The synthesis and structural characterization of the λ⁵-bis(phosphine sulfide) and the bimetalliccomplexes bis[phosphino-M(CO)₅] (M = Mo, W) of the 3,4-dimethyltetrathiafulvalene (ortho-DMTTF)-based rigid dimer (PPh)₂(o-DMTTF)₂, containing a central 1,4-dihydro-1,4-diphosphi-nine ring, are described. Single-crystal X-ray analyses have been performed for the trans isomers(PhPX)₂(o-DMTTF)₂ (X = S, Mo(CO)₅, and W(CO)₅) and for the cis isomer [PhPW(CO)₅]_2-(o-DMTTF)₂. Planar or slightly folded boat-type conformations are observed for the central six-membered ring, together with different packings characterized by short intermolecular S · · · Scontacts. The optical signature of the oxidized species in the case of the free ligand (PPh)_2-(o-DMTTF)₂ has been evidenced by UV-vis spectroelectrochemistry measurements. SolutionEPR measurements on the radical cation species of (PPh)₂(o-DMTTF)₂ definitely assess the fulldelocalization of the unpaired electron over both electroactive TTF units, with an associatedcoupling of 0.48 G with 12 equivalent protons. The EPR signal of the dication proves the radicalnature of this species, in favor of a triplet ground state. The radical cation of the cis-[PhPW(CO)₅]_2-(o-DMTTF)₂ isomer was also investigated by EPR, for which the observed hyperfine structuredemonstrates the extended delocalization of the electron, together with a larger coupling constantwith the phosphorus nuclei. DFT calculations for the radical cation of (PPh)₂(o-DMTTF)₂ afford aboat-type conformation for the central ring and a SOMO consistent with a full delocalization of theelectron over both TTF units. Moreover, the calculations indicate that in the case of the dication of(PPh)₂(o-DMTTF)₂ the triplet state is more stable by 11.7 kcal mol^-1 than the singlet state.

We describe the preparation of a helicate containing four closely spaced, linearly arrayed copper(I) ions. This product may be prepared either directly by mixing copper(I) with a set of precursor amine and aldehyde subcomponents, or indirectly through the dimerization of a dicopper(I) helicate upon addition of 1,2-phenylenediamine. A notable feature of this helicate is that its length is not limited by the lengths of its precursor subcomponents: each of the two ligands wrapped around the four copper(I) centers contains one diamine, two dialdehyde, and two monoamine residues. This work thus paves the way for the preparation of longer oligo- and polymeric structures. DFT calculations and electrochemical measurements indicate a high degree of electronic delocalization among the metal ions forming the cores of the structures described herein, which may therefore be described as "molecular wires".

A new type of stable radical ligand featuring a 1,1-bis-phosphinosulfide alkene backbone has been prepared and characterized on the basis of X-ray diffraction, EPR and DFT studies.

The synthesis and characterization of two ortho-dimethyltetrathiafulvalene (o-DMTTF)-based rigid dimers containing dimethylsilicon (Me₂Si) or dimethylgermanium (Me₂Ge) linkers are described. Single-crystal X-ray analysis reveals planar geometry for the central 1,4-disilicon or 1,4-digermanium six-membered rings. DFT calculations provide optimized conformations in agreement with the experimental ones, and also emphasize the role of the heteroatomic linkers in the conjugation between the two redox active units. Cyclic voltammetry measurements show sequential oxidation into radical cation, and then dication species. Solution EPR measurements on the radical-cation species indicate full delocalization of the unpaired electron over both electroactive TTF units, with an associated coupling of 0.42 G with twelve equivalent protons. DFT calculations afford fully planar geometry for the radical-cation species and confirm the experimental isotropic coupling constant. Single-crystal X-ray analyses of two charge-transfer compounds obtained upon chemical oxidation, formulated as [(Me₂Si)₂(o-DMTTF)₂]-1/2[TCNQ]·1/2[TCNQF₄] and [(Me₂Ge)₂(o-DMTTF)₂]·[TCNQ], demonstrate the occurrence of genuine mixed-valence radical-cation species, as well as a three-dimensional network of short S···S intermolecular contacts. Temperature-dependent conductivity measurements demonstrate semiconducting behavior for both charge-transfer compounds, with an increase of the absolute value of the conductivity upon applying external pressure. Band structure calculations reveal peculiar pseudo-two-dimensional electronic structures, also confirming electronic interactions through SiMe₂ and GeMe₂ bridges.

One-electron reduction of a diphosphafulvenium dication gives the first stable diphosphafulvenium monoradical cation (see scheme). An X-ray crystal structure analysis, EPR measurements, and DFT calculations clearly show that reduction takes place at the exocyclic double bond and that the excess of electron density is stabilized by the two electron-withdrawing phosphonium groups (see SOMO; P orange, C dark gray, H light gray).

The radical cation of the redox active ligand 3,4-dimethyl-3',4'-bis-(diphenylphosphino)-tetrathiafulvalene ( P2) has been chemically and electrochemically generated and studied by EPR spectroscopy. Consistent with DFT calculations, the observed hyperfine structure (septet due to the two methyl groups) indicates a strong delocalization of the unpaired electron on the central S₂C=CS₂ part of the tetrathiafulvalene (TTF) moiety and zero spin densities on the phosphine groups. In contrast with the ruthenium(0) carbonyl complexes of P2 whose one-electron oxidation directly leads to decomplexation and produces P2^•+, one-electron oxidation of [Fe( P2)(CO)₃] gives rise to the metal-centered oxidation species [Fe^(I)( P2)(CO)₃], characterized by a coupling with two ³¹P nuclei and a rather large g-anisotropy. The stability of this complex is however modest and, after some minutes, the species resulting from the scission of a P–Fe bond is detected. Moreover, in presence of free ligand, [Fe^(I)( P2)(CO)₃] reacts to give the complex [Fe^(I)( P2)₂(CO)] containing two TTF fragments. The two-electron oxidation of [Fe( P2)(CO)₃] leads to decomplexation and to the P2^•+ spectrum. Besides EPR spectroscopy, cyclic voltammetry as well as FTIR spectroelectrochemistry are used in order to explain the behaviour of [Fe( P2)(CO)₃] upon oxidation. This behaviour notably differs from that of the Ru(0) counterpart. This difference is tentatively rationalized on the basis of structural arguments.