The structure of di(2,3,6,7-tetramethyl-1,4,5,8-tetraselenafulvalenium) hexafluorophosphate, (TMTSF)2PF6, the first superconducting organic solid

Abstract

The structure of 2C10H12SeX/2+.pF~ -, M r = 1041.06, a solid which exhibits superconductivity at 1.2 GPa below 0.9 K, has been determined at ambient pressure and temperature (295 K). (TMTSF)2PF 6 crystallizes in the triclinic space group P1 with a = 7.297 (1) mm-k Least-squares refinement of the structure gave R = 0.038 and R~ = 0.043 for 1466 reflections. The nearly planar TMTSF units are almost perpendicular to a (deviation 1.1 °) and form stacks along a. Within a stack the units repeat by an inversion leading to overlap displacements alternating in the direction of the long molecular axis and two independent interplanar distances of 3.63 and 3.66/k. The slight dimerization is clearly reflected in the intermolecular Se-Se distances. PF~ is centrosymmetric and shows considerable thermal motion.

The structures of di(2,3,6,7-tetramethyl-1,4,5,8-tetraselenafulvalenium) perrhenate, (TMTSF)2ReO4, and perchlorate, (TMTSF)2ClO4

“…1 is shown Se(2)-C(3)-C(13) 125.5 (7) 126 (2) 121.9 (6) Se(l)-C(3)-C (13) 121. l (7) 119 (2) 123.6 (5) Se(l 1)-C(13)-C (3) 125.2 (7) 128 (2) 121.1 (6) Se(12)-C(13)-C (3) 121.1 (7) 121 (2) 123.2 (5) Se(l)-C(3)-Se (2) 113.4 (5) 114 (2) 114.6 (5) Se(l 1)-C(13)-Se (12) 113.7 (5) III (2) (2) 119.2 (8) 120 (2) 119.9 (6) C(2)-C(l)-Se(l) 118-1 (7) 118 (2) 116-8 (6) C (12) 125.7 (10) 124 (3) 125.7 (8) values are all in good agreement with those found in the charge-transfer salts (1"1 compounds) with DMTCNQ, 2,5-dimethyl-7,7,8,8-tetracyano-p-quinodimethane (Andersen, Bechgaard, Jacobsen, Rindorf, Soling & Thorup, 1978), and in (TMTSF)2PF6 (Thorup, Rindorf, Soling & Bechgaard, 1981). There is no statistically significant difference in bond lengths or bond angles between TMTSF at 295 K and at 120 K in (TMTSF)2ReO4.…”

Competition between triplet superconductivity and antiferromagnetism in quasi-one-dimensional electron systems

“…Such interactions are weak, and furthermore are irrelevant in the RG sense for K Ͼ 1/4 (we remind the readers that we are interested in the regime near the SDW/TSC boundary, where K Ϸ 1). 53 On the other hand, due to structural dimerization in Bechgaard salts, 54 a gap splits the conduction band into a completely filled lower band and a halffilled upper band. Hence, Bechgaard salts are half-filled systems.…”

“…The bare value of g 3 in ͑TMTSF͒ 2 PF 6 is small, since it is proportional to dimerization, which in this compound is very weak. 54 Assuming that Coulomb interactions are of the order of the bandwidth, this leads to a bare value of g 3 of about 0.01. Furthermore, it is not the bare value of g 3 that enters the GL free energy, but its effective (renormalized) value at the 1d -3d crossover scale.…”

“…The latter assumption is well justified for ͑TMTSF͒ 2 PF 6 , since the observed dimerization in this material is less than 1%. 54 For small g 3 , modes found assuming SO(4) symmetry will have a finite overlap with the actual excitations of the system. In particular, the quantum numbers of the ⌰ mode discussed in Sec.…”

On a Field-Induced Spin-Density Wave in Bechgaard Salts

“…They crystallize in the triclinic system with the unit cell parameters α = 7.3 Å , b = 7.7 Å and d = 13.5 Å, and the angles between the unit cell axes α = 83°, β = 860 and γ = 71º [2]. The electronic stucture is very anisotropic, and can be described in a first approximation by the energy band with the transfer integrals t a : tb :…”