Cationic dithiolene metal complexes with 5,6-dihydro-1,4-dithiin-2,3-dithiol: Highly conducting metal complex analogues of BEDT-TTF salts

Metal Complexes of Dithiolate Ligands: 5,6-Dihydro-1,4-dithiin-2,3-dithiolato (dddt2-), 5,7-Dihydro-1,4,6-trithiin-2,3-dithiolato (dtdt2-), and 2-Thioxo-1,3-dithiole-4,5-dithiolato (dmit2-). Synthesis, Electrochemical Studies, Crystal and Electronic Structures, and Conducting Properties

“…(1′-3′) The first two oxidation waves observed, which are quasireversible even at low scan rate, correspond to the [M(dddt) 2 ] 2-/ [M(dddt) 2 ] -and [M(dddt) 2 ] -/[M(dddt) 2 ] 0 couples. In the present case, reaction 3′, which could have been expected [ Ni(dmit) [52][53][54][55] results from the reaction between the [M(dddt) 2 ] 0 and [M(dddt) 2 ] + species. (6′) In the case of the nickel compounds, oxidation-decomposition processes make the mechanism more complicated and explain the irreversibility of the third wave.…”

“…Thus, the [M(dddt) 2 ] complexes may be readily used for the preparation of NIOS radical cation salts. [52][53][54][55] Moreover, the [M(dddt) 2 ] complexes may also be used as donor molecules in the preparation of [M(dddt) 2 ][M′-(dmit) 2 ] x compounds (Vide infra). By contrast, as reaction 3′ does not seem to take place, the preparation of (cation)-[M(dddt) 2 ] z NIOS radical anion salts should not be possible.…”

“…(4‘) A third electron transfer, which appears quasi-reversible only at fast potential scan rates, generates the [M(dddt) 2 ] + cation. (5‘) The formation of the {[M(dddt) 2 ] x + } p+q radical cation, from which several examples of salts have been reported, − results from the reaction between the [M(dddt) 2 ] 0 and [M(dddt) 2 ] + species. (6‘) In the case of the nickel compounds, oxidation−decomposition processes make the mechanism more complicated and explain the irreversibility of the third wave…”

Direct Observation of the Electron-Donating Property of the 5,6-Dihydro-1,4-dithiin-2,3-dithiolate (dddt) Ligands in Square Planar M(dddt)2Complexes (M = Ni, Pd, Pt, and Au)

“…The donor molecule bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF, 1 ) forms radical cations of varying charges between +0.5 and +2. Many salts of BEDT-TTF are metallic, and some are superconductors with critical temperatures ranging from 1 to 13 K. − The 5,6-dihydro-1,4-dithiin-2,3-dithiolate dianions, dddt 2- , generated in situ from a precursor 2,5,7,9-tetrathiabicyclo[4.3.0]non-1(6)-en-8-one (TTBEO), form stable square planar metal complexes [M(dddt) 2 ] - (M = Ni, Pd, Pt, and Au). , The [M(dddt) 2 ] - anions are easily oxidized by chemical oxidants to neutral species [M(dddt) 2 ] ( 2 ), which can be used as a starting material to form conducting salts [M(dddt) 2 ] m X n with monovalent anion X - (e.g., m = 2, n = 1; m = 3, n = 2) with use of electrocrystallization techniques. − More than 20 such salts have been synthesized, and a few of them are metallic from room temperature to 1.3 K. , In describing the electron-donating properties of the [M(dddt) 2 ] (M = Ni, Pd, Pt, and Au) complexes, one faces a similar problem as that found for metal bis(dithiene) complexes [M(S 2 C 2 R 2 ) 2 ] q (M = Ni, Pd, Pt; R = CN, Ph, CF 3 ; q = 0, −1, −2). , In principle, the dddt ligand can carry a charge from 0 in the dithioketone form to −2 in the dithiolato dianion form, and the metal M can also take on various oxidation states. For [Ni(dddt) 2 ] - , both Ni 3+ (d 7 ) and Ni 2+ (d 8 ) electronic configurations have been proposed. ,, So far, there has been no direct experimental proof.…”

“…The synthesis of the dddt compounds studied in our work has been described elsewhere. − All specimens were crystalline samples, and the chemical compositions for majority of the samples were based on X-ray structure determination (see Table ). All Raman measurements were carried out at room temperature with a Raman microscope spectrometer (Renishaw, Ltd.) equipped with a He−Ne laser (λ 0 = 6328 Å).…”