Crystal chemistry and physical properties of superconducting and semiconducting charge transfer salts of the type (BEDT-TTF)(4)[A(I)M(III)(C2O4)(3)]center dot PhCN (A(I) = H3O, NH4, K; M-III = Cr, Fe, Co, Al; BEDT-TTF = bis (ethylenedithio)tetrathiafulvalene)

Synthesis, structure determination by single-crystal X-ray diffraction, and physical properties are reported and compared for superconducting and semi conducting molecular charge-transfer salts with stoichiometry (BEDT-TTF)(4) [A(I)M(III)(C2O4)(3)] . PhCN, where A(I) = H3O, NH4, K; M-III = Cr, Fe, Co, Al; BEDT-TTF = bis(ethylenedithio) tetrathiafulvalene. Attempts to substit ute M-III with Ti, Ru, Rh, or Gd are also described. New compounds with M = Co and Al are prepared and detailed structural comparisons are made across the whole series. Compounds with A = H3O+ and M = Cr, Fe are monoclinic (s pace group C2/c), at 150, 120 K a = 10.240(1) Angstrom, 10.232(12) Angstrom ; b = 19.965(1) Angstrom, 20.04(3) Angstrom; c = 34.905(1) Angstrom, 34.97( 2) Angstrom; beta = 93.69(1)degrees, 93.25(11)degrees, respectively, both w ith Z = 4. These salts are metallic at room temperature, becoming supercond ucting at 5.5(5) or 8.5(5) K, respectively. A polymorph with A = H3O+ and M = Cr is orthorhombic (Pbcn) with a = 10.371(2) Angstrom, b = 19.518(3) Ang strom, c = 35.645(3) Angstrom, and Z = 4 at 150 K. When A = NH4+, M = Fe, C o, Al, the compounds are also orthorhombic (Pbcn), with a = 10.370(5) Angst rom, 10.340(1) Angstrom, 10.318(7) Angstrom; b = 19.588(12) Angstrom, 19.50 2(1) Angstrom, 19.460(4) Angstrom c = 35.790(8) Angstrom, 35.768(1) Angstro m, 35.808(8) Angstrom at 150 K, respectively, with Z = 4. All of the Pbcn p hases are semiconducting with activation energies between 0.15 and 0.22 eV. For those compounds which are thought to contain H3O+, Raman spectroscopy or C=C and C--S bond lengths of the BEDT-TTF molecules confirm the presence of H3O+ rather than H2O. In the monoclinic compounds the BEDT-TTF molecule s adopt a beta" packing motif while in the orthorhombic phases (BEDT-TTF)2 dimers are surrounded by monomers. Raman spectra and bond length analysis f or the latter confirm that each molecule of the dimer has a charge of +1 wh ile the remaining donors are neutral. All of the compounds contain approxim ately hexagonal honeycomb layers of [AM(C2O4)(3)] and PhCN, with the solven t occupying a cavity bounded by [M(C2O4)(3)](3-) and A. In the monoclinic s eries each layer contains one enantiomeric conformation of the chiral [M(C2 O4)(3)](3-) anions with alternate layers having opposite chirality, whereas in the orthorhombic series the enantiomers form chains within each layer. Analysis of the supramolecular organization at the interface between the ca tion and anion layers shows that this difference is responsible for the two different BEDT-TTF packing motifs, as a consequence of weak H-bonding inte ractions between the terminal ethylene groups in the donor and the [M(C2O4) (3)](3-) oxygen atoms.