Search

A pi-donor molecule, 4,5;4',5'-bis(1,4-dioxanediyl-2,3-dithio)tetrathiafulvalene (BDDT-TTF), identical to bis(ethylenedithio)tetrathiafulvalene (ET) is synthesized. BDDT-TTF has its central region identical to ET but has additional oxygen heteroatoms due to dioxane ring substitution to terminal ethylene bridges of ET. Cyclic voltammetric data show no significant alterations in the electronic structure due to addition of dioxane rings to the ET structure. New conductive radical cation salts with inorganic anions are prepared by donor BDDT-TTF.

The structure and properties of the radical cation salt based on [pi]-donor BETS (BETS = bis(ethylenedithio)tetraselenafulvalence) with tri(dicyanaamido)manganate(II) anion, [(BETS).sub.2]Mn[N(CN).sub.2]].sub.3] are reported. The crystal structure shows a transition into a superconducting state with [T.sub.c] = 5 K at P = 0.3 kbar and at ambient pressure the compound exhibits a metal-insulator transition at [T.sub.1] = 21 K and an AFM ordering at [T.sub.0] = 5 K.

Analysis of the data of the experimental study of a large family of low-dimensional organic conductors based on trihalides of ET and some of its analogues is presented. It is shown that the family of radical cation salts (ET)(sub 2) X, is characterized by a wide variety of conducting properties, rich polymorphism, and phase transitions.

The article reports on a study of the structure and properties of the radical cation salt based on pie-donor bis(ethylenedithio)tetraselenafulvalene with tri(dicyanamido)manganate anion. The compound is metallic and superconducting. It is necessary to conduct detailed studies in magnetic fields to clarify the nature of the low-temperature magnetic state and its influence on the conduction system.

A potassium salt of the N 2 S 2 O 2 -coordination Fe(III) anion K[Fe(5Cl-thsa) 2 ] ( 1 ) (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K + cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K + cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T 1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to 57 Fe Mössbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)-ligand bond lengths. In addition, the final step of the spin conversion (Δγ HS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic ( Pbcn ) to the monoclinic ( P 2 1 / n ) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, 57 Fe Mössbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds.

The syntheses, structure and magnetic properties are reported for five novel 1D polymeric azido-bridged lanthanide complexes with the general formula {[Ln(DAPMBH)(N 3 )C 2 H 5 OH]C 2 H 5 OH} n where H 2 DAPMBH = 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)-a new pentadentate pyridine-base [N 3 O 2 ] ligand and Ln = Dy ( 1 ), Y 0.930 Dy 0.070 ( 2 ), Er ( 3 ), Y 0.923 Er 0.077 ( 4 ), and Gd ( 5 ). X-ray diffraction analysis of 1 - 5 show that the central lanthanide atoms are eight-coordinated with the N 5 O 3 donor set originating from the ligand DAPMBH, one coordinated ethanol molecule and two end-to-end type N 3 - bridges connecting the metal centers into infinite chain. The [LnN 5 O 3 ] coordination polyhedron can be regarded as a distorted dodecahedron ( D 2 d ). AC magnetic measurements revealed that compounds 1 - 4 show field-induced single-molecule magnet behavior, with estimated energy barriers U eff ≈ 47-17 K. The experimental study of magnetic properties was complemented by theoretical analysis based on crystal-field calculations. Direct current magnetic susceptibility studies revealed marginally weak intrachain exchange interaction between Ln 3+ ions mediated by the end-to-end azide bridging groups ( J ≈ -0.015 cm -1 for 5 ). Comparative analysis of static and dynamic magnetic properties of magnetically concentrated ( 1 , 3 ) and diluted ( 2 , 4 ) Dy and Er compounds showed that, despite fascinating 1D azido-bridged chain structure, compounds 1 and 3 are not single-chain magnets; their magnetic behavior is largely due to single-ion magnetic anisotropy of individual Ln 3+ ions.

Two one-dimensional cyano-bridged coordination polymers, namely, {[Mn II (dapsc)][Mn III (CN) 6 ][K(H 2 O) 2.75 (MeOH) 0.5 ]} n ·0.5n(H 2 O) (I) and {[Mn II (dapsc)][Mn III (CN) 6 ][K(H 2 O) 2 (MeOH) 2 ]} n (II), based on alternating high-spin Mn II (dapsc) (dapsc = 2,6-diacetylpyridine bis(semicarbazone)) complexes and low-spin orbitally degenerate hexacyanomanganate(III) complexes were synthesized and characterized structurally and magnetically. Static and dynamic magnetic measurements reveal a single-chain magnet (SCM) behavior of I with an energy barrier of U eff ≈ 40 K. Magnetic properties of I are analyzed in detail in terms of a microscopic theory. It is shown that compound I refers to a peculiar case of SCM that does not fall into the usual Ising and Heisenberg limits due to unconventional character of the Mn III -CN-Mn II spin coupling resulting from a nonmagnetic singlet ground state of orbitally degenerate complexes [Mn III (CN) 6 ] 3- . The prospects of [Mn III (CN) 6 ] 3- complex as magnetically anisotropic molecular building block for engineering molecular magnets are critically analyzed.