Heavy Alkali Metals Research Articles

S-Block metal inverse crowns: synthetic and structural synergism in mixed alkali metal–magnesium (or zinc) amide chemistry

This article focuses on the special chemistry that can take place when certain lithium (or other heavier alkali metal) amides are combined with certain magnesium (or zinc) bisamides. Some of the reaction mixtures studied follow a straightforward path leading to simple heterobimetallic compositions with predictable structures, whereas others take an unexpected turn to behave as powerful oxygen scavengers or as regioselective bases to yield novel products with unpredictable host–guest macrocyclic structures. We refer to these new compounds as ‘inverse crown ethers’ or ‘inverse crowns’ because their arrangement of Lewis acidic and Lewis basic sites is opposite to that encountered in conventional crown ether complexes. This developing phenomenon appears to be a direct result of pairing together the two distinct metal types in the same complex, as the chemistry cannot be replicated by complexes containing one or the other metal type on its own.

Wetting transitions of4Heon alkali-metal surfaces from density-functional calculations

We have studied the wetting properties of ${}^{4}\mathrm{He}$ adsorbed on the surface of heavy alkali metals by using a nonlocal free-energy density functional which describes accurately the surface properties of liquid ${}^{4}\mathrm{He}$ in the temperature range $0<T<3$ K. Our results for ${}^{4}\mathrm{He}$ on the Cs surface give both the temperature dependence of the contact angle and the wetting temperature in good agreement with the experimental findings. For the ${}^{4}\mathrm{He}/\mathrm{Rb}$ system we find that a wetting transition on the Rb surface occurs at $T\ensuremath{\sim}1.4$ K, whereas the experiments show either wetting down to $T=0$ or a wetting transition at $T\ensuremath{\sim}0.3$ K. We suggest that this disagreement is due either to an inaccuracy of the fluid-substrate potential used in our calculations or the consequence of substrate roughness, which is known to affect the Rb surface, and whose effect would be to lower the wetting temperature. The sensitivity of the wetting transition to the He-surface potential is stressed for the He/Rb surface, which may justify the controversial experimental findings for this system.

ChemInform Abstract: Reaction of Organolithium Compounds with Alkali Metal Alkoxides - A Route to Superbases

Organolithium compounds and lithium alkoxides form adducts, the reactivities of which are similar to those of the parent organolithium compounds. On the other hand, with heavy alkali metal alkoxides a metal interchange takes place, which gives rise to heavy alkali metal organic compounds. This is accompanied by a dramatic increase in the reactivity of the system, hence the name “Superbase” (SB) may be applied. This metal interchange is a general reaction and proceeds not only with organolithium compounds but also with lithium amides and lithium enolates of ketones and esters. SBs readily react with organic substrates to give heavy alkali metal derivatives of the substrate. Such reactions, followed by conversion with an electrophile, find wide application in organic synthesis. The properties of SBs may be further enhanced by using a greater than equimolar amount of a highly-branched heavy alkali metal alkoxide (R2OM). In this review, the mechanism of SB reactions with substrates is discussed and the stoichiometric participation rather than catalytic effect of R2OM is documented. Although various routes for the reaction of SBs with substrates may be envisaged, a heavy alkali metal organic compound is involved in all cases.

Chemical trends of the rattling phonon modes in alloyed germanium clathrates

Alloys based on Ge clathrates are promising thermoelectric materials because of their expected “rattling” properties. We have incorporated the elements of columns I and II into the cages of (Ge, Ga)46 type-I clathrates as cation guests and have theoretically examined their “rattling” behavior using density functional theory. The potential energy curves of guest atoms in the cages are evaluated to understand the nature of the weak guest–framework interaction. Some atoms are unstable at the center of the cages, while others appear to be bonded by weak restoring forces. We calculate the phonon modes and the Raman spectra and find that heavy alkali-earth elements, such as Sr and Ba, induce low-frequency “rattling” phonon modes as predicted by Slack’s model, while heavy alkali metal atoms (K, Rb, and Cs) are less “rattler-like” since they interact less with the acoustic modes of the Ge-based clathrate framework.

Predicting the liquid-vapor critical point from the crystal anharmonicity

A "universal" dependence is predicted of the reduced critical parameters, k(B)T(c) / E0(gamma), V(c) / V0(gamma), and P(c)V(c)/k(B)T(c) = Z(c)(gamma), on the crystal anharmonicity gamma (closely related to the Gruneisen parameter gamma(G)). It is based on a simplified embedded-atom type approach which enables one to utilize the universal zero-temperature equation of state in a version of fluid perturbation theory. This model's critical temperature and density agree with the experimental results for both the heavy rare gases ( gamma approximately 2.85) and heavy alkali metals ( gamma approximately 1.35). Predicted critical parameters for many other liquid metals are consistent with previous estimates, but the model is not applicable when directional bonding is important.

Doping of Carbon Nanotubes by Heavy Alkali Metals

Multiwall (MWNT) and single wall (SWNT) carbon nanotubes were intercalated with heavy alkali metals. From the point of view of their composition, alkali 2D superlattice, EPR and 13C NMR characteristics, the intercalation compounds of MWNT (1st and 2nd stage) are close to their parent GIC. An expansion of the 2D triangular lattice of SWNT bundles was clearly detected, showing that the alkali atoms are intercalated in the free space between the tubes.

EPR, 13C and 11B NMR of Boronated Carbons Intercalated with Heavy Alkali Metals (K, Rb and Cs)

BxC1−x host materials (0.1 < × < 0.25) and their intercalation compounds with heavy alkali metals prepared from the vapor reaction or from the reaction of cesium in ammonia solution were characterized using 13C and 11B NMR and EPR. 13C NMR shifts and EPR dysonian lines (typical of conductors) found in intercalation compounds are qualitatively similar to those observed in their GIC analogues. Evidence are reported in favor of a breaking of the local axial symmetry due to interstitial boron atoms for highest × values and partial recover of this symmetry in the intercalation compounds.

Alkali metal ion exchange by the framework titanium silicate M 2Ti 2O 3SiO 4· nH 2O (M=H, Na)

The ion-exchange properties of the titanium silicate, M 2Ti 2O 3SiO 4· nH 2O (M=H,Na), towards alkali ions has been examined. Potentiometric titration of the highly crystalline phase in the proton form, H 2Ti 2O 3(SiO 4)·1.6H 2O, showed a dependency of the exchange on the size and charge of the ion and the pH of the solution. It was found that the accessability of three different ion-exchange sites in the titanium silicate framework controls the uptake of ions: 100% of the total amount of the ion-exchange sites could be occupied at pH 12.5 by sodium and lithium ions, about 75% by potassium and rubidium ions and only 25% by cesium ion. The ion-exchange isotherms of alkali metal ions were determined and the corrected selectivity coefficients as a function of metal loading were analyzed. Sodium titanium silicate exhibits a high affinity for heavy alkali metals with the selectivity order Cs +>Rb +>K +. By studying the cesium and strontium uptake in the presence of NaNO 3, CaCl 2, NaOH, NaOH+KOH, and HNO 3 (in the range of 0.01–6 M) the titanium silicate was found to be an efficient Cs + ion exchanger in acid, neutral and alkaline media, which makes it promising for treatment of different types of nuclear waste and contaminated environmental and biological liquors.

Rubidium-IV: A High Pressure Phase with Complex Crystal Structure

The crystal structure of the high-pressure phase rubidium-IV was investigated using synchrotron x-ray diffraction. Full profile refinements of angle-dispersive powder diffraction data resulted in a solution with the space group $I4/\mathrm{mcm}$. The structure is made up of columns of face-sharing square antiprisms formed by one subset of Rb atoms (16 per unit cell). Quasi-one-dimensional channels in between these columns are occupied by a second subset of Rb atoms. These results demonstrate that a quite complex crystal structure is adopted by a heavy alkali metal during the progression of the pressure-driven electronic $s\ensuremath{\rightarrow}d$ transition. The structure of Rb-IV exhibits a close resemblance to the metal sublattice of the ${\mathrm{W}}_{5}{\mathrm{Si}}_{3}$-type structure.

Nuclear magnetic resonance study of platinum catalysts containing alkali atoms

We have used NMR to study the effects of adding alkali metals (Na, K, Rb, or Cs) to silica supported platinum clusters. Alkali metals are frequently added to metal catalysts, and to other catalysts as well, to serve as ‘promoters’. We have also examined the effect of the alkali metals on adsorbed CO. The properties of the alkali metal itself were studied in samples containing Na. By performing a 23 Na – 13C double resonance with adsorbed CO, we determined that at least 26% of the sodium in the samples is on the platinum clusters. The 23 Na line shows no indication of a Knight shift and the 23 Na spin-lattice relaxation time varies as 1/ T 2, suggesting that the sodium orbitals mix with the platinum conduction band to a much lesser degree than do those of adsorbed CO. The NMR results lead us to conclude that the Na forms three-dimensional structures on the Pt, most likely small Na 2O clusters with sizes approaching molecular dimensions. We observed the effect of the alkali metals Na, K, Rb, and Cs on the NMR properties of adsorbed CO. In all cases the effects are small. The CO line is narrowed and shifted to higher frequency in the presence of the alkali metal while the CO spin lattice relaxation is slowed. The effect of the alkali metal is greater in the samples with the heavier alkali metals K, Rb and Cs. In the case of CO with Rb, for which the effect of the alkali metal is greatest, a modest change of about 10–15% in the parameters used to describe the NMR results is adequate to account for the effect of the Rb.

Heavy Alkali Metal Arenedithiocarboxylates: A Facile Synthesis, Dimeric Structure, and Nonbonding Interaction between the Metals and Aromatic Ring Carbons.

Dithiocarboxylic acids and their trimethylsilyl esters were found to readily react with potassium, rubidium, and cesium fluorides to give the corresponding alkali metal dithiocarboxylates 3-5 in moderate to good yields. A series of tetramethylammonium dithiocarboxylates 8 have been prepared in good yields by the reaction of sodium dithiocarboxylates 7 with tetramethylammonium chloride. The structures of potassium (3b), rubidium (4g), cesium (5f), and tetramethylammonium 4-methylbenzenecarbodithioates (8e) and tetramethylammonium 2-methoxybenzenecarbodithioate (8f) were characterized crystallographically. These heavier alkali metal salts (3b, 4g, 5f) have a dimeric structure [(RCSSM)(2), M = K, Rb, Cs] in which the two dithiocarboxylate groups are chelated to the metal cations which are located on the upper and lower sides of the plane involving the two opposing dithiocarboxylate groups. The K(+) cations interact with the tolyl fragment of a neighboring molecule, while the Rb(+) and Cs(+) cations interact with two neighboring tolyl fragments, in which the ipso and ortho carbons are positioned close to the metals. The interaction number of the metals with surrounding atoms is 8 for K(+) and Rb(+) and 12 for Cs(+). The C-S distances of the dithiocarboxylate group are different for the potassium salt 3b. In contrast, those of the rubidium salt 4g and cesium salt 5f are equal. Similarly, the chelating sulfur-metal bond distances of 3b are different, while those of 4g and 5f are almost equal. The dihedral angles of the phenyl ring and dithiocarboxylate plane increase in the order of the K, Rb, and Cs salts. The structural analysis of sodium 4-methylbenzenecarbodithioate (7g) revealed the presence of 4-CH(3)C(6)H(4)CS(2)Na(0.36). In contrast, the tetramethylammonium salts 8 are monomeric where the cation moieties are located out of the dithiocarboxylate plane. The potassium 3, rubidium 4, and cesium dithiocarboxylates 5 readily reacted with methyl iodide or triorganotin chlorides at room temperature to give the corresponding methyl 9 and triorganotin dithioesters 10 in good yields. At 0 degrees C, the reactivity of the rubidium 4 and cesium salts 5 to methyl iodides decreases dramatically compared with those of the sodium salts 7 and potassium salts 3.

Facile Synthesis and Structure of Heavy Alkali Metal Thiocarboxylates: Structural Comparison with the Selenium and Tellurium Isologues.

Potassium, rubidium, and cesium thiocarboxylates were found to be synthesized by the reaction of thiocarboxylic acid or its O-trimethylsilyl esters with KF, RbF, and CsF. Tetramethylammonium thiocarboxylates were prepared in good yields by the reaction of sodium thiocarboxylates with tetramethylammonium chloride. The structures of potassium benzene-, 2-methoxybenzene-, and 4-methoxybenzenecarbothioates, rubidium 2-methoxybenzenecarbothioate, tetramethylammonium 2-methoxy- and 2-trifluoromethylbenzenecarbothioates, potassium 2-methoxybenzenecarboselenoate, and rubidium 2-methoxybenzenecarbotelluroate were characterized by X-ray structural analysis. All of these alkali metal salts exhibit a dimeric structure in which the oxygen and/or sulfur atom is associated with the metal of the opposite molecule, while the tetramethylammonium thiocarboxylates are monomeric. In potassium 2-methoxybenzenecarbothioate, the two thiocarboxylate groups chelate to the potassium atoms above and below the plane which involves the thiocarboxylate groups. In potassium 4-methoxybenzenecarbothioate, one thiocarboxylate group chelates to potassium. Without exception, the o-methoxy oxygen intermolecularly coordinates to the metal of the opposite molecule. The C-O bond lengths of the thiocarboxylate group are in the range 1.22-1.24 Å, which is slightly longer than those of common thioesters. The C(sp(2))-S distances are in the range 1.70-1.72 Å, which is close to that of a typical C-S single bond and suggests that the negative charge may be somewhat localized on the sulfur atom. The interaction number of the metals with oxygen and sulfur atoms was 7 for K and 8 for both Rb and Cs. The dihedral angle between the thiocarboxyl group and the phenyl ring is substantially increased by the introduction of the o-methoxy group. In these alkali metal thio-, seleno-, and tellurocarboxylates, only cesium 2-methoxybenzenecarbotelluroate showed an intermolecular nonbonding interaction between the cesium and the phenyl ring carbons.

Phosphorus-31 contact shifts as a measure of weak ligand affinities. Interaction between alkali metal fluorenone radical anions and certain phosphorus(III or V) ligands

The nuclear magnetic resonance shifts, δobs, induced to 31P in Ph3P, (MeO)3P and (MeO)3PO by alkali metal fluorenone radical anions in tetrahydrofuran solutions were measured. These parameters, which depend significantly on the cation for a given ligand, and also on the ligand for a given cation, were used to extract the corresponding 31P contact shifts, δc(M). The latter parameters are proposed as a measure of the ligand affinity of a given phosphorus compound for a particular alkali metal. Trimethyl phosphate exhibits the greatest affinity for the lithium cation. The magnitudes of δc(M) imply some covalency between the cation and the radical anion and the ‘paradox’ of a heavier alkali metal such as potassium being covalently bonded to fluorenone radical anion has been explained. The transferability of the reported ligand affinities of Li+, Na+ and K+ is discussed. © John Wiley & Sons, Ltd.

Hydantoin Derivatives as Spacers for Crystal Engineering in the Chemistry of Heavy Alkali Metal Ions: Synthesis and Crystal Structure of Layered (CsLOH)(infinity) (L = 5,5-Dimethyl-4-oxoimidazolidine-2-thione).

In the (CsLOH)∞ layered structure (L = 5,5-dimethyl-4-oxoimidazolidine-2-thione) L acts as a polyhapting molecule bridging four different Cs+ ions; each cation displays an eightfold coordination involving four ligand molecules and three OH- groups. The hydroxo groups are triply bridging three cesium atoms.

ION EXCHANGE PROPERTIES OF THE SODIUM PHLOGOPITE AND BIOTITE

ABSTRACT The ion exchange behavior of three sodium micas (phlogopite, Ward's Sci.; phlogopite, Suzorite Inc., biotite, Ward's Sci.) towards Li+, K+, Rb+, Cs+, Mg2+. Ca2+, Sr2+, Ba2+, Pb2+ Hg2+, Co2+, Cu2+ Cd2+ and Zn2+ ions has been studied. The ion exchange isotherms of alkali, alkaline earth and some other divalent cations were determined and concentration equilibrium constants as a function of metal loading and temperature were analyzed. Sodium micas exhibit high affinity for heavy alkali metals with the selectivity order Rb+ > Cs+ > K+. By studying the cesium uptake in the presence of NaNO3, CaCl2, NaOH, NaOH+KOH, HNO3 electrolytes (in the range of 0.01–6 M) it was found that sodium micas could remove cesium efficiently in neutral and alkaline media, which make them promising for certain types of nuclear waste treatment.

A Convenient Synthetic Strategy toward Heavy Alkali Metal Bis(trimethylsilyl)phosphides: Crystal Structures of the Ladder-Type Polymers [A(thf)P(SiMe(3))(2)](infinity) (A = K, Rb, Cs).

A series of highly reactive heavy alkali metal phosphides was prepared by treating trimethylsilyl-substituted phosphines with alkali metal tert-butyl alcoholates. The compounds are formed in excellent yield and purity, and the side product can be easily removed in a vacuum. The high synthetic potential of this reaction route was further shown by utilizing excess alkali metal tert-butyl alcoholates in reaction with silyl substituted phosphines. In all cases, only monometalated products were isolated. In the course of this work the crystal structures of the bis(trimethylsilyl)phosphides [K(thf)P(SiMe(3))(2)](infinity), 1a, [Rb(thf)P(SiMe(3))(2)](infinity), 1b, and [Cs(thf)P(SiMe(3))(2)](infinity), 1c, were obtained. The compounds display polymeric ladder-type structures. Compounds 1a,b are isomorphous, while compound 1c displays a slightly altered local geometry. Despite small differences in local geometry, the coordination spheres for the phosphorus atoms and the alkali metal are fairly similar. The five coordinate phosphorus atoms are connected to three alkali metal centers in addition to two trimethylsilyl groups. The alkali metals are four coordinate with ligations to three phosphorus centers in addition to one thf oxygen donor. Compounds 1a-c were characterized using elemental analysis, NMR spectroscopy, and X-ray crystallography. Crystal data with Mo Kalpha (lambda = 0.710 73 Å) at 150 K are as follows: 1a, a = 6.4261(2) Å, b = 12.4119(2) Å, c = 21.5447(4) Å, V = 1718.41(7) Å(3), Z = 4, orthorhombic, space group P2(1)2(1)2(1), 3427 independent reflections, R1 (all data) = 0.0351; 1b, a = 6.5338(2) Å, b = 12.5664(3) Å, c = 21.5537(5) Å, V = 1769.70(8) Å(3), Z = 4, orthorhombic, space group P2(1)2(1)2(1), 4195 independent reflections, R1 (all data) = 0.0776; 1c, a = 11.3515(1) Å, b = 22.3445(3) Å, c = 7.2501(1) Å, beta = 96.017(1) degrees, V = 1828.81(4) Å(3), Z = 4, monoclinic, space group P2(1)/c, 4343 independent reflections, R1 (all data) = 0.0811.

Triple-resonance method for the detection of hyperfine transitions in heavy-alkali metals

The triple-resonance method for the detection of hyperfine transitions in heavy-alkali metals is studied theoretically. The evolution equations of the reduced fictitious tensorial components of the dressed-atom density matrix in an extended fictitious formalism are determined and solved for the stationary state. Illustrative numerical examples of dressed-caesium are included. Previously unexplained triple-resonance experiments on rubidium and caesium are interpreted in detail.

Solvent Extraction of Alkali Metal (Li - Cs) Picrates with 18-Crown-6 into Various Diluents. Elucidation of Fundamental Equilibria which Govern the Extraction-Ability and -Selectivity

The actual constants of the overall extraction equilibrium, the distribution for various organic solvents having low dielectric constants, and the aqueous ion-pair formation (KMLA) of 18-crown-6 (18C6)-alkali metal (Li - Cs) picrate 1:1:1 complexes were determined at 25°C; the partition constants of 18C6 were also measured at 25°C. The log KMLA values are 2.53±0.21 for Li, 3.29±0.23 for Na, 4.76±0.27 for K, 4.62±0.36 for Rb, and 4.49±0.36 for Cs. The relatively large difference in the log KMLA value between light (Li, Na) and heavy alkali metals (K, Rb, Cs) reflects the difference in the structure of the 18C6-alkali metal ion 1:1 complex between light and heavy alkali metals. Almost all of the partition behavior of 18C6 and its 1:1:1 complexes with alkali metal picrates can be explained by regular solution theory. The molar volumes and solubility parameters of 18C6 and the complexes were determined. For every diluent, the extraction-selectivity order of 18C6 is K > Rb > Cs > Na > Li. The extraction-ability and -selectivity of 18C6 for the alkali metal ion were completely elucidated in terms of the four fundamental equilibria.

Intercalation of Heavy Alkali Metals in Boron Substituted Carbons BxC1−x

First stage intercalation compounds were obtained using vapor reaction of heavy alkali metals (M ˭ K, Rb and Cs) with BXC1−x platelets (x=0.1 and x=0.25). Depending on the value of x, M(B0.1C0.9)8±1 and M(B0.25C0.75)10±1 compounds were formed. Intensity calculations of the 001 lines suggested domains of M(BXC1−x)5 first stage dense structure. As formed B0.25C0.75 was incompletely intercalated by cesium from its liquid ammonia solution whereas extended intercalation was obtained with heat treated B0.25C0.75 host (T=1600°C) giving a first stage Cs(B0.25C0.75)12 derivative.

Intercalation of Lithium Hydride into Graphite and Electrochemical Behavior

The lithium hydride does not intercalate by itself, on the contrary, the reaction of hydrogen in LiC6 leads to a mixture of LiH and high stages lithium intercalated compounds. However, in the presence of a heavy alkali metal (potassium or cesium), LiH intercalates to give quatenary phases M2LiHC8s, s being the stage. Those compounds contain large amounts of intercalated metal per carbon atom (M/C = 3/8s) and may be interesting as electrode material for secondary batteries.