Synthesis of Gd-DTPA Carborane-Containing Compound and Its Immobilization on Iron Oxide Nanoparticles for Potential Application in Neutron Capture Therapy.

Cancer is one of the leading causes of global mortality, and its incidence is increasing annually. Neutron capture therapy (NCT) is a unique anticancer modality capable of selectively eliminating tumor cells within normal tissues. The development of accelerator-based, clinically mountable neutron sources has stimulated a worldwide search for new, more effective compounds for NCT. We synthesized magnetic iron oxide nanoparticles (NPs) that concurrently incorporate boron and gadolinium, potentially enhancing the effectiveness of NCT. These magnetic nanoparticles underwent sequential modifications through silane polycondensation and allylamine graft polymerization, enabling the creation of functional amino groups on their surface. Characterization was performed using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive X-ray (EDX), dynamic light scattering (DLS), thermal gravimetric analysis (TGA), and transmission electron microscopy (TEM). ICP-AES measurements indicated that boron (B) content in the NPs reached 3.56 ppm/mg, while gadolinium (Gd) averaged 0.26 ppm/mg. Gadolinium desorption was observed within 4 h, with a peak rate of 61.74%. The biocompatibility of the NPs was confirmed through their relatively low cytotoxicity and sufficient cellular tolerability. Using NPs at non-toxic concentrations, we obtained B accumulation of up to 5.724 × 1010 atoms per cell, sufficient for successful NCT. Although limited by its content in the NP composition, the Gd amount may also contribute to NCT along with its diagnostic properties. Further development of the NPs is ongoing, focusing on increasing the boron and gadolinium content and creating active tumor targeting.

Preparation and application of stimuli-responsive PET TeMs: RAFT graft block copolymerisation of styrene and acrylic acid for the separation of water-oil emulsions.

Stimuli-responsive membranes play an important role in the fields of biomedicine, food and chemical industries, and environmental applications, including separation of water-oil emulsions. In this study, we present a method to fabricate pH-sensitive membranes using UV-initiated RAFT graft copolymerization of styrene (ST) and acrylic acid (AA) on poly(ethylene terephthalate) (PET) track-etched membranes (TeMs). The optimization of polymerization conditions led to successful grafting of polystyrene (PS) and poly(acrylic acid) (PAA) onto PET TeMs, resulting in membranes with stable hydrophobicity and pH change responsiveness. The membranes show a contact angle of 65° in basic environments (pH 9) and 97° in acidic environments (pH 2). The membranes were characterized by atomic force microscopy (AFM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), thermogravimetric analyses (TGA), Fourier transform infrared spectroscopy (FTIR), contact angle (CA) methods. The PET TeMs-g-PS-g-PAA exhibited good performance in separating water-oil emulsions with a high efficiency of more than 90% and flux for direct chloroform-water 2500 L m-2 h-1 and reverse emulsions of benzene-water 1700 L m-2 h-1. This method of preparing stimuli-responsive membranes with controlled wettability and responsiveness to environmental pH provides versatility in their use in separating two types of emulsions: direct and reverse.

Effect of hydrophobized PET TeMs membrane pore-size on saline water treatment by direct contact membrane distillation.

This paper describes the desalination process by membrane distillation (MD) using track-etched membranes (TeMs). Hydrophobic track-etched membranes based on poly(ethylene terephthalate) (PET TeMs) with pore diameters from 700 to 1300 nm were prepared by UV-initiated graft polymerization of lauryl methacrylate (LMA) inside the nanochannels. Modified PET TeMs were investigated by Fourier transform infrared (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and contact wetting angle (CA) measurements. Hydrophobic PET TeMs were tested for treating saline solutions of different concentrations by the direct contact membrane distillation (DCMD) method. The influence of membrane pore diameter and salt solution concentration on the water flux and rejection degree were investigated. Membranes with CA 94 ± 4° were tested in the direct contact membrane distillation (DCMD) of 7.5-30 g L-1 saline solution. Hydrophobic membranes with large pore sizes showed water fluxes in the range of 1.88 to 11.70 kg m-2 h-1 with salt rejection values of up to 91.4%.

Potassium and Cesium Fluorinated ß-Diketonates: Effect of a Cation and Terminal Substituent on Structural and Thermal Properties.

As potential precursors for the synthesis of fluoroperovskites, a family of heavy alkali metal (MI = K, Cs) fluorinated ß-diketonates were prepared and characterized by elemental analysis, IR, and powder-XRD. The crystal structures of the new six complexes, MI(ß-dikF)(H2O)X, X = 0 or 1, were also determined. The structural diversity of this poorly explored class of complexes was discussed, including the preferred types of cation polyhedra and the ligand coordination modes, and the thermal properties of the metal ß-diketonates were studied by TG-DTA in an inert (He) atmosphere. The data obtained allowed us to reveal the effect of the metal cation and the terminal substituent on the structural and thermal features of this family of complexes.

Stimuli-Responsive Track-Etched Membranes for Separation of Water-Oil Emulsions.

In this work, we have developed a method for the preparation of pH-responsive track-etched membranes (TeMs) based on poly(ethylene terephthalate) (PET) with pore diameters of 2.0 ± 0.1 µm of cylindrical shape by RAFT block copolymerization of styrene (ST) and 4-vinylpyridine (4-VP) to be used in the separation of water-oil emulsions. The influence of the monomer concentration (1-4 vol%), the molar ratio of RAFT agent: initiator (1:2-1:100) and the grafting time (30-120 min) on the contact angle (CA) was studied. The optimal conditions for ST and 4-VP grafting were found. The obtained membranes showed pH-responsive properties: at pH 7-9, the membrane was hydrophobic with a CA of 95°; at pH 2, the CA decreased to 52°, which was due to the protonated grafted layer of poly-4-vinylpyridine (P4VP), which had an isoelectric point of pI = 3.2. The obtained membranes with controlled hydrophobic-hydrophilic properties were tested by separating the direct and reverse "oil-water" emulsions. The stability of the hydrophobic membrane was studied for 8 cycles. The degree of purification was in the range of 95-100%.

Structure and Properties of Heterometallics Based on Lanthanides and Transition Metals with Methoxy-ß-Diketonates.

The possibility of obtaining volatile polynuclear heterometallic complexes containing lanthanides and transition metals bound by methoxy-ß-diketonates was studied. New compounds were prepared by cocrystallization of monometallic complexes from organic solvents. Ln(tmhd)3 were used as initial monometallic complexes (Ln = La, Pr, Sm, Gd, Tb, Dy, Lu; tmhd = 2,2,6,6-tetramethylheptane-3,5-dionate) in combination with TML2 in various ratios (TM = Cu, Co, Ni, Mn; L: L1 = 1,1,1-trifluoro-5,5-dimethoxypentane-2,4-dionate, L2 = 1,1,1-trifluoro-5,5-dimethoxy-hexane-2,4-dionate, L3 = 1,1,1-trifluoro-5-methoxy-5-methylhexane-2,4-dionate). Heterometallic complexes of the composition [(LnL2tmhd)2TM(tmhd)2] were isolated for light lanthanides Ln= La, Pr, Sm, Gd, and L= L1 or L2. By single crystal XRD, it has been established that heterometallic compounds containing La, Pr, Cu, Co, and Ni are isostructural linear coordination polymers of alternating mononuclear transition metal complexes and binuclear heteroleptic lanthanide complexes, connected by donor-acceptor interactions between oxygen atoms of the methoxy groups and transition metal atoms. A comparison of powder XRD patterns has shown that all heterometallic complexes obtained are isostructural. Havier lanthanides Ln = Tb, Dy, Lu did not form heterometallics. Instead, homometallic complexes Ln(L3)3 were identified for Ln = Dy, Lu as well as for Ln = La. The thermal properties of the complexes were investigated by TG-DTA and vacuum sublimation tests. The heterometallic complexes were found to be not volatile and decomposed under heating to produce inorganic composites of TM oxides and Ln fluorides. In contrast, Ln(L3)3 is volatile and may be sublimed in a vacuum. Results of magnetic measurements are discussed for several heterometallic and homometallic complexes.

Graft Polymerization of Stearyl Methacrylate on PET Track-Etched Membranes for Oil-Water Separation.

In this article, results of PET track-etched membranes (PET TeMs) hydrophobized by photo-induced graft polymerization of stearyl methacrylate (SM) inside the pores were presented. The effects of monomer concentration, time of irradiation and the nature of the solvent on the degree of grafting and membrane morphology were investigated. The PET TeMs with pore diameters ranging from 350 nm (pore density of 1 × 108 pore/cm2) to 3.05 µm (pore density of 1 × 106 pore/cm2) were hydrophobized and tested for oil-water separation by using hexadecane-water and chloroform-water emulsions. Studies have shown high separation performance for membranes (up to 1100 mL/m2·s) with large pore diameters while achieving a high degree of purification.

Preparation of Hydrophobic PET Track-Etched Membranes for Separation of Oil-Water Emulsion.

The paper describes the separation of an oil-water emulsion by filtration using poly(ethylene terephthalate) track-etched membranes (PET TeMs) with regular pore geometry and narrow pore size distribution. PET TeMs were modified with trichloro(octyl)silane to increase their hydrophobic properties. Conditions for the modification of PET TeMs with trichloro(octyl)silane were investigated. The results of changes in the pore diameters and the contact angle depend on the concentration of trichloro(octyl)silane and the soaking time are presented. The obtained samples were characterized by FTIR, AFM, SEM-EDX and gas-permeability test. Chloroform-water and cetane-water emulsions have been used as a test liquid for oil-water separation.

Recent Progress in the Membrane Distillation and Impact of Track-Etched Membranes.

Membrane distillation (MD) is a rapidly developing field of research and finds applications in desalination of water, purification from nonvolatile substances, and concentration of various solutions. This review presents data from recent studies on the MD process, MD configuration, the type of membranes and membrane hydrophobization. Particular importance has been placed on the methods of hydrophobization and the use of track-etched membranes (TeMs) in the MD process. Hydrophobic TeMs based on poly(ethylene terephthalate) (PET), poly(vinylidene fluoride) (PVDF) and polycarbonate (PC) have been applied in the purification of water from salts and pesticides, as well as in the concentration of low-level liquid radioactive waste (LLLRW). Such membranes are characterized by a narrow pore size distribution, precise values of the number of pores per unit area and narrow thickness. These properties of membranes allow them to be used for more accurate water purification and as model membranes used to test theoretical models (for instance LEP prediction).

Boron and Gadolinium Loaded Fe3O4 Nanocarriers for Potential Application in Neutron Capture Therapy.

In this article, a novel method of simultaneous carborane- and gadolinium-containing compounds as efficient agents for neutron capture therapy (NCT) delivery via magnetic nanocarriers is presented. The presence of both Gd and B increases the efficiency of NCT and using nanocarriers enhances selectivity. These factors make NCT not only efficient, but also safe. Superparamagnetic Fe3O4 nanoparticles were treated with silane and then the polyelectrolytic layer was formed for further immobilization of NCT agents. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive X-ray (EDX), ultraviolet-visible (UV-Vis) and Mössbauer spectroscopies, dynamic light scattering (DLS), scanning electron microscopy (SEM), vibrating-sample magnetometry (VSM) were applied for the characterization of the chemical and element composition, structure, morphology and magnetic properties of nanocarriers. The cytotoxicity effect was evaluated on different cell lines: BxPC-3, PC-3 MCF-7, HepG2 and L929, human skin fibroblasts as normal cells. average size of nanoparticles is 110 nm; magnetization at 1T and coercivity is 43.1 emu/g and 8.1, respectively; the amount of B is 0.077 mg/g and the amount of Gd is 0.632 mg/g. Successful immobilization of NCT agents, their low cytotoxicity against normal cells and selective cytotoxicity against cancer cells as well as the superparamagnetic properties of nanocarriers were confirmed by analyses above.

Unexpected Polymorphism in Bromoantimonate(III) Complexes and Its Effect on Optical Properties.

Reactions of [SbBr6]3- containing HBr solutions with bromide salts of 1,1'-(1,2-ethanediyl)bis(pyridine) (PyC22+) or 1,1'-(1,2-ethanediyl)bis(3,5-dimethylpyridine) (3,5-MePyC22+) initially result in the formation of the deep orange complexes Cat[SbBr5] (1 and 2), featuring unusual Sb···Br interactions in the solid state. In the mother liquor, 1 transforms into discrete binuclear (C2Py)2[Sb2Br10], which demonstrates polymorphism (triclinic 3 and monoclinic 4), while 2 transforms into polymeric (3,5-MePy){[SbBr4]} (5). DFT calculations reveal that the system of noncovalent Sb···Br contacts may be responsible for the appearance of the observed optical properties (unusual deep orange coloring).

Modification of PET Ion-Track Membranes by Silica Nanoparticles for Direct Contact Membrane Distillation of Salt Solutions.

The paper describes desalination by membrane distillation (MD) using ion-track membranes. Poly(ethylene terephthalate) (PET) ion-track membranes were hydrophobized by the immobilization of hydrophobic vinyl-silica nanoparticles (Si NPs). Si NPs were synthesized by the sol-gel method, and the addition of the surfactant led to the formation of NPs with average size of 40 nm. The thermal initiator fixed to the surface of membranes allowed attachment of triethoxyvinyl silane Si NPs at the membrane surface. To further increase hydrophobicity, ethoxy groups were fluorinated. The morphology and chemical structure of prepared membranes were characterized by SEM, FTIR, XPS spectroscopy, and a gas permeability test. Hydrophobic properties were evaluated by contact angle (CA) and liquid entry pressure (LEP) measurements. Membranes with CA 125-143° were tested in direct contact membrane distillation (DCMD) of 30 g/L saline solution. Membranes showed water fluxes from 2.2 to 15.4 kg/(m2·h) with salt rejection values of 93-99%.

Functionalization of PET Track-Etched Membranes by UV-Induced Graft (co)Polymerization for Detection of Heavy Metal Ions in Water.

Nowadays, water quality monitoring is an essential task since environmental contamination and human exposure to heavy metals increased. Sensors that are able to detect ever lower concentrations of heavy metal ions with greater accuracy and speed are needed to effectively monitor water quality and prevent poisoning. This article shows studies of the modification of flexible track-etched membranes as the basis for the sensor with various polymers and their influence on the accuracy of detection of copper, cadmium, and lead ions in water. We report the UV-induced graft (co)polymerization of acrylic acid (AA) and 4-vinylpyridine (4-VPy) on poly(ethylene terephthalate) track-etched membrane (PET TeMs) and use them after platinum layer sputtering in square wave anodic stripping voltammetry (SW-ASV) for detection of Cu2+, Cd2+, and Pb2+. Optimal conditions leading to functionalization of the surface and retention of the pore structure were found. Modified membranes were characterized by SEM, FTIR, X-ray photoelectron spectroscopy (XPS) and colorimetric analysis. The dependence of the modification method on the sensitivity of the sensor was shown. Membrane modified with polyacrylic acid (PET TeMs-g-PAA), poly(4-vinylpyridine) (PET TeMs-g-P4VPy), and their copolymer (PET TeMs-g-P4VPy/PAA) with average grafting yield of 3% have been found to be sensitive to µg/L concentration of copper, lead, and cadmium ions. Limits of detection (LOD) for sensors based on PET TeMs-g-PAA are 2.22, 1.05, and 2.53 µg/L for Cu2+, Pb2+, and Cd2+, respectively. LODs for sensors based on PET TeMs-g-P4VPy are 5.23 µg/L (Cu2+), 1.78 µg/L (Pb2+), and 3.64 µg/L (Cd2+) µg/L. PET TeMs-g-P4VPy/PAA electrodes are found to be sensitive with LODs of 0.74 µg/L(Cu2+), 1.13 µg/L (Pb2+), and 2.07 µg/L(Cd2+). Thus, it was shown that the modification of membranes by copolymers with carboxylic and amino groups leads to more accurate detection of heavy metal ions, associated with the formation of more stable complexes.

Fe3O4 Nanoparticles for Complex Targeted Delivery and Boron Neutron Capture Therapy.

Magnetic Fe3O4 nanoparticles (NPs) and their surface modification with therapeutic substances are of great interest, especially drug delivery for cancer therapy, including boron-neutron capture therapy (BNCT). In this paper, we present the results of boron-rich compound (carborane borate) attachment to previously aminated by (3-aminopropyl)-trimethoxysilane (APTMS) iron oxide NPs. Fourier transform infrared spectroscopy with Attenuated total reflectance accessory (ATR-FTIR) and energy-dispersive X-ray analysis confirmed the change of the element content of NPs after modification and formation of new bonds between Fe3O4 NPs and the attached molecules. Transmission (TEM) and scanning electron microscopy (SEM) showed Fe3O4 NPs' average size of 18.9 nm. Phase parameters were studied by powder X-ray diffraction (XRD), and the magnetic behavior of Fe3O4 NPs was elucidated by Mössbauer spectroscopy. The colloidal and chemical stability of NPs was studied using simulated body fluid (phosphate buffer-PBS). Modified NPs have shown excellent stability in PBS (pH = 7.4), characterized by XRD, Mössbauer spectroscopy, and dynamic light scattering (DLS). Biocompatibility was evaluated in-vitro using cultured mouse embryonic fibroblasts (MEFs). The results show us an increasing of IC50 from 0.110 mg/mL for Fe3O4 NPs to 0.405 mg/mL for Fe3O4-Carborane NPs. The obtained data confirm the biocompatibility and stability of synthesized NPs and the potential to use them in BNCT.

A Novel Family of Polyiodo-Bromoantimonate(III) Complexes: Cation-Driven Self-Assembly of Photoconductive Metal-Polyhalide Frameworks.

In the presence of different cations, reactions of [SbBr6 ]3- and I2 result in a new family of diverse supramolecular 1D polyiodide-bromoantimonate networks. The coordination number of Sb, as well as geometry of assembling {Ix }n- polyhalide units, can vary, resulting in unprecedented structural types. The nature of I⋅⋅⋅Br interactions was studied by DFT calculations; estimated energy values are 1.6-6.9 kcal mol-1 . Some of the compounds showed strong photoconductivity in thin films, suggesting multiple feasible applications in optoelectronics and solar energy conversion.

Multifunctional Metal-Organic Frameworks Based on Redox-Active Rhenium Octahedral Clusters.

The redox-active rhenium octahedral cluster unit [Re6Se8(CN)6]4- was combined with Gd3+ ions and dicarboxylate linkers in novel types of metal-organic frameworks (MOFs) that display a set of functional properties. The hydrolytically stable complexes [{Gd(H2O)3}2(L)Re6Se8(CN)6]·nH2O (1, L = furan-2,5-dicarboxylate, fdc; 2, L = thiophene-2,5-dicarboxylate, tdc) exhibit a 3D framework of trigonal symmetry where 1D chains of [{Gd(H2O)3}2(L)]4+ are connected by [Re6Se8(CN)6]4- clusters. Frameworks contain spacious channels filled with H2O. Solvent molecules can be easily removed under vacuum to produce permanently porous solids with high volumetric CO2 uptake and remarkable CO2/N2 selectivity at room temperature. The frameworks demonstrate an ability for reversible redox transformations of the cluster fragment. The orange powders of compounds 1 and 2 react with Br2, yielding dark-green powders of [{Gd(H2O)3}2(L)Re6Se8(CN)6]Br·nH2O (3, L = fdc; 4, L = tdc). Compounds 3 and 4 are isostructural with 1 and 2 and also have permanently porous frameworks but display different optical, magnetic, and sorption properties. In particular, oxidation of the cluster fragment "switches off" its luminescence in the red region, and the incorporation of Br- leads to a decrease of the solvent-accessible volume in the channels of 3 and 4. Finally, the green powders of 3 and 4 can be reduced back to the orange powders of 1 and 2 by reaction with hydrazine, thus displaying a rare ability for fully reversible chemical redox transitions. Compounds 1-4 are mentioned as a new class of redox-active cluster-based MOFs with potential usage as multifunctional materials for gas separation and chemical contamination sensors.

Volatile heterometallics: structural diversity of Pd-Pb ß-diketonates and correlation with thermal properties.

Volatile heterobimetallics based on Pb(ii) hexafluoroacetylacetonate as a host material and a range of Pd(ii) complexes containing both various donor atoms and terminal substituents in the ß-diketonate ligand have been studied to trace the influence of the nature of the initial monometallic complexes on the structure, composition and thermal properties of heterobimetallic compounds. The structural variety and stoichiometry of the heterobimetallic compounds are caused by various combinations of the competing donor-acceptor interactions between the constituting monometallic moieties. The major structure forming factor is the metallophilic interaction between Pd and Pb atoms resulting in polynuclear structures with a specific topology. The structural motif (discrete or polymeric) for the compounds significantly depends on the structure and composition of the initial monometallic complexes. The approach for explaining and predicting the thermal stability of these compounds is proposed by using their structural data and the results of quantum chemistry calculations.

Ln(iii) complexes (Ln = Eu, Gd, Tb, Dy) with a chiral ligand containing 1,10-phenanthroline and (-)-menthol fragments: synthesis, structure, magnetic properties and photoluminescence.

A series of lanthanide(iii) complexes based on the new chiral ligand L, which contains 1,10-phenanthroline and (-)-menthol fragments, namely [LnL2(NO3)3] (Ln = Eu (1), Gd (2), Tb (3), Dy (4)), have been synthesized and structurally characterized. Complexes 1-4 are isostructural and crystallize in the non-centrosymmetric space group P41212. The mononuclear complexes comprise a 10-coordinate Ln3+ ion with two bidentate N,N-donor ligands (L) and three bidentate chelating nitrate groups. The magnetic properties of complexes 1-4 are determined mainly by the Ln3+ ions. In the case of complexes 3 and 4, significant anisotropy results in nonlinear field dependences of magnetization at low temperature. Complexes 1, 3 and 4 exhibit metal-centered red (Eu3+), green (Tb3+) and yellow (Dy3+) luminescence, respectively, whereas complex 2 displays blue ligand-based luminescence in the solid state at room temperature. The luminescence quantum yield for the solid samples increases in the order 4 < 2 ≈ 3 < 1. The europium(iii) complex shows long luminescence lifetimes (up to 1750 µs) and a very high quantum yield (φf = 0.87); these make this compound promising for application in sensing and optoelectronics.

Prototypical iron(ii) complex with 4-amino-1,2,4-triazole reinvestigated: an unexpected impact of water on spin transition.

The magnetic and thermodynamic properties of the prototypical 1D polymeric complex Fe(ATrz)3(NO3)2·H2O (ATrz = 4-amino-1,2,4-triazole) were reinvestigated to gain an insight into the impact of water molecules on the spin transition. Variations in the outerspheric water molecule content in the complex induce drastic and unpredictable changes in its spin crossover regimes. Under vacuum the complex loses water molecules and shows a wide (ca. 30 K) and reproducible hysteresis loop, Tc↑ = 337-345 K and Tc↓ = 316-313 K. In sealed ampoules the complex Fe(ATrz)3(NO3)2·H2O shows a narrow hysteresis (ca. 1-4 K), Tc↑ = 326-329 K and Tc↓ = 326-324 K. After adsorption of water the complex Fe(ATrz)3(NO3)2·nH2O (n = 1.25-1.6) demonstrates a narrow two-step spin transition. In all these cases the kinetics of the LS → HS and HS → LS transitions has decelerating non-cooperative character. For the system Fe(ATrz)3(NO3)2·nH2O (n = 3.6-16.6) wide hysteresis (ca. 5-20 K) re-appears near room temperature (Tc↑ = 319-321 K and Tc↓ = 300-315 K). Surprisingly, the kinetics of the HS → LS spin transition for the systems with high water content switches from decelerating to sigmoidal (cooperative). The activation energy of the LS → HS transition was estimated for the first time for iron(ii) spin crossover complexes with 1,2,4-triazoles (ca. 1000-2000 kJ mol-1). The systems Fe(ATrz)3(NO3)2 and Fe(ATrz)3(NO3)2·nH2O show compensation effects (ΔH - ΔS, ln A - Ea). A correlation between the Tonset↑, the ΔH values and the water content in the complex is observed: the highest ΔH values (27-29 kJ mol-1) and the lowest Tonset↑ values (317-320 K) correspond to the samples with high water content, whereas the lowest ΔH values (19-23 kJ mol-1) and the highest Tonset↑ values (337-345 K) correspond to water-free samples, Fe(ATrz)3(NO3)2. Our results provide the first experimental evidence that the presence of water (and even air humidity) produces dramatic changes in the spin crossover behavior of the prototypical 1D polymeric complex Fe(ATrz)3(NO3)2·H2O (ATrz = 4-amino-1,2,4-triazole).

A mononuclear iron(II) complex: cooperativity, kinetics and activation energy of the solvent-dependent spin transition.

The system [FeL2](BF4)2 (1)-EtOH-H2O (L is 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-(pyridin-2-yl)-6-methylpyrimidine) shows a complicated balance between the relative stabilities of solvatomorphs and polymorphs of the complex [FeL2](BF4)2. New solvatomorphs, 1(LS)·EtOH·H2O and ß-1(LS)·xH2O, were isolated in this system. They were converted into four daughter phases, 1(A/LS), 1(D/LS), 1(E/LS)·yEtOH·zH2O and 1(F/LS). On thermal cycling in sealed ampoules, the phases 1(LS)·EtOH·H2O and ß-1(LS)·xH2O transform into the anhydrous phase 1(A/LS). The hysteresis loop width for the (A/LS) ↔ (A/HS) spin transition depends on the water and ethanol contents in the ampoule and varies from ca. 30 K up to 145 K. The reproducible hysteresis loop of 145 K is the widest ever reported one for a spin crossover complex. The phase 1(A/LS) combines the outstanding spin crossover properties with thermal robustness allowing for multiple cycling in sealed ampoules without degradation. The kinetics of the 1(A/LS) → 1(A/HS) transition is sigmoidal which is indicative of strong cooperative interactions. The cooperativity of the 1(A/LS) → 1(A/HS) transition is related to the formation of a 2D supramolecular structure of the phase 1(A/LS). The activation energy for the spin transition is very high (hundreds of kJ mol(-1)). The kinetics of the 1(A/HS) → 1(A/LS) transition can either be sigmoidal or exponential depending on the water and ethanol contents in the ampoule. The phases 1(D/LS) and 1(F/LS) show gradual crossover, whereas the phase 1(E/LS)·yEtOH·yH2O shows a reversible hysteretic transition associated with the solvent molecule release and uptake.