A series of bis[N,N-di-(4-methoxylphenyl)amino]arene dications 1²⁺–3²⁺ have been synthesized and characterized. Their electronic structures were investigated by various experiments assisted by theoretical calculations. It was found that they are singlets in the ground state and that their diradical character is dependent on the bridging moiety. 3²⁺ has a smaller singlet–triplet energy gap and its excited triplet state is thermally readily accessible. The work provides a nitrogen analogue of Thiele’s hydrocarbon with considerable diradical character.

A series of bis[N,N-di-(4-methoxylphenyl)amino]arene dications 1²⁺–3²⁺ have been synthesized and characterized. Their electronic structures were investigated by various experiments assisted by theoretical calculations. It was found that they are singlets in the ground state and that their diradical character is dependent on the bridging moiety. 3²⁺ has a smaller singlet–triplet energy gap and its excited triplet state is thermally readily accessible. The work provides a nitrogen analogue of Thiele’s hydrocarbon with considerable diradical character.

Metalloradical species [Co₂Fv(CO)₄]^.+ (1^.+, Fv=fulvalenediyl) and [Co₂Cp₂(CO)₄]^.+ (2^.+, Cp=η⁵-C₅H₅), formed by one-electron oxidations of piano-stool cobalt carbonyl complexes, can be stabilized with weakly coordinating polyfluoroaluminate anions in the solid state. They feature a supported and an unsupported (i.e. unbridged) cobalt–cobalt three-electron σ bond, respectively, each with a formal bond order of 0.5 (hemi-bond). When Cp is replaced by bulkier Cp* (Cp*=η⁵-C₅Me₅), an interchange between an unsupported radical [Co₂Cp*₂(CO)₄]^.+ (anti-3^.+) and a supported radical [Co₂Cp*₂(μ-CO)₂(CO)₂]^.+ (trans-3^.+) is observed in solution, which cocrystallize and exist in the crystal phase. 2^.+ and anti-3^.+ are the first stable thus isolable examples that feature an unsupported metal–metal hemi-bond, and the coexistence of anti-3^.+ and trans-3^.+ in one crystal is unprecedented in the field of dinuclear metalloradical chemistry. The work suggests that more stable metalloradicals of metal–metal hemi-bonds may be accessible by using metal carbonyls together with large and weakly coordinating polyfluoroaluminate anions.

Metalloradical species [Co₂Fv(CO)₄]^.+ (1^.+, Fv=fulvalenediyl) and [Co₂Cp₂(CO)₄]^.+ (2^.+, Cp=η⁵-C₅H₅), formed by one-electron oxidations of piano-stool cobalt carbonyl complexes, can be stabilized with weakly coordinating polyfluoroaluminate anions in the solid state. They feature a supported and an unsupported (i.e. unbridged) cobalt–cobalt three-electron σ bond, respectively, each with a formal bond order of 0.5 (hemi-bond). When Cp is replaced by bulkier Cp* (Cp*=η⁵-C₅Me₅), an interchange between an unsupported radical [Co₂Cp*₂(CO)₄]^.+ (anti-3^.+) and a supported radical [Co₂Cp*₂(μ-CO)₂(CO)₂]^.+ (trans-3^.+) is observed in solution, which cocrystallize and exist in the crystal phase. 2^.+ and anti-3^.+ are the first stable thus isolable examples that feature an unsupported metal–metal hemi-bond, and the coexistence of anti-3^.+ and trans-3^.+ in one crystal is unprecedented in the field of dinuclear metalloradical chemistry. The work suggests that more stable metalloradicals of metal–metal hemi-bonds may be accessible by using metal carbonyls together with large and weakly coordinating polyfluoroaluminate anions.

Three bis(triarylamine) dications were isolated by using weakly coordinating anions. Their electronic structures in the ground state were investigated by various experiments in conjunction with theoretical calculations. The ground-state electronic structures of these species were tunable by substituent effects, with two of them as closed-shell singlets and one of them as an open-shell singlet in the solid state. The excited state of the latter is thermally accessible, indicated by EPR and SQUID measurements. The work provides a new and stable diradicaloid structure motif with an excited triplet sate.

Three bis(triarylamine) dications were isolated by using weakly coordinating anions. Their electronic structures in the ground state were investigated by various experiments in conjunction with theoretical calculations. The ground-state electronic structures of these species were tunable by substituent effects, with two of them as closed-shell singlets and one of them as an open-shell singlet in the solid state. The excited state of the latter is thermally accessible, indicated by EPR and SQUID measurements. The work provides a new and stable diradicaloid structure motif with an excited triplet sate.

Sterically unprotected thiophene/phenylene co-oligomer radical cation salts BPnT^.+[Al(OR_F)₄]⁻ (OR_F=OC(CF₃)₃, n=1–3) have been successfully synthesized. These newly synthesized salts have been characterized by UV/Vis-NIR absorption and EPR spectroscopy, and single-crystal X-ray diffraction analysis. Their conductivity increases with chain length. The formed meso-helical stacking by cross-overlapping radical cations of BP2T^.+ is distinct from previously reported face-to-face overlaps of sterically protected (co-)oligomer radical cations.

Salts that contain radical cations of benzidine (BZ), 3,3′,5,5′-tetramethylbenzidine (TMB), 2,2′,6,6′-tetraisopropylbenzidine (TPB), and 4,4′-terphenyldiamine (DATP) have been isolated with weakly coordinating anions [Al(OR_F)₄]⁻ (OR_F=OC(CF₃)₃) or SbF₆⁻. They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of benzidine or its alkyl-substituted derivatives in CH₂Cl₂. The salts were characterized by UV absorption and EPR spectroscopy as well as by their single-crystal X-ray structures. Variable-temperature UV/Vis absorption spectra of BZ^.+[Al(OR_F)₄]⁻ and TMB^.+[Al(OR_F)₄]⁻ in acetonitrile indicate an equilibrium between monomeric free radical cations and a radical-cation dimer. In contrast, the absorption spectrum of TPB^.+SbF₆⁻ in acetonitrile indicates that the oxidation of TPB only resulted in a monomeric radical cation. Single-crystal X-ray diffraction studies show that in the solid state BZ and its methylation derivative (TMB) form radical-cation π dimers upon oxidation, whereas that modified with isopropyl groups (TPB) becomes a monomeric free radical cation. By increasing the chain length, π stacks of π dimers are obtained for the radical cation of DATP. The single-crystal conductivity measurements show that monomerized or π-dimerized radicals (BZ^.+, TMB^.+, and TPB^.+) are nonconductive, whereas the π-stacked radical (DATP^.+) is conductive. A conduction mechanism between chains through π stacks is proposed.