the ligands atrz and pyz are bridged between iron centers forming a 2D layer polymer. A zigzag chain of water molecules is found between the layers, and there is a distinct correlation between the thermal hysteresis with the amount of water molecules the exist in the crystal.     

Mössbauer study of the influence of ligands and anions of the second coordination sphere in Fe(II) complexes with 1,2,4-triazole and 4-amino-1,2,4-triazole on the temperature of the 1A 1⇆5 T 2 spin transitions

For Fe(II) complexes with 1,2,4-triazole (Tr) and 4-amino-1,2,4-triazole (ATr) in low-spin phases, it has been revealed that the ligand and anion of the second coordination sphere affect the electronic state of the central atom and the symmetry of its local environment. For low-spin phases, a correlation between the Mössbauer spectrum parameters—the chemical shift and the bandwidth of the weakly resolved quadrupole doublet—and the spin transition temperature T_c has been established. The mechanism of the influence of complex composition on the spin transition temperature is accounted for by assuming that T_c is determined by the lattice energy of a complex compound.     

Coulometric determination of amine-substituted derivatives of 1,2,4-triazole in mono- and mixed-ligand complexes of metals

A procedure is developed for the coulometric determination of amine-substituted derivatives of 1,2,4-triazole. Stoichiometric coefficients of 1,2,4-triazoles and transition metal complexes with these ligands in bromination reactions are determined. The data obtained are used to determine the concentration of 4-amino-1,2,4-triazole in iron(II) mixed-ligand complexes of the composition Fe(TR)_3x(4-ATR)_{3 ? 3x}(ClO₄)₂, where TR is 1,2,4-triazole and 4-ATR is 4-amino-1,2,4-triazole that are characterized by the thermoinduced ¹A₁ ai ⁵T₂ spin transition and thermochromism (color change from pink to white and vice versa).     

Synthesis of Spin-Crossover Nano- and Micro-objects in Homogeneous Media

New methods are proposed for the synthesis of spin-crossover nano- and micro-objects. Several nano-objects that are based upon the spin-crossover complex [Fe(hptrz)(3) ](OTs)(2) (hptrz=4-heptyl-1,2,4-triazole, Ts=para-toluenesulfonyl) were prepared in homogeneous media. The use of various reagents (Triton X-100, PVP, TOPO, and PEGs of different molecular weights) as stabilizing agents yielded materials of different size (6?nm-2?μm) and morphology (nanorods, nanoplates, small spherical particles, and nano- and micro-crystals). In particular, when Triton X-100 was used, a variation in the morphology from nanorods to nanoplates was observed by changing the nature of the solvent. Interestingly, the preparation of the nanorods and nanoplates was always accompanied by the formation of small spherical particles. Alternatively, when PEG was used, 200-400?nm crystals of the complex were obtained. In addition, a very promising polymer-free synthetic method is discussed that was based on the preparation of relatively stable Fe(II) -triazole oligomers in CHCl(3) . Their specific treatment led to micro-crystals, small nanoparticles, or gels. The size and morphology of all of these objects were characterized by TEM and by dynamic light scattering (DLS) where possible. Their spin-crossover behavior was studied by optical and magnetic measurements. The spin-transition features for large particles (>100?nm) were very similar to that of the bulk material, that is, close to room temperature with a hysteresis width of up to 8?K. The effects of the matrix and/or size-reduction led to modification of the transition temperature and an abruptness of the spin transition for oligomeric solutions and small nanoparticles of 6?nm in size.     

一个基于[Cu4(μ2-OH)2N12]的10-连接3D配合物的合成、结构和光催化性质

通过扩散法合成了一个新的配位聚合物{[Cu₂（OH）（btre）_1.5（1,2,4-btc）]·13H₂O}_n（1·13H₂O）（btre=1,2-二（4H-1,2,4-三唑）乙烷,1,2,4-btc=1,2,4-苯三甲酸根）。测试了1·13H₂O的晶体结构,并用红外光谱、元素分析、粉末X射线衍射对其进行表征。单晶X射线衍射表明1是基于四核铜簇[Cu₄（μ₂-OH）₂N₁₂]构筑的10-连接的3D框架,其拓扑符号为3¹²·4²⁸·5⁵。研究了1·13H₂O的热稳定性以及对甲基橙的催化降解作用。     

Spin Crossover Behavior of FeII Complexes Bridged by Thiophene-Functionalized Triazole Ligands with Different Sizes and Rigidities

Four thiophene functionalized triazole ligands (L1=4-(thenyl)-1,2,4-triazole, L2=4-(thiophene ethyl)-1,2,4-triazole, L3=N-Thiophenylidene-4H-1,2,4-triazole-4-amine, and L4=(4-[(E)-2-(5-sulfothiophene)vinyl]-1,2,4-triazole) were synthesized. These ligands have different lengths and rigidities, while ligand L4 has a sulfonic acid group that can form a hydrogen bond. Five 1D Fe^II chain complexes were synthesized: [Fe(L1)₃](X)₂ ⋅ nH₂O [X=BF₄⁻, n=1.5 ( C1 ); X=ClO₄⁻, n=1 ( C2 )], [Fe(L2)₃](BF₄)₂ ⋅ 1.5H₂O ( C3 ); [Fe(L3)₃](X)₂ ⋅ nH₂O [X=BF₄⁻, n=2 ( C4 ); X=ClO₄⁻, n=2.5 ( C5 )]. The results of temperature-dependent magnetic susceptibility reveal that complexes C1 , C2 , and C3 experienced the transition between two spin states. And C4 and C5 maintain high spin states at all temperature ranges. Binuclear complex [Fe₂(L3)₅(SCN)₄] ( C6 ) and mononuclear material [Fe(L4)₂(H₂O)₄] ⋅ 2H₂O ( C7 ), these two zero-dimensional molecules were also synthesized. They all display weak antiferromagnetic exchange coupling and a high spin state in the whole process.     

A novel electron transport material with triazole and diphenylphosphine oxide moieties for high efficiency OLEDs

A novel electron transport material with 1,2,4-triazole and diphenylphosphine oxide moieties (TPO) has been designed and synthesized. The material exhibits wide energy gap (3.77 eV), deep HOMO level (−6.28 eV), high triplet energy (2.86 eV), high glass transition temperature (133 °C) and high thermal stability (decomposition temperature at 423 °C). Device using TPO as electron transport material showed lower driving voltage and higher efficiency compared with the commonly used electron transport materials, such as 3,5-bis(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ), 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBI) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP).     

Electronic and spatial structure of spin transition iron(II) tris(4-amino-1,2,4-triazole) nitrate and perchlorate complexes

Electronic and spatial structure of polynuclear iron(II) complexes Fe(ATr)₃(ClO₄)₂, Fe(ATr)₃(NO₃)₂, and Fe_0.34Zn_0.66(ATr)₃(NO₃)₂ (where ATr is 4-amino-1,2,4-triazole) is investigated using EXAFS and XANES spectroscopy and X-ray fluorescent spectroscopy. Changes in the distances to the first four coordination spheres of Fe and Zn atoms upon spin transitions induced by variations of the anion or temperature are analyzed. It is shown that in polynuclear complexes the spin transition (from S=2 to S=0) is accompanied by pronounced variations in the electronic and spatial structure. A mutual effect of Fe and Zn atoms was found which alters the local environment of the low-spin Fe atoms in a magnetically diluted complex as compared to the initial one. Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 4, pp. 96–104, July–August, 1994. Translated by L. Smolina     

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.     

Application of N-(ω-bromoalkyl)tetrazoles for the preparation of bitopic ligands containing pyridylazole chelators or azole rings as building blocks for iron(II) spin crossover polymeric materials

1-(3-Bromopropyl)tetrazole, 2-(3-bromopropyl)tetrazole, 1-(4-bromobutyl)tetrazole, and 2-(4-bromobutyl)tetrazole were synthesized with the aim to prepare flexible bitopic ligands contaning 1- or 2-substituted tetrazole ring linked through 1,3-propylene or 1,4-butylene spacer with pyridylazole or azole unit. Twenty-six novel ligands i.e., α-(pyridylazolyl)-ω-(tetrazolyl)alkanes, α-(tetrazolyl)-ω-(1,2,3-triazolyl)alkanes, and α-(tetrazol-1-yl)-ω-(tetrazol-2-yl)alkanes were prepared by an alkylation of sodium salts of 5-(2-pyridyl)tetrazole, 3-(2-pyridyl)-1,2,4-triazole, 3-(2-pyridyl)pyrazole, 1,2,3-triazole, and 1,2,3,4-tetrazole with N-(ω-bromoalkyl)tetrazoles. An alkylation of 5-(2-pyridyl)tetrazole, 1,2,3,4-tetrazole, and 1,2,3-triazole afforded both N1- and N2-regioisomer whereas in the case of 3-(2-pyridyl)-1,2,4-triazole and 3-(2-pyridyl)pyrazole only N1 isomers were isolated. The positions of alkylation were confirmed by X-ray diffraction studies of 1-(5-(2-pyridyl)tetrazol-2-yl)-4-(tetrazol-1-yl)butane, 1-(3-(2-pyridyl)-1,2,4-triazol-1-yl)-4-(tetrazol-2-yl)butane, 1-(3-(2-pyridyl)pyrazol-1-yl)-4-(tetrazol-1-yl)butane, and 1-(tetrazol-1-yl)-4-(1,2,3-triazol-1-yl)butane. Preliminary investigations of magnetic properties of iron(II) complex with 1-(3-(2-pyridyl)-1,2,4-triazol-1-yl)-4-(tetrazol-1-yl)butane revealed that obtained product exhibit thermally induced spin transition accompanied by the thermochromic effect.     

Poly(<Emphasis Type="Italic">N</Emphasis>-vinylimidazole) as an efficient and recyclable catalyst of the aza-Michael reaction in water

Poly(N-vinylimidazole) effectively catalyzed Michael addition of 1H-1,2,4-triazole, 3,5-dimethyl-1H-1,2,4-triazole, uracil, oxazolidin-2-one, and succinimide to but-3-en-2-one, cyclohex-2-en-1-one, methyl acrylate, and methyl vinyl sulfone in water at room temperature. The catalyst can readily be regenerated and repeatedly used at least five times without loss in activity, as shown in the reaction of 1H-1,2,4-triazole with but-3-en-2-one as an example.     

A facile route for the preparation of nanoparticles of the spin-crossover complex [Fe(Htrz)2(trz)](BF4) in xerogel transparent composite films

Films and monoliths containing the spin crossover complex [Fe(Htrz)(2)(trz)](BF(4)) (trz = 1,2,4-triazole) as nanoparticles have been obtained. The dispersion and consecutive inclusion of the Fe complex in a silica matrix prepared from tetramethoxysilane or tetraethoxysilane afford monoliths or films with a violet colour at room temperature, which turns white above 380 K. This change of colour is reversible. This thermochromic behaviour has been characterized by measuring the magnetic properties together with thermogravimetric studies and Raman spectroscopy, the result of which all demonstrate that both films and monoliths undergo a spin crossover. Microscopy studies confirm the occurrence of the Fe complex as nanoparticles, in both the monoliths and the films. The facile synthesis of these materials as nanoparticles in transparent films should open the possibility of the synthesis of high quality films.     

1,4-Di(1,2,3-triazol-1-yl)butane as building block for the preparation of the iron(II) spin-crossover 2D coordination polymer

The novel bidentate ligand 1,4-di(1,2,3-triazol-1-yl)butane (bbtr) reacts with Fe(ClO4)2 x 6H2O to form the 2D coordination polymer with (3,6) network topology. The {[Fe(bbtr)3](ClO4)2}infinity represents an example of spin-crossover material based on 1,2,3-triazole as donor group, and displays an abrupt spin transition accompanied by a thermal hysteresis loop (T(1/2)decrease = 101 K and T(1/2)increase = 109 K).     

Crystal structure, magnetic properties, and 57Fe Mössbauer spectroscopy of the two-dimensional coordination polymers [M(1,2-bis(1,2,4-triazol-4-yl)ethane)2(NCS)2] (MII = Fe, Co)

New coordination polymers of the formula [M(btre)(2)(NCS)(2)] (btre = 1,2-bis(1,2,4-triazol-4-yl)ethane; M(II) = Fe, Co) have been synthesized, and their crystal structures have been determined at 293 K by X-ray analysis. The Fe(II) compound (C(7)H(8)FeN(7)S(2)) crystallizes in the monoclinic space group P2(1)/n, a = 12.439(5) A, b = 8.941(2) A, c = 9.321(3) A, beta = 90.88(2) degrees , V = 1036.6(6) A(3), Z = 2, 3791 reflections [I > 3sigma(I)], R(F) = 0.036, wR2 = 0.123. The Co(II) compound is isostructural to the Fe(II) compound. The crystal structure consists of a 2D sheet in which the metal ions are linked by bis monodentate (N1, N1') 1,2,4-triazole ligands. The structure is stabilized by pi-bond interactions between two adjacent sheets and by S...S interactions. Temperature-dependent SQUID, (57)Fe M?ssbauer, and X-ray diffraction measurements indicate that [Fe(btre)(2)(NCS)(2)] retains a HS ground state upon cooling from 293 K down to 8 K. The surprising absence of spin-crossover behavior for this Fe(II)-1,2,4-triazole polymeric coordination compound that has been confirmed by pressure experiments up to approximately 12 kbar and by light irradiation experiments at 10 K is discussed on the basis of its structural features. Insight into the origin of the cooperative effects of the spin transition in [Fe(btr)(2)(NCS)(2)].H(2)O (btr = 4,4'-bis-1,2,4-triazole) is also given thanks to a re-evaluation of its distortion parameters in the high- and low-spin states.