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New organic (super)conductors of the β''-(BEDT-TTF)4A+[M3+(C2O4)3]G family, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene; M is Fe; A is the monovalent cation NH4+; G is 2-fluoropyridine (2-FPy) (1); 2,3-difluoropyridine (2,3-DFPy) (2); 2-chloro-3-fluoropyridine (2-Cl-3-FPy) (3); 2,6-dichloropyridine (2,6-DClPy) (4); 2,6-difluoropyridine (2,6-DFPy) (5), have been prepared and their crystal structure and transport properties were studied. All crystals have a layered structure in which the conducting layers of BEDT-TTF radical cations alternate with paramagnetic supramolecular anionic layers {A+[Fe3+(C2O4)3]³-G0}2-.Crystals 1 undergo a structural phase transition from the monoclinic (C2/c) to the triclinic (P1) symmetry in the range 100-150 K, whereas crystals 2-5 have a monoclinic symmetry in the entire range of the X-ray experiment (100-300 K). The alternating current (ac) conductivity of salts 1-4 exhibits metallic behavior down to 1.4 K, whereas the salt 5 demonstrates the onset of a superconducting transition at 3.1 K. The structures and conducting properties of 1-5 are compared with those of the known monoclinic phases of the family containing different monohalopyridines as "guest" solvent molecules G. [ABSTRACT FROM AUTHOR]

Three radical cation salts of BDH-TTP with the paramagnetic [ReF6]2- and diamagnetic [ReO4]- anions have been synthesized: K-(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. [ABSTRACT FROM AUTHOR]