Radical Anion Complex Research Articles

Assessing the Character of the C6F5 Ligand from the Electrochemical and Photophysical Properties of [Ni(C6F5)2(N∧N)] Complexes.

Organonickel complexes containing α-diimine ligands [Ni(C6F5)2(N∧N)] (N∧N = 2,2'-bipyridine (bpy), 2,9-dimethyl-1,10-phenanthroline (dmphen), 3,4,7,8-tetramethyl-1,10-phenanthroline (tmphen), dipyrido[3,2-a:2',3'-c]phenazine (dppz), 1,4-bis(isopropyl)-1,4-diazabutadiene (iPr-DAB), and 1,4-bis(2,6-dimethylphenyl)-1,4-diazabutadiene (Xyl-DAB) were prepared and studied structurally, spectroscopically, and electrochemically. Their molecular structures from single-crystal X-ray diffraction show near-perfect square planar Ni(II) coordination except in the case of dmphen. Primary reversible electrochemical reductions in the range from -1 to -2 V vs ferrocene/ferrocenium couple lead to mainly diimine-localized radical anion complexes, while secondary reductions in the range from -2 to -2.5 V lead to dianion complexes, as shown through spectroelectrochemistry. Irreversible metal-centered oxidations at around 0.7 V result in rapid aryl-aryl reductive elimination and formation of decafluorobiphenyl. No photoluminescence was detected for the complexes containing chromophoric α-diimine ligands at room temperature. At 77 K in frozen glassy 2-Me-THF matrices, weak photoluminescence was detected for the dmphen and tmphen derivatives, with broad emission bands peaking around 570 nm. All results are rationalized with the support of (TD-)DFT calculations, highlighting the role of the C6F5 ligand in different systems.

N‒N hydrazonyl bond cleavage in benzothiazolyl-hydrazino-phenathrenequinone mediated by ruthenium(II) via an anion radical intermediate

The complexes [Ru(LBenz)H(CO)(PPh3)2] 2, [Ru(LBenz)Cl(CO)(PPh3)2] 3, (ligand behaving as bidentate monoanionic) and [Ru(LBenz)Cl(CO)(PPh3)] 4, (ligand is tridentate monoanionic) have been synthesized starting from benzothiazolyl-hydrazino-phenathrenequinone (HL) 1 and [RuH(CO)Cl(PPh3)3]. These are characterized by electrochemical and spectral methods as well as single crystal X-ray diffractometry (SCXRD). Upon treating with NaBH4, 3 accepts an electron within the coordinated ligand framework and the anionic hydrazonyl-N takes up a proton to be transformed to meta-stable hydrazinoquinone anion radical complex of ruthenium(II) [Ru(HLBenz•‒)Cl(CO)(PPh3)2] 5, possibly via concerted proton electron transfer process (CPET). Thus, the redox non-innocent character of the ligand upon complexation with ruthenium(II), has been disclosed and it is attributed to presence of low lying π* orbitals of almost entirely of phenanthraquinone and hydrazone character. In 5, the π‒acceptor ability of the ligand donor centres are reduced due to the existence of an odd electron in SOMO and hence the M-L distances around the coordination sphere are altered. The N‒N (hydrazonyl bond length increases from 1.296(6) Å in 3 to 1.429 Å in 5, leading to lesser thermodynamic stability of the latter and upon standing, the N‒N bond is cleaved to be transformed to 6+, possibly via the formation of iminoquinone anion radical complex, [6] (reported elsewhere). Also, it is via the dissociation of N‒N (hydrazonyl) bond, the biologically important molecule 2-aminobenzothiazole is formed along with 6+, so as to provide a novel route for its synthesis.

Coligands Controlled Reactivities of Ruthenium(II) Precursors: Antiferromagnetically Coupled Ruthenium(III)-Phenoxyl versus Ruthenium(II)-Phenoxyl Forms.

The study disclosed that the reactivities of [RuII (PPh3)3Cl2] and [RuII(PPh3)3(CO)(H)Cl] precursors toward a trimethoxyarylimino-phenol derivative are sensibly different. The former promotes methoxy demethylation reaction affording a [Phenolato-RuIII-Phenolato] unit, while the latter containing π-acidic CO and hydride as coligands leads to C-H activation reaction, generating a [Phenolato-RuII-Aryl] unit. Notably, the oxidized analogues of these two forms produce antiferromagnetically coupled [RuIII-phenoxyl] and paramagnetic [RuII-phenoxyl] forms, which exhibit diverse reactivities. Surprisingly, the magnetically coupled [RuIII-phenoxyl] form obtained from [Phenolato-RuIII-Phenolato] motif leads to coligand, PPh3 oxidation and undergoes dimerization, making a Ru-Ru bond (2.599(2) Å), while the [RuII-phenoxyl] form obtained from [Phenolato-RuII-Aryl] motif leads to C-C coupling and H abstraction reactions. The coupling reaction affords a 4,4'-dibenzosemiquinonate anion radical complex, but the H-abstraction of the phenoxyl form gives a [RuII-Phenol] complex. For comparison, [RuII(IQR0)] and [RuII(ISQR·-)] complexes were also isolated, where IQR0 and ISQR·- are p-R-o-iminobenzoquinone and p-R-o-iminobenzosemiquinonate anion radicals. However, they fail to promote any bond-formation reaction. The molecular and electronic structures of the ruthenium (II/III) complexes were confirmed by single-crystal X-ray crystallography, EPR spectroscopy, and DFT calculations.

Monovalent Thulium. Synthesis and Properties of TmI

The reaction of thulium shavings with iodine at 680°C gave a poorly separable product mixture A, consisting of thulium metal (65%), TmI2 (14%), and TmI (21%). Monovalent thulium iodide could not be isolated in a pure state, but its presence among the products was confirmed, apart from magnetic measurements, by reactions with naphthalene and perylene, which proceed under mild conditions. The reaction of TmI with naphthalene, which takes place at –40°C, affords the trivalent thulium complex with naphthalene dianion, [TmI(C10H8)(DME)3]. The multistep reaction with perylene starts with the formation of the divalent thulium radical anion complex, [(TmI)+(C20H12)–•(DME)3], and ends in the formation of trivalent thulium complex, [(TmI)2+(C20H12)2–(DME)3]. The presence of a radical anion intermediate in the reaction mixture in an early stage was confirmed by ESR spectroscopy.

Reliable Isotropic Electron-Paramagnetic-Resonance Hyperfine Coupling Constants from the Frozen-Density Embedding Quasi-Diabatization Approach.

We present a systematic benchmark of isotropic electron-paramagnetic-resonance hyperfine coupling constants calculated for radical cation and anion complexes of molecules contained in the S22 test set using the frozen-density embedding quasi-diabatization (FDE-diab) approach. The results are compared to those from Kohn-Sham density-functional theory and frozen-density embedding, employing the domain-based local pair natural orbital coupled cluster singles and doubles method as a reference. We demonstrate that our new approach outperforms frozen-density embedding in all cases and provides reliable hyperfine couplings for radical cations using rather simple generalized-gradient approximation-type functionals. By contrast, more sophisticated and computationally less efficient exchange-correlation approximations are required for Kohn-Sham density-functional theory. For the radical anions, FDE-diab can at least provide an accuracy similar to that of Kohn-Sham density-functional theory. Finally, we demonstrate the computational advantages of FDE-diab for a π-stacked benzene octamer radical cation.

Azo-oximate metal-carbonyl to metallocarboxylic acid via the intermediate Ir(III) radical congener: quest for co-ligand driven stability of open- and closed-shell complexes.

The redox non-innocent behavior of the diaryl-azo-oxime ligand LNOH1 has been accentuated via the synthesis of metastable anion radical complexes of type trans-[Ir(LNO˙-)Cl(CO)(PPh3)2] 2 (CO is trans to azo group of the ligand) by the oxidative coordination reaction of 1 with Vaska's complex. The stereochemical role of co-ligands vis-à-vis the interplay of π-bonding has been found to be decisive in controlling the aptitude of the coordinated redox non-innocent ligand to accept or reject an electron. This has been clarified via the isolation of quite a few complexes as well as the failure to synthesize some others. The oxidized analogues of type trans-[Ir(LNO-)Cl(CO)(PPh3)2]+2+ (CO and azo group of the ligand are trans) as well as its cis isomer cis-[Ir(LNO-)Cl(CO)(PPh3)2]+3+ (CO and azo group of the ligand are cis) have been structurally characterized but the radical anion congener of the latter could not be synthesized. Furthermore, the closed shell complexes [Ir(LNO-)Cl2(PPh3)2] 4 and [Ir(LNO-)2Cl(PPh3)] 5 have been well characterized by diffraction as well as spectral techniques but their corresponding azo anion radical complexes could not be isolated and this is attributed to the trans influence of ancillary ligands. The anion radical complexes trans-[Ir(LNO˙-)Cl(CO)(PPh3)2] 2 may be rapidly transformed to the metallocarboxylic acids trans-[Ir(LNO-)Cl(CO2H)(PPh3)2] 6via a proton-coupled electron transfer (PCET) process, thereby demonstrating the role of odd electron over the coordinated ligand framework to trigger metal-mediated carbonyl to carboxylic acid functionalization. Complexes 6 are further stabilized via intramolecular -CO2H⋯ON- (carboxylic acid⋯oximato) H-bonding. The optoelectronic properties as well as the origin of transitions in the complexes were analyzed by TD-DFT and theoretical analysis, which further disclose that the odd electron in trans-[Ir(LNO˙-)Cl(CO)(PPh3)2] 2 is primarily azo-oxime centric with very low contribution from the iridium center.

Analysis of Non-innocence of Phosphaquinodimethane Ligands when Charge and Aromaticity Come into Play.

Several phosphaquinodimethanes and their M(CO)5 complexes (M=Cr, Mo, W) and model derivatives have been theoretically investigated regarding the quest of non‐innocence. Computed structural and electronic properties of the P‐Me/NH2 substituted phosphaquinodimethanes and tungsten complexes revealed an interesting non‐innocent ligand behaviour for the radical anion complexes with distonic ion character and a strong rearomatization of the middle phenyl ring. The latter was further probed taking also geometric aromaticity (HOMA) and quinoid distortion parameters (HOMQc) into account, as well as NICS(1). Furthermore, the effect of the P‐substitution was investigated for real (or plausible) complexes and their free ligands focusing on the resulting aromaticity at the middle phenyl ring and vertical one‐electron redox processes. The best picture of ligand engagement in redox changes was provided by representing NICS(1) values versus HOMA and the new geometric distortion parameter HOMQc8.

Introducing Selenium in Single-Component Molecular Conductors Based on Nickel Bis(dithiolene) Complexes.

Two selenated analogues of the all-sulfur single-component molecular conductor [Ni(Et-thiazdt)2] (Et-thiazdt = N-ethylthiazoline-2-thione-4,5-dithiolate) have been prepared from their precursor radical-anion complexes. Replacement of the thione by a selenone moiety gives the neutral [Ni(Et-thiazSedt)2] complex. It adopts an unprecedented solid-state organization (for neutral nickel complexes), with the formation of perfectly eclipsed dimers and very short intermolecular Se···Se contacts (81% of the van der Waals contact distance). Limited interactions between dimers leads to a large semiconducting gap and low conductivity (σRT = 1.7 × 10-5 S cm-1). On the other hand, going from the neutral [Ni(Et-thiazdt)2] dithiolene complex to the corresponding [Ni(Et-thiazds)2] diselenolene complex gives rise to a more conventional layered structure built out of uniform stacks of the diselenolene complexes, different, however, from the all-sulfur analogue [Ni(Et-thiazdt)2]. Band structure calculations show an essentially 1D electronic structure with large band dispersion and a small HOMO-LUMO gap. Under high pressures (up to 19 GPa), the conductivity increases by 4 orders of magnitude and the activation energy is decreased from 120 meV to only 13 meV, with an abrupt change observed around 10 GPa, suggesting a structural phase transition under pressure.

Anion-Radical Polymerization of Sulfur- and Selenium-Substituted N-Type Conjugated Polymers

While controlled chain-growth polymerizations have been developed for a handful of p-type conjugated polymers, most n-type conjugated polymers are still synthesized through step-growth methods that offer little to no control over the polymerization. The anion-radical polymerization of thiophene-flanked naphthalene diimides has been shown to exhibit non-living chain-growth behavior; however, anion-radical polymerizations are limited to a few examples that exhibit varying degrees of control. Strategies to improve and expand the scope of this promising methodology have not been developed. In this study, we investigate the anion-radical polymerization of a series of oxygenated and thionated, thiophene- and selenophene-flanked naphthalene diimides. We show, through optical and spectroelectrochemical studies, that anion-radical monomers likely consist of a complex mixture of organic radicals with varying oxidation states. Surprisingly, subtle changes in monomer structure afforded by sulfur and selenium substitution result in significant changes in polymer synthesis. Notably, selenophene-flanked naphthalene diimides polymerize more rapidly to reach higher degrees of polymerization when compared to thiophene-flanked analogues. While thionated naphthalene diimides form anion-radical complexes and exhibit signs of catalyst insertion, they do not undergo polymerization. These results provide insights into the further development of anion-radical polymerization as a promising route to well-defined n-type conjugated polymers.

Pre-Sodiated Ti3C2Tx MXene Structure and Behavior as Electrode for Sodium-Ion Capacitors.

Layered titanium carbide (Ti3C2Tx) MXene is a promising electrode material for use in next-generation electrochemical capacitors. However, the atomic-level information needed to correlate the distribution of intercalated cations with surface redox reactions, has not been investigated in detail. Herein we report on sodium preintercalated MXene with high sodium content (up to 2Na per Ti3C2Tx formula) using a solution of Na-biphenyl radical anion complex (E0 ≈ -2.6 SHE). Multiple sodiation sites and formation of a two-dimensional sodium domain structure at interfaces/surfaces is identified through combined computational simulations with neutron pair distribution function analysis. The induced layer charges and the redox process characterized by the density-functional tight-binding method on a local scale are found to greatly depend on the location of sodium ions. Electrochemical testing of the pre-sodiated MXene as an electrode material in a sodium-ion capacitor shows excellent reversibility and promising performance, indicating the feasibility of chemical preintercalation as an approach to prepare MXene electrodes for ion capacitors.

Structure and Magnetic Properties of Superoxide Radical Anion Complexes with Low Binding Energy at the Graphene Edges

The complexes of superoxide radical anions formed at the zigzag edges of curved graphene sheets upon microwave excitation were studied by electron spin resonance and quantum chemical density functional theory. The binding energy of the complex decreases from 700 to 42 meV as the distance between the oxygen atom and the zigzag graphene edge increases from 1.46 to 1.64 A. The configurations and binding energies of the complexes depend both on the topology of the underlying graphene layer (single- or double-layer, flat, or curved) and on the type of atomic groups terminating the edge carbon atoms via σ-bonds. Complexes with low dissociation energy (<70 meV) can be formed only at cryogenic temperatures as a result of electronic charge transfer from the edge towards the O2 molecule. The temperature behavior of the paramagnetic spin susceptibility of the complex indicates an antiferromagnetic interaction of the spin S = 1/2 of the $${\text{O}}_{2}^{{-*}}$$ radical anions with the edge spins located outside the area “demagnetized” due to its depletion by the electronic charge. At T > 50 K, the complex irreversibly dissociates and the O2 molecule is detached from the edge. The existence of complexes with a low dissociation energy expands the views on the ionic chemical bond with a large distance between the interacting species.

Visible-Light-Driven Anti-Markovnikov Hydrocarboxylation of Acrylates and Styrenes with CO 2

Light-driven carbon dioxide (CO2) capture and utilization is one of the most fundamental reactions in Nature. Herein, we report the first visible-light-driven photocatalyst-free hydrocarboxylation ...

Oxidation State Assignments in the Organoplatinum One‐Electron Redox Series [(N^N)PtMes2]n, n = +,0, –,2‐

The neutral complexes [(N^N)PtMes2], N^N = bis(1‐methyl‐2‐imidazolyl)ketone (bik) or N,N'‐disubstituted 1,2‐bis‐iminoacenaphthenes (R‐BIAN), Mes = mesityl, were obtained and characterized as PtII species with planar N2PtC2 configuration and charge transfer transitions in the visible. Reversible one‐electron reduction produces radical anion complexes with the spin predominantly localized in the N^N ligand, according to EPR, UV/Vis‐IR spectroelectrochemistry, DFT and TD‐DFT studies. Reversible one‐electron oxidation was also possible, attributed to the steric and electronic influence from the mesityl ligands. The EPR silent cation [(bik)PtMes2]+ was characterized by UV/Vis‐NIR spectroscopy and TD‐DFT calculations as a system with spin density contributions from Pt (31 %) and two mesityl groups (69 %).

Evidence For a Water-Stabilised Ion Radical Complex: Photoelectron Spectroscopy and Ab Initio Calculations

A photoelectron spectrum corresponding to an unknown 174m/z anion complex has been recorded. Initially believed to be I−…CH3CH2OH (173m/z), the spectrum has been assigned as belonging to that of an I−…H2O…CH3CH2 radical anion complex. The major peaks in the photoelectron spectrum occur at 3.54eV and 4.48eV as the 2P3/2 and 2P1/2 spin-orbit states of iodine respectively. Ab initio calculations were performed in order to rationalise the existence of the complex, with all structures converging to a ‘ring-like’ geometry, with the iodide anion bound to both the water molecule as well as a hydrogen of the ethyl radical, with the other hydrogen of water bound to the unpaired electron site of the ethyl. Simulated vertical detachment energies of 3.59eV and 4.53eV were found to be in agreement with the experimental results.

Radical Anions, Radical-Anion Salts, and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles.

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1-3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [1].- and [2].- , RA [3].- was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1-3 was performed and new thermally stable RA salts [K(THF)]+ [2].- (8) and [K(18-crown-6)]+ [2].- (9) were isolated in addition to known salt [K(THF)]+ [1].- (7). On contact with air, RAs [1].- and [2].- underwent fast decomposition in solution with the formation of anions [ECN]- , which were isolated in the form of salts [K(18-crown-6)]+ [ECN]- (10, E=S; 11, E=Se). In the case of 3, RA [3].- was detected by EPR spectroscopy as the first representative of tellurium-nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]+ 2 [3-Te2 ]2- (12) featuring a new anionic complex with coordinate Te-Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]+ 2 [3-Te4 -3]2- (13) containing an anionic complex with two coordinate Te-Te bonds. The structures of 8-13 were confirmed by XRD, and the nature of the Te-Te coordinate bond in [3-Te2 ]2- and [3-Te4 -3]2- was studied by DFT calculations and QTAIM analysis.

Real-time observation of interfragment vibration and charge transfer within the TCNQF4 dimer

The organic electron acceptors, 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF4), are widely used to synthesize multivalent charge-transfer complexes. Their corresponding radical anion complexes have specific electronic, optical, and magnetic characters that have attracted attention in the field of materials development. In the present work, we have performed time-resolved absorption spectroscopy of the (Na+)2(TCNQF4−)2 radical anion complex to elucidate the reaction dynamics ([TCNQF4−]2→TCNQF4+TCNQF42−). A visible sub-10fs laser pulse was used to observe the ultrafast dynamics of the charge transfer and real-time change of the molecular structure during the reaction. Unlike our previous work on the (Na+)2(TCNQ−)2 radical anion complex, the interfragment vibrational mode was clearly observed for (Na+)2(TCNQF4−)2. The difference in the intermolecular interaction is considered to reflect the difference in the π-π interaction and/or the difference in the flexibility of the molecular plane predicted by theoretical calculations.

Solution Synthesis, Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3 )2 ]3 }.

The first crystallographically characterizable complex of Sc2+ , [Sc(NR2 )3 ]- (R=SiMe3 ), has been obtained by LnA3 /M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR2 )3 with K in the presence of 2.2.2-cryptand (crypt) and 18-crown-6 (18-c-6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]+ , [K(18-c-6)]+ , and [Cs(crypt)]+ salts of the [Sc(NR2 )3 ]- anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight-line EPR spectra arising from the I=7/2 45 Sc nucleus. The Sc(NR2 )3 reduction differs from Ln(NR2 )3 reactions (Ln=Y and lanthanides) in that it occurs under N2 without formation of isolable reduced dinitrogen species. [K(18-c-6)][Sc(NR2 )3 ] reacts with CO2 to produce an oxalate complex, {K2 (18-c-6)3 }{[(R2 N)3 Sc]2 (μ-C2 O4 -κ1 O:κ1 O'')}, and a CO2- radical anion complex, [(R2 N)3 Sc(μ-OCO-κ1 O:κ1 O')K(18-c-6)]n .

Solution Synthesis, Structure, and CO2 Reduction Reactivity of a Scandium(II) Complex, {Sc[N(SiMe3)2]3}−

AbstractThe first crystallographically characterizable complex of Sc2+, [Sc(NR2)3]− (R=SiMe3), has been obtained by LnA3/M reactions (Ln=rare earth metal; A=anionic ligand; M=alkali metal) involving reduction of Sc(NR2)3 with K in the presence of 2.2.2‐cryptand (crypt) and 18‐crown‐6 (18‐c‐6) and with Cs in the presence of crypt. Dark maroon [K(crypt)]+, [K(18‐c‐6)]+, and [Cs(crypt)]+ salts of the [Sc(NR2)3]− anion are formed, respectively. The formation of this oxidation state of Sc is also indicated by the eight‐line EPR spectra arising from the I=7/2 45Sc nucleus. The Sc(NR2)3 reduction differs from Ln(NR2)3 reactions (Ln=Y and lanthanides) in that it occurs under N2 without formation of isolable reduced dinitrogen species. [K(18‐c‐6)][Sc(NR2)3] reacts with CO2 to produce an oxalate complex, {K2(18‐c‐6)3}{[(R2N)3Sc]2(μ‐C2O4‐κ1O:κ1O′′)}, and a CO2− radical anion complex, [(R2N)3Sc(μ‐OCO‐κ1O:κ1O′)K(18‐c‐6)]n.

An Azobenzenyl Anion Radical Complex of Magnesium: Synthesis, Structure, and Reactivity Studies.

Azobenzenyl anion radical complex of magnesium [HC(C(Me)N-2,6-iPr2C6H3)2]Mg(PhNNPh) (THF) (2) was obtained for the first time through the reaction of [HC(C(Me)N-2,6-iPr2C6H3)2]MgBr (1) with potassium graphite in the presence of azobenzene. Complex 2 is a useful electron-transfer reagent as shown by the reactivity with diphenyl disulfide, diphenyl diselenide, oxygen, sulfur, and Me3SiN3 yielding the magnesium thiolate [HC(C(Me)N-2,6-iPr2C6H3)2]Mg(SPh)(THF) (3), magnesium selenolate [HC(C(Me)N-2,6-iPr2C6H3)2]Mg(SePh)(THF) (4), peroxido complex {[HC(C(Me)N-2,6-iPr2C6H3)2]Mg(THF)}2(μ-η2-η2-O2) (5), persulfido complex {[HC(C(Me)N-2,6-iPr2C6H3)2]Mg(THF)}2(μ-η2-η2-S2) (6), and azido complex [HC(C(Me)N-2,6-iPr2C6H3)2]MgN3 (7), respectively. Furthermore, treatment of 2 with Me3SiCHN2 results in a rearrangement product {[HC(C(Me)N-2,6-iPr2C6H3)2]Mg[CNN(SiMe3)]}2 (8).

Localization versus Delocalization in Chiral Single Component Conductors of Gold Bis(dithiolene) Complexes.

The first examples of chiral single component conductors are reported. Both (S,S) and (R,R) enantiomers of 5,6-dimethyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (dm-dddt) ligand have been used to prepare anionic metal bis(dithiolene) complexes formulated as ([(n-Bu)4N][M(dm-dddt)2] (M = Au, Ni), which are isostructural according to single crystal X-ray analysis. Single crystal transport measurements indicate semiconducting behavior for the anionic radical Ni complexes, with low room temperature conductivity values and high activation energies. Electrocrystallization experiments provided neutral [M(dm-dddt)2] (M = Au, Ni) complexes. The neutral radical gold compounds show intermolecular S···S interactions in the solid state giving rise to layers interconnected through weak C-H···S hydrogen bonds. The most peculiar structural feature concerns a dissymmetry between the two dithiolene moieties, while the nickel counterpart is symmetric. Single crystal resistivity measurements show thermally activated behavior for the open-shell gold complexes, with room temperature conductivity values of 0.02-0.04 S·cm(-1) and activation energies strongly influenced by hydrostatic pressure. A thorough theoretical study on nickel anion radical and gold neutral radical bis(dithiolene) complexes applied to the chiral complexes [M(dm-dddt)2] (M = Au, Ni(-)) and to a series of previously reported compounds addressed the issue of symmetry versus asymmetry from an electronic coupling perspective between the two dithiolene ligands. It results that neutral gold complexes with dithiolene ligands without extended delocalization are Class II mixed-valent compounds in the Robin and Day classification, presenting an inherent tendency toward asymmetric structures, which can be however modulated by the intermolecular organization in the solid state.