Heavier Alkali Metal Cations Research Articles

Investigations on the Solubility of Sn4‐Cluster Compounds in Liquid Ammonia

AbstractBy using different transition metal containing precursors and liquid ammonia as solvent, single crystals of Sn44‐ cluster containing ammoniates were grown, and three new compounds have been characterized by single crystal structure determination. K4Sn4 ⋅ 8 NH3 (1) (P63, a=13.0370(6) Å and c=39.0889(11) Å) has been obtained by dissolving a precursor with the nominal composition “KRuSn4” in liquid ammonia, and Rb2Na2Sn4 ⋅ 4.8 NH3 (2) (Pc, a=9.4005(3) Å, b=15.3663(6) Å, c=12.7312(6) Å, β=94.675(3)°) from a similar solution of “Rb9Na9Co16Sn24“. 1 represents the last missing ammoniate of the A4Sn4 compounds with heavier alkali metal cations. K6[OH]2[Sn4] ⋅ 5 NH3 (3) was crystallized from solutions of the binary Zintl phase K12Sn17 in presence of AuPPh3Cl and cryptand[2.2.2] (P21/c, a=10.3655(1) Å, b=12.7489(2) Å, c=16.9137(3) Å, β=103.212(2)°), and is the Sn44‐ cluster compound that appears to be stable in presence of the highest amount of hydroxide so far.

Unveiling the potential of superalkali cation Li3+ for capturing nitrogen.

The potential of the superalkali cation Li3+ for capturing N2 and its behavior in gaseous nitrogen have been theoretically studied at the MP2/6-311+G(d) level. The evolution of structures and stability of the Li3+(N2)n (n = 1-7) complexes shows that the N2 molecules tend to bind to different vertices of the Li3+ core, and that Li3+ might have the capacity to capture up to twelve nitrogen molecules in the first coordination shell. Based on natural population and molecular orbital analyses, Li3+ keeps its superatom identity in the lowest-lying Li3+(N2)n (n = 1-4) complexes. The change in the Gibbs free energies of possible fragmentation channels also indicates the thermodynamic stability of Li3+ in the (N2)n clusters when n ≤ 4. Different from the case of Li3+(H2O)n, where the electrostatic interaction is dominant, the electrostatic and polarization components are found to make nearly equal contributions to Li3+(N2)n complex formation. In addition, it can be concluded that the superalkali cation Li3+ surpasses heavy alkali metal cations in capturing N2 molecules, since it has a larger binding energy with N2 than Na+ and K+ ions.

Experimental and Computational Study of the Group 1 Metal Cation Chelates with Lysine: Bond Dissociation Energies, Structures, and Structural Trends.

The kinetic energy dependence of the collision-induced dissociation (CID) of Group 1 metal cations (M+ = Li+, Na+, K+, Rb+, and Cs+) chelated to the amino acid lysine (Lys) was measured by threshold CID using a guided ion beam tandem mass spectrometer. The simple loss of neutral lysine is the only dissociation channel observed with the heavier alkali metal cations, whereas CID of Li+(Lys) yields other competing channels including loss of NH3 (the dominant channel at low energy) and eight other reactions. Analysis of the kinetic energy-dependent cross sections yields experimental M+(Lys) bond dissociation energies (BDEs) of 376 ± 30, 219 ± 13, 160 ± 10, 141 ± 6, and 128 ± 4 kJ/mol for Li+, Na+, K+, Rb+, and Cs+, respectively. Computational searches yielded 18 distinct, low-energy structural families related to sites of M+ binding in M+(Lys) complexes and 10 distinct, low-energy structural families for neutral lysine. Among the four levels of theory and three basis sets used, four different ground conformers of M+(Lys) and four different ground conformers of lysine were found, including a ground conformer of K+(Lys) and Cs+(Lys), [Nε,CO(OH)], and its higher energy zwitterionic analogue, [Nε,CO2-], that better explains recent infrared multiple photon dissociation action spectroscopy results. Computational results for predicted ground structures of M+(Lys) complexes yielded computed BDEs in reasonable agreement with experiment.

Synthesis and crystal structure of K3[NpO4(OH)2

Attempts were made to isolate anhydrous compounds of [NpO4(OH)2]3− anions with heavy alkali metal cations (K, Rb, Cs) by crystallization at elevated temperatures, and the salt K3[NpO4(OH)2] was isolated and studied. Crystals of K3[NpO4(OH)2] consist of tetragonal bipyramidal [NpO4(OH)2]3− anions and K+ cations. The [NpO4(OH)2]3− anion occupies the position in the symmetry center. The Np-O distances in this anion are 1.8992(7) and 1.9100(7) A in the equatorial plane of the bipyramid and 2.3231(8) A with OH groups. The OH hydrogen atoms participate in weak H bonds [O⋯O 3.0250(11) A] linking the anions in layers [NpO4(OH)2] 3− parallel to the (010) plane. In the interlayer space, there are two crystallographically different K atoms. Their coordination number (CN) can be considered to be equal to 7 and 8. Comparison with the structures of the known compounds Na3[NpO4(OH)2] and K3[NpO4(OH)2]·2H2O was made. The structure of the latter compound was redetermined with higher accuracy. The failure of attempts to prepare the anhydrous rubidium and cesium compounds is probably due to large ionic radius of these cations, requiring high coordination number.

Hydrates of the Alkali Trioxidomonosulfidomolybdates and -tungstates: K2[(Mo/W)O3S] · 1.5H2O and (Rb/Cs)2[(Mo/W)O3S] · H2O

Abstract The trioxidomonosulfidomolybdate and -tungstate anions [(Mo/W)O3S]2– are the first products formed when passing H2S gas through a solution of the oxidometalates. Their potassium, rubidium and cesium salt hydrates form as crystalline precipitates from these solutions depending on pH, the polarity of the solvent, educt concentrations and temperature. The structures of the sesqui- (K) and mono- (Rb, Cs) hydrates have been determined by means of X-ray single crystal diffraction data. The potassium sesquihydrates K2[(Mo/W)O3S] · 1.5H2O are isotypic and crystallize with a new structure type (monoäclinic, space group C2/c, M = Mo/W: a = 987.0(2)/993.13(11), b = 831.75(14)/831.10(11), c = 1868.9(4)/1865.2(2) pm, β = 99.34(2)/99.153(8)°, R1 = 0.0352/0.0390). In the crystal structure the [(Mo/W)O3S]2– anions are connected via hydrogen bonds to form columns along the c direction. Channels containing only water molecules run along the [101] direction. The dehydration process proceeds in a topotactic reaction between 60 to 95 °C and yields crystals of the anhydrous salts K2[(Mo/W)O3S]. The two different K+ cations exhibit a 5 + 3 and 5 + 2 O/S coordination. The heavier alkali metal cations form the four monohydrates (Rb/Cs)2[(Mo/W)O3S] · H2O (trigonal rhombohedral, space group R-3m) with lattice parameters for the Rb/Cs molybdates of a = 621.17(6)/624.62(10), c = 3377.9(4)/3388.6(8) pm (R1 = 0.0505/0.0734) and the tungstates of a = 642.80(3)/643.3(4), c = 3532.8(3)/3566(4) pm (R1 = 0.0348/0.0660). In the structures the 3m symmetrical tetrahedra are arranged to form double layers in such a way, that the O3 bases of the tetrahedra are pointing towards each other in a staggered conformation. These double layers are stacked in the c direction in a rhombohedral sequence. In these hydrates, there are no distinct hyrdogen bonds. Instead, partially disordered pairs of H2O molecules are situated in large cavities between the double layers. With a number of 10, the cation coordination sphere is increased compared to the K salts. The crystallographic results are confirmed by vibrational spectroscopy (Raman/IR) and thermal analytical studies of the new compounds.

Gas–phase complexes of cyclic and linear polyethers with alkali cations

The flexibility of polymer backbones constitutes one key aspect in their molecular recognition properties. This investigation characterizes the structure of the gas-phase complexes formed by the cyclic and linear polyethers with the heavier alkali metal cations. In particular, the cyclic 15-crown-5 ether (15c5), (OCH(2)CH(2))(5), and the polyethylene glycol linear chains PEG4 and PEG9, H(OCH(2)CH(2))(n=4,9)OH, are considered. Infrared multiple photon dissociation spectroscopy is applied to probe the polymer vibrational modes within the spectral range 800-1500 cm(-1), in combination with Density Functional Theory calculations. The experimental spectra of the 15c5-M(+) (M = K, Rb, Cs) complexes correlate with distorted asymmetric backbone structures in which the cation lies above the ether ring, and four oxygens are oriented toward the cation. In contrast, the PEG4-K(+) complex features an inclusion-like fivefold coordination structure in which the cation and four oxygens are quasi-coplanar and one terminal oxygen lies out of plane. For the PEG9-K(+) complex, the ether chain builds stable cages involving a coordination of eight oxygens with the cation, sustained by hydrogen bonds between the terminal hydroxyl groups.

Syntheses and crystal structures of rubidium and cesium 3,5-dinitropyrid-2-onate, 3,5-dinitropyrid-4-onate and 3,5-dinitro-4-pyridone-N-hydroxylate

Six complexes, rubidium and cesium 3,5-dinitropyrid-2-onate (2DNPO), 3,5-dinitropyrid-4-onate (4NDPO), 3,5-dinitropyrid-4-one-N-hydroxylate (4DNPNO), were synthesized and characterized by elemental analysis, FT-IR, TG-DTG and X-ray single-crystal diffraction analysis. All the complexes crystallized from water and one of them was a hydrate. Rubidium 3,5-dinitropyrid-4-one-N-hydroxylate was crystallized with the 1 : 2 stoichiometry as Rb[H(4DNPNO)2] upon absorption of carbon dioxide. The structural determinations showed that the coordination sphere around a metal centre is made up of oxygen atoms and nitrogen atoms, except for the 4DNPNO complexes, where the coordination sphere accommodates exclusively oxygen atoms. The coordination numbers of the metal centers vary from 8, 10, 11 to 12, while the ligands, each employing its pyridone tautomer, link with metal cations. Bridging oxygen atoms play an important role in construction of two- and/or three-dimensional networks of these complexes. Hydrogen bonding contributes to the connectivity within a given sheet in Rb[H(4DNPNO)2]; aromatic π–π stacking interactions exist only in Cs(4DNPNO). The interactions between metal atoms and ligands are generally very weak. The organization of all layer structures appears to be governed mainly by steric effects and electrostatic forces with very little directional influence of the cations. The thermogravimetric analyses of these complexes showed the following consecutive processes: loss of NO2 groups, collapse of the pyridyl ring backbones and finally inorganic residue formation. These complexes could be used as probes in template effects of heavy alkali-metal cations in the organization of biorelevant ligands and as environment-friendly energetic catalysts in solid propellants.

The Mechanism of the Reaction of Alkai Metal Phenoxides with Hexahalocyclotriphosphazenes

In both specific reaction rate studies and in intermolecular competition reactions, sodium phenoxide preferentially reacts with hexafluorocyclotriphosphazene (1) over hexachlorocyclotriphosphazene (2). In an intramolecular competition experiment using difluorotetrachlorocyclotriphosphazene (3), sodium phenoxide reacts exclusively at the fluorinated phosphorus site. These results are consistent with the NBO charges at the phosphorus centers. DFT calculations also indicate that in the case of pentacoordinate intermediate formation, an associative mechanism is kinetically favored. The variations of the rate of reaction of 2 with temperature, solvent and alkali metal cation have been determined. The activation parameters for the chlorophosphazene system show positive enthalpies and entropies of activation. The reaction rates of 2 increase with solvent basicity. The rates of reaction for the heavier alkali metal cations are greater than those for the lighter cations. The addition of a crown ether results in a significant rate increase. Consideration of all of these data suggest a mechanism where the rate has a major contribution from a preequilibrium wherein the metal phenoxide cluster dissociates into kinetically active speicies which adds, in the rate determining step, to the phosphorus (V) center.

Tl2[B12H12]: Thallium(I) Dodecahydro‐closo‐dodecaborate with Cs2[B12H12]‐type Crystal Structure

The preparation of thallium(I) dodecahydro-closo-dodecaborate Tl2[B12H12] was studied over 40 years ago by Muetterties et al. [1], its crystal structure, however, was never determined. Colourless octahedral single crystals of this title compound were obtained by neutralizing an aqueous solution of the free acid (H3O)2[B12H12] with Tl2CO3 and recrystallization of the crude product from water. The crystal structure of Tl2[B12H12] (cubic, Fm3, Z 4; a 1075.51(6) pm) is isostructural to that one of the dodecahydrocloso-dodecaborates with heavy alkali-metal cations K , Rb and Cs reported previously [2, 3]. It can be described as an anti-CaF2type arrangement in which Tl cations occupy all the tetrahedral interstices within the cubic closest-packed host lattice of the quasiicosahedral [B12H12]-cluster dianions.

Calixarenes as Polyhapto-aromatic Ligands: Alkali Metal Ions and Sulfonated Calixarenes

Crystal structure determinations for the hexarubidium and octacesium derivatives of calix[6]arene hexasulfonic acid, as well as of a new solvate of the pentasodium derivative of calix[4]arene tetrasulfonic acid, and comparison with structural data from the literature for alkali metal complexes of sulfonated calixarenes, have provided further evidence for the importance of interactions with aromatic ~ -electrons for the heavier alkali metal cations. There is evidence as well that this interaction can be enhanced by extended ionization of the sulfonated calixarene.