Effect of External Pressure on the Metal–Insulator Transition of the Organic Quasi-Two-Dimensional Metal K-(BEDT-TTF)2Hg(SCN)2Br

The metal–insulator transition in the organic quasi-two-dimensional metal κ-(BEDT-TTF)2Hg(SCN)2Br at TMI ≈ 90 K has been investigated. The crystal structure changes during this transition from monoclinic above TMI to triclinic below TMI. A theoretical study suggested that this phase transition should be of the metal-to-metal type and brings about a substantial change of the Fermi surface. Apparently, the electronic system in the triclinic phase is unstable toward a Mott insulating state, leading to the growth of the resistance when the temperature drops below TMI ≈ 90 K. The application of external pressure suppresses the Mott transition and restores the metallic electronic structure of the triclinic phase. The observed quantum oscillations of the magnetoresistance are in good agreement with the calculated Fermi surface for the triclinic phase, providing a plausible explanation for the puzzling behavior of κ-(BEDT-TTF)2Hg(SCN)2Br as a function of temperature and pressure around 100 K. The present study points out interesting differences in the structural and physical behaviors of the two room temperature isostructural salts of κ-(BEDT-TTF)2Hg(SCN)2X with X = Br, Cl.The work at the Federal Research Center of Problems of Chemical Physics and Medicinal Chemistry was carried out within the project of state assignment number AAAA-A19-119092390079-8. V.N.Z. acknowledges the support of the Russian Foundation for Basic Research No. 21-52-12027. The work in Spain was supported by the MICIU (Grant PGC2018-096955-B-C44) and Generalitat de Catalunya (2017SGR1506). E.C. acknowledges the support of the Spanish MICIU through the Severo Ochoa FUNFUTURE (CEX2019-000917-S) Excellence Center distinction.With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe

Biomimetic Water Oxidation Catalyzed by a Binuclear Ruthenium (IV) Nitrido-Chloride Complex with Lithium Counter-Cations

The lithium salt of the binuclear nitrido complex of ruthenium (IV) Li3(Ru2NCl8·2H2O) was synthesized. Using UV spectroscopy and voltammetry, we studied complex behavior in aqueous solutions. It was found that in dilute solutions of this compound, Cl− ions are replaced by H2O molecules, and the intra-sphere redox reaction between Ru (IV) and H2O, as well as the oxidation of water with the formation of oxygen and the acidic dissociation of coordinated water molecules also have been taking place. It was established by IR spectroscopy and ESI mass spectrometric analysis that not only the binuclear structure of the complex is preserved in acidic solutions, but also its dimerization product into the tetra-ruthenium dinitrido cluster Ru4N2O5+, which is a catalyst for the water oxidation reaction. The activity of the catalyst was TOF = 0.33 s−1, TON = 304

The Organic Ammonium Counterion Effect on Slow Magnetic Relaxation of the [Er(hfac)₄]⁻ Complexes

The first mononuclear anionic erbium complex [Er(hfac)4]− (hfac = hexafluoroacetylacetone) with an organic ammonium cation [(CH3)4N+] as the counterion was synthesized and structurally and magnetically characterized. The coordination geometries around the Er ions are square antiprisms with pseudo-D4d symmetry. The complex shows distinct field-induced slow magnetization relaxation, which is described by a combination of Orbach (Ueff/kB~28.54(8) K.) and direct mechanisms. Quantum chemical calculations were performed to analyze the magnetic properties of the complex under consideration

Layered Organic Conductors Based on BEDT-TTF and Ho, Dy, Tb Chlorides

Molecular semiconductors with lanthanide ions have been synthesized based on BEDT-TTF and lanthanide chlorides: (BEDT-TTF)2[HoCl2(H2O)6]Cl2(H2O)2 (1, which contains a 4f holmium cation), and (BEDT-TTF)2LnCl4(H2O)n (Ln = Dy, Tb, Ho (2–4), which contain 4f anions of lanthanides). Conductivity and EPR measurements have been carried out along with the SQUID magnetometry, and the crystal structure has been established for 1. The structure of 1 is characterized by an alternation of organic radical cation layers composed of BEDT-TTF chains and inorganic layers consisting of chains of the [HoCl2(H2O)6]+ cations interlinked by chlorine anions and crystallization water molecules. The magnetic susceptibility of 1–3 determined mainly by lanthanide ions follows the Curie–Weiss law with the Weiss temperatures of −3, −3, −2 K for 1–3, respectively, indicating weak antiferromagnetic coupling between paramagnetic lanthanide ions. The signals attributed to the BEDT-TTF+· radical cations only are observed in the EPR spectra of 1–3, which makes it possible to study their magnetic behavior. There are two types of chains in the organic layers of 1: the chains composed of neutral molecules and those formed by BEDT-TTF+· radical cations. As a result, uniform 1D antiferromagnetic coupling of spins is observed in the BEDT-TTF+· chains with estimated exchange interaction J = −10 K. The study of dynamic magnetic properties of 1–3 shows that these compounds are not SMMs

Layered Organic Conductors Based on BEDT-TTF and Ho, Dy, Tb Chlorides

Molecular semiconductors with lanthanide ions have been synthesized based on BEDT-TTF and lanthanide chlorides: (BEDT-TTF)2[HoCl2(H2O)6]Cl2(H2O)2 (1, which contains a 4f holmium cation), and (BEDT-TTF)2LnCl4(H2O)n (Ln = Dy, Tb, Ho (2–4), which contain 4f anions of lanthanides). Conductivity and EPR measurements have been carried out along with the SQUID magnetometry, and the crystal structure has been established for 1. The structure of 1 is characterized by an alternation of organic radical cation layers composed of BEDT-TTF chains and inorganic layers consisting of chains of the [HoCl2(H2O)6]+ cations interlinked by chlorine anions and crystallization water molecules. The magnetic susceptibility of 1–3 determined mainly by lanthanide ions follows the Curie–Weiss law with the Weiss temperatures of −3, −3, −2 K for 1–3, respectively, indicating weak antiferromagnetic coupling between paramagnetic lanthanide ions. The signals attributed to the BEDT-TTF+· radical cations only are observed in the EPR spectra of 1–3, which makes it possible to study their magnetic behavior. There are two types of chains in the organic layers of 1: the chains composed of neutral molecules and those formed by BEDT-TTF+· radical cations. As a result, uniform 1D antiferromagnetic coupling of spins is observed in the BEDT-TTF+· chains with estimated exchange interaction J = −10 K. The study of dynamic magnetic properties of 1–3 shows that these compounds are not SMMs

Effect of External Pressure on the Metal–Insulator Transition of the Organic Quasi-Two-Dimensional Metal κ-(BEDT-TTF)₂Hg(SCN)₂Br

The metal–insulator transition in the organic quasi-two-dimensional metal κ-(BEDT-TTF)2Hg(SCN)2Br at TMI ≈ 90 K has been investigated. The crystal structure changes during this transition from monoclinic above TMI to triclinic below TMI. A theoretical study suggested that this phase transition should be of the metal-to-metal type and brings about a substantial change of the Fermi surface. Apparently, the electronic system in the triclinic phase is unstable toward a Mott insulating state, leading to the growth of the resistance when the temperature drops below TMI ≈ 90 K. The application of external pressure suppresses the Mott transition and restores the metallic electronic structure of the triclinic phase. The observed quantum oscillations of the magnetoresistance are in good agreement with the calculated Fermi surface for the triclinic phase, providing a plausible explanation for the puzzling behavior of κ-(BEDT-TTF)2Hg(SCN)2Br as a function of temperature and pressure around 100 K. The present study points out interesting differences in the structural and physical behaviors of the two room temperature isostructural salts of κ-(BEDT-TTF)2Hg(SCN)2X with X = Br, Cl

Effect of External Pressure on the Metal–Insulator Transition of the Organic Quasi-Two-Dimensional Metal κ-(BEDT-TTF)2Hg(SCN)2Br

The metal–insulator transition in the organic quasi-two-dimensional metal κ-(BEDT-TTF)2Hg(SCN)2Br at TMI ≈ 90 K has been investigated. The crystal structure changes during this transition from monoclinic above TMI to triclinic below TMI. A theoretical study suggested that this phase transition should be of the metal-to-metal type and brings about a substantial change of the Fermi surface. Apparently, the electronic system in the triclinic phase is unstable toward a Mott insulating state, leading to the growth of the resistance when the temperature drops below TMI ≈ 90 K. The application of external pressure suppresses the Mott transition and restores the metallic electronic structure of the triclinic phase. The observed quantum oscillations of the magnetoresistance are in good agreement with the calculated Fermi surface for the triclinic phase, providing a plausible explanation for the puzzling behavior of κ-(BEDT-TTF)2Hg(SCN)2Br as a function of temperature and pressure around 100 K. The present study points out interesting differences in the structural and physical behaviors of the two room temperature isostructural salts of κ-(BEDT-TTF)2Hg(SCN)2X with X = Br, Cl

New Radical Cation Salts Based on BDH-TTP Donor: Two Stable Molecular Metals with a Magnetic [ReF6]2− Anion and a Semiconductor with a [ReO4]− Anion

Three radical cation salts of BDH-TTP with the paramagnetic [ReF6]2− and diamagnetic [ReO4]− anions have been synthesized: κ-(BDH-TTP)4ReF6 (1), κ-(BDH-TTP)4ReF6·4.8H2O (2) and pseudo-κ″-(BDH-TTP)3(ReO4)2 (3). The crystal and band structures, as well as the conducting properties of the salts, have been studied. The structures of the three salts are layered and characterized by alternating κ-(1, 2) and κ″-(3) type organic radical cation layers with inorganic anion sheets. Similar to other κ-salts, the conducting layers in the crystals of 1 and 2 are formed by BDH-TTP dimers. The partial population of positions of Re atoms and disorder in the anionic layers of 1–3 are their distinctive features. Compounds 1 and 2 show the metallic character of conductivity down to low temperatures, while 3 is a semiconductor. The ac susceptibility of crystals 1 was investigated in order to test the possible slow relaxation of magnetization associated with the [ReF6]2− anion.This research was funded by the Ministry of Science and Higher Education of the Russian Federation (Grant No. 075-15-2020-779). Work in Spain was supported by MICIU (through the Severo Ochoa FUNFUTURE (CEX2019-000917-S) Excellence Centre distinction and Grant PGC 2018-096955-B-C44), and by Generalitat de Catalunya (2017SGR1506).Peer reviewe

Zero-Field Slow Magnetic Relaxation in Binuclear Dy Acetylacetonate Complex with Pyridine-N-Oxide

A new complex [Dy(C5H7O2)3(C5H5NO)]2·2CHCl3 (1) has been synthesized by the reaction of pyridine-N-oxide with dysprosium (III) acetylacetonate in an n-heptane/chloroform mixture (1/20). X-ray data show that each dysprosium atom is chelate-like coordinated by three acetylacetonate ligands and the oxygen atom from two bridging molecules of pyridine-N-oxide, which unite the dysprosium atoms into a binuclear complex. Static (constant current) and dynamic (alternating current) investigations and ab initio calculations of the magnetic properties of complex 1 were performed. The complex was shown to exhibit a frequency maximum under alternating current. At temperatures above 10 K, the maximum shifts to a higher frequency, which is characteristic of SMM behavior. It is established that the dependence of ln(τ) on 1/T for the relaxation process is nonlinear, which indicates the presence of Raman relaxation mechanisms, along with the Orbach mechanism

Synthesis and Properties of Ethylene/propylene and Ethylene/propylene/5-ethylidene-2-norbornene Copolymers Obtained on Rac-Et(2-MeInd)2ZrMe2/Isobutylaluminium Aryloxide Catalytic Systems

Ethylene/propylene (E/P) and ethylene/propylene/5-ethylidene-2-norbornene (E/P/ENB) copolymers were obtained on rac-Et(2-MeInd)2ZrMe2 activated by a number of isobutylaluminium aryloxides: (2,6-tBu2PhO-)AliBu2 (1-DTBP) (2,6-tBu2,4-Me-PhO-)AliBu2 (1-BHT), (2,4,6-tBu2PhO-)AliBu2 (1-TTBP), (2,6-tBu2,4-Me-PhO-)2AliBu (2-BHT), (2,6-tBu2PhO-)2AliBu (2-DTBP), [(2-Me,6-tBu-C6H3O)AliBu2]2 (1-MTBP), [(2,6-Ph2-PhO)AliBu2]2 (1-DPP). This study shows how the structure of an activator influences catalytic activity and polymer properties, such as the copolymer composition, molecular weight characteristics, and thermophysical and mechanical properties. It has been shown that both the introduction of a bulky substituent in the para-position of the aryloxy group and the additional aryloxy group in the structure of an activator lead to a significant decrease in activity of the catalytic system in all studied copolymerization processes. Moreover, activation by bulkier aryloxides leads to lower levels of comonomer insertion and gives rise to higher molecular weight polymers. Broad or multiple endothermic peaks with different values of melting points are observed on the DSC curves of the copolymers obtained with different catalytic systems. The DSC of the thermally fractionated samples makes it possible to reveal the heterogeneity of the copolymer microstructure, which manifests itself in the presence of a set of lamellar crystallites of different thickness. The results also present the mechanical properties of the copolymers, such as the tensile strength (σ), elongation at break (ε), and engineering strain (EL). The synthesized E/P and E/P/ENB copolymers contain about 1–4 wt.% of the sterically hindered phenols obtained in situ as a residue of the hydrolyzed activators in the course of reaction quenching. This determines the increased thermooxidative stability of the copolymers