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Cooling [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) triggers very slow spin crossover below 80 K (T1/2↓=76 K). The spin crossover (SCO) is accompanied by a hysteresis loop (T1/2↑=89 K). In contrast to isostructural perchlorate analogue [Fe(bbtr)3](ClO4)2 in which spin crossover during cooling is preceded by phase transition at TPT=126 K in tetrafluoroborate phase transition does not occur to the beginning of spin crossover (80 K). Studies of mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.5≤x≤0.9) showed that a phase transition precedes spin crossover, however, for x≅0.46 intersection of T1/2(x) and TPT(x) dependencies takes place. The application of pressure of 1 GPa shifts the spin crossover in [Fe(bbtr)3](BF4)2 to a temperature above 270 K. High‐pressure studies of neat tetrafluoroborate and perchlorate, as well as mixed crystals [Fe(bbtr)3](BF4)2(1‐x)(ClO4)2x (0.1≤x≤0.9), revealed that at 295 K P1/2 value changes linearly with x indicating similar mechanism of spin crossover under elevated pressure in all systems under investigation. Variable pressure single crystal X‐ray diffraction studies confirmed that in contrast to thermally induced spin crossover undergoing differently in tetrafluoroborate and perchlorate an application of high pressure removes this differentiation leading to a similar mechanism depending at first on start spin crossover and then P‐3→P‐1 phase transition occurs. In this report we have shown that 2D coordination polymer [Fe(bbtr)3](BF4)2 (bbtr=1,4‐di(1,2,3‐triazol‐1‐yl)butane) treated to date as spin crossover silent shows thermally induced spin crossover phenomenon. Spin crossover in tetrafluoroborate is extremely slow. Determination of the spin crossover curve required carrying measurement in the settle mode‐cooling from 85 to 70 K took about 600 h (average velocity of change of temperature ca. 0.0004 K/min). [ABSTRACT FROM AUTHOR]

Reaction of 1,2‐di(tetrazol‐2‐yl)ethane (ebtz) with Fe(BF4)2⋅6 H2O in different nitriles yields one‐dimensional coordination polymers [Fe(ebtz)2(RCN)2](BF4)2⋅nRCN (n=2 for R=CH3 (1) and n=0 for R=C2H5 (2) C3H7 (3), C3H5 (4), CH2Cl (5)) exhibiting spin crossover (SCO). SCO in 1 and 3–5 is complete and occurs above 160 K. In 2, it is shifted to lower temperatures and is accompanied by wide hysteresis (T1/2↓=78 K, T1/2↑=123 K) and proceeds extremely slowly. Isothermal (80 K) time‐resolved single‐crystal X‐ray diffraction studies revealed a complex nature for the HS→LS transition in 2. An initial, slow stage is associated with shrinkage of polymeric chains and with reduction of volume at 77 % (in relation to the difference between cell volumes VHS−VLS) whereas only 16 % of iron(II) ions change spin state. In the second stage, an abrupt SCO occurs, associated with breathing of the crystal lattice along the direction of the Fe–nitrile bonds, while the nitriles reorient. HS→LS switching triggered by light (808 nm) reveals the coupling of spin state and nitrile orientation. The importance of this coupling was confirmed by studies of [Fe(ebtz)2(C2H5CN/C3H7CN)2](BF4)2 mixed crystals (2 a, 2 b), showing a shift of T1/2 to higher values and narrowing of the hysteresis loop concomitant with an increase of the fraction of butyronitrile. This increase reduces the capability of nitrile molecules to reorient. Density functional theory (DFT) studies of models of 1–5 suggest a particular possibility of 2 to adopt a low (140–145°) value of its Fe‐N‐C(propionitrile) angle. [ABSTRACT FROM AUTHOR]

1,4-Di(1-ethyl-1,2,3-triazol-5-yl)butane (bbtre) was prepared by lithiation of 1-ethyl-1,2,3-triazole, followed by alkylation with 1,4-dibromobutane. The ligand bbtre forms a three-dimensional network with Fe(II), [Fe(bbtre)3](ClO4)2·2CH3CN, that exhibits thermally induced spin crossover (SCO). A change of temperature or change of spin state results in various types of structural transformation, leading to different structures that are stable in strictly defined temperature ranges. As a result, there are three spin crossover transitions arranged via two different paths. Thus, cooling below 280 K involves a HT(HS) → LT(HS) (HT, high temperature structure; LT, low temperature structure; HS, high spin) phase transition (PT), which is associated with conformational changes of the bbtre molecules and with deformation of the polymeric skeleton. In the LT phase incomplete and reversible LT(HS) LT(HS/LS) spin crossover occurs (LS, low spin). In contrast, rapid cooling (of a sample not previously thermally treated) allows the HT(HS) → LT(HS) phase transition to be avoided, and so complete HT(HS) → HT1(LS) SCO occurs. This means that the PT plays the role of a switch, which allows a choice of one of two ways in which the SCO will proceed. After rapid cooling, further heating to 150 K and subsequent cooling results in a reversible HT1(HS) HT1(LS) spin crossover (T ↓1/2 = 130 K, T ↑1/2 = 131 K). However, raising the temperature to 170–200 K leads to formation of a modulated structure HT2(HS) exhibiting the next reversible HT2(HS) HT2(LS) SCO (T ↓1/2 = 121 K, T ↑1/2 = 123 K). Finally, heating above 200 K involves the HT2(HS) → LT(HS) PT and results in a LT(HS) structure exhibiting incomplete LT(HS) LT(HS/LS) spin crossover. [ABSTRACT FROM AUTHOR]

In [Fe(ebbtr)2(CH3CN)2](CF3SO3)2·4CH3CN spin crossover is associated with the occurrence of “normal” and “reverse” hysteresis loops separated by a region of stable HS form. This results from trans–trans→gauche–trans conformational changes of ebbtr molecules and anion reorientation, which occur in different ways during cooling and during heating. [ABSTRACT FROM AUTHOR]

The abrupt high spin (HS)→low spin (LS) transition (T↓1/2=136 K) in [Fe(hbtz)2(CH3CN)2](BF4)2 (hbtz=1,6‐di(tetrazol‐2‐yl)hexane) is finished at 100 K and further thermal treatment influences the spin crossover. Subsequent heating involves a change of the spin state in the same way (T↑1/2=136 K) on cooling. In contrast, cooling below 100 K triggers different behavior and T↑1/2 is shifted to 170 K. The extraordinary structural changes that occurred below 100 K are responsible for the observed diversity of properties. A unique feature of the low‐temperature phase is the rebuilding of the anion network expressed by a shift of anions inside the polymeric layer at a distance of 1.2 Å as well as the relative shift of neighboring layers at over 4 Å. These structural alterations, connected with a phase transition, become the origin of the strain, which in most cases causes crystal cleaving. In a sample composed from crystals crushed as a result of the phase transition or as a result of mechanical crumbling, the hysteresis loop vanishes; however, annealing the sample allows to its partial restoration. A replacement of acetonitrile by other nitriles leads to preservation of the polymeric structure and spin crossover, but no phase transition follows. Spin and phase transitions: Two‐dimensional coordination network [Fe(hbtz)2(CH3CN)3](BF4)2 (hbtz=1,6‐di(tetrazol‐2‐yl)hexane) exhibits a high spin (HS)⇄low spin (LS) transition, which is accompanied by significant structural changes, in particular, involving the shift of neighboring polymeric layers at distances above 4 Å. Occurrence of a structural phase transition as well as hysteresis loop is blocked by crystal cleavage, however, sample annealing restores hysteretic behavior (see scheme). [ABSTRACT FROM AUTHOR]

In the two dimensional network [Fe(ebbtr)2(CH3CN)2](ClO4)2·4CH3CN a sequence of LS → HS → LS → HS transitions occurs as the exclusive result of the change in temperature. This property results from the extraordinary flexibility/elasticity manifested in the hierarchical arrangement of structural events involving the reorientation of coordinated/noncoordinated molecules as well as with the deformation and the mutual shift of the polymeric units. [ABSTRACT FROM AUTHOR]

The complexes [M(3ditz)3]X2 [X = ClO4-, M = FeII (1), ZnII (2); X = BF4-, M = FeII (3), ZnII (4); 3ditz = 1,3-di(tetrazol-1-yl)propane] were prepared. Disordering of the propylene chain in 3ditz is not affected by thermally induced spin crossover in 1 (T1/2↓ = 149 K, T1/2↑ = 150 K) and 3 (T1/2↓ = 158, T1/2↑ = 161 K). Low-spin to high-spin (LS→HS) switching triggered by laser-light irradiation (520 nm) also does not influence the disordering of the ligand, leading to restoration of the initial HS phase. Pressurization of crystals results in a reduction of the Fe-N distances by about 0.19 Å, which indicates practically complete spin crossover (SCO). Also, in this case, the disordering of the ligand remains unchanged, although thermally and pressure-induced SCO is accompanied by different changes of 3ditz molecules. Upon thermally induced SCO, perturbation resulting from the reduction of the Fe-N distances is accompanied by a slight elongation of the bridging ligand. In contrast, in the range 0.25-0.55 GPa, the pressure-induced SCO is associated with shrinkage of the 3ditz molecule. Further elevation of pressure results in the inversion of structural changes and - similar to temperature-induced spin crossover - a slight elongation of the ligand molecule takes place. [ABSTRACT FROM AUTHOR]

Reactions between 1,2-di(tetrazol-2-yl)ethane (ebtz), 1,6-di(tetrazol-2-yl)hexane (hbtz) or 1,1′-di(tetrazol-1-yl)methane (1ditz) and Fe(BF4)2 in the presence of adiponitrile (ADN), glutaronitrile (GLN) or suberonitrile (SUN) resulted in the formation of coordination polymers [Fe(μ-ebtz)2(μ-ADN)](BF4)2 (1), [Fe(μ-hbtz)2(μ-ADN)](BF4)2 (2), [Fe(μ-1ditz)2(GLN)2](BF4)2·GLN (3) and [Fe(μ-1ditz)2(μ-SUN)](BF4)2·SUN (4). It was established that the application of dinitriles allows an increase in the dimensionality of the ebtz and hbtz based systems while maintaining the structure of the polymeric units characteristic of previously studied mononitrile based analogues. In 3 and 4, regardless of the type of dinitrile coligand, the motif of 2D polymeric layers constituted by 1ditz molecules remains preserved. However, the dimensionality of 1ditz based networks is governed by the coordination modes of dinitriles. 3, based on a shorter molecule of glutaronitrile, crystallizes as a two-dimensional (2D) coordination polymer. In this compound, dinitriles coordinate monodentately or play the role of guest molecules. The substitution of glutaronitrile with suberonitrile enables the bridging of neighboring polymeric layers, resulting in a 3D network. The intentional selection of bis(tetrazoles) and dinitriles as building blocks has led, as expected, to obtaining systems with the structure of the first coordination sphere consisting of four tetrazole rings and two axially coordinated nitrile molecules. It created the conditions required for the occurrence of thermally induced spin crossover. Magnetic measurements and single crystal X-ray diffraction studies were used for the characterization of the spin crossover properties of 1–4. [ABSTRACT FROM AUTHOR]

New ligand (Z)-2-(1-methyl-2-(pyridine-2-ylmethylene)hydrazinyl)benzoxazole ( L ) reacts with Fe(II) ions what results in formation of mononuclear complexes of 2:1 stoichiometry (complexes 1 and 2 ), which crystallize in the rare space group Ia–3d (No. 230) with solvent–acetonitrile–molecules in the crystal structure. Obtained complexes were studied in terms of their properties in the solid state concerning thermal stability and magnetism. N 3 -donor Schiff base type L is a strong crystal field ligand, therefore both obtained Fe(II) complexes are diamagnetic at room temperature what has been confirmed by magnetic susceptibility measurements and Mössbauer spectroscopy. However, the reversible LS ( 1 A 1 ) ↔ HS ( 5 T 2 ) spin-transitions may be observed starting above room temperature, remaining incomplete even up to 400 K. The thermal stability and electronic reflectance spectra of complexes were determined as well. [ABSTRACT FROM AUTHOR]

Abstract: The photochemistry and molecular structure of 1-allyltetrazole (1-ALT) and 2-allyltetrazole (2-ALT) were studied in argon matrices by infrared spectroscopy and B3LYP/6-311++G(2d,2p) calculations. Both allyltetrazoles were found to possess three stable conformers (1-ALT1, 1-ALT2, 1-ALT3 and 2-ALT1, 2-ALT2, 2-ALT3) differing in the orientation of the allyl group relative to the ring. Matrix isolation technique together with the annealing experiments allowed for detection of all 1-ALT and 2-ALT conformers. A conformational cooling phenomenon was observed for the 1-ALT3→1-ALT1 process in agreement with the predicted low energy barrier of 4.84kJmol−1 for this reaction. The broad-band UV irradiation of 1-ALT/Ar and 2-ALT/Ar matrices led to the same photoproducts. The main product N-allylcarbodiimide (P1) and two minor photoproducts allylcyanamide (P2) and C-allylnitrilimine (P3) are formed through the tetrazole ring cleavage and N2 elimination. None of these molecules have been described before. [Copyright &y& Elsevier]

A bitopic ligand 2-hydroxy-1-(tetrazol-1-yI)-3-(tetrazol-2-yl)propane (12pbtzOH) was synthesized and reacted with Fe(ClO4)2 · 6H2O, giving a 1D coordination polymer {(Fe(12pbtzOH)2(CH3CN)2](ClO4)2 · 2CH3CN}∞ that exhibits a high-spin to low-spin transition (T1/2↓ = T1/2↑ ≅ 104 K). This is an unprecedented example of an iron(II) complex containing Fe(tetrazolyl)4(MeCN)2 cores. [ABSTRACT FROM AUTHOR]

An amino acid containing octanuclear heterometallic {[Mn III3 Ca]2} cluster has been synthesized, alongside a structurally-related trigonal prismatic [Mn III6 Ca]2+ cage. [ABSTRACT FROM AUTHOR]

The electrostatic self-assembly reaction of the [Cu(HL)]2+ cation, where HL = 2-(2-aminoethylamino) ethanol, and the N3− or [Fe(CN)6]4− anion leads to the formation of two coordination polymers with the general formula of [Cu6(μ1,1-N3)6(μ1,3-N3)2(μ1,1,3-N3)2(μ1,1,1,3-N3)2(HL)2]n (1) and {[Cu(HL)]2[Fe(CN)6]·H2O}n (2), respectively. The resulting compounds have been structurally characterized by a single-crystal X-ray diffraction technique. Compound 1 possesses a rare 3D structure. It contains centrosymmetric hexanuclear repeating units, which act as six-connected nodes in the final network and copper(ii) ions are joined together by azide anions with four different types of bridging modes, μ1,1, μ1,1,3, μ1,1,1,3, and μ1,3. The structure of compound 2 is a 2D heterometallic CuII/FeII layer in which the [Cu(HL)]2 nodes and the octahedral [Fe(CN)6]4− linkers are joined by μ2- and unusual μ3-CN bridging modes. Detailed static and dynamic magnetic analyses of 1 reveal a dominant ferromagnetic intracluster interaction and a ferromagnetic 3D ordering transition below Tc = 5 K. The variable temperature magnetic susceptibility measurements of compound 2 show a very weak ferromagnetic coupling between the nearest Cu(ii) ions. Also, EPR spectroscopy of these compounds has been investigated in the solid state. Nanocrystals of compound 2 have also been synthesized by a sonochemical process under different reaction conditions. The results show that the crystallinity degree and uniform distribution of nanosheets are inversely dependent on the irradiation time. [ABSTRACT FROM AUTHOR]

A new family of [3 + 3] hexanuclear 3d–4f complexes [(μ3-CO3){CoIILnIIIL(μ3-OH)(OH2)}3]-(ClO4)·mC2H5OH·nH2O (1–5) [Ln = La (1), Gd (2), Tb (3), Dy (4), and Ho (5)] have been prepared in moderate to high yields (62–78%) following a self-assembly reaction between the ligand 6,6′,6′′-(nitrilotris(methylene))tris-(2-methoxy-4-methylphenol) (H3L), Co(OAc)2·4H2O and the lanthanide ion precursors in the mandatory presence of tetrabutylammonium hydroxide. During the reaction, atmospheric carbon dioxide is fixed in the product molecule as a bridging carbonato ligand which connects all the three lanthanide centers of this molecular assembly through a rare η2:η2:η2–μ3 mode of bridging as revealed from X-ray crystallography. The metal centers in all these compounds, except the GdIII analogue (2), are coupled in antiferromagnetic manner while the nature of coupling in the CoII3GdIII3 complex is ferromagnetic. DFT calculations revealed that this ferromagnetic interaction occurs most likely by the CoII–GdIII superexchange, mediated via the bridging oxygen atoms. Only the CoII–DyIII compound (4) displayed a slow relaxation of the magnetization at a very low temperature as established by AC susceptibility measurements. The data provides an estimation of the activation energy U/kB = 9.2 K and the relaxation time constant τ0 = 1.0 × 10−7 s. [ABSTRACT FROM AUTHOR]

(C3N2H5)2[CoCl4] (ICC) was characterized in a wide temperature range by the single-crystal X-ray diffraction method. Differential scanning calorimetry revealed two structural phase transitions: continuous at 245.5 K (from phase I to II) and a discontinuous one at 234/237 K (cooling/heating) (II → III). ICC adopts monoclinic space groups C2/c and P21/c in phase (I) and (III), respectively. The intermediate phase (II) appears to be incommensurately modulated. Dynamic properties of polycrystalline ICC were studied by means of dielectric spectroscopy and proton magnetic resonance (¹H NMR). The presence of a low frequency dielectric relaxation process in phase III reflects libration motion of the imidazolium cations. The temperature dependence of the ¹H spin-lattice relaxation time indicated two motional processes with similar activation energies that are by about an order of magnitude smaller than the activation energy obtained from dielectric studies. There are no abrupt changes in the ¹H relaxation time at the phase transitions indicating that the dynamics of the imidazolium rings gradually varies with temperature; that is, it does not change suddenly at the phase transition. Negative values of the Weiss constant and the intermolecular exchange parameter were obtained, confirming the presence of a weak antiferromagnetic interaction between the nearest cobalt centers. Moreover, the magnitude of zero field splitting was determined. The AC susceptibility measurements show that a slow magnetic relaxation is induced by small external magnetic field. [ABSTRACT FROM AUTHOR]

The first representatives of pentanuclear carbacylamidophosphate complexes of composition Ln 5 L 6 (μ-L) 4 (μ 3 -OH) 4 (μ 4 -OH) (Ln III = Eu (1), Gd (2), Tb (3), L − = dimethylbenzoylamidophosphate ion [C 6 H 5 C(O)–N–P(O)(OCH 3 ) 2 ] − ) were obtained. The single crystal X-ray analysis revealed that polynuclear core of 1 contains five europium ions, connected by the μ 3 - and μ 4 -hydroxo groups and carbacylamidophosphate ligands. Compounds 1 – 3 were found to be isostructural. Temperature dependencies of magnetic susceptibility ( χ M ) of the compounds 1 and 2 could be explained by spin-orbit coupling of Eu III ions or antiferromagnetic exchange interactions of four Gd III ions located in the base of Gd 5 pyramid, respectively. In the case of 3, the value of χ M increases with temperature decreasing from 300 K to 50 K, and then falls down during temperature decrease till 2 K. Such behavior can be explained by comparable contribution of spin-orbit coupling and exchange interactions. No signs of single-molecule magnet behavior for 3 were found at 2 K. Phosphorescence, emission and excitation spectra at 298 K and 77 K for the complexes were measured, as well as luminescence decay times were determined. The compounds 1 and 3 showed intense luminescence with decay time at 298 K equal to 0.66 and 1.44 ms respectively. Intrinsic quantum yield for 1 determined from its emission spectrum was found to be 25%. [ABSTRACT FROM AUTHOR]

2D structurally related iron(ii) coordination networks {[Fe(hbtz)2(RCN)2](ClO4)2}∞ featuring, besides tetrazol-2-yl rings in the first coordination sphere, also axially coordinated propionitrile or allyl cyanide molecules (R = C3H5–, 1; R = C2H5–, 2) were synthesized. Thermally induced spin crossover (SCO) in 1 takes place in two poorly resolved stages (T11/2↓ = T11/2↑ = 198 K, T21/2↓ = 170 K, T21/2↑ = 171 K) whereas in 2 complete and relatively gradual one step SCO (T1/2↓ = T1/2↑ = 160 K) occurs. Diversification of the SCO properties of the complexes originates from the ability of coordinated allyl cyanide in 1 to undergo conformational alterations, which is not observed for propionitrile molecules in 2. SCO in 1 is accompanied by a non-monotonic change of the contribution of allyl cyanide conformers which is related to reconstruction of the network of intermolecular contacts established between polymeric layers. The coordination network 1 exhibits extraordinary elasticity and in the second stage SCO, accompanied by conformational changes of allyl cyanide, triggers a crystallographic phase transition which leads to the formation of a superstructure. What is important, the formation of the superstructure is not caused by long range ordering of HS and LS iron(ii) ions. The structural alteration is associated with corrugation of the polymeric skeleton and disappearance of nitrile disorder. Irradiation of a single crystal of 1 at 15 K with laser light (520 nm) allowed producing a novel low temperature HS phase of 1 in which, contrary to the high temperature HS phase, disordering of anion and allyl cyanide molecules is not observed and the corrugated nature of the polymeric layer, characteristic of the LS phase, is preserved. [ABSTRACT FROM AUTHOR]

Eu III and Tb III complexes with a benzoate and a tripod N 7 ligand, [Ln III (H 3 L)benzoate](ClO 4 ) 2 ·H 2 O·2MeOH (Ln III = Eu III and Tb III ; H 3 L = tris[2-(((imidazol-4-yl)methylidene)amino)ethyl]amine), were synthesized and crystallized into an isomorphous structure. Each Ln III ion is coordinated by one tripod ligand and one benzoate, resulting in a nona-coordinated capped square antiprism geometry. The solid-state emission spectra displayed sharp bands of the f–f transitions. Tb III complex exhibits a magnetic anisotropy and the ac susceptibility measurements exhibited an out-of-phase signal under 1000 G bias field, indicative slow relaxation of magnetization. [ABSTRACT FROM AUTHOR]

The role of the covalent connections of iron(II) spin-crossover centres in the transmission of perturbation produced by the HS ↔ LS transition has been investigated for the new 3D coordination polymer {[Fe(qbtr)3](ClO4)2}∞ [qbtr = 1,5-di(1,2,3-triazol-1-yl)pentane]. In this complex, a sequence of structural phase transitions occurs. A Ph1 (HS,HS) → Ph2 (HS,HS,HS) transition precedes spin crossover and is associated with an increased number of crystallographically unique iron(II) ions, whereas the change of spin state Ph2 (HS,HS,HS) → Ph3 (HS,LS) triggers another structural phase transition accompanied by a reduction in the number of the unique iron(II) sites. Iron(II) ions occupying two crystallographically unique Fe1 and Fe2 sites form the nodes of a coordination network in the Ph1 phase. The characteristic feature of the polymeric skeleton is the presence of three kinds of ligand bridges tethering the Fe1 ···Fe1, Fe1 ···Fe2 and Fe2 ···Fe2 sites. The ligand linkages differ from each other in rigidity, and the diversification of their properties arises from the susceptibility of the ligand molecules to undergo conformational changes. The high rigidity of the bridge established in the Ph2 phase between iron(II) ions occupying Fe2 sites allows for the propagation of the perturbation produced by the HS (Fe2) → LS (Fe2) transition through the crystal lattice. A strong compression along the Fe2 ···Fe2 bridging direction occurs. In contrast, the ligand molecules that form the two remaining types of bridge are disordered in the Ph2 phase and the change of spin state for the iron(II) ions occupying Fe2 sites induces their ordering, which leads to an increase in the separation between donor atoms. In effect, perturbation cannot be effectively transmitted along the Fe1 ···Fe1 and Fe1 ···Fe2 linkage directions because the 'elongation' of conformationally labile ligand molecules compensates for the shortening of the Fe2-N bond lengths. [ABSTRACT FROM AUTHOR]

Novel tripodal ligand 1,1',l"-tris(tetrazol- I-ylnsethyl)methane (IIItz) and products of its reactions with perchlorate as well as with tetrafluoroborate salts of iron(II) are presented The isostructural complexes, [Fe(IIItz)2](C104)2 and [Fe(IIItv)2](BF4)2, were isolated as two-dimen- I sional (2D) coordination networks revealing a honeycomb-like pattern with cages occupied by disordered anions. IIItz molecules act as a tridentate ligand bridging three adjacent Fe(II) ions, and the nitrogen N4 atom of six tetrazole rings (tz) is placed in octahedron vertices of FeN6 chromophores. The complexes, crystallizing in the P3 space group, were characterized by variable-temperature single-crystal X-ray diffraction and variable-temperature magnetic susceptibility measurements. Variable-temperature magnetic susceptibility measurements show that both systems undergo abrupt and complete spin transition with T↑½ =T↓½ = 176 K for perchlorate and T↑½ = 193.8 and T↓½ = 192.8 K for the tetrafluoroborate analogue. Change of spin state in both complexes is accompanied by a thermochromic effect. The HS→LS transition in [Fe(IIItz)2](C104)2 involves shortening of the Fe-N4 bond lengths from 2.171(2) A (293 K) to 2.002(1) A (100 K). In [Fe(IIItz)2](BF4)2, lowering of temperature from 293 to 100 K is accompanied by shortening of the Fe-N4 distances from 2.179(2) to 1.987(2) A, respectively. Perchlorate in [Fe(IIItz2](C104)2 or tetrafluoroborate anions in [Fe(IIItz)2](BF4)2 are engaged in the formation of intermolecular contacts within as well as with the neighboring 2D layer. [ABSTRACT FROM AUTHOR]

In a 1D network of ¹8{[Fe(CH3CN)4(pyrazine)](ClO4)2}, the presence of four neutral nitrile molecules besides the pyrazine donors in the first coordination sphere of iron(II) allows one to achieve a ligand field strength appropriate for the "spin-crossover" occurrence. [ABSTRACT FROM AUTHOR]

• Study of fructan structure and properties by using several methods. • Separation of low and high-molecular-weight levan with ethanol fractionation. • Low-molecular-weight levan with antioxidant properties is non-toxic for human cells. Levan is a polysaccharide composed of fructose units with β-2,6-glycoside bonds. Microorganisms synthesize levan by levansucrase as a mixture of low- and high-molecular-weight fractions. Due to its properties, it has a wide range of applications in cosmetics, pharmaceuticals, food and medicine; it appears that the molecular weight of levan might impact its industrial use. To obtain one fraction of levan after biotransformation, ethanol precipitation with an increasing volume of alcohol was conducted. This precipitation process was also optimized. Several types of analyses were used. Low-molecular-weight levan was evaluated for toxicity in a normal human dermal fibroblast cell line and hemolytic potential on human erythrocytes. Levan was found to be non-cytotoxic and non-hemolytic in concentrations ranging from 0.01 to 1.00 mg/ml. Moreover, levan demonstrated antioxidant potential expressed as an ability to inhibit of oil/water emulsion oxidation and DPPH radical scavenging. [ABSTRACT FROM AUTHOR]

Polycrystalline compounds of the Zn x Mn y Cr z Se 4 system (x + y + z ≈ 3) crystallizing in a cubic spinel structure were successfully synthesized in the concentration range of x = 0.11 ÷ 0.46 using the ceramic method. The influence of manganese on microstructure, magnetic, thermal and electronic properties was investigated. X-ray studies confirmed that the spinel phase forms throughout the entire range (x = 0.1 ÷ 0.5). The results of magnetic measurements showed that the studied compounds are antiferromagnets with the Néel temperature of T N = 12 ÷ 25 K and the Curie-Weiss temperature increasing from θ = 87 K for x = 0.11 to θ = 110 K for x = 0.46. Below T N , the magnetic field dependence of magnetization shows two peculiarities at critical fields H c1 (connected with metamagnetic threshold accompanied with transition from a helical to a conical phase) and H c2 (where the conical magnetic structure transforms into a ferromagnetic phase). The values of H c1 remain almost constant while the values of H c2 shift into lower magnetic fields as the Mn content increases. These effects are interpreted in terms of the superexchange integrals for the first two coordination spheres including spin defects and non-stoichiometry. The XPS study is consistent with FPLO calculation and discerned Mn2+ charge states. The effects of different concentrations of Zn, Mn and Cr have been demonstrated by XPS experimental results. DSC/TG analysis indicates that the presence of Mn ions in the ZnCr 2 Se 4 crystal lattice affects the stability and resistance of the doped compounds in comparison with the pure ZnCr 2 Se 4. Image 10811 • The semiconducting polycrystalline Zn x Mn y Cr z Se 4 – compounds were obtained using ceramic method. • The magnetic parameters increase with increasing Mn concentration. • Magnetic studies indicated increase of the ferromagnetic component of the bond frustrated system Zn x Mn y Cr z Se 4. • The XPS study is consistent with FPLO calculation and discerned Mn2+ charge states. • The DSC/TG measurements confirmed the thermal stability of obtained Zn x Mn y Cr z Se 4 – compounds. [ABSTRACT FROM AUTHOR]