The first molecular superconductor based on BEDT-TTF radical cation salt with the paramagnetic tris(oxalato)ruthenate anion, β′′-(BEDT-TTF)₄K_x(H₃O)_1−x[Ru^III(ox)₃]C₆H₅Br (x ∼ 0.8), is synthesized and its crystal and electronic structure as well as transport and magnetotransport properties are studied. The single crystals have monoclinic C2/c symmetry and β′′-packing of the conducting BEDT-TTF layer. The samples were found to be superconductors with T_c = 2.8–6.3 K (depending on the sample). Well pronounced Shubnikov–de Haas oscillations are observed in the field range 7–17 T. The Fourier spectrum of the oscillations mainly consists of two frequencies, which correspond to the Fermi surface cross sections 6.3% and 0.85% of the Brillouin zone. The first one with good accuracy corresponds to the calculated cross section 7.5%, the origin of the second one is discussed. Semiconducting orthorhombic phase ‘pseudo-κ’-(BEDT-TTF)₄K_x(H₃O)_1−x[Ru^III(ox)₃]C₆H₅CN is also synthesized and studied.

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.

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.