Counteranion-controlled water cluster recognition in a protonated octaamino cryptand

Structural aspects of binding of water cluster and halides in the octaamino cryptand L (1,4,11,14,17,24,29,36-octaazapentacyclo[12.12.12.2.(6,9)2.(19,22)2(31,34)]tetratetraconta-6(43),7,9(44),19(41),20,22(42),31(39),32,34(40)-nonaene, N(CH2CH2NHCH2-p-xylyl-CH2NHCH2CH2)3N) in a protonated state were examined. Crystallographic results show binding of the acyclic quasiplanar water tetramer [H4L(H2O)4](I)4.2.57H2O (1) in a tetraprotonated cryptand L having an iodide counteranion, where two water molecules reside inside the two tren-based cavity, bridged by a third water molecule, and a fourth external water molecule is hydrogen bonded to the bridged water molecule. In the case of complexes [H6L(Br)][(Br)6H].4H2O.2HBr (2) and [H6L(Cl)][(Cl)6H].10.86H2O (3), a single bromide and chloride occupied, respectively, the inside of the cryptand cavity, where L is in a hexaprotonated state. Monotopic recognition of bromide/chloride was observed at the center of the cryptand cavity where halides show C-H...halide interactions instead of the N-H...halide interactions reported in the ditopic complexes of halides with the same cryptand, 5 and 6. Thermal analyses on 1-3 were carried out, and the data obtained distinctly differentiate water cluster complex 1 from the anion-encapsulated cryptates 2 and 3. This study represents the first example of anion-controlled cluster formation inside the cavity of a cryptand.     

Spherical versus linear anion encapsulation in the cavity of a protonated azacryptand

Grams scale synthesis of an octaaminocryptand L(2) with high yield is obtained in one-pot by low-temperature [2 + 3] condensation of tris(2-aminoethyl)amine with isophthalaldehyde, followed by sodium borohydride reduction. Structural aspects of octaaminocryptand L(2) x MeOH, binding of iodide (spherical) and bichloride (linear) in L(2), (1,4,11,14,17,24,29,36-octa-azapentacyclo-[12.12.12..2(6,9).2(19,22).2(31,34)]-tetratetraconta 6(43),7,9(44),19(41),20,22(42),31(39),32,34(40)-nonane, N(CH2CH2NHCH2-m-xylyl-CH2NHCH2CH2)3N), in the hexaprotonated and tetraprotonated states, respectively, are examined. Crystallographic results show binding of single iodide [H6L(2)I](I)5 x 4 H2O, (2), in a hexaprotonated cryptand L(2). Monotopic recognition of iodide is observed via (N-H)(+)...iodide interactions. The tetraprotonation of L(2) by hydrochloric acid showed the formation and encapsulation of a bichloride inside the cavity, which is examined from the single-crystal X-ray study. Encapsulation and binding of a proton-bridged linear bichloride inside the cavity of tetraprotonated L(2), [H4L(2)(ClHCl)](Cl)3 x nH2O (3), via (N-H)(+)...chloride interactions is observed in the structural investigation. This study shows that degree of protonation and its distribution in the receptor architecture play an important role in guest encapsulation. Further, it represents the first example of an encapsulated bichloride inside the cavity of an organic host.     

Binding properties of octaaminocryptands

Complexation and protonation equilibria were studied in aqueous solution for a new range of aminocryptand ligands, N(CH2CH2NHCH2RCH2NHCH2CH2)3N, (R = m-xylyl, p-xylyl, 2,5-furan, 2,6-pyridine) and demonstrate that stability constants for first transition series ions Co2+ to Zn2+ are relatively high. X-ray crystallography shows that the cryptands are reasonably well preorganized for complexation. The furan-spaced cryptand L6.H2O crystallizes in the rhomobohedral space group R3 (no. 148) with a = 14.645(1), b = 14.645(1), and c = 25.530(4) A, whereas the m-xylyl-spaced cryptand L4 crystallizes in the triclinic space group P1 (no. 2) with a = 9.517(1), b = 15.584(2), and c = 23.617(4) A. The highest formation constant (log beta21 = 33.07) is observed for the dicopper cryptate of a pyridine-spaced cryptand, suggesting involvement in complexation of donors from the spacer link. This pyridine-spaced host also shows good selectivity for copper(II) over zinc(II), making it a possible candidate for treatment of copper-excess pathology.     

Molecular dynamics study of ion capture from water by a model ionophore, tetraprotonated cryptand SC24

A molecular dynamics study of chloride capture from water by the tetraprotonated cryptand SC24 is presented. The system under study consisted of a cryptand molecule, chloride ion, and 319 water molecules. Calculations were performed for 19 distances between the cryptand and the chloride. For each distance a trajectory of at least 60 ps was obtained. Two anion binding sites of comparable energy were found. The chloride can bind either inside the cryptand cavity or more loosely outside of the ligand. The binding sites are separated by an energy barrier of 20 kcal/mol. Chloride movement toward the cryptand is accompanied by stepwise dehydration of the anion. The energy loss due to this dehydration is offset by the electrostatic attraction between the anion and the ligand and by an increase in favorable water-water interactions. The most striking feature of chloride capture is a rapid cooperative change in the conformation of the cryptand when the Cl- starts to enter the ligand and just as it encounters the energy barrier. The conformational transition is associated with a shift of three N-H bonds from the pure endo orientation, so that they point toward the chloride. The shift provides electrostatic stabilization, which compensates for the loss of the remaining three water molecules from the hydration shell of the anion. The N-H bonds remain directed toward the anion during its further movement into the ligand and guide chloride into a stable position inside the cryptand cavity. The flexibility of the receptor, the stepwise dehydration of an ionic substrate, and the characteristic balance between different energy components in the system all may be features of ion binding common to a wide range of abiotic and biological ionophores.     

Metal binding characteristics of a laterally nonsymmetric aza cryptand upon functionalization with a pi-acceptor group

The laterally nonsymmetric aza cryptand synthesized by condensing tris(2-aminoethyl)amine (tren) with tris[[2-(3-(oxomethyl)phenyl)oxy]ethyl]amine readily forms mononuclear inclusion complexes with both transition and main-group metal ions. In these complexes, the metal ion occupies the tren-end of the cavity making bonds with the three secondary amino and the bridgehead N atoms. When a strong pi-acceptor group such as 2,4-dinitrobenzene is attached to one of the secondary amines, the binding property of the cryptand changes drastically. When perchlorate or tetrafluoroborate salts of Ni(II), Cu(II), Zn(II), or Cd(II) are used, the metal ion enters the cavity which can be monitored by the hypsochromic shift of the intramolecular charge-transfer transition from the donor amino N atom to the acceptor dinitrobenzene. However, in the presence of coordinating ions such as Cl(-), N(3)(-), and SCN(-), the metal ion comes out of the cavity and binds the cryptand outside the cavity at a site away from the dinitrobenzene moiety. Four such complexes are characterized by X-ray crystallography. Thus, a metal ion can translocate between inside and outside of the cryptand cavity depending upon the nature of the counter anion.     

A macrocyclic ligand as receptor and Zn(II)-complex receptor for anions in water: binding properties and crystal structures

Binding properties of 24,29-dimethyl-6,7,15,16-tetraoxotetracyclo[19.5.5.0(5,8).0(14,17)]-1,4,9,13,18,21,24,29-octaazaenatriaconta-Δ(5,8),Δ(14,17)-diene ligand L towards Zn(II) and anions, such as the halide series and inorganic oxoanions (phosphate (Pi), sulfate, pyrophosphate (PPi), and others), were investigated in aqueous solution; in addition, the Zn(II)/L system was tested as a metal-ion-based receptor for the halide series. Ligand L is a cryptand receptor incorporating two squaramide functions in an over-structured chain that connects two opposite nitrogen atoms of the Me(2)[12]aneN(4) polyaza macrocyclic base. It binds Zn(II) to form mononuclear species in which the metal ion, coordinated by the Me(2)[12]aneN(4) moiety, lodges inside the three-dimensional cavity. Zn(II)-containing species are able to bind chloride and fluoride at the physiologically important pH value of 7.4; the anion is coordinated to the metal center but the squaramide units play the key role in stabilizing the anion through a hydrogen-bonding network; two crystal structures reported here clearly show this aspect. Free L is able to bind fluoride, chloride, bromide, sulfate, Pi, and PPi in aqueous solution. The halides are bound at acidic pH, whereas the oxoanions are bound in a wide range of pH values ranging from acidic to basic. The cryptand cavity, abundant in hydrogen-bonding sites at all pH values, allows excellent selectivity towards Pi to be achieved mainly at physiological pH 7.4. By joining amine and squaramide moieties and using this preorganized topology, it was possible, with preservation of the solubility of the receptor, to achieve a very wide pH range in which oxoanions can be bound. The good selectivity towards Pi allows its discrimination in a manner not easily obtainable with nonmetallic systems in aqueous environment.     

CRYSTAL STRUCTURES OF COPPER (Ⅱ) AND COBALT (Ⅲ) COM- PLEXES OF o-HYDROXYBENZYLGLYCINATE (HBG)

<正> The structures of two complexes C(CuOC6H4CH2NHCH2COO)2 (H2 O)]·H2P(1) and [Co(NH3)6[Co(OC6H4CH2NHCH2COO)2]2[C1]·10H2O (2) were determined by X-ray analyses. Compound (1) crystallizes in the orthorhombic space group P212121 with a=11. 357(1),b= 24. 304(2),c=7.317(4) A,Z= 4;While compound (2) in the monoclinic space group A2/a(C2/c) with a=23. 486(9) ,b=26. 605(6) ,c= 10. 542(1) A,γ= 128. 42(4)°,Z= 4. In compound (1),two Cu(Ⅱ) ions are bonded together by the phenolic oxygen atoms of two tridentate chelating ligands and each of them is separately coordinated by the carboxyl oxygen,amino nitrogen of each chelate ligand and by the fifth oxygen atom as well (from aqua or the carbonyl group in adjacent molecule). Thus the coordination of each Cu(Ⅱ) is a square pyramid with distances of 1. 93- 1. 97A to the four corner atoms and 2. 30 and 2. 32 A to the apex atoms. The whole molecule has an approximately planar configuratioir with the two pyramid apexes pointing towards one side. Compound (2) consists of     

A molecular dynamics study of chloride binding by the cryptand SC24

The capture of chloride from water by the tetraprotonated form of the spherical macrotricyclic molecule SC24 was studied using molecular dynamics simulation methods. This model ionophore represents a broad class of molecules which remove ions from water. Two binding sites for the chloride were found, one inside and one outside the ligand. These sites are separated by a potential energy barrier of approximately 20 kcal mol⁻¹. The major contribution to this barrier comes from dehydration of the chloride. The large, unfavorable dehydration effect is compensated for by an increase in electrostatic attraction between the oppositely charged chloride and cryptand, and by energetically favorable rearrangements of water structure. Additional assistance in crossing the barrier and completing the dehydration of the ion is provided by the shift of three positively charged hydrogen atoms of the cryptand towards the chloride. This structural flexibility of the cryptand, leads to a decrease in the energy barrier, whereas, its structural rigidity is partially responsible for its selectivity.     

Hexabromide salt of a tiny octaazacryptand as a receptor for encapsulation of lower homolog halides: structural evidence on halide selectivity inside the tiny cage

Tiny azacryptand 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane (L) upon reaction with 48% hydrobromic acid (containing <0.05% chloride contamination) forms hexabromide salt (1). Single crystal X-ray crystallographic investigation of the hexaprotonated bromide (1) shows no guest encapsulation inside the tiny cage. This bromide salt 1 with an empty proton cage has been utilized as the receptor for encapsulation of chloride (2) and fluoride (3). Crystallographic results of mixed chloride/bromide (2) and fluoride/bromide (3) complexes of L are examined, which show monotopic recognition of chloride in the case of 2 and fluoride in the case of 3 inside the proton cage with five bromide and three water molecules outside the cavity. Single crystals obtained from an experiment on mixed anionic system (chloride and fluoride), 1 shows selective encapsulation of fluoride, which supports the formation of complex 3 and crystals obtained upon treatment of 2 with tetrabutyl ammonium fluoride also yields complex 3. In a separate reaction between L and 49% hydrobromic acid containing higher chloride contamination (<0.2%) forms chloride/bromide salt (2). ¹H NMR studies of 1 with sodium chloride and fluoride support the encapsulation of the respective anions inside the proton cage.     

Attachment of an electron-withdrawing fluorophore to a cryptand for modulation of fluorescence signaling

The laterally nonsymmetric aza cryptand synthesized by condensing tris(2-aminoethyl)amine (tren) with tris[2-[(3-(oxomethyl)phenyl)oxy]ethyl]mine readily forms mononuclear inclusion complexes with both transition- and main-group-metal ions. The fluorophore 7-nitrobenz-2-oxa-1,3-diazole is attached to one of the secondary amines, to give an integrated fluorophore-receptor configuration. The fluorophoric system does not show any appreciable emission when excited due to an efficient photoinduced intramolecular electron transfer (PET) from the nitrogen lone pair. When a metal ion enters the cavity, the PET is blocked, causing recovery of fluorescence; Cd(II) gives the highest quantum yield. The fluorophore, with pi-accepting ability, drastically alters the binding property of the cryptand. With perchlorate or tetrafluoroborate salts of Cd(II), the metal ion enters the cavity, causing recovery of fluorescence. However, in the presence of coordinating ions such as Cl-, N3-, and SCN-, the metal ion comes out of the cavity, causing PET to take place once again, and the fluorescence is lost. Thus, translocation of Cd(II) between the inside and outside of the cryptand cavity can lead to a reversible fluorescence on/off situation.     

Tight and Selective Caging of Chloride Ions by a Pseudopeptidic Host

The selective molecular recognition of chloride versus similar anions is a continuous challenge in supramolecular chemistry. We have designed and prepared a simple pseudopeptidic cage ( 1 a ) that defines a cavity suitable for the tight encapsulation of chloride. The interaction of the protonated form of 1 a with different inorganic anions was studied in solution by ¹H NMR spectroscopy and ESI‐MS, and in the solid state by X‐ray diffraction. The solution binding data showed that the association constants of 1 a to chloride are more than two orders of magnitude higher than to any other tested inorganic anion. Remarkably, 1 a displayed a high selectivity for chloride over other closely related halides such as bromide (selectivity=111), iodide (selectivity=719), and fluoride (selectivity >1000). Binding experiments (¹H NMR spectroscopy and ESI‐MS) suggested that 1 a has a high‐affinity (inner) binding site and an additional low‐affinity (external) binding site. The supramolecular complexes with F^?, Cl^?, and Br^? have been also characterized by the X‐ray diffraction of the corresponding [ 1 a? nHX] crystalline salts. The structural data show that the chloride anion is tightly encapsulated within the host, in a binding site defined by a very symmetric array of electrostatic H‐bonds. For the fluoride salt, the size of the cage cavity is too large and is occupied by a water molecule, which fits inside the cage efficiently competing with F^?. In the case of the bigger bromide, the mismatch of the anion inside the cage caused a geometrical distortion of the host and thus a large energetic penalty for the interaction. This minimalistic pseudopeptidic host represents a unique example of the construction of a simple well‐defined binding pocket that allows the highly selective molecular recognition of a challenging substrate.     

N3染料对F-的高选择性光学传感性质

采用紫外-可见吸收光谱和荧光光谱滴定方法研究了N3染料, cis-Ru(H2dcbpy)2(NCS)2 (H2dcbpy=4,4’-二羧酸-2,2’-联吡啶), 在二甲基亚砜(DMSO)溶液中对F-、Cl-和Br-的识别行为. 结果表明, F-能引起N3的吸收光谱和荧光光谱的明显变化, 能作为高选择性的荧光和比率色度F-传感器. N3与F-相互作用产生一个大的荧光增强因子40, 在已报道的基于Ru(II)配合物的F-传感器中较为罕见.     

Permselectivity between two anions in anion exchange membranes crosslinked with various diamines in electrodialysis

A membranous copolymer crosslinked with divinylbenzene reacted with N,N,N′,N′-tetra-methylethylenediamine, N,N,N′,N′-tetramethyl-1,3-propanediamine, and N,N,N′,N′-tetramethyl-1,6-hexanediamine to prepare highly crosslinked anion exchange membranes. More than 80% of both tertiary amino groups of the diamines reacted with chloromethyl groups of the membrane to form crosslinkage. After formation of the high crosslinkage of the membrane was confirmed with dialysis of a neutral molecule, electrochemical properties of the obtained membranes (mainly, relative transport number between two anions in electrodialysis) were evaluated: nitrate ions to chloride ions, sulfate ions to chloride ions, fluoride ions to chloride ions, and bromide ions to chloride ions. Though larger anions, in general, were difficult to permeate through the membranes due to high crosslinkage, the number of methylene groups of the diamines (which means the increase in hydrophobicity of anion exchange groups) also affected the relative transport number between two anions. The lower the hydration of anions, the higher the relative transport number of the anions through the membranes with the hydrophobic anion exchange groups. © 1996 John Wiley & Sons, Inc.     

New amine-templated zinc phosphates with a temperature-induced increase of structural dimensionality

Three new amine-templated zinc phosphates, [C4N2H14][Zn(HPO4)2].H2O, AU-I, [C4N2H14][Zn2(H(0.5)PO4)2(H2PO4)], AU-II, and [C4N2H14][Zn5(H2O)(PO4)4], AU-III, are prepared by hydrothermal synthesis using an organic amine, N,N'-dimethylethylendiamine CH3NHCH2CH2NHCH3, as structure-directing agent. The three materials are prepared from the same reaction mixture, 1Zn(CH3CO2)2:3.05H3PO4:2.25CH3NHCH2CH2NHCH3:138H2O (pH = 5.1), AU-I at RT, AU-II at 60 degrees C, and AU-III at 170 degrees C. The materials are built from corner-sharing ZnO4 and PO4 tetrahedra forming chains, layers, or framework structures for AU-I to III, respectively, and are linked together by hydrogen bonds via the diprotonated amine ions. The complete hydrogen-bond scheme is resolved for these new compounds and reveals some interesting phenomena, for example, a hydrogen shared between two phosphate groups in AU-II, thereby forming H(0.5)PO4 groups. Furthermore, the water molecules are different; that is, in AU-I they act as hydrogen-bond donor and acceptor, whereas they act as ligand in AU-III with coordination to Zn. The structures of the compounds are determined by single-crystal X-ray diffraction analysis. AU-I, [C4N2H14][Zn(HPO4)2].H2O, crystallizes in the triclinic space group P-1, a = 8.215(2), b = 8.810(3), c = 8.861(3) A, alpha = 88.001(4) degrees , beta = 89.818(5) degrees , and gamma = 89.773(5) degrees , Z = 2. AU-II, [C4N2H14][Zn2(H(0.5)PO4)2(H2PO4)], is monoclinic, P2/n, a = 11.7877(4), b = 5.2093(2), c = 12.2031(4) A, beta = 98.198(1) degrees , Z = 2. AU-III, [C4N2H14][Zn5(H2O)(PO4)4], crystallizes in the orthorhombic space group Pna2(1) with lattice parameters, a = 20.723(2), b = 5.2095(6), c = 17.874(2) A, Z = 4. The phase stability investigated by systematic hydrothermal synthesis is presented, and the materials are further characterized by 31P solid-state MAS NMR, for example, by determination of 31P chemical shift anisotropies for AU-III, while the thermal behavior is investigated by thermogravimetry (TG).     

Anion recognition of chloride and bromide by a rigid dicobalt(II) cryptate

The crystal structures of [Co 2L(Cl)](ClO 4) 3 ( 1), [Co 2L(Br)](ClO 4) 3 ( 2), [Co 2L(OH)(OH 2)]I 3 ( 3), and [Co 2L (1)(Cl)](ClO 4) 3 ( 4), the density functional theory calculations, as well as the binding constants of [Co 2L] (4+) toward Cl (-) and Br (-) and of [Co 2L (1)] (4+) toward Cl (-), are reported in this paper (L = N[(CH 2) 2NHCH 2(C 6H 4- p)CH 2NH(CH 2) 2] 3N, L (1) = N[(CH 2) 2NHCH 2(C 6H 4- m)CH 2NH(CH 2) 2] 3N). The rigid dicobalt(II) cryptate [Co 2L] (4+) shows the recognition of Cl (-) and Br (-) but not of F (-) and I (-), because of the size matching to its rigid cavity. We also found that the relative rigid tripodal skeleton of L than that of L (1) results in the higher affinity of [Co 2L] (4+) toward Cl (-). Magnetic susceptibility measurements of 1 and 2 indicate that the two Co(II) atoms in the cryptates are antiferromagnetically coupled through the Cl (-)/Br (-) bridge, with g = 2.19, J = -13.7 cm (-1) for 1, and g = 2.22, J = -17.1 cm (-1) for 2.     

Kinetics and mechanism of a catalytic chloride ion effect on the dissociation of model siderophore hydroxamate-iron(III) complexes

Proton-driven ligand dissociation kinetics in the presence of chloride, bromide, and nitrate ions have been investigated for model siderophore complexes of Fe(III) with the mono- and dihydroxamic acid ligands R(1)C(=O)N(OH)R(2) (R(1) = CH(3), R(2) = H; R(1) = CH(3), R(2) = CH(3); R(1) = C(6)H(5), R(2) = H; R(1) = C(6)H(5), R(2) = C(6)H(5)) and CH(3)N(OH)C(=O)[CH(2)](n)C(=O)N(OH)CH(3) (H(2)L(n); n = 2, 4, 6). Significant rate acceleration in the presence of chloride ion is observed for ligand dissociation from the bis(hydroxamate)- and mono(hydroxamate)-bound complexes. Rate acceleration was also observed in the presence of bromide and nitrate ions but to a lesser extent. A mechanism for chloride ion catalysis of ligand dissociation is proposed which involves chloride ion dependent parallel paths with transient Cl(-) coordination to Fe(III). The labilizing effect of Cl(-) results in an increase in microscopic rate constants on the order of 10(2)-10(3). Second-order rate constants for the proton driven dissociation of dinuclear Fe(III) complexes formed with H(2)L(n)() were found to vary with Fe-Fe distance. An analysis of these data permits us to propose a reactive intermediate of the structure (H(2)O)(4)Fe(L(n)())Fe(HL(n))(Cl)(OH(2))(2+) for the chloride ion dependent ligand dissociation path. Environmental and biological implications of chloride ion enhancement of Fe(III)-ligand dissociation reactions are presented.     

Perfluoroalkylated Calix[4]pyrroles: Fluoride Ion Extraction from an Aqueous Medium

Octaalkenyl calix[4]pyrrole ((CH₂=CH(CH₂)₂)₈C4P) is highly useful for the postfunctionalization of different calix[4]pyrroles with desired functionalities. Functionalization with perfluoroalkyl chains [CF₃(CF₂)_n ; R_fn ] gave perfluoroalkyl calix[4]pyrroles (R_fn (CH₂)₄)₈C4P; n =6, 8), having >60 % fluorine content, which created a hydrophobic environment inside the calix[4]pyrrole cavity and recognized fluoride and chloride ions in solution as well as in the solid state. The fluoride ion is extracted efficiently from aqueous CsF and TBAF solutions by using (R_f6(CH₂)₄)₈C4P, as droplets. The fluorinated chain generated a hydrophobic environment which broke the hydration shell associated with the anion and separated out fluoride ions as droplets from aqueous medium. Furthermore, the fluoride ions competitively replaced chloride ions from the (R_f6(CH₂)₄)₈C4P cavity.     

Pentanuclear Ba(II) complex of a macrocyclic ligand

We report here the first pentanuclear Ba(II) complex of a new tri-aza, tri-oxa macrocycle with two carboxymethyl "arms" pending from two N atoms, H2L2. The crystal structure corresponds to the formula [Ba5(H0.375L2)4(ClO4)(CH3CH2OH)(H2O)2](ClO4)2.5 x 9.5H2O and reveals the presence of four molecules of the ligand surrounding five Ba(II) ions, giving rise to an unusual structure with the metal ions inside a spherical organic cavity.     

Ion-molecule reactions in 4He droplets: flying nano-cryo-reactors

Ion-molecule reactions are studied inside large (approximately equal to 10(4) atoms) very cold (0.37 K) superfluid (4)He droplets by mass spectrometric detection of the product ions. He+ ions initially formed inside the droplets by electron impact ionization undergo charge transfer with either embedded D(2), N(2), or CH(4). For D(2) this charge transfer process was studied in detail by varying the pickup pressure. For either N(2) or CH(4) the reagent ions were formed by this charge transfer and the reaction pathways of the secondary reactions N(2) (+)+D(2), CH(4) (+)+D(2), and CH(3) (+)+D(2) each with an additionally embedded D(2) molecule were also determined from the pickup pressure dependencies. In several cases, notably He.N(2) (+) and CH(3)D(2) (+) reaction intermediates are observed. The analysis is facilitated by the tendency for molecular ion products to appear without (or with only very few) attached He atoms whereas the atomic ion products usually appear in the mass spectra with several attached He atoms, e.g., He(m).D+ ions with up to m=19.     

Synthesis and crystal structure of 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane Bis(citrate) hydrate

A crystalline salt of 2.2.2-cryptand and citric acid, 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis(citrate) hydrate [H₂(Crypt-222)]²⁺·2(C₆H₇O₇)^? · 1.65H₂O, was synthesized and studied by single crystal X-ray diffraction. In the crystal structure of this salt, the 2.2.2-cryptand dication is somewhat disordered, and its H atoms at two protonated N atoms are oriented inside the cryptand cavity. Two independent citrate anions are essentially different, as different COOH groups in them are deprotonated. The geometric parameters (bond lengths, bond angles, etc.) of the molecular ions and water molecules are determined with a relatively high accuracy. The structural units form a three-dimensional system of intermolecular (interionic) hydrogen bonds.