Observations of magic numbers in gas phase hydrates of alkylammonium ions

Hydration of alkylammonium ions under nonanalytical electrospray ionization conditions has been found to yield cluster ions with more than 20 water molecules associated with the central ion. These cluster ion species are taken to be an approximation of the conditions in liquid water. Many of the alkylammonium cation mass spectra exhibit water cluster numbers that appear to be particularly favorable, i.e., “magic number clusters” (MNC). We have found MNC in hydrates of mono- and tetra-alkyl ammonium ions, NH₃(C _m H_2m+1)⁺(H₂O) _n , m=1–8 and N(C _m H_2m+1) ₄ ⁺ (H₂O) _n , m=2–8. In contrast, NH₂(CH₃) ₂ ⁺ (H₂O) _n , NH(CH₃) ₃ ⁺ (H₂O) _n1 and N(CH₃) ₄ ⁺ (H₂O) _n do not exhibit any MNC. We conjecture that the structures of these magic number clusters correspond to exohedral structures in which the ion is situated on the surface of the water cage in contrast to the widely accepted caged ion structures of H₃O⁺(H₂O) _n and NH ₄ ⁺ (H₂O) _n .     

Muttiphoton Ionization of Benzene-Ammonia Clusters: Intracluster Reaction and Cluster Ion Stability

Neutral benzene-ammonia clusters, prepared in a supersonic expansion, were ionized using multiphoton ionization. The cluster ions were investigated with a time-of-flight mass spectrometer. The observed major cluster ions, under 355-nm laser irradiation, resulting from prompt intracluster ion-molecule reaction and fragmentation following ionization are (C₆H₆)_m(NH₃)_nH⁺, m = 1–6, n = 1–4 and (C₆H₆)_m⁺, m = 1–3. The results of isotopic labeling experiments clearly indicate that C₆H₆ does not participate in intracluster ion-molecule reactions to form (C₆H₆)_m(NH₃)_nH⁺. A local maximum appears at n = 2 in the intensity distribution of (C₆H₆)_m(NH₃) _nH⁺ for each value of m under all experimental conditions. This finding indicates that (C₆H₆)_m(NH₃)₂H⁺ is more stable than any other (C₆H₅)_m(NH₃)_mH⁺ (n = 1,3,4) for m = 1–6.     

Effect of method of ion preparation on low-energy collision-induced dissociation mass spectra

The collision-induced dissociation (CID) mass spectra of protonated cocaine and protonated heroin have been measured using a triple quadrupole mass spectrometer at 50 eV ion/neutral collision energy for protonated molecules prepared by different protonating agents. The CID mass spectra of protonated cocaine using H⁺(H₂O)_n, H⁺(NH₃)_n and H⁺((CH₃)₂NH)_n as protonating agents are essentially identical and it is concluded that, regardless of the initial site of protonation, the fragmentation reactions occurring on collisional activation are identical. By contrast, protonated heorin prepared with H⁺(H₂O)_n and H⁺(NH₃)_n as protonating agents show substantial differences. That formed by reaction of H⁺(H₂O)_n shows a much more abundant peak corresponding to loss of CH₃CO₂H. From a comparison with model compounds, and from a consideration of the three-dimensional structure of heroin, it is concluded that with H⁺(H₂O)_n as protonating agent significant protonation occurs at the acetate group attached to the alicyclic ring, leading to acetic acid loss on collisional activation, but that reaction of H⁺(NH₃)_n leads to protonation at the nitrogen function. The proton attached to nitrogen cannot interact with the acetate group and, consequently, the probability of loss of acetic acid on collislional activation is greatly reduced.     

Werner Complexes with ω‐Dimethylaminoalkyl Substituted Ethylenediamine Ligands: Bifunctional Hydrogen‐Bond‐Donor Catalysts for Highly Enantioselective Michael Additions

The racemic carbonate complex [Co(en)₂O₂CO]⁺ Cl^? (en=1,2‐ethylenediamine) and (S)‐[H₃NCH((CH₂)_nNHMe₂)CH₂NH₃]³⁺ 3 Cl^? (n=1–4) react (water, charcoal, 100 °C) to give [Co(en)₂((S)‐H₂NCH((CH₂)_nNHMe₂)CH₂NH₂)]⁴⁺ 4 Cl^? ( 3 a – d H⁴⁺ 4 Cl^?) as a mixture of Λ/Δ diastereomers that separate on chiral‐phase Sephadex columns. These are treated with NaOH/Na⁺ BAr_f^? (BAr_f=B(3,5‐C₆H₃(CF₃)₂)₄) to give lipophilic Λ‐ and Δ‐ 3 a–d ³⁺ 3 BAr_f^?, which are screened as catalysts (10 mol %) for additions of dialkyl malonates to nitroalkenes. Optimal results are obtained with Λ‐ 3 c ³⁺ 3 BAr_f^? (CH₂Cl₂, ?35 °C; 98–82 % yields and 99–93 % ee for six β‐arylnitroethenes). The monofunctional catalysts Λ‐ and Δ‐[Co(en)₃]³⁺ 3 BAr_f^? give enantioselectivities of <10 % ee with equal loadings of Et₃N. The crystal structure of Δ‐ 3 a H⁴⁺ 4 Cl^? provides a starting point for speculation regarding transition‐state assemblies.     

Distonic radical cations : Guidelines for the assessment of their stability

Ab initio molecular orbital calculations on the distonic radical cations CH₂(CH₂)_nN⁺H₃ and their conventional isomers CH₃(CH₂)_nNH₂+ (n = 0,1, 2 and 3) indicate a preference in each case for the distonic isomer. The energy difference appears to converge with increasing n towards a limit which is close to the energy difference between the component systems CH₃·H₂+CH₃^+NH₃ (representing the distonic isomer) and CH₃CH₃+CH₃NH₂+ (representing the conventional isomer). The generality of this result is assessed by using results for the component systems CH₃·Y+CH₃X⁺H and CH₃YH+CH₃X^+. (or CH₃YH^+. + CH₃X) to predict the relative energies of the distonic ions ·Y(CH₂)_nX⁺H and their conventional isomers HY(CH₂)nX^+. (X = NH₂, OH, F, PH₂, SH, Cl; Y = CH₂, NH, O) and testing the predictions through explicit calculations for systems with n = 0,1 and 2. Although the predictions based on component systems are often close to the results of direct calculations, there are substantial discrepancies in a number of cases; the reasons for such discrepancies are discussed. Caution must be exercised in applying this and related predictive schemes. For the systems examined in the present study, the conventional radical cation is predicted in most cases to lie lower in energy than its distonic isomer. It is found that the more important factors contributing to a preference for distonic over conventional radical cations are the presence in the system of a group(X) with high proton affinity and the absence of a group (X, Y or perturbed (C—C) with low ionization energy.     

Electron impact ionization of ethylene–methanol heteroclusters: Stable configurations and mechanisms in intracluster ion–molecule reactions

Reactions that proceed within mixed ethylene–methanol cluster ions were studied using an electron impact time-of-flight mass spectrometer. The ion abundance ratio, [(C₂H₄)_n(CH₃OH)_mH⁺]/[(C₂H₄)_n(CH₃OH)_m⁺], shows a propensity to increase as the ethylene/methanol mixing ratio increases, indicating that the proton is preferentially bound to a methanol molecule in the heterocluster ions. The results from isotope-labelling experiments indicate that the effective formation of a protonated heterocluster is responsible for ethylene molecules in the clusters. The observed (C₂H₄)_n(CH₃OH)_m⁺ and (C₂H₄)_n(CH₃OH)_m–1CH₃O⁺ ions are interpreted as a consequence of the ion–neutral complex and intracluster ion–molecule reaction, respectively. Experimental evidence for the stable configurations of heterocluster species is found from the distinct abundance distributions of these ions and also from the observation of fragment peaks in the mass spectra. Investigations on the relative cluster ion distribution under various conditions suggest that (C₂H₄)_n(CH₃OH)_mH⁺ ions with n + m ≤ 3 have particularly stable structures. The result is understood on the basis of ion–molecule condensation reactions, leading to the formation of fragment ions, $ {\rm CH}_2=\!=\mathop {\rm O}\limits^ + {\rm CH}_3 $ and (CH₃OH)H₃O⁺, and the effective stabilization by a polar molecule. The reaction energies of proposed mechanisms are presented for (C₂H₄)_n(CH₃OH)_mH⁺(n + m ≤ 3) using semi-empirical molecular orbital calculations.     

A potentiometric and calorimetric study of the protonation and complexation with Cu2+ and Ni2+ of some sulphur-containing α,ω-amino acids

The behaviour in aqueous solution of some aminocarboxylates of the type NH₂(CH₂)_nS(CH₂)_m-1COO^? (abbreviated as n,m-NSO; n and m = 2 or 3) in equilibria with H⁺, Cu²⁺ and Ni²⁺ ions has been investigated potentiometrically and calorimetrically at 25° C in a 0.5 M KNO₃ medium.The protonation of the amino function and especially the carboxylate function is attended by strong desolvation effects, which are characterized by low exothermic enthalpies and strongly positive entropies of protonation.In [Cu(n,m-NSO)]⁺ and [Ni(n,m-NSO)]⁺ the aminocarboxylates act as tridentate ligands, forming complexes with a strong hard—hard character. The biligand species [Ni(n,m-NSO)₂] behave as six-coordinated complexes whereas in [Cu(n,m-NSO)₂] the second ligand is bound only through the N and S donor, forming a five-coordinated species.Finally, the n,m-NSO ligands also form protonated species with the Cu²⁺ ion.     

Complexes of benzo-15-crown-5 with protonated primary amines and diamines

Three complexes of benzo-15-crown-5 (B15C5) with protonated primary amines [PhCH₂NH₃(B15C5)](ClO₄), [p-C₆H₄(CH₂NH₃)₂(B15C5)₂](ClO₄)₂, and [(CH₂)₄(NH₃)₂(B15C5)₂](SCN)₂ were isolated and studied in acetonitrile solutions by NMR, and in the solid state by X-ray crystallography. In all complexes, one B15C5 molecule was bound with each R-NH₃⁺ moiety with characteristic small separation of 1.84-1.86 Å between the nitrogen of the R-NH₃⁺ group and the O₅ mean plane of the crown residue. No sandwich-type complexes with a 1:2 R-NH₃⁺/B15C5 stoichiometry were observed. Binding affinities of B15C5 in acetonitrile were similar for all ammonium cations studied: K₁=550±10 M⁻¹ for [PhCH₂NH₃]⁺; K₁=1100±100 and K₂=400±30 M⁻¹ for [p-C₆H₄(CH₂NH₃)₂]²⁺; and K₁=1100±100 and K₂=300±30 M⁻¹ for [H₃N(CH₂)₄NH₃]²⁺. The complexation is primarily enthalpy-driven (ΔH°=−4.9±0.5 kcal/mol, ΔS°=−3.8±1.0 eu for PhCH₂NH₃⁺-B15C5), as determined by variable temperature ¹H NMR titrations.     

FTMS studies of sputtered metal cluster ions (IV): size-selective effects in the chemistry of Fe n + with NH3 and Pd n + with D2 or C2H4

Fe _n ⁺ and Pd _n ⁺ clusters up ton=19 andn=25, respectively, are produced in an external ion source by sputtering of the respective metal foils with Xe⁺ primary ions at 20 keV. They are transferred to the ICR cell of a home-built Fourier transform mass spectrometer, where they are thermalized to nearly room temperature and stored for several tens of seconds. During this time, their reactions with a gas leaked in at low level are studied. Thus in the presence of ammonia, most Fe _n ⁺ clusters react by simply adsorbing intact NH₃ molecules. Only Fe ₄ ⁺ ions show dehydrogenation/adsorption to Fe₄(NH) _m ⁺ intermediates (m=1, 2) that in a complex scheme go on adsorbing complete NH₃ units. To clarify the reaction scheme, one has to isolate each species in the ion cell, which often requires the ejection of ions very close in mass. This led to the development of a special isolation technique that avoids the use of isotopically pure metal samples. Pd _n ⁺ cluster ions (n=2...9) dehydrogenate C₂H₄ in general to yield Pd _n (C₂H₂)⁺, yet Pd ₆ ⁺ appear totally unreactive. Towards D₂, Pd ₇ ⁺ ions seem inert, whereas Pd ₈ ⁺ adsorb up to two molecules.     

Thermal behaviour of mixed long-chain alkylammonium tetrachlorozincates

Mixed crystals of composition (n-C_mH_2m+1NH₃)_2xm(n-C_nH_2n+1 · NH₃)_2?2xm ZnCl₄ (m= 12; n=14, 16, 18) are formed upon annealing mechanical mixtures of layer compounds (n-C_nH_2n+1NH₃)₂ZnCl₄, through solid state diffusion of the n-alkylammonium cations. From a common high temperature monophasic modification, in which the polymethylenic chains are conformationally molten, different modifications are obtained on cooling [depending on the (n ? m) value] in which chain crystallinity is developed. The structure of such modifications is speculated on the grounds of DSC and preliminary X-ray diffractometric and IR data, and compared with that of similar previously characterized systems.     

Nonisothermal membrane phenomena across perfluorosulfonic acid-type membranes,Flemion S: part I. Thermoosmosis and transported entropy of water

Solvent transports across the perfluorosulfonic acid-type membrane Flemion S were measured for aqueous electrolyte solutions under a temperature difference and under an osmotic pressure difference. H⁺, Li⁺, Na⁺, K⁺, NH ₄ ⁺ , CH₃NH ₃ ⁺ , (CH₃)₂NH ₂ ⁺ , (CH₃)₃NH⁺, (CH₃)₄N⁺, (C₂H₅)₄N⁺, (n-C₃H₇)₄N⁺ and (n-C₄H₉)₄N⁺ were used as counterions. Water flux across the membrane in HCl solution is higher than that in the other electrolyte solutions because hydrogen ions can exchange with the hydrogen of the neighbor water molecules and contribute to the water transport across the membrane as a proton jump in conductivity. The direction of thermoosmosis across the membrane in HCl, NaCl, (CH₃)₄NCl and (C₂H₅)₄NCl solutions was from the cold side to the hot side and that in LiCl, KCl, NH₄Cl, CH₃NH₃Cl, (CH₃)₂NH₂Cl and (n-C₄H₉)₄NBr solutions was from the hot side to the cold side, although thermoosmosis across anion-exchange membranes always occurs toward the hot side.     

Formation and fragmentation of gas-phase ion-molecule complexes of transition-metal ions with organic molecules containing two functional groups

A mass spectrometer fast atom bombardment source has been used to synthesize, in the gas phase, the ion-molecule complexes of transition-metal ions (Ni⁺, CO⁺, Fe⁺, and Mn⁺) with α- or β-unsaturated alkenenitriles, RCH=CHCN (R=H, CH₃, and C₂H₅) and CH₃CH=CHCH₂CN, and 2-methyl glutaronitrile. The metastable ion fragmentations of the complexes are monitored in the first held-free region by B/E linked scans. Surprisingly, an intense HCN loss via an intermediate (C _n H_2n ?2)?M⁺?(HCN) is observed for the complexes of the alkenenitriles. The metal ions significantly affect the fragmentation processes. The coexistence of both end-on and side-on coordination modes is suggested to explain the fragmentations.     

Mesogens based on palladium orthometallated complexes with carboxylato bridges: tuning and shaping a non-planar molecule

The binuclear cyclopalladated compounds [Pd₂(μ-OH)₂(Lⁿ)₂] (1) derived from imines HLⁿ = p-C_nH_2n + 1O-C₆H₄-CHN-C₆H₄-OC_nH_2n + 1-p (n = 6,10) react with carboxylic acids to give the derivatives [Pd₂(μ-ox)₂(Lⁿ)₂] (2) with a planar core for oxalic acid, and [Pd₂(μ-OOCR)₂(Lⁿ)₂] (3-7) compounds with a non-planar ridge tent structure for other RCOOH acids: (3) R = C_mH_2m + 1 (m = 1, 3, 5, 7, 9, 11, 13, 15, 17); (4) R = CH₂(OCH₂CH₂)_pOCH₃ (p = 1, 2); (5) R = CH₂-C₆H₄-OC_qH_2q + 1-p (q = 2, 4, 6, 8, 10, 12); (6) R = C₆H₄-OC_rH_2r + 1-p (r = 4, 10); (7) R = C*H(OH)CH₃. The acids used were designed to explore the effect on the thermal properties of the compounds prepared of systematic variations in the type of carboxylato ligand, which induce structure, packing, and polarity changes, and in the length of the carboxylato chain. Most of the complexes prepared, even when far from planar, show liquid crystal behavior and display nematic, smectic A and smectic C phases.     

1,2-Eliminations from (CH3)2NH+CH2CH3 and (CH3)2NH 2+ : Guided dissociations

1,2-Eliminations are a varied and extensive set of dissociations of ions in the gas phase. To understand better such dissociations, elimination of CH₂=CH₂ and CH₃CH₃ from (CH₃)₂NH⁺CH₂CH₃ (1) and of CH₄ from (CH₃)₂NH₂⁺ are characterized by quantum chemical calculations. Stretching of the CN bond to ethyl is followed by shift of an H from methyl to the bridging position in ethyl and then to N to reach (CH₃)₂NH₂⁺ + CH₂=CH₂ from 1. CH₃CH₃ elimination by H-transfer to C₂H₅⁺ to form CH₃NH⁺=CH₂ + CH₃CH₃ also takes place. (CH₃)₂NH₂⁺ eliminates methane by CN bond extension followed by β-H-transfer to give CH₂=NH⁺ + CH₄. Low-energy reactions resembling complex-mediated 1,2-eliminations occur and constitute a hitherto largely unrecognized type of reaction. As in many complex-mediated reactions, these reactions transfer H between incipient fragments. They are distinguished from complex-mediated processes by the fragments not being able to rotate freely relative to each other near the transition state for reaction, as they do in complexes. Most 1,2-eliminations are ion-neutral complex-mediated, occur by the just described lower energy reactions, have 1,1-like transition states, or utilize highly asynchronous 1,2 transition states. All of these avoid synchronized 1,2-transition states that would violate conservation of orbital symmetry.     

Synthesis and structure of a 1,6-hexyldiamine heptaborate, [H3N(CH2)6NH3][B7O10(OH)3]

A new 1,6-hexyldiamine heptaborate, [H₃N(CH₂)₆NH₃][B₇O₁₀(OH)₃] (1), has been solvothermally synthesized and characterized by single-crystal X-ray diffraction, FTIR, elemental analysis, and thermogravimetric analysis. Compound 1 crystallizes in monoclinic system, space group P2₁/n with a=8.042(2) Å, b=20.004(4) Å, c=10.103(2) Å, and β=90.42(3)°. The anionic [B₇O₁₀(OH)₃]_n²ⁿ⁻ layers are interlinked via hydrogen bonding to form a 3D supramolecular network containing large channels, in which the templated [H₃N(CH₂)₆NH₃]²⁺ cations are located.     

Hydrothermal Synthesis and Characterization of (H3N(CH2)4NH3)[V6O14]

A new layered vanadium oxide [H₃N(CH₂)₄NH₃](V₆O₁₄) was synthesized hydrothermally under autogenous pressure at 180°C for 48 h from a mixture of H₂N(CH₂)₄NH₂ and V₂O₅ in aqueous solution. Its structure was determined from single-crystal X-ray diffraction at room temperature with final R=0.0774 and R_w=0.0893. It crystallizes in the monoclinic system (space group P2₁/n with a=9.74(2) Å, b=6.776(5) Å, c=12.60(2) Å, β=96.1(1)°, V=827(2) ų and Z=2). This compound contains mixed-valence V⁵⁺/V⁴⁺ vanadium oxide layers built from [V^VO₄] tetrahedra and pairs of edge-sharing [V^IVO₅] square pyramids with protonated organic amines occupying the interlayer space.     

Guest‐Induced 2‐D Metallopolycapsular Networks Based on a 1,3‐Alternate Calix[4]arene Derivative

Solvothermal reactions of the calix[4]arene tetraacetic acid (H₄CTA) with zinc nitrate in the presence of α,ω‐diaminoalkanes afford two‐dimensional metallopolycapsular networks of the formula {[Me₂NH₂]₂[G@(Zn₂(CTA)₂)] ? (DMF)₂ ? (H₂O)₄}_n (G=⁺NH₃–(CH₂)_n–NH₃⁺, n=2, 3, 4; DMF=N,N‐dimethylformamide). These metallopolycapsular networks are built up of metallocapsules that consist of two CTA and two Zn^II ions. Short alkanediyldiammonium (⁺NH₃–(CH₂)_n–NH₃⁺, n=2, 3, 4) guest ions are accommodated in each capsule of the metallopolycapsular network through a variety of supramolecular interactions. The thermal behaviours and the solid‐state photoluminescent properties of these complexes were also investigated.     

Analytical application of ion-molecule reactions. Reactions of various substituted cyclopropane molecular ions with ammonia

By ion cyclotron resonance it is found that various substituted cy clopropanes after ionization react with ammonia to give products which allow identification of the degree and kind ofsubstitution on the cyclopropl ring. For example, cyclopropyle reacts to give [CH₂NH₂]⁺ (m/e 30), methylcyclopropane gives [CH₂NH₂]⁺ (m/e 30) and the ethyl substituted [CH(C₂H₃)NH₂]⁺ (m/e 44) and ethylopropane gives [CH₂NH₂]⁺ (m/e 30) and the ethyl substituted [CH(C₂H₅)NH₂]⁺ (m/e 58). It is suggested that reactions of stable molecular ions with reagent neutrals may be a source of highly specific structural information for organic compounds.     

Influence of the outer-sphere cation nature on the crystal structures of salts with a cis-[Rh(NH3)2(NO2)4]− anion

Complex rhodium(III) salts of the composition cis-M[Rh(NH₃)₂(NO₂)₄]·nH₂O, where M = K⁺, Cs⁺, Ag⁺, (CH₃)₄N⁺, are synthesized and described. Their molecular and crystal structures are determined by single crystal X-ray diffraction.     

The [CH5NO]+ ˙ potential energy surface: Distonic ions,lon-dipole complexes and hydrogen-bridged radical cations

By combining results from a variety of mass spectrometric techniques (metastable ion, collisional activation, collision-induced dissociative ionization, neutralization-reionization spectrometry, ²H, ¹³C and ¹⁸O isotopic labelling and appearance energy measurements) and high-level ab initio molecular orbital calculations, the potential energy surface of the [CH₅NO]^{+ ˙} system has been explored. The calculations show that at least nine stable isomers exist. These include the conventional species [CH₃ONH₂]^{+ ˙} and [HO? CH₂? NH₂]^{+ ˙}, the distonic ions [O? CH₂? NH₃]^{+ ˙}, [O? NH₂? CH₃]^{+ ˙}, [CH₂? O(H)? NH₂]^{+ ˙}, [HO? NH₂? CH₂]^{+ ˙}, and the ion-dipole complex CH₂?NH₂⁺ …? OH˙. Surprisingly the distonic ion [CH₂? O? NH₃]^{+ ˙} was found not to be a stable species but to dissociate spontaneously to CH₂?O + NH₃^{+ ˙}. The most stable isomer is the hydrogen-bridged radical cation [H? C?O …? H …? NH₃]^{+ ˙} which is best viewed as an immonium cation interacting with the formyl dipole. The related species [CH₂?O …? H …? NH₂]^{+ ˙}, in which an ammonium radical cation interacts with the formaldehyde dipole is also a very stable ion. It is generated by loss of CO from ionized methyl carbamate, H₂N? C(?O)? OCH₃ and the proposed mechanism involves a 1,4-H shift followed by intramolecular ‘dictation’ and CO extrusion. The [CH₂?O …? H …? NH₂]^{+ ˙} product ions fragment exothermically, but via a barrier, to NH₄^{+ ˙} HCO^…? and to H₃N? C(H)?O^{+ ˙} H˙. Metastable ions [CH₃ONH₂]^+…? dissociate, via a large barrier, to CH₂?O + NH₃⁺ + and to [CH₂NH₂]⁺ + OH˙ but not to CH₂?O^{+ ˙} + NH₃. The former reaction proceeds via a 1,3-H shift after which dissociation takes place immediately. Loss of OH˙ proceeds formally via a 1,2-CH₃ shift to produce excited [O? NH₂? CH₃]^{+ ˙}, which rearranges to excited [HO? NH₂? CH₂]^{+ ˙} via a 1,3-H shift after which dissociation follows.