Tetrathiafulvalenes radical cations

Herve K, Cador O, GoUien S, Costuas K, Halet JF, Shirahata T, Muto T, Imakubo T, Miyazaki A, Ouahab L (2006) Iodine substituted tetrathiafulvalene radical cation salts with [M(isoq)2(NCS)4] anions where M=Cr °, Ga role of I -S and S -S contacts on structural and magnetic properties. Chem Mater 18 790-797... 

Pou-Amerigo, R. Orti, E. Merchan, M. Rubio, M. Viruela, P. M. Electronic Transitions in Tetrathiafulvalene and Its Radical Cation A Theoretical Contribution. J. Phys. Chem. A 2002, 106, 631-640. 

TTF (tetrathiafulvalene) and related compounds have been the subject of intense interest in the materials chemistry community because of their semi-conduction and superconduction properties. Recently, TTF has emerged as a unique radical initiator because its radical cation can be easily formed. The ease of formation is presumably derived from the favorable structure of the radical cation that incorporates an aromatic disulfonium salt and a very delocalized radical [49a]. Murphy et al. demonstrated a novel one-pot reaction cascade... 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

There is a long standing interest in the chemistry and the properties of cyclic compounds containing sulfur atom in modern material chemistry due to their redox chemistry. In particular, the focus has been on dithiole derivatives, e.g., dithiafulvenes and tetrathiafulvalenes, since the finding of metallic conductivity and low temperature superconductivity in radical cation salts. The quite low oxidation potentials of 1,4-dithiin compounds have been reported, recently [109]. On the other hand, thioketene dimers (2,4-bis(alkyli-dene)-l,3-dithietane) have been known for more than 100 years and synthesized by various methods [110-115]. The structure of these dimer compounds is similar to that of the redox-active sulfur compounds therefore, the potential electronic property of the thioketene dimer moiety is considerably attractive with the aim of application to a new and better -donor. 

Only a few X-ray crystal structure determinations on 1,3-dithioles have been carried out. Some typical bond lengths and bond angles of the tetrathiafulvalene (5), l,3-dithiole-2-thione derivative (6) and 1,3-dithiolanes (7) and (8) are given in Tables 2 and 3, respectively. Also bond lengths and bond angles of the radical cation of tetrathiafulvalene in the tetrathiafulvalene-7,7,8,8-tetracyanoquinodimethane complex have been determined <74AX(B)763>. 

Raman scattering spectra have been determined for tetrathiafulvalene (26), tetraselenaful-valene (28) and tetramethyltetraselenafulvalene (9) (82MI43501). The frequencies and assignment for these compounds are compiled in Table 6. The Raman spectra of various radical cation salts were determined as well. Both the IR and Raman spectra of these compounds were simple, reflecting the high degree of symmetry in these molecules. 

In the above radical-cation salts, the crystal contains partially oxidized donors, while the electroneutrality is achieved by the presence of closed shell anions. The structural requirements necessary for electrical conductivity in solid salts can also be met upon mixing of donors and acceptors in the resulting charge-transfer (CT) complexes both the donor and acceptor exist in a partially oxidized and reduced state, respectively. Famous examples are the conducting CT complexes formed upon mixing of perylene (112) [323. 324] and iodine or of tetrathiafulvalene (TTF, 119) as donor and 7,7,8,8-tetracyanoquinodimethane (TCNQ, 120) as acceptor [325-327] the crucial structural finding for the... 

During stepwise oxidation, each of the tetrathiafulvalene (TTF) or 4,5-dimethyltetrathiofulvalene (o-DMTTF) moieties in 90-92 donates two electrons so that exhaustive oxidation at potentials below IV (vs. SCE) leads to dications 90 + the tetracations 91" + and hexacations 92 +. In the initially formed radical cations... 

Despite their inherent electronic advantages, CT complexes and radical cation salts tend to be brittle and unprocessable. This problem might be overcome by the incorporation of oligomeric tetrathiafulvalenes in polymers, whereby the TTFs can be part of a main-chain or side-chain polymer. The key concern thereby is to achieve the suitable packing of the donor moieties, which is, of course, less perfect than in the crystalline state. Remarkably, the rigid-rod poly-TTF 164 could be made recently by a precursor route in which 164 is made by dimethyl disulfide extrusion of the precursor polymer (scheme 39). The electrical conductivity after iodine doping amounts to 0.6 S/cm [221]. Other examples of TTF-containing polymers, either in the backbone [222] or in the side-chain [223], are summarized in chart 25. 

Similarly to tetrathioethylenes and tetrathiafulvalenes, 1,4-dithiin (LV) and its benzoder-ivatives (LVI and LVII) are electron-rich compounds that can be easily oxidized to their corresponding cation radicals and dications. There are several reviews [2, 3, 186, 187] on the chemistry of the radical cations of dibenzo-1,4-dithiin (LVH) and related compounds. 

Tetraselenafulvalene and tetrathiafulvalene derivatives in conducting organic radical cation salts with organic and organometallic anions 04CRV5203. 

It is widely known that tetrathiafulvalene (15) - commonly known as TTF -can be easily oxidized to its radical cation and then on to its dicationic state. Previous research [36] from our laboratories had shown that reduction of the tetracationic cyclophane CBPQT4+ reduces enormously its binding affinity for 7i-electron-rich guests. In the light of this knowledge, it was considered possible to develop a pseudorotaxane-based switch in which the switching process is not only controlled and monitored electrochemically, but in which it can be accomplished [37] in one of two ways. 

Fig. 20. When the tetrathiafulvalene (TTF)-containing thread 16 is mixed in acetonitrile solution with cyclophane CBPQT4+, a pseudorotaxane is formed. This complex can be dissociated in one of two ways - reduction of the cyclophane to its diradical dication, or oxidation of the TTF portion of the thread 16 to its radical cation. Both processes are reversible, by oxidation of the cyclophane and reduction of 16, respectively...

Our approach to reduce the effects of swelling in negative resists was to use a high Tg polymer. Other approaches have been reported (38). Tetrathiafulvalene (TTF) is a strong electron donor and forms its radical cation by forming a complex with an electron acceptor such as tetracyanoquinodimethane and halogen. 

The radical cations of polythioalkenes are well known. The EPR spectra of the radical cations of dithioalkenes 100-104 [94], tetrathioalkenes 105-106 [94, 223-226], dibenzotetrathiafulvalene 107 [226], and tetrathiafulvalene (TTF) 43 [225-228] generated in sulfuric acid, by A1C13 in CH2C12, anodic oxidation, NOBF4 iodine or chlorine oxidation show gav values from 2.0077-2.0193. 

Many easily oxidized organic sulfides exist, but, of these, tetrathiafulvalene [2] (TTF) has been more extensively researched than most, because of interest in the electrical properties of its salts. Its oxidation potential makes it a reasonable electron donor [3]. Arenediazonium salts were chosen as the partner reagents since their electron-accepting properties had been well explored [4, 5]. Furthermore, reaction of TTF with diazonium salts had recently been discussed in the Russian literature [6], but this reported only the formation of the radical-cation, TTF+. We were keen... 

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