A modified procedure for the electrocrystallization of organic conductors with paramagnetic anions of the (BEDT-TTF)₄A^I[M^III(C₂O₄)₃]·G family has been proposed. It is found that single crystals of different phases of the family can be prepared if the electrocrystallization medium is represented by the mixture of 1,2,4-trichlorobenzene (or 1,3-dibromobenzene), 96% ethanol and different solvents (G), only the latter being included into the composition of the resulting salts as neutral guest molecules (G = benzonitrile, fluorobenzene, chlorobenzene, 1,2-dichlorobenzene, bromobenzene, nitrobenzene). Using this approach, a number of known and new BEDT-TTF salts with the tris(oxalato)ferrate anion have been synthesized. Among them, there are superconducting crystals of monoclinic β′′-series with different guest solvents (G) and their mixtures. For the first time, crystals of a triclinic phase (G = 1,2-dibromobenzene), with alternating α- and ‘pseudo-κ’ BEDT-TTF layers and metallic behaviour down to 1.5 K, were obtained. Additionally, monoclinic crystals having another stoichiometry and α-type donor packing were prepared.

The crystal and electronic structure of a new radical cation salt α-‘pseudo-κ’-(BEDT-TTF)₄H₃O[Fe(C₂O₄)₃]·C₆H₄Br₂ have been studied. The new triclinic crystals contain two conducting organic layers which are characterized by different BEDT-TTF packing motifs: a ‘pseudo-κ’-layer which is composed of charged dimers and neutral monomers of BEDT-TTF orthogonal to each other and an α-layer which consists of inclined, uniformly charged BEDT-TTF stacks. According to electronic band structure calculations, the ‘pseudo-κ’ layer has a large gap between the HOMO bands at the Fermi level and should be associated with an activated conductivity. In contrast, the α-layer is a strongly two-dimensional electronic system with uniform intermolecular interactions. The absence of any nesting in the Fermi surface of the α-layer suggests that this salt should be a stable metal down to low temperatures. Metallic properties have been observed in the crystals in the 300–0.4 K temperature range. Besides, well pronounced Shubnikov–de Haas oscillations of the magnetoresistance have been revealed at B > 8 T. The salt investigated is a new phase in the (BEDT-TTF)₄A^I[M^III(C₂O₄)₃]G family of organic molecular conductors with paramagnetic anions and different guest solvent molecules G in the anion layer. Structural features of the new α-‘pseudo-κ’-crystals and other known phases of the family (β″, ‘pseudo-κ’ and α-β″) have been compared.

Isostructural mononuclear complexes of heavy lanthanides with the pentadentate Schiff-base dapsc ligand were synthesized, [Ln(H₂dapsc)(H₂O)₄](NO₃)₃ (Ln = Tb, Dy, Ho, Er), and characterized structurally and magnetically. AC magnetic susceptibility measurements revealed that complexes of Dy³⁺ and Er³⁺ Kramers ions are field-induced single-ion magnets whereas the Tb and Ho complexes show no slow magnetic relation in DC fields up to 6000 Oe. DC and AC magnetic properties of these complexes were rationalized in terms of superposition crystal-field model calculations for Ln³⁺ ions, which have resulted in good agreement between the experiment and the theory. It is shown that low single-molecule magnet characteristics of the Dy and Er complexes and the absence of slow-magnetic relaxation in the Tb and Ho complexes are primarily due to the low-symmetry coordination of Ln³⁺ ions.

Three systems [Fe(III)(sal₂-trien)](TCNQ)_n·X (n = 1, 2, X = MeOH, CH₃CN, H₂O) showing spin-crossover transition, conductivity and ferromagnetic coupling were synthesized and studied by X-ray diffraction, Montgomery method for resistivity, SQUID magnetometry and X-band EPR. Spin-spin interactions between local magnetic moments of Fe(III) ions and electron spins of organic TCNQ network were discovered and discussed within the framework of intermolecular superexchange coupling.

A series of six seven-coordinate pentagonal-bipyramidal (PBP) erbium complexes, with acyclic pentadentate [N₃O₂] Schiff-base ligands, 2,6-diacetylpyridine bis-(4-methoxybenzoylhydrazone) [H₂DAPMBH], or 2,6-diacethylpyridine bis(salicylhydrazone) [H₄DAPS], and various apical ligands in different charge states were synthesized: [Er(DAPMBH)(C₂H₅OH)Cl] (1); [Er(DAPMBH)(H₂O)Cl]·2C₂H₅OH (2); [Er(DAPMBH)(CH₃OH)Cl] (3); [Er(DAPMBH)(CH₃OH)(N₃)] (4); [(Et₃H)N]⁺[Er(H₂DAPS)Cl₂]⁻ (5); and [(Et₃H)N]⁺[Y₀.₉₅Er₀.₀₅(H₂DAPS)Cl₂]⁻ (6). The physicochemical properties, crystal structures, and the DC and AC magnetic properties of 1–6 were studied. The AC magnetic measurements revealed that most of Compounds 1–6 are field-induced single-molecule magnets, with estimated magnetization energy barriers, U_eff ≈ 16–28 K. The experimental study of the magnetic properties was complemented by theoretical analysis based on ab initio and crystal field calculations. An experimental and theoretical study of the magnetism of 1–6 shows the subtle impact of the type and charge state of the axial ligands on the SMM properties of these complexes.