Dimer Cation Research Articles

Structure and capacitance of an electric double layer formed by fused dimer cations and monomer anions: a Monte Carlo simulation study

ABSTRACTCanonical Monte Carlo simulation results are obtained for the structure and differential capacitance of a planar electric double layer consisting of fused dimer cations and monomer anions in a dielectric continuum (solvent). The physical double layer model is mimicked by a uniformly charged, non-polarisable, planar electrode next to an electrolyte consisting of positively charged fused dimers and negatively charged monomer rigid spheres in a continuum dielectric. The fused dimer comprises two same sized hard spheres that are fused into one another, one of the hard spheres being charged and the other neutral. The various electrode-particle species singlet distribution functions and the mean electrostatic potential profiles are obtained for 1:1, 2:2, 2:1, and 1:2 valency systems for different degrees of fusion. The differential capacitance as a function of the electrode surface charge density is evaluated for a 1:1 system. Comparison of these results are made with those corresponding to the situation when the dimer spheres are simply tangentially tethered. It is seen that the fused dimer influences the double layer structure and capacitance substantially for a negatively charged electrode but less so for a positively charged electrode.

L-Tryptophan l-tryptophanium bromide: Anhydrous and monohydrate

l-Tryptophan l-tryptophanium bromide (I) and l-tryptophan l-tryptophanium bromide monohydrate (II) are new salts with (A⋯A+) type dimeric cation. The salt (I) crystallizes in the monoclinic system (space group P21, Z = 2) and is isostructural with respective chloride (V.V. Ghazaryan et al., Spectrochim. Acta A 136(2015) 743–750), while the salt (II) was obtained previously (T. Takigawa et al., Bull. Chem. Soc. Jap. 39(1966) 2369–2378) and described as hemyhydrate without structure determination. The salt (II) crystallizes in orthorhombic system (space group P212121, Z = 4). The dimeric cations in (I) and (II) are formed by O–H⋯O hydrogen bonds with the O⋯O distances equal to 2.538(3) Å and 2.481(3) Å respectively. The infrared and Raman spectra of the crystals are studied and compared with the spectra of l-tryptophan l-tryptophanium chloride and l-tryptophanium bromide.

ChemInform Abstract: Conjugated Radical Cation Dimerization‐Driven Generation of Supramolecular Architectures

AbstractReview: [32 refs.

L-serine picrates

Two crystalline salts have been obtained from the system l-serine - picric acid - H2O: l-serinium picrate monohydrate (I) and tris(l-serine) bis(l-serinium) dipicrate trihydrate (II). The salt (I) crystallizes in monoclinic system (space group P21, Z = 4). Asymmetric unit of (I) contains two formula units. Carboxyl groups of both l-serinium cations form hydrogen bonds with picrate anions with O···O distances: 2.595 (6) Å and 2.638 (5) Å. The salt (II) crystallizes in orthorhombic system (space group P212121, Z = 4). Asymmetric unit of (II) contains one formula unit. Carboxyl groups of both l-serinium cations form short O–H···O hydrogen bonds with two of three zwitterionic moieties, forming two dimeric (l-serine l-serinium) cations with O···O distances: 2.485 (3) Å and 2.487 (3) Å. The infrared and Raman spectra of obtained salts are recorded and discussed.

Unusual hydrogen bonding in L-cysteine hydrogen fluoride.

L-Cysteine hydrogen fluoride, or bis(L-cysteinium) difluoride-L-cysteine-hydrogen fluoride (1/1/1), 2C3H8NO2S(+)·2F(-)·C3H7NO2S·HF or L-Cys(+)(L-Cys···L-Cys(+))F(-)(F(-)...H-F), provides the first example of a structure with cations of the 'triglycine sulfate' type, i.e. A(+)(A···A(+)) (where A and A(+) are the zwitterionic and cationic states of an amino acid, respectively), without a doubly charged counter-ion. The salt crystallizes in the monoclinic system with the space group P2(1). The dimeric (L-Cys···L-Cys(+)) cation and the dimeric (F(-)···H-F) anion are formed via strong O-H···O or F-H···F hydrogen bonds, respectively, with very short O···O [2.4438 (19) Å] and F···F distances [2.2676 (17) Å]. The F···F distance is significantly shorter than in solid hydrogen fluoride. Additionally, there is another very short hydrogen bond, of O-H···F type, formed by a L-cysteinium cation and a fluoride ion. The corresponding O···F distance of 2.3412 (19) Å seems to be the shortest among O-H···F and F-H···O hydrogen bonds known to date. The single-crystal X-ray diffraction study was complemented by IR spectroscopy. Of special interest was the spectral region of vibrations related to the above-mentioned hydrogen bonds.

Optical absorption spectrum of the chromium dimer cation: Measurements by photon-trap and photodissociation spectroscopy

Optical excitation in the chromium dimer cation, Cr2+, is investigated by photon-trap and photodissociation-action spectroscopy under a cryogenic condition in an ion trap. The former provides direct measurement of an absorption spectrum with high sensitivity, where cross sections as small as 0.4Å2 at the maximum are detectable. The dissociation cross sections are thus compared with those of absorption quantitatively. The spectra in the 2.2-eV region obtained by both methods are found to be equivalent. The present results are consistent with our assignment that the excited state is repulsive, in contrast to a previous report suggesting predissociation.

New hydrophobic L-amino acid salts: maleates of L-leucine, L-isoleucine and L-norvaline.

Crystals of maleates of three amino acids with hydrophobic side chains [L-leucenium hydrogen maleate, C6H14NO2(+)·C4H3O4(-), (I), L-isoleucenium hydrogen maleate hemihydrate, C6H14NO2(+)·C4H3O4(-)·0.5H2O, (II), and L-norvalinium hydrogen maleate-L-norvaline (1/1), C5H11NO2(+)·C4H3O4(-)·C5H12NO2, (III)], were obtained. The new structures contain C2(2)(12) chains, or variants thereof, that are a common feature in the crystal structures of amino acid maleates. The L-leucenium salt is remarkable due to a large number of symmetrically non-equivalent units (Z' = 3). The L-isoleucenium salt is a hydrate despite the fact that L-isoleucine is a nonpolar hydrophobic amino acid (previously known amino acid maleates formed hydrates only with lysine and histidine, which are polar and hydrophilic). The L-norvalinium salt provides the first example where the dimeric cation L-Nva...L-NvaH(+) was observed. All three compounds have layered noncentrosymmetric structures. Preliminary tests have shown the presence of the second harmonic generation (SGH) effect for all three compounds.

Single crystal XRD, vibrational spectra, quantum chemical and thermal studies on a new semi-organic crystal: 4-Aminium antipyrine chloride

The new semi-organic crystal of 4-aminium antipyrine chloride was grown as a single crystal by slow evaporation solution growth method. The crystal and molecular structure of the grown crystal was determined by single crystal diffraction techniques. The single crystal XRD studies reveal that the phenyl ring and pyrazolone ring of the cation has been inclined at an angle of 52.3 (1)°. The molecular aggregations were stabilized through intricate three dimensional hydrogen bonding network formed by the classical N–H⋯O and N–H⋯Cl hydrogen bonds. The cationic dimer R22(10) motif formed through N–H⋯O intermolecular hydrogen bonds was observed around the inversion center of the unit cell. The amino group from the cation and the chlorine anion was linked through N–H⋯Cl intermolecular hydrogen bond leading to a R24 (8) ring motif. These two ring motifs were extended along the a-axis of the unit cell and forms a hydrophilic layer at z = 0 and 1, which is sandwiched between the hydrophobic layer at z = 1/2. Geometry optimization of the molecules was done by Density Functional Theory (DFT) using the B3LYP function and Hartree–Fock (HF) level with 6-311++G(d,p) basis set. The optimized molecular geometry and computed vibrational spectra were compared with experimental results which show a significant agreement. The natural bond orbital (NBO) analysis was carried out to interpret hyperconjucative interaction and intramolecular charge transfer (ICT). The chemical hardness, electro-negativity and chemical potential of the molecule were carried out by HOMO-LUMO plot. The lower band gap value of the frontier orbitals shows the possible bioactivity of the molecule.

Direct observation of high-spin states in manganese dimer and trimer cations by x-ray magnetic circular dichroism spectroscopy in an ion trap.

The electronic structure and magnetic moments of free Mn2 (+) and Mn3 (+) are characterized by 2p x-ray absorption and x-ray magnetic circular dichroism spectroscopy in a cryogenic ion trap that is coupled to a synchrotron radiation beamline. Our results directly show that localized magnetic moments of 5 μB are created by 3d(5)((6)S) states at each ionic core, which are coupled ferromagnetically to form molecular high-spin states via indirect exchange that is mediated in both cases by a delocalized valence electron in a singly occupied 4s derived antibonding molecular orbital with an unpaired spin. This leads to total magnetic moments of 11 μB for Mn2 (+) and 16 μB for Mn3 (+), with no contribution of orbital angular momentum.

Study of the competitive mechanisms of cyclohexane dehydrogenation by gas-phase Ni2(+) cationic dimer: one-face dehydrogenation versus flip dehydrogenation.

The mechanism of cyclohexane dehydrogenation catalyzed by the cationic dimer Ni2 (+) has been investigated at the B3LYP level of density functional theory. The first dehydrogenation occurs readily (it is exothermic by 30kcal/mol), whereas the second and third dehydrogenations show weaker exothermicity than the first (23 and 21kcal/mol, respectively). These three hydrogenations corresponding to the total dehydrogenation of one face of cyclohexane mainly proceed in the doublet state due to the presence of significant minimum-energy crossing points (MECPs). In addition, because the elimination of non-negligible amounts of [H2,2D2] and [2H2,D2] in this reaction was also observed in a previous experiment, we calculated a flip mechanism which would yield results that agree with those experimental results. This flip process includes two MECPs, meaning that the reaction mainly proceeds along the doublet potential energy surface but finishes in the quartet state. The rate-limiting step ((2)IM9 → (2)TS9/10 → (2)IM10) of the flip process is endothermic by 3kcal/mol and the barrier to this step is 33kcal/mol. Our calculations indicate that one-face dehydrogenation is a more favorable channel than the flip one. We excluded the possibility that eliminations of [H2,2D2] or [D2,2H2] could proceed through a mechanism involving Ni2 (+) dissociation, or that [H-D] scrambling could occur through (2)TS11/13 ((4)TS12/15), due to the large amounts of energy required. In the dissociation of (2)IM19, (2)[(H2)Ni2(C6H6)](+), a molecule of hydrogen first dissociates, leaving a final product of (2)[Ni2(C6H6)](+). Neither C6H6 nor (H2)Ni2 (+) can easily dissociate from (2)IM19 due to π backdonation.

Communication: Ion mobility of the radical cation dimers: (Naphthalene)2(+•) and naphthalene(+•)-benzene: Evidence for stacked sandwich and T-shape structures.

Dimer radical cations of aromatic and polycyclic aromatic molecules are good model systems for a fundamental understanding of photoconductivity and ferromagnetism in organic materials which depend on the degree of charge delocalization. The structures of the dimer radical cations are difficult to determine theoretically since the potential energy surface is often very flat with multiple shallow minima representing two major classes of isomers adopting the stacked parallel or the T-shape structure. We present experimental results, based on mass-selected ion mobility measurements, on the gas phase structures of the naphthalene(+⋅) ⋅ naphthalene homodimer and the naphthalene(+⋅) ⋅ benzene heterodimer radical cations at different temperatures. Ion mobility studies reveal a persistence of the stacked parallel structure of the naphthalene(+⋅) ⋅ naphthalene homodimer in the temperature range 230-300 K. On the other hand, the results reveal that the naphthalene(+⋅) ⋅ benzene heterodimer is able to exhibit both the stacked parallel and T-shape structural isomers depending on the experimental conditions. Exploitation of the unique structural motifs among charged homo- and heteroaromatic-aromatic interactions may lead to new opportunities for molecular design and recognition involving charged aromatic systems.

Density functional theory and chromium: Insights from the dimers.

The binding in small Cr clusters is re-investigated, where the correct description of the dimer in three charge states is used as criterion to assign the most suitable density functional theory approximation. The difficulty in chromium arises from the subtle interplay between energy gain from hybridization and energetic cost due to exchange between s and d based molecular orbitals. Variations in published bond lengths and binding energies are shown to arise from insufficient numerical representation of electron density and Kohn-Sham wave-functions. The best functional performance is found for gradient corrected (GGA) functionals and meta-GGAs, where we find severe differences between functionals from the same family due to the importance of exchange. Only the "best fit" from Bayesian error estimation is able to predict the correct energetics for all three charge states unambiguously. With this knowledge, we predict small bond-lengths to be exclusively present in Cr2 and Cr2 (-). Already for the dimer cation, solely long bond-lengths appear, similar to what is found in the trimer and in chromium bulk.

ReaxFF Reactive Molecular Dynamics Simulation of the Hydration of Cu-SSZ-13 Zeolite and the Formation of Cu Dimers

A new Cu/Si/Al/O/H reactive ReaxFF force field was developed and used in molecular dynamics simulations of the hydration of Cu-exchanged SSZ-13 catalyst. It was observed that at temperatures close to room temperarture, all Cu cations, including those at the faces of the double 6-member rings (6MRs), become fully hydrated and detach from the framework. The hydrated Cu cations can diffuse through the Cu-SSZ-13 zeolite pore windows. At higher temperatures, the formation of cationic OH-bridged Cu dimers Cu2OH and Cu2(OH)2 within the cages was observed. The simulations show that the temperature at which these species are formed is lower for zeolites that stabilize [CuOH]+ ions, as would be expected for relatively high-Cu- and low-Al-content zeolites. The stable dimers bind preferentially to 8MRs beside the large cages in a configuration that blocks the openings of the pores. The consequences of the present results for selective catalytic reduction and NO oxidation catalysis in Cu-SSZ-13 are discussed.

β-Alaninium tetrafluoroborate: A new salt with di-β-alaninium dimeric cation

β-Alaninium tetrafluoroborate crystallizes in the monoclinic system (space group P21/n, Z=4). The asymmetric unit contains one β-alaninium cation and one tetrafluoroborate anion, in which the fluorine atoms are disordered. All β-alaninium cations are connected with the symmetry related cations via an inversion center, thus forming dimeric centrosymmetric β-Ala+···β-Ala+ cations. The O···O distance (2.698(2)Å) in the dimeric cation is relatively long compared to known distances of previously reported salts with A+···A+ type dimeric cations. The infrared and Raman spectra are studied.

Maximum spin polarization in chromium dimer cations as demonstrated by X-ray magnetic circular dichroism spectroscopy.

X-ray magnetic circular dichroism spectroscopy has been used to characterize the electronic structure and magnetic moment of Cr2 (+) . Our results indicate that the removal of a single electron from the 4sσg bonding orbital of Cr2 drastically changes the preferred coupling of the 3d electronic spins. While the neutral molecule has a zero-spin ground state with a very short bond length, the molecular cation exhibits a ferromagnetically coupled ground state with the highest possible spin of S=11/2, and almost twice the bond length of the neutral molecule. This spin configuration can be interpreted as a result of indirect exchange coupling between the 3d electrons of the two atoms that is mediated by the single 4s electron through a strong intraatomic 3d-4s exchange interaction. Our finding allows an estimate of the relative energies of two states that are often discussed as ground-state candidates, the ferromagnetically coupled (12) Σ and the low-spin (2) Σ state.

Conjugated radical cation dimerization-driven generation of supramolecular architectures

Abstract This paper summarizes the recent advance in utilizing conjugated radical cation dimerization (CRCD) for constructing new unimolecular, such as foldamers, and supramolecular ordered structures, such as three-dimensional supramolecular polymers and two-dimensional supramolecular organic framework. Particularly, the stacking or dimerization of tetrathiafulvalene and 4,4′-dipyridium subunits has been highlighted, and the approaches for enhancing the stability of their radical cation dimers have been discussed.

Ferromagnetic spin coupling in the chromium dimer cation: measurements by photodissociation spectroscopy combined with coupled-cluster calculations.

The magnetic coupling of the chromium dimer cation, Cr2 (+), has been an outstanding problem for decades. An optical absorption spectrum of Cr2 (+) has been obtained by photodissociation spectroscopy in the photon-energy range from 2.0 to 5.0 eV. Besides, calculations have been performed by the equation-of-motion coupled-cluster singles and doubles method for vertical excitation of the species. Their coincidence supports our assignment that the ground electronic state exhibits a ferromagnetic spin coupling, which is contrary to those of neutral and negatively charged dimers, Cr2 and Cr2 (-), in their lowest spin states.

Unexpected methyl migrations of ethanol dimer under synchrotron VUV radiation.

While methyl transfer is well known to occur in the enzyme- and metal-catalyzed reactions, the methyl transfer in the metal-free organic molecules induced by the photon ionization has been less concerned. Herein, vacuum ultraviolet single photon ionization and dissociation of ethanol dimer are investigated with synchrotron radiation photoionization mass spectroscopy and theoretical methods. Besides the protonated clusters cation (C2H5OH)⋅H(+) (m/z = 47) and the β-carbon-carbon bond cleavage fragment CH2O⋅(C2H5OH)H(+) (m/z = 77), the measured mass spectra revealed that a new fragment (C2H5OH)⋅(CH3)(+) (m/z = 61) appeared at the photon energy of 12.1 and 15.0 eV, where the neutral dimer could be vertically ionized to higher ionic state. Thereafter, the generated carbonium ions are followed by a Wagner-Meerwein rearrangement and then dissociate to produce this new fragment, which is considered to generate after surmounting a few barriers including intra- and inter-molecular methyl migrations by the aid of theoretical calculations. The appearance energy of this new fragment is measured as 11.55 ± 0.05 eV by scanning photoionization efficiency curve. While the signal intensity of fragment m/z = 61 starts to increase, the fragments m/z = 47 and 77 tend to slowly incline around 11.55 eV photon energy. This suggests that the additional fragment channels other than (C2H5OH)⋅H(+) and CH2O⋅(C2H5OH)H(+) have also been opened, which consume some dimer cations. The present report provides a clear description of the photoionization and dissociation processes of the ethanol dimer in the range of the photon energy 12-15 eV.

Electromers of the benzene dimer radical cation.

The well-studied benzene dimer radical cation, which is prototypical for this class of species, has been reinvestigated computationally. Thereby it turned out that both the σ-hemibonded and the half-shifted sandwich structures of the benzene dimer cation, which had been independently proposed, represent stationary points on the B2PLYP-D potential energy surfaces. However, these structures belong to distinct electronic states, both of which are associated with potential surfaces that are very flat with regard to rotation of the two benzene rings in an opposite sense relative to each other. The surfaces of these two "electromers" of the benzene dimer cation are separated by only 3-4 kcal mol(-1) and do not intersect along the rotation coordinate, which represents a rather unique electronic structure situation. When moving on either of the two surfaces the title complex is an extremely fluxional species, in spite of its being bound by over 20 kcal mol(-1).

Metal ion influences distortion of the ligand in the structure of [M{2-MeO(O)CC6H4NHC(S)NP(S)(OiPr)2}2] (M = Zn(II), Cd(II)) complexes: a driving force for intermolecular aggregation.

Reaction of the in situ deprotonated N-thiophosphorylated thiourea 2-MeO(O)CC6H4NHC(S)NHP(S)(OiPr)2 () with MCl2 (M = Zn(II), Cd(II)) in aqueous ethanol leads to complexes of the formula . Both compounds crystallise in the triclinic space group P1[combining macron] with Z = 2 and the metal cations are found in a tetrahedral S2S coordination environment formed by the C-S and P-S sulfur atoms. The crystal structures reveal intramolecular N-HO[double bond, length as m-dash]C hydrogen bonds formed within the 2-MeO(O)CC6H4NH fragments. Both structures are further stabilised by intermolecular ππ stacking interactions, which are more efficient in . Here, a pronounced dimeric intermolecular aggregate is observed which goes along with a pronounced distortion of the chelate [(S)CNP(S)](-) backbone of the ligand upon coordination to Cd(II) as well as a significantly distorted coordination tetrahedron CdS2S. The aggregation is also reflected in the positive electrospray ionisation (ESI) mass spectrum of the Cd(II) complex, which exhibits peaks for the dimeric cations [Cd2L3](+), [Cd2L4 + H](+) and [Cd2L4 + Na](+), while for the Zn(II) analogue only monomeric species were observed. Quantum chemical ETS-NOCV (ADF) calculations confirm the higher stability of dimers in compared with . The ππ stacking interactions are prodominantly due to dispersion contributions, though the electrostatic and orbital interaction components are also important. QTAIM (ADF) type calculations additionally quantify the covalent and non-covalent interactions in the momomers.