Influence Of The Size And Shape Of Halopyridines Guest Molecules G On The Crystal Structure And Conducting Properties Of Molecular (Super)Conductors Of (Bedt-Ttf)(4)A(+)[M3+(C2o4)(3)]Center Dot G Family

New organic (super)conductors of the beta ''-(BEDT-TTF)(4)A(+)[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-)G(0)}(2-). Crystals 1 undergo a structural phase transition from the monoclinic (C2/c) to the triclinic (P1 over bar ) 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.