An N‐Heterocyclic‐Carbene‐Derived Distonic Radical Cation

We present the discovery of a novel radical cation formed through one‐electron oxidation of an N‐heterocyclic carbene–carbodiimide (NHC–CDI) zwitterionic adduct. This compound possesses a distonic electronic structure (spatially separate spin and charge regions) and displays persistence under ambient conditions. We demonstrate its application in a redox‐flow battery exhibiting minimal voltage hysteresis, a flat voltage plateau, high Coulombic efficiency, and no performance decay for at least 100 cycles. The chemical tunability of NHCs and CDIs suggests that this approach could provide a general entry to redox‐active NHC–CDI adducts and their persistent radical ions for various applications.     

On the Interaction between Deprotonated Cytosine [C(−H)]− and Ba2+: Infrared Multiphoton Spectroscopy and Dynamics

Gas-phase interactions between Ba²⁺ and deprotonated cytosine (C_(−H)) were studied in [C_(−H)Ba]⁺ and [C_(−H)BaC]⁺ complexes by IRMPD spectroscopy coupled to tandem mass-spectrometry in combination with DFT calculations. For the [C_(−H)BaC]⁺ complex only one [C_(−H)KAN1O−Ba-C_anti]⁺ isomer was found, although the presence of another structure cannot be excluded. This isomer features a central tetracoordinated Ba²⁺ that simultaneously interacts with keto-amino [C_(−H)]⁻ deprotonated on N1 and neutral keto-amino C. Both moieties are in different planes as a consequence of an additional NH…O=C hydrogen bond between C and [C_(−H)] ⁻ . A sequential IRMPD dynamics is observed in this complex. For the [C_(−H)Ba]⁺ complex produced by electrospray ionization two isomers ([C_(−H)KAN1OBa]⁺ and [C_(−H)KAN3OBa]⁺) were identified, in which Ba²⁺ interacts simultaneously with the C=O group and the N1 or N3 atom of the keto-amino [C_(−H)]⁻, respectively. A comparison with the related [C_(−H)Pb]⁺ complex (J. Y. Salpin et al., Chem. Phys. Chem. 2014 , 15, 2959–2971) is also presented.     

Calix[4]Resorcinarene Macrocycles Interactions with Cd2+, Hg2+, Pb2+, and Cu2+ Cations: A QCM‐I and Langmuir Ultra‐thin Monolayers Study

Stable ultra‐thin Langmuir monolayers of calix[4]resorcinarene derivatives, namely: C‐dec‐9‐enylcalix[4]resorcinarene‐O‐(R+)‐α‐methylbenzylamine (Ionophore I ), and C‐dec‐9‐enylcalix[4]resorcinarene‐O‐(S‐)‐α‐methylbenzylamine (Ionophore II ), were prepared at the air‐water interface. Their interactions with a series of heavy metals (HM) ions (Cu²⁺, Pb²⁺, Hg²⁺ and Cd²⁺) present in the aqueous subphase were investigated by measuring surface pressure‐area isotherms, at different concentrations. The surface pressure‐area (Π‐A) isotherms were stable and demonstrated the HM amounts influence on the limiting area (A_lim) values, therefore confirming the examined macrocycles capability to host the metallic toxicants. Additionally, a HM concentration dependence was realized and interpreted by a selective tendency of both ionophores towards Cu²⁺ and Cd²⁺ ions over Pb²⁺ and Hg²⁺, especially at high concentrations. The HM ions interactions with the applied calix[4]resorcinarene Langmuir ultra‐thin monolayers were interpreted based on the Gibbs‐Shishkovsky adsorption equation. Moreover, quartz crystal microbalance with impedance measurement (QCM‐I), was applied for the detection of HM ions in solutions. The QCM‐I results showed the effectiveness of the coated QCM‐I crystals in detecting the ions at different concentrations. The detection limit values were in the order of 0.16, 0.3, 0.65, 1.1 ppm (Ionophore I), as well 0.11, 0.45, 0.2, 0.89 (Ionophore II) for the Cu²⁺, Pb²⁺, Hg²⁺ and Cd²⁺ cations, respectively. Additionally, a selective tendency of both ionophores towards copper ions was shown.     

Coordination Chemistry and Methylation of Mixed-Substituted Tetraphosphetanes (RP−PtBu)2 (R=Ph,Py)

Synthesis of mixed-substituted tetraphosphetanes (RP−PtBu)₂ (R=Ph ( 4 ), Py ( 5 ); Py=2-pyridyl) is achieved from the condensation of dipyrazolylphosphanes RPpyr₂ (R=Py ( 1 ), Ph ( 3 ); pyr=3,5-dimethylpyrazolyl) as P₁-building block (R−P) and tBuPH₂ in an equimolar ratio. Compound 5 is of special interest since the presence of two pyridyl-substituents as well as the P₄-core allows for a rich coordination chemistry with coinage metal salts [Cu(MeCN)₄][OTf], Ag[OTf] and in situ formed [Au(tht)][OTf] (tht=tetrahydrothiophene). Both tetraphosphetanes undergo alkylation reaction with MeOTf to give a series of tetraphosphetanium and tetraphosphetanediium triflate salts with additional methylation of the pyridyl-moiety in case of 5 resulting in interesting novel cyclic trications. Harsh reaction condition and an excess of MeOTf converts 5 into the cyclic trication [-P(^MePy)PMe₂P(^MePy)PtBu-]³⁺ ( 13 ³⁺; ^MePy=1-methylpyridiniumyl) through the elimination of isobutene. This salt undergoes a complicated rearrangement reaction involving a P−P/P−P bond metathesis to form trication [-P(MePy)₃PtBu-]³⁺ ( 17 ³⁺) when reacted with Me₂PPMe₂.     

Synthesis of Low-Valent Dinuclear Group 14 Compounds with Element–Element Bonds by Transylidation

Dinuclear low-valent compounds of the heavy main group elements are rare species owing to their intrinsic reactivity. However, they represent desirable target molecules due to their unusual bonding situations as well as applications in bond activations and materials synthesis. The isolation of such compounds usually requires the use of substituents that provide sufficient stability and synthetic access. Herein, we report on the use of strongly donating ylide-substituents to access low-valent dinuclear group 14 compounds. The ylides not only impart steric and electronic stabilization, but also allow facile synthesis via transfer of an ylide from tetrylene precursors of type ^RY₂E to ECl₂ (E=Ge, Sn; ^RY=TolSO₂(PR₃)C with R=Ph, Cy). This method allowed the isolation of dinuclear complexes amongst a germanium analogue of a vinyl cation, [(^PhY)₂GeGe(^PhY)]⁺ with an electronic structure best described as a germylene-stabilized Ge^II cation and a ylide(chloro)digermene [^CyY(Cl)GeGe(Cl)^CyY] with an unusually unsymmetrical structure.     

Theoretical study of the desorption of neutral and ionic alkali metal atoms from the excited Li+(H2O)n = 1-4 and Na+(H2O)n = 1-4 cluster models: Electronic excitation charge transfer

In this work, the potential energy curves of several low-lying excited states of M⁺(H₂O)_{n = 1-4} (M = Li and Na) clusters with one M─O bond, related to the stretching of their M─O bond, were calculated in the gas phase. The time-dependent density functional theory and direct-symmetry-adapted cluster-configuration interaction were used in this study separately. Theoretical calculations showed that the charge transfer occurred between M⁺ and (H₂O)_n in the excited clusters so that the neutral metal atom was obtained at the dissociation limit of the potential curves. The excited potential curves of clusters were also calculated in the presence of the electrostatic field of water (EFW), and it was found that the charge transfer was blocked in the presence of EFW. The effect of the size of the (H₂O)_n cluster on the shape of the excited potential curves was investigated to observe how the M─O bond was affected in the excited states depending on the (H₂O)_n size. It was found that the increase in the size of the (H₂O)_n cluster increased the number of bonding excited potential curves. The difference between the electron density of the excited and ground electronic states was calculated to see how the charge transfer was affected by the size of the (H₂O)_n cluster.     

Nitrogen‐Based Lewis Acids: Synthesis and Reactivity of a Cyclic (Alkyl)(Amino)Nitrenium Cation

A room‐temperature‐stable crystalline cyclic (alkyl)(amino)nitrenium cation 2 features cationic nitrogen atom with a smaller HOMO–LUMO gap compared to that of a 1,2,3‐triazolium 5 (an N‐heterocyclic nitrenium cation). The low‐lying LUMO of 2 results in an enhanced electrophilicity, which allowed for the formation of Lewis adducts with neutral Lewis bases, such as Me₃P, nBu₃P, and IiPr. The N‐based Lewis acid 2 also forms an FLP with tBu₃P but subsequently reacts with (PrS)₂ to cleave the S?S bond. Both experimental and theoretical results suggest that the Lewis acidity of 2 is stronger than its N₃ analogues.     

Carbeniophosphines versus Phosphoniocarbenes: The Role of the Positive Charge

The chemistry of carbeniophosphines and phosphoniocarbenes, which have general structures derived formally from the three‐component “carbene/phosphine/positive charge” association, is presented. These two complementary classes of carbon–phosphorus‐based ligands, defined by the presence of an inverted cationic coordinating structure (C⁺～P: vs. P⁺～C:) have the common purpose of positioning a positive charge in the vicinity of the metal center. Through selected examples, the synthetic methods, coordination properties, and general reactivity of both cationic species is described. Particular emphasis is placed on the influence of the positive charge on the respective chemical behavior of the two classes of compound.