Bilayer Molecular Metals Based on Dissymmetrical Electron Donors

Abstract

The electrocrystallization from solutions of cyanobenzene-ethylenedithio-tetrathiafulvalene (CNB-EDT-TTF) in the presence of different anions X = ClO4(-), PF6(-), and I3(-), affords a new type of 2D molecular metals with composition (CNB-EDT-TTF)4X based on an unprecedented bilayer structure of the donors induced by effective head to head interdonor interactions through the nitrile groups, which is responsible for 2D metallic systems with unusual properties such as the higher band filling, larger effective mass of carriers, and almost degenerated double Fermi surfaces.

β”-(CNB-EDT-TTF)4BF4; Anion Disorder Effects in Bilayer Molecular Metals

“…This difference is certainly due to the severe anion disorder and it corresponds to a not so tight packing of the molecules in the layers. The donor bilayer structure is due to a network of bifurcated C-N … H interactions in an efficient combination of R 2 2(10) and R 2 2(8) synthons between coplanar molecules (Figure 3a) with contact distances (N1···H3 at 2.624 Å, N1···H5 at 2.505 Å) comparable to those previously found in β"-(CNB-EDT-TTF)4X salts [1][2][3]. However the stacking distance between successive planes of molecules interconnected by R 2 2(10) and R 2 2(8) synthons is slightly larger in this BF4 salt.…”

“…Due to the small interlayer interaction IV, associated with head to head intermolecular contacts, the bands are split in two almost degenerated ones. The Fermi surface corresponds to two elliptical cylinders, as typical of β"-salts [19], and their cross section area corresponds to about 1/8 of the first Brillouin Zone as previously calculated for identical β"-(CNB-EDT-TTF)4X salts [1,2].…”

“…However the stacking distance between successive planes of molecules interconnected by R 2 2(10) and R 2 2(8) synthons is slightly larger in this BF4 salt. The three in β"-(CNB-EDT-TTF) 4 X salts [1][2][3]. However the stacking distance between successive planes of molecules interconnected by R 2 2 (10) and R 2 2 (8) synthons is slightly larger in this BF 4 salt.…”

“…Dichloromethane and tetrahydrofuran (THF) were freshly distilled immediately before use. (1). A THF solution of the donor CNB-EDT-TTF (2.2 × 10 −3 M) and n-Bu4N BF4 (1.1 × 10 −2 M) was added to an H-shaped two-compartment cells separated by frit glass with Pt electrodes and sealed under nitrogen.…”

“…It has been recently shown that the dissymmetrical TTF derivative cyanobenzene-ethylenedithiotetrathiafulvalene (CNB-EDT-TTF) (Scheme 1) is an electron donating molecule that when combined with small anions X such as ClO 4 − , PF 6 − , and I 3 − , leads to a family of radical cation salts of composition (CNB-EDT-TTF) 4 X and characterized by a unique donor bilayer structure [1]. This bilayer arrangement is promoted by an effective arrangement of hydrogen bond dimeric C-N···H-C interactions involving the cyano groups, as a combination of R 2 2 (10) and R 2 2 (8) synthons in a two-dimensional network.…”