Functionalized Tetrathiafulvalene Derivatives and their Radical Cation Salts: Synthesis and X-Ray Crystal Structures
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Salt 1+" B r- was prepared by cooling a solution of compound 1 and Bu 4 N+ B r3- in acetonitrile. Salt 2+. H S 04- was prepared by electrocrystallization of 2 in acetonitrile containing concentrated H2 SO 4 at a constant current of l~IA [2f]. Complex 4c • TCNQ was obtained by cooling a solution of compound 4c and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ) in acetonitrile. Salt 9+' 13- was prepared by diffusion of iodine vapor into an acetonitrile solution of 9 in a sealed container. X-Ray Crystallography Single-crystal X-ray diffraction experiments were carried out on a Rigaku AFC6S 4-circle diffractometer or a Siemens 3-circle SMART diffractometer with a CCD area detector. Graphite-monochromated Mo-KQx radiation (X =0.71073 A) was used. The structures were 2
solved by direct methods and refined by full-matrix least squares against F of all data, using SHELXTL software [11].
S SRR 1 R=C(S)NHMe 2 R=1
S
R
S:.J
SSR R.
1
SSR'
R
3 a R=Me,R 1 =H b R=R 1 =Me c R=SMe,R 1 =H
N. me
S•.N.
S
_.R
R,
+
S-
Me
R
4
4 a R=Me,R,=H b R=Rl=Me c R=SMe,R,=H
Scheme 1. (i) LDA (1 equiv.), Et2 0, -78 'C, then MeNCS, -78 "C to 20 "C,then H2 0
Sr ==s
0)
S 5
(S
BrrSXs Br
S 6
Br 05S: S
R
S
S
R
S
R
R= S(0H 2)2CN
(ii,, ,
Br-
S-y
Br'
S
SMe S.~sme
9
7 R = S(CH 2)2 CN Scheme 2.
(i) LDA (3 equiv.), THF, -78 "C,then (CF 2 Br)2 , -78 to 20 "C; (ii)compound 7 (4 equiv.), P(OEt) 3 , PhMe, reflux; (iii)CsOH.H 2 0, MeOH-THF, 20 'C, then Met (excess).
RESULTS AND DISCUSSION N-Methylthiocarbamoyl-TTF Derivatives Compounds 1 and 4a-c were designed to explore intermolecular hydrogen bonding interactions involving the thiocarbamoyl group, in conjunction with stacking of the TTF system. The attachment of this electron-withdrawing substituent is known to raise the first oxidation potential of TTF by 90 mV [3a]. We have previously shown that compound 1 packs in a kappa fashion in the crystal structure [3a,b] (that is, the 7r-donor forms orthogonal dimers which are coupled through weak intermolecular forces); such an arrangement in the neutral state is very rare [4, 12]. This is an important packing motif to explore, as all the TTF-based superconductors with Tc > 10 K possess kappa-phase structures [13]. We, therefore,
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synthesized analogues 4a-c, and we now report the molecular structures of 4a and 4b, the 1:1 salt 1+* Br- and the 1:1 complex 6c TCNQ. For both compounds 4a (Fig. la) and 4b (Fig. lb) it is notable that the S(2)-C(3) bond is significantly shorter than the other C-S bonds, by 0.036 A in 4a and 0.013 A in 4b (cf.0.03 A in 1 [3a]); this is in agreement with our suggestion [14] that the mesomeric effect of the C=S group gives rise to a significant contribution from the dipolar canonical form 4'. The S(2)-C(3) bond contraction is smaller [and the C(2)-C(7) bond marginally longer] in 4b, wherein the methyl substituent at C(3) interferes with the conjugation. Compound 4a exhibits a highly-distorted kappa-packing of molecular dimers, with the TTF moieties in a boat conformation, with 3.4 A separation betwe
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