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We developed recently [A. Fert\'e, et al., J. Phys. Chem. Lett. 11, 4359 (2020)] a method to compute single site double core hole (ssDCH or K$^{-2}$) spectra. We refer to that method as NOTA+CIPSI. In the present paper this method is applied to the O K$^{-2}$ spectrum of the CO$_2$ molecule, and we use this as an example to discuss in detail its convergence properties. Using this approach, a theoretical spectra in excellent agreement with the experimental one is obtained. Thanks to a thorough interpretation of the shake-up states responsible for the main satellite peaks and with the help of a comparison with the O K$^{-2}$ spectrum of CO, we can highlight the clear signature of the two non equivalent carbon oxygen bonds in the oxygen ssDCH CO$_2$ dication., Comment: 16 pages, 7 figures, 7 tables

Two homoleptic copper(II) complexes [Cu(L1)2] and [Cu(L2)2] with anionic redox‐active ligands were synthesised, one with urea azine (L1) and the other with thio‐urea azine (L2) ligands. One‐electron oxidation of the complexes initiates an unprecedented redox‐induced electron transfer process, leading to monocationic copper(I) complexes [Cu(L1)2]+ and [Cu(L2)2]+ with two oxidised ligands. While [Cu(L1)2]+ is best described as a CuI complex with two neutral radical ligands that couple antiferromagnetically, [Cu(L2)2]+ is a CuI complex with two clearly different ligand units in the solid state and with a magnetic susceptibility close to a diamagnetic compound. Further one‐electron oxidation of the complex with L1 ligands results in a dication [Cu(L1)2]2+, best described as a CuI complex with a twofold oxidised, monocationic ligand and a neutral radical ligand. The stability in at least three redox states, the accumulation of spin density at the ligands and the facile ligand‐metal electron transfer make these complexes highly attractive for a variety of applications; here the catalytic aerobic oxidation of alcohols to aldehydes is tested., Oxidation‐induced reduction: The oxidation of mononuclear CuII complexes with novel unsymmetric redox‐active urea azine or thio‐urea azine ligands leads to metal reduction and formation of complexes with intriguing electronic structures. The stability in several redox states is the basis for their first application in catalytic aerobic alcohol oxidation.

Catalysis reactions under metal-free and ambient conditions have received great interest in terms of economic and environmental issues. Especially, the applications of Lewis acids for the processes are having special interest due to their unique roles in a huge number of organic reactions. In this sense, a recent compound PIII dication has played an important role in the catalytic hydrosilylation of carbonyls and olefins. Herein theoretical calculations were carried out to elucidate the mechanisms of the experimentally reported and unknown reactions. The proposed mechanisms show that the reactions of a-d can occur spontaneously, whereas the formation of pyridine has endergonic nature.

The NHC-stabilised diboryne (B\(_2\)(SIDep)\(_2\); SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P−P bond activation with tetraethyldiphosphine at room temperature to form a B\(_2\)P\(_2\) heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B−B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B\(_2\)P\(_2\) rings, with their diradicaloid, planar-ring isomers lying close in energy.

Two isomeric methylxanthines, theobromine and theophilline, and their Zn+2 containing composites are considered within the restrictions of density functional theory (B3LYP/ 6-31++G(d,p)). Certain quantum chemical, thermodynamic and spectral data have been harvested, compared and interpreted. The results revealed that theophilline+Zn+2 system is thermodynamically more exothermic, more favorable and electronically stable compared to the analogous system, theobromine+Zn+2.

With the aim of assessing whether polydiphenylamine (PDPA) can be used as an inductor layer for stabilizing the radical cation in the polymer matrix of poly(3-hexylthiophene) (P3HT), as used in photovoltaic devices, interphases between P3HT and PDPA films were prepared electrochemically on platinum (Pt), tin-doped indium oxide (ITO), and gold (Au) electrodes in lithium perchlorate-acetonitrile (LiClO4-ACN) solution, being denoted as Pt/PDPA:P3HT, ITO/PDPA:P3HT, and Au/PDPA:P3HT, respectively. To characterize the interphases deposited on the different electrodes, Raman spectroscopy was used to monitor the behavior of the segments in the blend matrix compared with homopolymer films deposited on the different conducting electrodes, to study the stability of the quinone and semiquinone segments of PDPA and P3HT. Bode phase diagrams obtained by electrochemical impedance spectroscopy (EIS) were used to verify the prepared systems as a function of time since preparation. It was found that the polaron structure (oxidized thiophene ring radical cation segments) was stable for 97 h when the blend was synthesized under controlled temperature (22°C) conditions at constant potential of 1.70 V applied for 60 s to the surface of the Pt electrode. For the blends synthesized on ITO and Au, these conditions resulted in greater stabilization of the bipolaron structure (dication segments). These findings reveal the effect of PDPA induction over the P3HT layer in stabilizing the semiquinone and quinone forms, compared with interfaces formed solely by homopolymers in contact with the different electrodes.

A cyclopenta-fused macrocyclic tetraradicaloid, MC4-S, containing alternating phenanthrene (Phen) and dibenzo[b,d]thiophene (DBTh) units was synthesized and isolated in single-crystal form. Compared with its all-carbon isoelectronic structure, CPTP-M, the incorporation of two sulfur atoms leads to a smaller radical character and a larger singlet–triplet energy gap. X-ray crystallographic analysis reveals that the spin–spin coupling through the DBTh unit is stronger than that through the Phen moiety. In addition, the electron-rich sulfur atoms also raise the energies of both the HOMO and LUMO in MC4-S, but the overall optical and electronic energy gaps are close to that of the CPTP-M. MC4-S displays global anti-aromaticity according to the NMR measurements and theoretical calculations (NICS, ACID and 2D ICSS), with a 36π ring current circuit along the all-carbon periphery excluding the two sulphur atoms. Its dication becomes globally aromatic due to the existence of a dominant 34π-conjugation pathway. This study sheds some light on the effect of heteroatoms on the electronic properties of open-shell polyradicaloids.

Two series a and b of 3d metal based complexes 1-4 [MII{(4-R-NCOC6H4)2CH}2], (with M = Mn (1), Fe (2), Co (3), Ni (4) and R = H (a) or Me (b)) were synthesised and structurally characterized. The complexes were found to crystallize differently depending on the dication ionic radius and the ligand substitution. All complexes showed remarkable X-ray diffraction resolution that will allow further advanced diffraction experiments. Subsequently, their spectroscopic and magnetic properties were analysed. Complexes 3a and 3b notably show slow magnetic relaxation of their magnetization and represent simple model systems relaxing through a phonon-bottleneck process (3a) or as a field-induced single-molecule magnet (3b, Ueff = 45.0 cm-1). Remarkably, the magnetic anisotropy in the manganese complex 1b results in induced slow magnetic relaxation. The influence of the dual 4-methylation of the ligands was investigated and found to generate important variations in the physical features of the corresponding complexes. Accessible via one-pot synthesis, these are highly robust against oxidation and moisture. Through smart ligand engineering, they represent stable and tuneable compounds for benchmarking purposes through standard and less-standard characterization methods.

The employment of the hexyl-substituted anion [HexCB11 Cl11 ]- allowed the synthesis of a ZnII species, Zn[HexCB11 Cl11 ]2 , 3, in which the Zn2+ cation is only weakly coordinated to two carborate counterions and that is soluble in low polarity organic solvents such as bromobenzene. DOSY NMR studies show the facile displacement of at least one of the counterions, and this near nakedness of the cation results in high catalytic activity in the hydrosilylation of 1-hexene and 1-methyl-1cyclohexene. Fluoride ion affinity (FIA) calculations reveal a solution Lewis acidity of 3 (FIA=262.1 kJ mol-1 ) that is higher than that of the landmark Lewis acid B(C6 F5 )3 (FIA=220.5 kJ mol-1 ). This high Lewis acidity leads to a high activity in catalytic CO2 and Ph2 CO reduction by Et3 SiH and hydrogenation of 1,1-diphenylethylene using 1,4-cyclohexadiene as the hydrogen source. Compound 3 was characterized by multinuclear NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, and DFT studies.

Observation of the neutrinoless double β decay is the only practical way to establish that neutrinos are their own antiparticles. Because of the small masses of neutrinos, the lifetime of neutrinoless double β decay is expected to be at least ten orders of magnitude greater than the typical lifetimes of natural radioactive chains, which can mimic the experimental signature of neutrinoless double β decay. The most robust identification of neutrinoless double β decay requires the definition of a signature signal—such as the observation of the daughter atom in the decay—that cannot be generated by radioactive backgrounds, as well as excellent energy resolution. In particular, the neutrinoless double β decay of Xe could be established by detecting the daughter atom, Ba, in its doubly ionized state. Here we demonstrate an important step towards a ‘barium-tagging’ experiment, which identifies double β decay through the detection of a single Ba ion. We propose a fluorescent bicolour indicator as the core of a sensor that can detect single Ba ions in a high-pressure xenon gas detector. In a sensor made of a monolayer of such indicators, the Ba dication would be captured by one of the molecules and generate a Ba-coordinated species with distinct photophysical properties. The presence of such a single Ba-coordinated indicator would be revealed by its response to repeated interrogation with a laser system, enabling the development of a sensor able to detect single Ba ions in high-pressure xenon gas detectors for barium-tagging experiments., We also acknowledge support from the following agencies and institutions: the European Research Council (ERC) under Advanced Grant 339787-NEXT; the Ministry of Science and Innovation of Spain and FEDER under grants FIS2014-53371-C04, FIS2016-76163-R, MAT2016-78293-C6-5-R, MINECO/FEDER CT2016-80955-P, CTQ2016-80375-P and CTQ2014-51912-REDC; Interred PCTEFA V-A Spain/France/Andorra Program (EFA 194/16/TNSI); the Basque Government (GV/EJ) under grants IT-1346-19 and IT-1180-19; andAgencia de Ciencia y Tecnología de la Región de Murcia (19897/GERM/15). The authors also thank the SGI/IZO-SGIker UPV/EHU, Fundación Séneca and DIPC for computational and analytical resources.

One- and two-electron oxidation of a digallene stabilized by an N-heterocyclic carbene afforded the first stable gallium-based radical cation and dication salts, respectively. Structural analysis and theoretical calculations reveal that the oxidation occurs at the Ga=Ga double bond, leading to removal of π electrons of the double bond and a decrease of the bond order. The spin density of the radical cation mainly locates at the two gallium centers as demonstrated by EPR spectroscopy and theoretical calculations. Moreover, the reactivity of the radical cation salt toward nBu3 SnH and cyclo-S8 was studied; a digallium-hydride cation salt containing a Ga-Ga single bond and a gallium sulfide cluster bearing an unprecedented ladder-like Ga4 S4 core structure were obtained, respectively.

In the title hydrated complex, [Co(C15H10ClN3)2]Cl2·4H2O, the complete dication is generated by symmetry. In the crystal, O—H⋯Cl and C—H⋯O hydrogen bonds link the components into (001) sheets. The complex exhibits blue-light emission., In the title hydrated complex, [Co(C15H10ClN3)2]Cl2·4H2O, the complete dication is generated by symmetry. The CoN6 moiety shows distortion from regular octa­hedral geometry with the trans bond angles of two N—Co—N units being 160.62 (9)°. In the crystal, O—H⋯Cl and C—H⋯O inter­actions link the components into (001) sheets. The title compound exhibits blue-light emission, as indicated by photoluminescence data, and a HOMO–LUMO energy separation of 2.23 eV was obtained from its diffuse reflectance spectrum.

A tridentate [PPP] ligand has been used to construct a series of dimeric cobalt complexes and explore cooperative multielectron redox processes that are both metal- and ligand-centered. Reduction of (PPClP)CoCl2 (1) with excess magnesium affords the CoICoI N-heterocyclic phosphido (NHP-)-bridged symmetric dimer [(μ-PPP)Co]2 (2). Two-electron oxidation of 2 with FcPF6 generates an asymmetrically bridged dication [(μ-PPP)Co]2[PF6]2 (3) in which the oxidation has occurred in a delocalized fashion throughout the Co2P2 core. In contrast, [(μ-PPP)Co]2+ (5), which can be generated either by one-electron oxidation of 2 with FcPF6 or comportionation of 2 and 3, features an asymmetric geometry and localized mixed valence. Treatment of 1 with the milder reductants CoCp2 and KBEt3H does not lead to formation of 2, 3, or 5 but instead generates dimeric species [(PPP)CoCl]2 (6) and [(PPP)CoH]2 (7). Unlike 2-5, where the phosphine side arms of the tridentate [PPP] ligand span the two Co centers, complex 6 and 7 are connected solely by NHP- ligands that bridge the two (PPP)Co fragments.

Calcium dication has an important role at various stages of blood coagulation mechanism. On the other hand, pindone is an important anticoagulant rodenticide which undergoes 1,3-type proton tautomerism to yield two enolic isomers of pindone. Although, the anticoagulant mode of action of pindone is attributed to blocking of a liver enzyme responsible for the recycling of vitamin K, nothing is known about whether the interaction of it with calcium dication has some role as well. In the present study, the interactions of pindone and its tautomers with Ca++ have been investigated within the restrictions of density functional theory at the level of B3LYP/6-311++G(d,p). It has been found that Ca++ highly affects pindone and its tautomers in many respects at the molecular level, hence their anticoagulation effect should vary.

Double chloride abstraction from Cp*SbCl2 (Cp* = pentamethylcyclopentadienyl) affords an arene-stabilized η5-Cp*-bound antimony dicationic compound [(η5-Cp*)Sb(tol)][B(C6F5)4]2 (1) (tol = toluene), which exhibits strong Lewis acidity, abstracting chloride from Ph3CCl. 1 reacts with different Lewis bases via divergent pathways, giving rise to release of either Sb+ or Sb3+ cations.

Coordination of 1-isopropyl-3,5-dipyridyl-6-oxoverdazyl to cobalt results in a dication best described in the solid state as a high spin cobalt(ii) ion coordinated to two radical ligands with an S = 3/2 ground state. On dissolution in acetonitrile, the cobalt(ii) form equilibrates with a cobalt(iii) valence tautomer with an S = 1/2 ground state.

The organisation of the p-xylylenebis(triphenylphosphonium) dication in the solid state, in crystals formed under a variety of conditions, at different pH values and in the presence of THF and other potential building moieties including p-sulfonatocalix[4]arene, 1-methyl-3-butylimidazolium and aquated gadolinium(III) has been investigated using single crystal X-ray diffraction studies. Striking changes in the dication conformations (cis- and trans-) that contribute to the different crystal packings of the dication (two-dimensional layerings and three-dimensional scaffoldings) have been established for five different compounds. The interplay and the self-assembled arrays of the dication with other incorporated components and the overall non-covalent interactions have been quantified using Hirshfeld surface analyses.

Oxidation of 1,5-bis(dimethylamino)naphthalene with iodine leads directly to a bis(dimethyliminium) derivative of acridino[2,1,9,8-klmna]acridine, containing six fused six-membered rings, as a bis triiodide salt. The cation has a twisted structure due to the minimisation of peri interactions between each dimethyliminium group and a hydrogen atom. Use of TCNQ as oxidizing agent leads to the same dication as a tetrakis(TCNQ) salt, while use of TCNQ-F4 gave a related monocation which is dimethylated on a ring nitrogen atom.

In the centrosymmetric title complex, [Cu2Cl2(C15H11N3)2](CF3O3S)2, the CuII metal center is fivefold coordinated by two chloride ions and three nitrogen atoms of the terpyridine ligand in a distorted square-pyramidal geometry; two trifluoromethanesulfonate ions complete the outer coordination sphere. π–π stacking interactions between the pyridyl rings in adjacent molecules contribute to the alignment of the complexes in columns along the a-axis. This structure represents the first example of a binuclear dication of formula [Cu(terpy)2Cl2]2+ with trifluoromethanesulfonate as counter-ions.

Upon stabilization by 5,6-bis(diisopropylphosphino)acenaphthene to form compound 1, the fugitive antimony (I) cation exhibited nucleophilic behavior towards coinage metals. Compound 1 was strategically synthesized at room temperature from SbCl3 , the bis(phosphine), and trimethylsilyl trifluoromethanesulfonate taken in a 1:2:3 ratio, whereby the bis(phosphine) plays the dual role of a reductant and a supporting ligand. The generation of 1 involves two-electron oxidation of the ligand to form a P-P bonded diphosphonium dication. Compound 1 was separated from this dication to give both products in pure form in moderate yields. Despite the overall positive charge, the SbI site in 1 was found to bind to metal centers, forming complexes with AuI , AgI and CuI . Compound 1 reduced CuII to CuI and formed a coordination complex with the resulting CuI species. The effects of the electron-rich bis(phosphine) and the constrained peri geometry in stabilizing and enhancing the nucleophilicity of 1 have been rationalized through computational studies.

Pentacoordinate carbon atoms are theoretically predicted here in a ferrocene dication derivative in both staggered- [Fe(Si2C5H2)2]2+ (1; C2h) and eclipsed-[Fe(Si2C5H2)2]2+ (2; C2v) forms for the first time. Relative energy difference between these two ranges from -40.34 to 2.47 kJ/mol at different levels. The planar tetracoordinate carbon atom in the ligand Si2C5H2 becomes a hypervalent pentacoordinate carbon upon complexation.

The reaction of 1,2‐dipiperidinoacetylene (1) with 0.5 equivalents of SnCl2 or GeCl2⋅dioxane afforded the 1,2,3,4‐tetrapiperidino‐1,3‐cyclobutadiene tin and germanium dichloride complexes 2 a and 2 b, respectively. A competing redox reaction was observed with excess amounts of SnCl2, which produced a tetrapiperidinocyclobutadiene dication with two trichlorostannate(II) counterions. Heating neat 1 to 110 °C for 16 h cleanly produced the dimer 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne (3); its reaction with stoichiometric amounts of SnCl2 or GeCl2⋅dioxane furnished the 1,3,4,4‐tetrapiperidino‐1,2‐cyclobutadiene tin and germanium dichloride complexes 4 a and 4 b, respectively. Transition‐metal complexes containing this novel four‐membered cyclic bent allene (CBA) ligand were prepared by reaction of 3 with [(tht)AuCl], [RhCl(CO)2]2, and [(Me3N)W(CO)5] to form [(CBA)AuCl] (5), [(CBA)RhCl(CO)2] (6), and [(CBA)W(CO)5] (7). The molecular structures of all compounds 2–7 were determined by X‐ray diffraction analyses, and density functional theory (DFT) calculations were carried out to rationalise the formation of 3 and 4 a., Cyclic bent allenes as ligands: The thermal dimerisation of 1,2‐dipiperidinoacetylene affords 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne, which provides access to main‐group and transition‐metal complexes of a strongly electron‐donating four‐membered cyclic bent allene ligand. The formation of these complexes as well as the dimerisation of 1,2‐dipiperidinoacetylene were also studied by computational methods.

The isolation and characterization of the first silicon analogue of the aromatic cyclobutadiene dication is reported. The aromatic 2π-electron tetrasilacyclobutadiene dication in [(LPhSi)4](BPh4)2 ...

Although the chemistry of uranium-ligand multiple bonding is burgeoning, analogous complexes involving other actinides such as thorium remain rare and there are not yet any terminal thorium nitrides outside of cryogenic matrix isolation conditions. Here, we report evidence that reduction of a thorium-azide produces a transient Th≡N triple bond, but this activates C-H bonds to produce isolable parent imido derivatives or it can be trapped in an N-heterocycle amine. Computational studies on these thorium-nitrogen multiple bonds consistently evidences a σ > π energy ordering. This suggests pushing-from-below for thorium, where 6p-orbitals principally interact with filled f-orbitals raising the σ-bond energy. Previously this was dismissed for thorium, being the preserve of uranium-nitrides or the uranyl dication. Recognising that pushing-from-below perhaps occurs with thorium as well as uranium, and with imido ligands as well as nitrides, suggests this phenomenon may be more widespread than previously thought., Despite the burgeoning nature of uranium–ligand multiple bonding, analogous thorium complexes remain incredibly rare. Here the authors report evidence for a transient thorium–nitride species, which, together with data on parent imido derivatives, suggests that the pushing-from-below phenomenon may be more widespread than previously thought.

The structures of the elusive cyclobutane dication, (CH2)42+, were investigated at the MP2/cc-pVTZ and CCSD(T)/cc-pVTZ levels. Calculations show that the two-electron four-center (2e-4c) bonded structure 1 involving four carbon atoms is a minimum. The structure contains formally two tetracoordinate and two pentacoordinate carbons. The non-classical σ-delocalized structure can be considered as a prototype for a 2e-4c Woodward–Hoffmann frozen transition state. The planar rectangular shaped structure 2 with a 2e-4c bond was found not to be a minimum.

Invited for the cover of this issue is Ajay Venugopal from the Indian Institute of Science Education and Research Thiruvananthapuram. The cover image shows dication Tp(Me2)Bi](2+) catalyzing olefin hydrosilylation under mild conditions.

An acyclic flexible bis(α-iminopyridine) ligand has been employed for the stabilization of chlorostannyliumylidene and a tin(II) dication. The syntheses involve the abstraction of chloride from the tin dichloride precursor using trimethylsilyl trifluoromethane sulfonate. The apically disposed tin(II) dication exhibits electrophilic behaviour and undergoes transmetallation reaction with GeCl2.dioxane resulting in stabilizing the Ge(II) dication. All the compounds have been characterized by NMR techniques and single crystal X-ray crystallography.

Double chloride abstraction of Cp*AsCl2 gives the dicationic arsenic species [(η5 -Cp*)As(tol)][B(C6 F5 )4 ]2 (2) (tol=toluene). This species is shown to exhibit Lewis super acidity by the Gutmann-Beckett test and by fluoride abstraction from [NBu4 ][SbF6 ]. Species 2 participates in the FLP activation of THF affording [(η2 -Cp*)AsO(CH2 )4 (THF)][B(C6 F5 )4 ]2 (5). The reaction of 2 with PMe3 or dppe generates [(Me3 P)2 As][B(C6 F5 )4 ] (6) and [(σ-Cp*)PMe3 ][B(C6 F5 )4 ] (7), or [(dppe)As][B(C6 F5 )4 ] (8) and [(dppe)(σ-Cp*)2 ][B(C6 F5 )4 ]2 (9), respectively, through a facile cleavage of C-As bonds, thus showcasing unusual reactivity of this unique As-containing compound.

The 3-fold interpenetration of the β-quartz-type hydrogen-bonded organic framework (HOF) from the dication salts of tetrakis(4-pyridyl)methane develops a host–guest system featuring flexibility and durability in accordance with the state change of guest molecules. Water molecules are incorporated into HOF and form a one-dimensional helical-shaped molecular chain in nanopores. X-ray crystallographic analysis and the dielectric dispersion in the impedance measurements revealed that guest water molecules behave dynamically and show a concerted freezing process to produce water pentamers at 100 K. Structural changes in the host framework mediate interactions between guest water molecules within and between the nanopores through the weak host–guest interactions based on hydrogen-bonding interaction. In addition, the triangular arrangement of nanopores gives rise to the topologically unsettled guest molecules in the freezing process.

The air-stable Lewis acid [(terpy)PPh][B(C6F5)4]21 mediates the hydrosilylation of aldehydes, ketones, and olefins. The mechanism of these hydrosilylations is considered.

The dissociative ionization processes of the methanol monocation CH3OH+ to H3+ + CHO and H2O+ + CH2 are studied by ab initio method, and hydrogen migration processes are confirmed in these two dissociation processes. Due to the positive charge assignment in dissociation processes, the fragmentation pathways of CH3OH+ to H3 + CHO+ and CH3OH+ to H2O + CH2+ are also calculated. The calculation results show that a neutral H2 moiety in the methanol monocation CH3OH+ is the origin of the formation of H3+, and the ejection of fragment ions H3+ and H2O+ is more difficult than CHO+ and CH2+ respectively. Experimentally, by using a dc-slice imaging technique under an 800 nm femtosecond laser field, the velocity distributions of fragment ions H3+, CHO+, CH2+, and H2O+ are calculated from their corresponding sliced images. The presence of low-velocity components of these four fragment ions confirms that the formation of these ions is not from the Coulomb explosion of the methanol dication. Hence, the four hydrogen migration pathways from the methanol monocation CH3OH+ to H3+ + CHO, CHO+ + H3, H2O+ + CH2, and CH2+ + H2O are securely confirmed. It can be observed in the time-of-flight mass spectrum of ionization and dissociation of methanol that the ion yields of fragment ions H3+ and H2O+ are lower than CHO+ and CH2+ respectively, which is consistent with the theoretical results according to which dissociation from the methanol monocation to H3+ and H2O+ is more difficult than CHO+ and CH2+ respectively.

We have reported here the synthesis, structure and spectroscopic properties of the NiII–FeIII heterobimetallic ethene-bridged porphyrin dimer and investigate the effect upon step-wise one- and two-electron oxidations to produce a mixed-valence π–cation radical dimer and a dication diradical complex, respectively. We then investigate their electronic structure and spin coupling model and compare them with the corresponding homobimetallic analog. Detailed UV-vis-NIR, IR, and variable temperature magnetic studies and EPR and NMR spectroscopic investigations along with X-ray structure determination of the 2e-oxidized complex have demonstrated strong electronic communications through the bridge between two porphyrin π–cation radicals. The structure and geometrical parameters revealed the stabilization of the high-spin state of iron and the low-spin state of nickel in the 2e-oxidized complex. The extensive conjugation between the two porphyrin π–cation radicals has also altered the bridge from an ethylene to an exo-methylene moiety. Variable temperature magnetic studies of the 2e-oxidized complex revealed stronger antiferromagnetic coupling between two π–cation radical spins (Jr1–r2) of the NiII–FeIII heterodimer which is in sharp contrast to its diiron(III) analog where the porphyrin π–cation radical undergoes stronger antiferromagnetic coupling predominantly with the corresponding Fe(III) unpaired spin (JFe–r). The experimental observations are also strongly supported by DFT calculations.

A novel complex with the stoichiometry [(NH2)2CSSC(NH2)2]2[OsIVCl6]Cl2·3H2O (1) is isolated as a product of the reaction of H2[OsCl6] with thiourea in concentrated HCl under deliberately optimized conditions favoring a partial thiourea oxidation to α,α′-dithiobisformamidinium dication but preserving hexachloroosmate [OsCl6]2- anions. A bromide analogue [(NH2)2CSSC(NH2)2]2[OsIVBr6]Br2·3H2O 2 is afforded by a similar reaction. A counter synthesis of 1 is accomplished via the direct ion-exchange reaction between H2[OsCl6] and [S2C2(NH2)4]Cl2. Crystal structures of 1 and 2 are unambiguously established by synchrotron radiation-based single-crystal X-ray diffraction at 100 K. The two compounds are isostructural and are crystallized in the orthorhombic space group Cmcm, Z = 4. Unit cell parameters are for 1: a = 11.279(2) A, b = 13.611(3) A, c = 16.731(3) A; for 2: a = 11.695(2) A, b = 14.005(3) A, c = 17.015(3) A. The osmium atoms in [OsX6]2− (X = Cl or Br) anions adopt slightly distorted octahedral coordination. The α,α′-dithiobisformamidinium cations are paired into rings via the NH…Cl− hydrogen bonds. The rings are further linked into a spatial network by H-bonds with water molecules and S…Cl nonvalence interactions.

Syntheses and structures of anionic arylphosphate monoesters [ArOP(O)2(OH)]- (Ar = 2,6-CHPh2-4-R-C6H2; R = Me/Et/iPr/tBu) with different counter cations are reported. The counter cations were varied systematically: imidazolium cation, 2-methyl imidazolium cation, N-methyl imidazolium cation, N,N'-alkyl substituted imidazolium cation, 1,4-diazabicyclo[2.2.2]octan-1-ium cation, 4,4'-bipyridinium dication, and magnesium(II) dication. The objective was to examine if the supramolecular structure of anionic arylphosphate monoesters could be modulated by varying the cation. It was found that an eight-membered P2O4H2-hydrogen-bonded dimeric motif involving intermolecular H-bonding between the [P(O)(OH)] unit of the anionic phosphate monoester along with the counter cation is formed with 2-methyl imidazolium cation, N-methyl imidazolium cation, N,N'-alkyl substituted imidazolium cation, 1,4-diazabicyclo[2.2.2]octan-1-ium cation, and magnesium(II) dication; both discrete and polymeric H-bonded structures are observed. In the case of imidazolium cations and 1,4-diazabicyclo[2.2.2]octan-1-ium cation, the formation of one-dimensional polymers (single lane/double lane) was observed. On the other hand, two types of phosphate motifs, intermolecular H-bonded dimer and an open-form, were observed in the case of 4,4'-bipyridinium dication.

Polynitrile anions are known for their ability to combine with transition metals and co-ligands to form ternary systems. Here we report on the crystal structure of tris­(2–2′-bi­pyridine)­cobalt(II) bis­(1,1,3,3-tetra­cyano-2-eth­oxy­propenide)., In the title compound, [Co(C10H8N2)3](C9H5N4O)2, the tris­(2,2′-bi­pyridine)­cobalt(II) dication lies across a twofold rotation axes in the space group C2/c. The N atoms of the three bi­pyridine ligands form a distorted octa­hedron around the cobalt ion. All the N atoms of the polynitrile 1,1,3,3-tetra­cyano-2-eth­oxy­propenide anions participate in C—H⋯N hydrogen bonds ensuring crystal cohesion and forming a three-dimensional structure. The structure is further stabilized by C—H⋯π(cation) and anion⋯π(cation) inter­actions.

Two synthetic approaches to install metallodithiolate ligands on molybdenum centers using the synthons [Mo2(CH3CN)10]4+ and (N2S2)Co(NO) [N2S2 = N,N-bis(2-mercaptoethyl)-1,4-diazacycloheptane and NO = nitric oxide], or [Mo(NO)2(CH3CN)4]2+ (CH3CN = acetonitrile) and [(N2S2)Co]2 lead to a bis-nitrosylated, trimetallic dication, CoMoCo'. This unique asymmetric butterfly complex, with S = 1, has a bent NO within the small {Co(NO)}8 wing (denoted as Co), reflecting CoIII(NO-), and is S-bridged to a linear {Mo(NO)}6 diamagnetic unit. The latter is further S-bridged to a pentacoordinate (N2S2)CoIII(CH3CN) donor in the larger wing and is the origin of the two unpaired electrons, denoted as Co'. The asymmetry in Mo-Co distances, 3.33 A in the Co wing and 2.73 A in the Co' wing, indicated a Mo-Co' bonding interaction. The transfer of NO from (N2S2)Co(NO) in the former path is needed to cleave the strong quadruple bond in [Mo≣Mo]4+, with the energetic cost compensated for via a one-electron bond between Mo and Co', as indicated by natural bonding orbital analysis.

Inspired by the metal active sites of [FeFe]- and [NiFe]‑hydrogenases, a series of mononuclear Ni(II) ethanedithiolate complexes [{(Ph2PCH2)2×}Ni(SCH2CH2S)] (X = NCH2C5H4N-p (2a), NCH2C6H5 (2b), NCH2CHMe2 (2c), and CH2 (2d)) with chelating diphosphines were readily synthesized through the room-temperature treatments of mononuclear Ni(II) dichlorides [{(Ph2PCH2)2×}NiCl2] (1a-1d) with ethanedithiol (HSCH2CH2SH) in the presence of triethylamine (Et3N) as acid-binding agent. All the as-prepared complexes 1a-1d and 2a-2d are fully characterized through elemental analysis, nuclear magnetic resonance (NMR) spectrum, and by X-ray crystallography for 1b, 2a-2d. To further explore proton-trapping behaviors of this type of mononuclear Ni(II) complexes for catalytic hydrogen (H2) evolution, the protonation and electrochemical proton reduction of 2a-2c with aminodiphosphines (labeled PCNCP = (Ph2PCH2)2NR) and reference analogue 2d with nitrogen-free diphosphine (dppp = (Ph2PCH2)2CH2) are studied and compared under trifluoroacetic acid (TFA) as a proton source. Interestingly, the treatments of 2a-2d with excess TFA resulted in the unexpected formation of dinuclear Ni(II)-Ni(II) dication complexes [{(Ph2PCH2)2×}2Ni2(μ-SCH2CH2S)](CF3CO2)2 (3a-3d) and mononuclear Ni(II) N-protonated complexes [{(Ph2PCH2)2N(H)R}Ni(SCH2CH2S)](CF3CO2) (4a-4c), which has been well supported by high-resolution electrospray ionization mass spectroscopy (HRESI-MS), NMR (31P, 1H) as well as fourier transform infrared spectroscopy (FT-IR) techniques, and especially by X-ray crystallography for 3d. Additionally, the electrochemical properties of 2a-2d are investigated in the absence and presence of strong acid (TFA) by using cyclic voltammetry (CV), showing that the complete protonation of 2a-2d gave rise to dinuclear Ni2S2 species 3a-3d for electrocatalytic proton reduction to H2.

The discovery of ferrocene nearly 70 years ago marked the genesis of metallocene chemistry. Although the ferrocenium cation was discovered soon afterwards, a derivatized ferrocenium dication was only isolated in 2016 and the monoanion of ferrocene has only been observed in low-temperature electrochemical studies. Here we report the isolation of a derivatized ferrocene anion in the solid state as part of an isostructural family of 3d metallocenates, which consist of anionic complexes of a metal centre (manganese, iron or cobalt) sandwiched between two bulky Cpttt ligands (where Cpttt is {1,2,4-C5H2 tBu3}). These thermally and air-sensitive complexes decompose rapidly above −30 °C; however, we were able to characterize all metallocenates by a wide range of physical techniques and ab initio calculations. These data have allowed us to map the electronic structures of this metallocenate family, including an unexpected high-spin S = 3/2 ground state for the 19e− derivatized ferrocene anion. Unlike ferrocene and its cationic counterpart ferrocenium, the ferrocene monoanion is an unusual species that has been observed through low-temperature electrochemical studies. Now, a family of isostructural 3d metallocenates has been isolated that consists of a manganocene, a cobaltocene and a high-spin ferrocene anion stabilized by cyclopentadienyl ligands bearing bulky aliphatic groups.

The hexacoordinated antimony(V) dication [(ppy)3 Sb]2+ ([1]2+ ; ppy=2-(2-pyridyl)phenyl), stabilized by three intramolecular donor-acceptor interactions, has been isolated as its hexachloroantimonate salt [1][SbCl6 ]2 , prepared by the oxidative addition of chlorine to the neutral stibine [(ppy)3 Sb] (1), followed by the abstraction of chloride. Air-stable [1][SbCl6 ]2 exhibits remarkable thermal stability and the three ppy ligands on the antimony atom are shown to be magnetically inequivalent in the 1 H and 13 C NMR spectra. A hexacoordinated, meridional octahedral bonding geometry has been determined for [1][SbCl6 ]2 by X-ray crystallographic analysis. Theoretical calculations were performed to investigate why the meridional form was generated preferentially over the facial form. In addition, the dynamics of the ppy ligands were investigated by variable-temperature 1 H NMR spectroscopy. The potential to generate dications by using a single-electron-transfer reagent has also been investigated. The dication [1]2+ is the first [12-Sb-6]2+ chemical species to have been structurally determined.

International audience; A series of “N2O2-type” manganese dipyrrin-bisphenols (DPP), formulated as (Ar)DPPMn, where Ar = pentafluorophenyl (F5Ph), phenyl (Ph), or mesityl (Mes), were electrochemically and spectroscopically characterized in nonaqueous media with and without added anions in the form of tetrabutylammonium salts (TBAX where X = ClO4–, PF6–, BF4–, F–, Cl–, OH–, or CN–). Two major one-electron reductions are observed under most solution conditions, the first of which is assigned as a MnIII/II process and the second as electron addition to the π-ring system as confirmed by spectroelectrochemistry. Each MnIII complex also exhibits one or two one-electron oxidations, the exact number depending upon the positive potential limit of the electrochemical solvent. The two oxidations are separated by 580–590 mV in CH3CN containing 0.1 M TBAPF6 and are assigned as π-ring-centered electron transfers to stepwise form a (Ar)DPPMnIII π-cation radical and dication under these solution conditions. Comparisons are made between redox properties of (Ar)DPPMn and manganese(III) porphyrins, corroles, and corrolazines each of which contains an innocent trianionic complexing ligand. The redox behavior and spectroscopic properties of [(Ar)DPPMn]n where n = 0, −1, or +1 are also compared to that of other structurally related [(Ar)DPPM]n complexes under similar solution conditions where M = CoII, CuII, BIII, or AuIII.

The possibility of carbon tetravalence in geometries other than tetrahedral and of carbon hypervalence has been taken seriously since the 1970s. Computational modeling and subsequent experimental validation have established the existence of molecules with carbon atoms with planar tetravalence and as many as six objects in carbon’s coordination sphere. In this work, we develop insight into the nature of bonding to carbon in these unusual environs as provided by Bader’s Atoms in Molecules (AIM) analysis of the electron density, along with the electron localization function (ELF) and the non-covalent index (NCI). We review several well-established systems (spiropentadiene dication, hexamethyl benzene dication, dimethanospiro[2.2]octaplane dication, and 1,8-dimethoxy-9-dimethoxyanthracene cation) and propose new D2d–symmetric variants of a hexacoordinated species.

Benzyl viologen (BV) was deposited at copper in the presence of chloride anions to generate a benzyl viologen-chloride layer at copper, where the viologen was present as a dication, stabilised by the negatively charged chloride anions. This layer provided good protective properties to the underlying copper substrate. On polarising the BV-modified copper in 0.1 M NaCl significantly lower currents, typically 28 μA cm−2, were observed at 0.40 V vs SCE compared to the higher currents of 1.75 mA cm−2 evident with the unmodified copper. The charge-transfer resistance at −0.15 V vs SCE, obtained from impedance data recorded in 0.1 M NaCl after 60 min, was measured as 21 kΩ cm2 for copper indicating the build-up of corrosion products, while a lower resistance of 8 kΩ cm2 was seen with the BV-modified copper. The estimated chloride content at the copper surface following immersion in chloride solutions was reduced from about 22% to 4% on modification with BV. Less protective properties were observed when the benzyl viologen was deposited from oxalate, sulfate and acetate solutions, and when the benzyl viologen was replaced with methyl or ethyl viologens, illustrating the importance of the supporting anions and viologen compound. The reduction of the di-cationic BV2+ to the radical cation was observed at −0.57 V vs SCE, while the further reduction of the radical species was seen at −0.73 V vs SCE, indicating that the deposited benzyl viologen exhibits its characteristic redox properties.

The known Rh(2-Me-8-Oxq)(CO)2 complex (1) was prepared through treatment of dicarbonyl(acetylacetonate)rhodium (I) with 2-methyl-8-hydroxyquinoline for the first time. The reactions of 1 with triphenylphosphine and triphenylphosphite result in complexes Rh(2-Me-8-Oxq)(PPh3)(CO) (2) and Rh(2-Me-8-Oxq)[P(OPh)3](CO) (3) that were characterized by IR and NMR spectroscopy. The structures of complexes 2 and 3 were determined by single-crystal X-ray diffraction analysis. The complexes show the 2-methyl-8-quinolinolato ligand in the expected coordination mode with a slightly disordered square planar geometry at the rhodium center. In the crystal, molecules of Rh(2-Ме-8-Oxq)(CO)(PPh3) (2) form centrosymmetric dimers due to π-stacking interactions. No intermolecular contacts are observed in the crystal of 3. The UV spectroscopic and electrochemical properties of complexes 1–3 were studied. Their electronic spectra in CH3CN show three quinoline-centered absorptions. The electrochemical study revealed that the oxidation of the complexes 1–3 is two-electron and leads to the formation of dication Rh (III) species while their reduction gives radical anions, which undergoes rapid decomposition.

Summary Abstraction of chloride from (Cp*PCl2) with the silylium salt [Et3Si][B(C6F5)4] afforded [(η2-Cp*)PCl][B(C6F5)4] (1), whereas further chloride abstraction using another equivalent [Et3Si][B(C6F5)4] was unsuccessful. The corresponding species [(η2-Cp*)PF][B(C6F5)4] (2) was derived by fluoride abstraction from (Cp*PF2). Treatment of (Cp*PF2) with 2 equiv of [Et3Si][B(C6F5)4] gave [(η5-Cp*)P][B(C6F5)4]2 (3), representing an η5-Cp that is bound to phosphorus. 3 behaves as a phosphorus-based Lewis super acid, abstracting fluoride from [SbF6]− anion with concurrent η5-η2-Cp* rearrangement to give 2. Similarly, the extremely high Lewis acidity and chlorophilicity of 3 is indicated by the equilibration of 3 with Et3SiCl to generate 1 and [Et3Si][B(C6F5)4]. The coordination of 2,2′-bipyridine (bipy) to the phosphorus of 3 induces the η5-η1-Cp* rearrangement, leading to a “slipped sandwich” compound [(η1-Cp*)P(bipy)][B(C6F5)4]2 (4). 3 also reacts with Et3SiH via η5-σ-Cp* rearrangement, affording [(σ-Cp*)PH2SiEt3][B(C6F5)4] (5) and [Et3Si][B(C6F5)4].

A porphyrinogen macrocycle incorporating two azulenes, phenylene and thiophene into the framework, joined by four C(sp3 ) atoms has been obtained as a mixture of six isomers. They were successfully separated and characterized spectroscopically. The identity of two of them was confirmed by X-ray crystallography. One isomer was tested in reaction with [Ru3 (CO)12 ] yielding exclusively π-complex with two clusters attached to azulenes. The partial oxidation of porphyrinogens yielded dication with two unmodified meso bridges. The stepwise oxidation followed by reaction with water as nucleophile afforded the dicationic species with two hydroxyl groups and a trication with one OH group. The hydroxy-dication can be reversibly transformed into hydroxy-trication by addition of HBF4 etherate.

The synthesis of two η5 -aminoborole complexes of germanium(II) from the reaction of a germole dianion with aminoboron dichlorides is reported. This reaction constitutes a remarkable example of a germole-to-borole transformation. The two aminoborole complexes of germanium(II) were fully characterized by multinuclear NMR spectroscopy, IR spectroscopy, HRMS, and, in one case, by X-ray crystallography. The results of quantum-mechanical calculations favor the electronic structure of a half-sandwich complex of GeII over an ionic representation with a germanium dication stabilized by an aromatic aminoborole dianion.

The enhanced electron-donor properties of the bulky bisimino ligand 1,2-(LMes N)2 -C2 H4 (1; LMes =1,3-bis(mesityl)-imidazolin-2-ylidene), mesityl=2,4,6-trimethylphenyl) were exploited for the stabilization of elusive electron-deficient and low-coordinate boron dication species. The reaction of 1 with PhBBr2 or (B(Cl)NMe2 )2 afforded a dicationic mononuclear boron(III) complex or a dicationic dinuclear boron(II) complex, respectively (42+ , 62+ ). The bonding situations of 42+ and 62+ were examined by means of single crystal X-ray diffraction analysis, as well as theoretical methods. Significant allocation of positive charge density into the ligand system was diagnosed for both dications. However, the metalloid-centered Lewis acidity of the dications was confirmed via hydride transfer reactions.

4,4′-Bipyridinium cobalt(II) 2,6-pyridinedicarboxylate hexahydrate forms host–guest complexes with hydroxy-aromatic compounds 2,3- or 2,7-dihydroxynaphthalene and phloroglucinol. Impressive aspect of the complex is the modification of protonated species in different ways while forming host–guest complexes with hydroxyaromatics. Complex with 2,3-dihydroxynaphthalene has 4,4′-bipyridinium monocation and dication as counter-ions, whereas 2,7-dihydroxynaphthalene complex has only 4,4′-bipyridinium dication. Host-guest complex with phloroglucinol has two 4,4′-bipyridinium monocations. Guest dependent templates are formed in each case. In the case of 2,3-dihydroxynaphthalene, interactions among amine-water-naphthalenediol resulted in chain-like structures within the self-assembly; whereas host–guest complex having 2,7-dihydroxynaphthalene holds water clusters within self-assembly. Substrate dependent host–guest complexes with variations on amounts of guest intake per unit cell was observed; for example with 1, 3, 5-trihydroxybenzene as guest molar ratio of cobalt ion with respect to guest is unity, whereas three equivalents of 2, 3- or 2, 7-dihydroxynaphthalene molecules per cobalt complex were observed.

The electrochemical properties of a series of ruthenium complexes bearing the redox noninnocent bis(imino)pyridine ligand were investigated with cyclic voltammetry. An unexpected electrochemical feature in one of the complexes indicated a possible electrochemical-chemical-electrochemical (ECE) process. Further investigation into the oxidation mechanism included the synthesis and isolation of cationic and dicationic analogues of the complex. Density functional theory calculations suggested that a solvent interaction facilitated the ECE mechanism, so a solvent adduct was also synthesized and isolated. Calculations of this series of compounds were used to investigate the stabilizing role of the ligands over various oxidation states. As the overall charge of the complex was varied from anion to dication, a relatively constant Ru metal center oxidation state was found over all four states probed. This result suggests the strong involvement of the coligands in the redox behavior of the complexes investigated.

The cyclometalated dinuclear platinum acetylide with a 9,9-dioctylfluorene spacer and two terminal triphenylamine groups has been successfully synthesized and characterized by 1H NMR, 13C NMR and MALDI-TOF MS. The active triphenylamine groups efficiently trigger the oxidative electropolymerization process to form a reddish-orange film on the working Pt and ITO electrodes by cyclic voltammetry. The compact film shows a polyaniline-like AC impedance behavior and an inverse dependence of AC impedance on its thickness. As a result of switching of the MLCT/ICT and dication absorption transitions between 0 and + 1.8 V, this metallopolymer film exhibits the near-IR electrochromism with significant optical contrast ratio (ΔT% = 78.3% at λ = 775 nm), comparative response time (3.8 s for the coloration step and 11.0 s for the bleaching step) and high anodic coloration efficiency (CE = 208.3 C− 1·cm2).