“…Per unit cell there are eight face-to-face stacked pyrene molecules. Strikingly similar structures have been found in perylene, pyrene, and other fused aromatic radical cation salts. ,− The overall topology of crystal structure 1 is apparently stable to variations in the fused aromatic system as well as the counterion.…”
Section: Resultsmentioning
confidence: 56%
“…These C···C contact distances range from 3.18 to 3.49 Å; many of these distances are shorter than twice the standard carbon van der Waals radius (3.40 = 2 × 1.70 Å) . The two observed stacking orientations have been observed in other radical cation pyrene salts. ,, We explain the molecular orbital basis for the two orientations in a later section of this paper. 1 Crystal structure of (pyrene) 10 (I 3 - ) 4 (I 2 ) 12 , 1 (in stereoview).…”
Section: Resultsmentioning
confidence: 70%
“…It is now well-accepted that substantial increases in critical temperatures will require greater control of molecular packing. − Indeed, it is crystal packing that determines whether a partially filled organic π-system is a Mott insulator, − a one-dimensional metal that Peierls distorts at low temperature, − or a bona fide multidimensional metal that upon cooling can enter the desired superconducting state. − Understanding the factors that control crystal structures is thus essential.…”
We report here the synthesis, crystal structures, and electronic band structures of
(pyrene)10(I3
-)4(I2)10, 1, and of [1,3,6,8-tetrakis(methylthio)pyrene]3(I3)3
-(I2)7, 2. In both
systems, the organic molecules form face-to-face cationic stacks that are separated from
one another by a polyiodide network. Band calculations at the extended Hückel (eH) level
suggest that the stacks of pyrene molecules in 1 have undergone a Peierls distortion. This
Peierls distortion is abetted by rotation of the pyrene molecules within the face-to-face stacks.
Within the chains, the pyrene HOMO bands are 3/4-filled. Band calculations on 2, at both
the LDA-DFT and eH levels, suggest that 2 is a Mott insulator. The various intermolecular
interactions in these crystals are assessed. Strongest are the I···I contacts. These contacts
are rationalized as being Lewis acid−Lewis base (charge-transfer) interactions between
HOMO and LUMO orbitals. HOMO interactions also are responsible for the stacking
sequence observed in 1. In 1, the strength of intermolecular interactions follows the order
inorganic−inorganic (i.e., I···I) > organic−organic (i.e., π − π) > organic−inorganic (i.e.,
C−H···I). Thus, 1 belongs to the family of two-component systems (here, organic and
inorganic) where the interface of the two components has a relatively high free energy. An
analogy is made to other two-component systems, such as block copolymers. The topology of
the interface is analyzed, and a relationship between the dimensionality of the organic
network and the ratio of the inorganic volume to the total volume is presented.
“…Per unit cell there are eight face-to-face stacked pyrene molecules. Strikingly similar structures have been found in perylene, pyrene, and other fused aromatic radical cation salts. ,− The overall topology of crystal structure 1 is apparently stable to variations in the fused aromatic system as well as the counterion.…”
Section: Resultsmentioning
confidence: 56%
“…These C···C contact distances range from 3.18 to 3.49 Å; many of these distances are shorter than twice the standard carbon van der Waals radius (3.40 = 2 × 1.70 Å) . The two observed stacking orientations have been observed in other radical cation pyrene salts. ,, We explain the molecular orbital basis for the two orientations in a later section of this paper. 1 Crystal structure of (pyrene) 10 (I 3 - ) 4 (I 2 ) 12 , 1 (in stereoview).…”
Section: Resultsmentioning
confidence: 70%
“…It is now well-accepted that substantial increases in critical temperatures will require greater control of molecular packing. − Indeed, it is crystal packing that determines whether a partially filled organic π-system is a Mott insulator, − a one-dimensional metal that Peierls distorts at low temperature, − or a bona fide multidimensional metal that upon cooling can enter the desired superconducting state. − Understanding the factors that control crystal structures is thus essential.…”
We report here the synthesis, crystal structures, and electronic band structures of
(pyrene)10(I3
-)4(I2)10, 1, and of [1,3,6,8-tetrakis(methylthio)pyrene]3(I3)3
-(I2)7, 2. In both
systems, the organic molecules form face-to-face cationic stacks that are separated from
one another by a polyiodide network. Band calculations at the extended Hückel (eH) level
suggest that the stacks of pyrene molecules in 1 have undergone a Peierls distortion. This
Peierls distortion is abetted by rotation of the pyrene molecules within the face-to-face stacks.
Within the chains, the pyrene HOMO bands are 3/4-filled. Band calculations on 2, at both
the LDA-DFT and eH levels, suggest that 2 is a Mott insulator. The various intermolecular
interactions in these crystals are assessed. Strongest are the I···I contacts. These contacts
are rationalized as being Lewis acid−Lewis base (charge-transfer) interactions between
HOMO and LUMO orbitals. HOMO interactions also are responsible for the stacking
sequence observed in 1. In 1, the strength of intermolecular interactions follows the order
inorganic−inorganic (i.e., I···I) > organic−organic (i.e., π − π) > organic−inorganic (i.e.,
C−H···I). Thus, 1 belongs to the family of two-component systems (here, organic and
inorganic) where the interface of the two components has a relatively high free energy. An
analogy is made to other two-component systems, such as block copolymers. The topology of
the interface is analyzed, and a relationship between the dimensionality of the organic
network and the ratio of the inorganic volume to the total volume is presented.
“…1͒ have shown that there exist typically 2 -3ϫ10 Ϫ2 Curie paramagnetic defects per formula unit in our (PY) 12 (SbF 6 ) 7 crystals. 10,7 Nevertheless, in contrast to the low-temperature behavior of perylene-PF 6 salts, 3 (PY) 12 (SbF 6 ) 7 shows only one Lorentzian-shaped ESR signal over the whole temperature range between 4.2 K and 290 K, with a linewidth of only about 50 mG at room temperature. Thus there must exist a strong exchange coupling between the defect spins mutually and with the conduction electrons.…”
Section: Angular Dependence Of the Electron-spin-resonance Linewidthmentioning
confidence: 99%
“…The formula for the ac and bc planes is similar. The principal values of the g tensor for (PY) 12 (SbF 6 ) 7 and their relation to the molecular geometry are listed in Table I. The z direction is equivalent to the c direction of the measurement in Fig.…”
The electron spin resonance ͑ESR͒ of (pyrene) 12 (SbF 6 ) 7 is measured as function of crystal orientation for temperatures above and below the Peierls transition temperature T P ϭ116 K. The principal values of the pyrene g tensor ͑2.00274, 2.00235, 2.00225͒ are determined. In spite of a defect concentration amounting to 2 -3ϫ10 Ϫ2 per formula unit, the ESR linewidth is below 60 mG in the metallic phase. The temperature dependence of the intrastack exchange interaction between localized defects and conduction electrons is derived. The exchange integral decreases by a factor of 8 between T P and room temperature.
Electron spin resonance imaging is a technique using similar principles to the established nuclear magnetic resonance imaging; however, the very fast electron-spin relaxation time constants of the former are an experimental challenge. In order to obtain T2-weighted as well as functional images spatially resolved in the micrometer range, we use temperature-dependent pulsed X-band ESR and the back-projection reconstruction method. We present here recent results of our imaging project focussing on quasi one-dimensional organic conductors, where even pulsed conduction electron-spin resonance is possible.
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