Crystal structures and properties of two modifications of the molecular charge-transfer salt (BEDT-TTF)2Ag(CN)2[BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene]
1993; Royal Society of Chemistry; Volume: 3; Issue: 11 Linguagem: Inglês
10.1039/jm9930301161
ISSN1364-5501
AutoresMohamedally Kurmoo, Peter Day, Andrew M. Stringer, Judith A. K. Howard, Laurent Ducasse, Francis L. Pratte, John Singletons, W. Hayes,
Tópico(s)Molecular Junctions and Nanostructures
ResumoCrystal structures are reported of two modifications of the molecular charge-transfer salt (BEDT-TTF)2Ag(CN)2[BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene]. Both structures contain alternating layers of BEDT-TTF and [Ag(CN)2]–. Structure I is orthorhombic (P21212), a= 9.519(2)Å, b= 4.952(1)Å, c= 33.927(7)Å, Z= 2, R= 0.054, and structure II is monoclinic (P21/n), a= 10.996(1)Å, b= 4.281(1)Å, c= 34.093(5)Å, β= 93.13(2)°, Z= 2, R= 0.084. The modes of packing of the BEDT-TTF within layers are similar; the BEDT-TTF are inclined to the stacking axis and there are no significant S⋯S contacts within stacks. In adjacent stacks in I the molecules are inclined in the opposite sense, with dihedral angles of 77.3° and 81.5° for the two crystallographically independent layers, giving a number of short S⋯S distances. In II the dihedral angle between adjacent stacks is smaller (55.3°). Phase I is metallic from 300 to 1 K, while for II electron paramagnetic resonance (EPR) gives evidence for a metal–insulator transition near 100 K. The EPR linewidths are 25–30G (I) and 17–27 G (II). Analysis of the reflectivity data of I gives plasma frequencies of 9200 cm–1(‖a) and 7000 cm–1(‖b). The band structures of both materials are broadly similar, with a Fermi surface consisting of a nearly symmetric hole pocket centred at the zone centre of ca. 50% of the Brillouin zone. In I the two layers are found to have slightly different Fermi surfaces.
Referência(s)