The contrasted structural and magnetic behaviour of two single-component paramagnetic dithiolene complexes

International audienceThe neutral organometallic/dithiolene radical complexes [CpNi(oxddt)] and [CpNi(bddt)] were prepared, respectively, from the reactions of [Ni(oxddt)2] with [Cp2Ni] and (NBu4)[Ni(bddt)2] with [CpNi(cod)](BF4) (oxddt = o-xylenediyldithioethylene-1,2-dithiolato, bddt = 1,4- butanediyldithioethylene-1,2-dithiolato). Both complexes exhibit reversible oxidation and reduction waves to the cation and anion forms, respectively. A NIR absorption is observed around lmax = 825 for [CpNi(oxddt)] and 774 nm for [CpNi(bddt)] in dichloromethane solution. The X-ray crystal structures of the two complexes show two-legged piano-stool geometries around the central nickel atom (formally NiIII) and strong distortions from planarity of the eightmembered ring moieties. In the solid state, the stronger rigidity of [CpNi(oxddt)] allows for a face-to-face p-p stacking of the radicals into dyads, confirmed by a singlet-triplet magnetic behaviour while the more flexible [CpNi(bddt)] radical complexes only interact through a lateral antiferromagnetic interaction giving rise to Heisenberg-type uniform spin chains

Helical organization of chiral binaphthyl tetrathiafulvalene primary amides through hydrogen bonding interactions

International audienceChiral tetrathiafulvalenes, (R) or (S), or racemic, (R,S), are obtained from a phosphite-mediated cross coupling reaction of a 1,3-dithiole-2-thione derivative bearing one binaphthol moiety, and are transformed into binaphthol-based tetrathiafulvalene ortho-diamides. The X-ray crystal structures of five intermediate chiral 1,3-dithiole-2-one and 1,3-dithiole-2-thione derivatives reveal the formation of helical structures through p-p interactions. The binaphthol-based tetrathiafulvalene ortho-diamides, as THF or DMSO solvates, adopt different solid-state organisations, characterised either by short intramolecular hydrogen bonds or with solely intermolecular hydrogen bonds and chiral solid-state structures with short intermolecular S/S contacts

Experimental and theoretical evaluation of magnetic coupling in organometallic radicals: the eloquent case of face-to-face CpCp interactions

International audienceThe solid state magnetic properties of an extensive series of neutral radical (S = ½) complexes associating cyclopentadienyl (Cp) and dithiolene ligands and formulated as [CpNi(dithiolene)]˙, are successfully rationalized through a combination of structural analysis of the crystal structures and broken symmetry DFT calculations. The highly delocalized spin density of these complexes allows for strong antiferromagnetic interactions between radical species, which involve not only short intermolecular SS contacts but also SCp and CpCp contacts, demonstrating that the cyclopentadienyl moiety can effectively act as a non-innocent ligand in metal complexes where it bears a sizeable fraction of the spin density, for example, up to 20% in these [CpNi(dithiolene)]˙ neutral radical complexes

A binaphthol-substituted tetrathiafulvalene with axial chirality and its enantiopure TCNQF4 charge-transfer salts

International audienceA chiral tetrathiafulvalene (1) bearing a binaphtholdimethylene moiety on one side, an ethylenedithio substituent on the other side, is prepared from atropoisomeric (R)-, (S)- and racemic (R,S)-binaphthol. Its oxidation potential (0.49 V vs. SCE) allows for its oxidation with TCNQF4. Crystal structures of the neutral racemic (R,S)-1 and enantiopure (R)-1 were determined together with those of the enantiopure charge-transfer salts formulated as [(R)-1][TCNQF4]*CH2Cl2 and [(S)-1][TCNQF4]*CH2Cl2, the first enantiomeric salts of chiral TTFs with axial chirality. Despite the peculiar geometry adopted by the binaphthyl moieties in the constrained ten-membered ring in 1, stacking of the donor molecules is observed, both in the neutral state and in the TCNQF4 charge transfer salts where the (1)+˙ and (TCNQF4)−˙ radical species are associated, respectively, into [(1)2]2+ and [(TCNQF4)2]2− homodyads, both in their singlet state

Hybrid Material Based on the Lindquist Polyoxometalate [W6O19]2− and the organosulfur donor o-Me2TTF: A Combined Structural and Spectroscopic Study

International audienceThe synthesis, crystal structure and spectroscopic properties of the hybrid radical cation salt containing oxidized o-3,4-dimethyltetrathiafulvalene (o-Me2TTF) and the Lindquist polyoxometalate anion [W6O19]2− are reported. The title salt represents the first time a Lindquist polyoxometalate has been utilized as the counter anion with this unsymmetrical member of the TTF family of derivatives. The salt crystallizes in the triclinic space group P1¯ with a = 7.6211(7) Å, b = 9.5231(9) Å, c = 12.2148(11) Å, α = 105.5870(10)°, β = 106.8340(10)° and γ = 95.6950(10)°. Resolution of the solid state structure revealed that the o-Me2TTF radical cations aggregate as isolated face-to-face dimers with intradimer interactions between neighboring sulfur atoms at distances <3.6 Å. Hydrogen bonding was also observed between hydrogen atoms bound to sp 2-hybridized carbon atoms of o-Me2TTF and bridging oxygen atoms of [W6O19]2−. Single crystal IR and Raman spectra were also collected and provide further evidence that the o-Me2TTF donors have been oxidized to their corresponding radical cationic states

The thiocyanate anion as a polydentate halogen bond acceptor

International audienceCo-crystallisation of the Et4N+ or n-Bu4N+ salts of the thiocyanate anion with o-, m- and p-diodoperfluorobenzene or the sym-trifluorotriiodobenzene allowed for the isolation of six different salts which were structurally characterized by single crystal X-ray diffraction. Halogen bonding interactions are observed between the neutral iodinated molecules acting as halogen bond donors and the S or N ends of the thiocyanate anion, with a variety of bonding modes (terminal as well as bridging), and characterised by short I(N,S) contacts and linear C-I(N,S) motifs. On the other hand, the IN≡C angles present deviations from linearity (145-170°) while the IS-C angles are close to 90°, revealing a type II halogen bond interaction with the S atom acting as pseudo halogen. The observation of structures where only the S or the N atom are engaged in halogen bonding suggests that the two coordination modes are close in energy, as confirmed by DFT calculations and ELF analysis which give also a rationale for the observed structural preferences. This bidentate nature of the SCN− anion in halogen bonding interactions is reminiscent of its various coordination modes with the Cd2+ cation, best understood in terms of the hard-soft acid-base concept

Paramagnetic dithiolene complexes as metallo-ligands: ether/thioether coordination.

International audienceThe secondary coordination ability of a paramagnetic nickel dithiolene complex, bearing an ether coordinating function within a nine-membered flexible ring, has been demonstrated in its [NiCl(DMF)(2)](+) complex, through coordination by both ether and thioether functions, allowing for a ferromagnetic interaction between both paramagnetic entities

Electron-molecular vibration coupling in (DMtTTF)Br and (o-DMTTF)2[W6O19] salts studied by vibrational spectroscopy

International audienceA novel 1:1 salt encompassing radical cations of DMtTTF (DMtTTF = dimethyltrimethylene-tetrathiafulvalene) and the Br−anion has been synthesized. Close inspection of the salt's solid state structure revealed the presence of quasi-isolated dimers containing DMtTTF radical cations, a specific arrangement whereby the microscopic parameters of DMtTTFradical dot+ might be studied. Analysis of the corresponding single crystal IR and Raman spectra of (DMtTTF)Br allowed us to study the material's electronic and vibrational structure and to evaluate the electron-molecular coupling constants via the isolated dimer model. Additionally, using previously published IR data, analogous calculations were performed on the salt (o-DMTTF)2[W6O19] (o-DMTTF = o-3,4-dimethyltetrathiafulvalene), which also contains well isolated dimers of o-DMTTF radical cations. These calculations revealed that the coupling constants for the unsymmetrical donors studied herein are comparable to those for symmetric TTF derivatives

Redox-active proligands from the direct connection of 1,3-dithiol-2-one to tetrathiafulvalene (TTF): syntheses, characterizations and metal complexation

International audienceIn the search for novel tetrathiafulvalene-substituted dithiolene ligands, two tetrathiafulvalene (TTF) molecules directly connected to 1,3-dithiol-2-one fragments have been synthesized and characterized by single crystal X-ray diffraction, electrochemical and spectroscopic analyses. TTF1 was obtained, in moderate yield, by the cross-coupling of 4,5-bis(methylthio)-1,3-dithiole-2-one with 4,4′-bis(1,3-dithiole-2-one) in triethylphosphite, whereas for TTF2, the 1,3-dithiol-2-one fragment was introduced, in high yield, by an original reaction of the alkyne group of an ethynyl TTF (Me3TTF-C[triple bond, length as m-dash]CH) with xanthogen in the presence of a radical initiator. Opening of the 1,3-dithiol-2-one fragments with sodium methanolate leads to the formation of two new 1,2-dithiolate ligands functionalized with redox-active TTF moieties, which can efficiently coordinate metals. As an illustration, two original heteroleptic bis(cyclopentadienyl)dithiolene titanium complexes were isolated and characterized

Halogen Bonding Interactions in DDQ Charge Transfer Salts with Iodinated TTFs

International audienceOxidation of 3,4-ethylenedithio-3'-iodo-tetrathiafulvalene (EDT-TTF-I) and 3,4-ethylenedithio-3',4'-diiodo-tetrathiafulvalene (EDT-TTF-I2) with DDQ afforded two different salts formulated as (EDT-TTF-I)(DDQ) and (EDT-TTF-I2)2(DDQ)*(CH3CN), both characterized with a full charge transfer to the DDQ acceptor moiety and by short and linear halogen bonding interactions between the iodine atom as halogen bond donor, and the carbonyl oxygen or the nitrile nitrogen atoms of reduced DDQ