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This is the sixth electride whose crystal structure has been determined and the fourth to show polymorphism. Crystals of the title electride prepared from mixed solvents have a structure similar to that of Li

The use of sodium in alumina and silica gels for the reductive cleavage of the N–O bond of N-methoxy-N-methylamides, commonly referred to as Weinreb amides, has been investigated. This method reduces a diverse set of Weinreb amides with different functional groups to give modest to excellent yields. In the course of the studies to explore mechanisms and functional group tolerance, an apparently novel group transfer emerged, implying base-promoted cleavage of the Weinreb amide to form formaldehyde, followed by aldol condensation.

Liquid alkali metals and their alloys can be absorbed into the 15 nm diameter pores of nanostructured silica gel (SG) at loadings up to 40 wt %. Characterization of the resultant materials was done by measuring the amount of hydrogen produced by addition of alcohols and/or water, by differential scanning calorimetry, and by static 23Na NMR spectroscopy. While sodium must be heated above 100 °C to form Na in SG, absorption of Na–K alloys at ambient temperatures yields nanoscale metallic clusters in the pores (Stage 0). In both cases, some of the encapsulated metal may dissolve in the silica and ionize to produce highly mobile M+ ions with reversible electron transfer to the silica. This presumption is consistent with literature observations that sodium is soluble in silica films at ambient temperatures at levels up to 35 mol percent and is presumed to form highly mobile Na+-O– species (Lagarde, P.; Flank, A.-M.; Mazzara, C.; Jupille, J. Surf. Sci.2001, 482–485, 376–380). Heating M-SG materials leads to red...

Electrides are ionic solids with cavity-trapped electrons, which serve as the anions. Localization of electrons in well-defined trapping sites and their mutual interactions provide early examples of quantum confinement, a subject of intense current interest. We synthesized the first crystalline electride, Cs(+)(18-crown-6)(2)e(-), in 1983 and determined its structure in 1986; seven others have been made since. This Account describes progress in the synthesis of both organic and inorganic electrides and points to their promise as new electronic materials. Combined studies of solvated electrons in alkali metal solutions and the complexation of alkali cations by crown ethers and cryptands made electride synthesis possible. After our synthesis of crystalline alkalides, in which alkali metal anions and encapsulated alkali cations are present, we managed to grow crystalline electrides from solutions that contained complexed alkali cations and solvated electrons. Electride research is complicated by thermal instability. Above approximately -30 degrees C, trapped electrons react with the ether groups of crown ethers and cryptands. Aza-cryptands replace ether oxygens with less reactive tertiary amine groups, and using those compounds, we recently synthesized the first room-temperature-stable organic electride. The magnetic and electronic properties of electrides depend on the geometry of the trapping sites and the size of the open channels that connect them. Two extremes are Cs(+)(15-crown-5)(2)e(-) with nearly isolated trapped electrons and K(+)(cryptand 2.2.2)e(-), in which spin-pairing of electrons in adjacent cavities predominates below 400 K. These two electrides also differ in their electrical conductivity by nearly 10 orders of magnitude. The pronounced effect of defects on conductivity and on thermonic electron emission suggests that holes as well as electrons play important roles. Now that thermally stable organic electrides can be made, it should be possible to control the electron-hole ratio by incorporation of neutral complexant molecules. We expect that in further syntheses researchers will elaborate the parent aza-cryptands to produce new organic electrides. The promise of electrides as new electronic materials with low work functions led us and others to search for inorganic electrides. The body of extensive research studies of alkali metal inclusion in the pores of alumino-silicate zeolites provided the background for our studies of pure silica zeolites as hosts for M(+) and e(-) and our later use of nanoporous silica gel as a carrier of high concentrations of alkali metals. Both systems have some of the characteristics of inorganic electrides, but the electrons and cations share the same space. In 2003, researchers at the Tokyo Institute of Technology synthesized an inorganic electride that has separated electrons and countercations. This thermally stable electride has a number of potentially useful properties, such as air-stability, low work function, and metallic conductivity. Now that both organic and inorganic electrides have been synthesized, we expect that experimental and theoretical research on this interesting class of materials will accelerate.

Alkali metals absorbed in silica gel (the M-SG reagents) efficiently cleave C-P bonds in triaryl- and diarylphosphines. The resulting alkali metal phosphides can serve as useful building blocks for a variety of phosphines. Alkyldiarylphosphines undergo exclusive aryl group cleavage.

The use of sodium in alumina and silica gels for the reductive cleavage of the N–O bond of N-methoxy-N-methylamides, commonly referred to as Weinreb amides, has been investigated. This method reduces a diverse set of Weinreb amides with different functional groups to give modest to excellent yields. In the course of the studies to explore mechanisms and functional group tolerance, an apparently novel group transfer emerged, implying base-promoted cleavage of the Weinreb amide to form formaldehyde, followed by aldol condensation.

An electride has been synthesized that is stable to auto-decomposition at room temperature. The key was the theoretically directed synthesis of a per-aza analogue of cryptand[2.2.2] in which each of the linking arms contains a piperazine ring. This complexant was designed to provide strong complexation of Na+ via pre-organization of a "crypt" that contains eight nonreducible tertiary amine nitrogens. The structure and properties indicate that, as with other electrides, the "anions" are electrons trapped in the cavities formed by close-packing of the complexed cations. The isostructural sodide, with Na- anions in the cavities, is also stable at and above room temperature.

Up to 4 Cs or Rb atoms per 32 Si atoms can be incorporated into the channels of the all-silica (SiO2) zeolites ITQ-4 and beta with effective oxidation states of zero. The optical properties and 29Si MAS NMR spectra suggest partial or complete ionization within the channels to yield M+ ions and relatively free electrons. This view is supported by a published structural model (Petkov, V.; Billinge, S. I.; Vogt, T.; Ichimura, A. S.; Dye, J. L. Phys. Rev. Lett. 2002, 89, 075502) based on pair distribution functions for Cs in ITQ-4. As with solutions of alkali metals in ammonia, however, the trapped electrons in this inorganic electride interact with the cations, and spin-pairing between adjacent electrons also occurs. The crystal morphology is unaffected by the inclusion of alkali metals. Structural distortions that reduce or eliminate long-range order are completely reversed upon oxidation and removal of the metal. At higher temperatures, Na and K can also be incorporated, but the optical spectra indicate th...

The first barium sodide, with stoichiometry Ba(2+)(H(5)Azacryptand[2.2.2](-))Na(-).2MeNH(2), was synthesized by the reaction of Ba, Na, and H(6)Azacryptand[2.2.2] in NH(3)-MeNH(2) solution. It was characterized by X-ray crystallography, (23)Na MAS NMR, hydrogen evolution, DSC, optical spectroscopy, and magnetic susceptibility. This is the first sodide in which the sodium anions form (Na(2))(2)(-) dimers. Previous theoretical predictions were verified by a calculation of the potential energy curve for the dimer in the field of the surrounding charges, whose positions were determined from the crystal structure.

Alkali metal compounds have been known since antiquity. In 1807, Sir Humphry Davy surprised everyone by electrolytically preparing (and naming) potassium and sodium metals. In 1808, he noted their interaction with ammonia, which, 100 years later, was attributed to solvated electrons. After 1960, pulse radiolysis of nearly any solvent produced solvated electrons, which became one of the most studied species in chemistry. In 1968, alkali metal solutions in amines and ethers were shown to contain alkali metal anions in addition to solvated electrons. The advent of crown ethers and cryptands as complexants for alkali cations greatly enhanced alkali metal solubilities. This permitted us to prepare a crystalline salt of Na − in 1974, followed by 30 other alkalides with Na − , K − , Rb − and Cs − anions. This firmly established the −1 oxidation state of alkali metals. The synthesis of alkalides led to the crystallization of electrides, with trapped electrons as the anions. Electrides have a variety of electronic and magnetic properties, depending on the geometries and connectivities of the trapping sites. In 2009, the final surprise was the experimental demonstration that alkali metals under high pressure lose their metallic character as the electrons are localized in voids between the alkali cations to become high-pressure electrides!

Single-crystal conductivity measurements of the electride K+(cryptand[2.2.2])e- show pronounced anisotropy. Conductivity of the sheetlike crystals is 10−30 times greater in the “easy” than in the “hard” in-plane direction and 105−106 times greater than that perpendicular to the plane. The magnetic susceptibility is well-described by the alternating linear chain Heisenberg antiferromagnetic model. Both phenomena are consistent with the structure, which has very open pseudo-1D channels that connect large dumbbell-shaped two-electron cavities to form a chain of coupled electron spins. Slightly smaller channels interconnect these chains to form a 2D network of channels and cavities. The proposed conductivity mechanism is the random 2D hopping of hole defects that are highly mobile down the open 1D chain. They undergo activated transport to adjacent chains as a result of defect sites (such as K-) in the primary chain.

The synthesis and characterization of 4,7-dimethyl-4,7,10,11,15, 18-hexaazabicy-clo[8.5.5]octane ( L ) is described. The ligation properties of the macrobicyclic ligand towards alkaline metal cations are considered. The crystalline structures of the ligand L and of the first small azacage complexes with six-coordinate lithium geometry, [Li L ]+[BPh4]−and [Li L ]+[ClO4]−, are presented.

Thermionic electron emission from 2000−4000 A thick films of K+(cryptand[2.2.2])e- and Rb+(cryptand[2.2.2])e- was studied as a function of temperature and time. The total charge collected was generally several hundred nanocoulombs with peak currents in the range of 5−100 pA. Although electron emission was not a direct result of thermal decomposition of the films, the peak current correlated with the decomposition rate. At a given temperature, the current increased gradually to a peak value and then decreased to near zero. Interrupting the process by cooling before complete decay, followed by a return to the same temperature, restored the previous current−time behavior. Once the current had decayed to near zero, the only way to restore emission was to raise the temperature above the previous value. The process of growth and decay was then repeated. The origin of emission is unknown, but the behavior suggests the presence of surface defect sites at grain boundaries that are initially empty. Sample decomposi...

This is the sixth electride whose crystal structure has been determined and the fourth to show polymorphism. Crystals of the title electride prepared from mixed solvents have a structure similar to that of Li+(cryptand[2.1.1])e-. Electrons occupy cavities that are connected by “ladder-like” channels. The static and spin magnetic susceptibilities of polycrystalline samples that contain this polymorph (called phase α) show Heisenberg 1D antiferromagnetic behavior with −J/kB = 30 K. Similar to other electrides with “localized” electrons, this electride is a poor conductor (σ < 10- 4 ohm-1cm-1). Thin films prepared by high vacuum co-deposition of Rb metal and cryptand[2.2.2] have optical spectra and near-metallic electrical conductivity nearly identical with those of K+(cryptand[2.2.2])e-. These properties would not be expected if the film structure were the same as that obtained for crystals. Rather, they suggest that the films consist of microcrystals whose structure is similar to that of K+(cryptand[2.2.2]...

The macrobicyclic Schiff base cryptand, 1, with a m-phenyl group in each of the arms was reduced in tertrahydrofuran with the alkali metals Na through Cs to yield mono-, di-, and trianions. The crystal structure of a salt of 1-, formed by reduction of 1 with potassium metal in mixed dimethyl ether−methylamine solutions, shows that K+ is not encapsulated in the cavity of the cryptand. Instead, it forms methylamine-separated ion pairs arranged in symmetric fashion to give overall C3 symmetry. Solution studies by optical and EPR/ENDOR spectroscopies revealed complex ion pair equilibria that are compatible with external contact ion pair and solvent-separated ion pair formation. The rate of electron (and cation) transfer between strands is

Crystalline Cs+(18-crown-6)2e- was found to be a linear chain Heisenberg antiferromagnet (J/kB = −38.3 K). It undergoes a slow, irreversible transition above ∼230 K from a crystalline low temperature (LT) phase to a disordered Curie−Weiss paramagnetic high temperature (HT) phase. A 100 ppm diamagnetic (more shielded) shift of the 133Cs MAS NMR peak accompanies this transition. EPR studies confirm the transition and are in accord with the conversion of the known crystal structure to a disordered phase. This HT phase undergoes an additional first-order reversible transition upon cooling below ∼220 K (ΔH = 0.33 kJ mol-1 upon rewarming) accompanied by the formation of two peaks in the 133Cs NMR spectrum. Variable-temperature powder X-ray diffraction confirms the disordered or microcrystalline nature of the HT phase(s).

Alkali metals in silica gel (the Na(2)K-SG(I) reagent) cleanly effect Birch reductions of substrates with at least two or more aromatic rings. The reaction conditions are alcohol-free, ammonia-free, and achieve excellent yields and high selectivities at room temperature.

Alkali metals in silica gel (the M-SG materials) are effective reagents for reductive deallylation, debenzylation, debenzhydrylation, and detritylation of amines. As such, these reagents provide a convenient alternative to traditional metal ammonia solutions for this class of deprotections.

Alkali metal radical anion salts in which the cations are coordinated directly by the radical anions have been studied extensively in solution, but relatively little in the solid state. We have prepared and characterized two such salts from 2,3-bis(2-pyridyl)quinoxaline (dpq) and potassium metal at −60 °C and 10-5 Torr. Crystals from THF show a zig-zag contact ion pair chain structure whereas a dimeric structure is obtained from methylamine. In both systems, the potassium ions occupy sites consisting of four quinoxaline nitrogens and solvent molecules. These salts have been further characterized by thin-film and solution optical spectroscopy, solution EPR and ENDOR spectroscopies, magnetic susceptibility, and cyclic voltammetry measurements.

Crystal structures have been obtained for the sodide (IUPAC, natride) salts, K+(12–crown–4)2–Na− (I), Na+(cryptand[2.2.1])Na−(II), Rb+(18–crown–6)Na−·CH3NH2 (III), K+(18–crown–6) Na−·2(CH3NH2)·3(18–crown–6)(IV), Cs+(cryptand[3.2.2])Na−(V), and (Li+)2(TMPAND)2–(Na−)2·(CH3NH2)(VI), in which TMPAND is 5,12,17–trimethyl–1,5,9,12,17–pentaazabicyclo [7.5.5] nonadecane). The synthesis, handling and crystal growth techniques are described and the properties and structures are compared with those of other alkalides.

Optical and electrical measurements on vapor co-deposited thin films of the most conducting electride, K+(cryptand[2.2.2])e-, show results similar to those obtained with polycrystalline pellets and with thin films prepared by solvent evaporation. Initial optical absorbance spectra of films deposited below −50 °C showed contributions from several species, but these spectra evolved with time (annealed) at low temperatures to yield mostly plasmalike spectra, characteristic of marginal metals. Most films deposited at −40 °C showed no change in shape with time, indicating that annealing had occurred during deposition. Four-probe conductivity measurements showed activated temperature dependence with an activation energy of about 0.03 eV, while two-probe conductivity measurements showed similar activation energies, but with a variable resistive barrier at the sample−electrode interfaces. The correlation between conductivities and the decay of the absorbance spectra during decomposition was investigated. Thermal ...

Electron transfer from an alkali metal to a suitable complexant for the cation can yield crystalline ionic solids that contain the complexed cation and either an alkali metal anion (alkalide) or a trapped electron (electride). The nature and properties of electrides are emphasized in this paper. When the organic complexant contains aromatic groups, the anionic species is an aromatic radical anion. Preliminary work on the addition of alkali metals to LOGEAs (large organic globular electron acceptors) is described and strategies for the synthesis of mixed electride-anion compounds are considered.

The peraza analogue of polyether cryptand [2.2.2], 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane, has been synthesized in 70% yield via a two-step one-pot procedure by the condensation of tris(2-aminoethyl)amine (tren) with glyoxal in isopropanol at -78 °C followed by reduction of the intermediate with Na/liquid NH 3 . This preparation is significantly faster, simpler, and higher yielding than the previously reported two-step procedure, with its lengthy isolation process and 45% overall yield.

Electrides are ionic compounds in which the cations are complexed by cryptands or crown ethers and the “anions” are trapped electrons. The crystal structures of five electrides are known and are similar to the corresponding alkalides (in which the anions are alkali metal anions) except that the anionic sites are “empty”. Theory and experiment strongly support a model in which the “excess” electrons are trapped in these anionic cavities and interact with each other through connecting channels, whose geometries vary significantly from one electride to another. Measurements of optical, alkali metal NMR, and EPR spectra, magnetic susceptibilities, and conductivities provide many data that can be correlated with the structures. Three electrides have essentially 1D chains of cavities connected by channels through which the electrons communicate, as indicated by magnetic susceptibilities that are well described by a 1D Heisenberg model. The electride, K+(cryptand[2.2.2])e- has a 2D array of cavities and channels...

The optical properties of the alkalide Na+(cryptand[2.2.2])Na- are sensitive to the presence of defect electrons and can be dramatically altered by irradiation with light. Fluorescence intensities decrease markedly at excitation power densities above about 1 mW cm-2, even though this power level is some 107 times lower than that required to affect the absorbance. Partial recovery occurs in powder samples over a period of several minutes at 30−100 K. The enhanced quenching of fluorescence is attributed to the presence of photoproduced trapped electrons. Pronounced changes occur in the optical absorbance spectra of vapor-deposited thin films of Na+(cryptand[2.2.2])Na- following irradiation by high intensity doubled- and tripled-YAG laser pulses. The effects are attributed to the intermediate formation of a “p-band metal” in which half of the electrons in the ground s2 state of Na- are promoted to the p-level, resulting in a high concentration of electrons trapped at some distance from the parent anion site.

Transition-metal nitrides have been synthesized by heating nanoscale metal particles under flowing N2(g) or NH3(g). In some cases reaction temperatures are significantly lower than those required by conventional heating procedures. Nanoscale metal particles of Mo, Nb, Ta, Fe−Mo, Fe−Nb, and Cu−Nb were prepared by reduction of the respective metal chloride or mixture of chlorides with the sodide, [K+(15-crown-5)2]Na-, in dimethyl ether solution. The previously characterized nitrides that were prepared (with synthesis conditions indicated) include γ-Mo2N (800 °C, N2) and Mo2N (720 °C, N2), Ta3N5 (650 °C, NH3), Fe3Mo3N (>650 °C, N2), and a mixture of niobium nitride phases (800 °C, N2). A previously unreported phase has been found in the Ba−Nb−N system.

The title electride crystallizes in the orthorhombic space group Pbcn with a = 10.060(4) A, b = 23.134(8) A, c = 8.380(4) A, and z = 4. A second powdered phase of unknown structure, but with rather different properties, forms when rapidly precipitated “seed” powder is used. The crystalline phase contains electron-trapping cavities, each of approximate diameter 4.3 A, connected in zigzag fashion along the c axis by rather open channels of minimum diameter 2.4 A (center-to-center distance 7.9 A). Each cavity is also connected to next-neighbor cavities, 8.2 A away along c, by channels of diameter 1.5 A. Inter-chain channels are

Alkali metal anions generally have narrow NMR lines that are only slightly shifted from those calculated for the gaseous anion. When, however, the anions form contact dimers, as in K+(cryptand[2.2.2])K- and Rb+(cryptand[2.2.2])Rb-, or chains, as in Rb+(18-crown-6)Rb-, the NMR peak of the alkali metal anion is significantly broadened and shifted paramagnetically. In order to obtain reliable quadrupole coupling constants, asymmetry parameters, and chemical shifts from polycrystalline samples of alkalides and electrides, spin−echo 87Rb, 85Rb, and 39K static NMR spectra were obtained for 9 alkalides, 3 electrides, and 11 model compounds. A puzzling distortion of the powder line shapes of two alkalides, an electride, and a model salt was traced to orientation-dependent transverse relaxation times (T2) by studies of the single-crystal 87Rb NMR spectra of Rb+(cryptand[2.2.2])Cl-. To analyze the NMR powder patterns, a general computer program was developed and coupled to a nonlinear least-squares fitting program.

The properties of the simplest sodide, LiNa(CH3NH2)n, are reported as a function of n. The phase diagram, established by using differential thermal analysis, shows the presence of a compound with n ≈ 6, which melts congruently at 168.5 ± 0.5 K. Two eutectics are present with n = 7.3 ± 0.3, T1 = 166 ± 1 K and n = 3.0 ± 0.2, T2 = 151 ± 1 K. The phase diagram was extended to metal concentrations that correspond to n = 1.45 and indicated the presence of a second compound with 2 ≤ n ≤ 3. The properties of these systems were investigated by EPR and alkali metal NMR spectroscopies and static magnetic susceptibilities. The 23Na NMR results clearly show that sodium is present as Na- for n ≥ 8. At higher metal concentrations the resonance line shifts smoothly toward more paramagnetic values (positive), with larger shifts at higher temperatures. EPR spectroscopy shows a transition from a single nearly symmetric line at large values of n to a strongly asymmetric signal characteristic of conduction electron spin reson...

The three-dimensional geometries of cavities and channels in four electrides are determined in detail with the aid of computer graphics methods. Previous theoretical and experimental studies suppor...

The optical absorbance from 6000 to 29 000 cm-1 of vapor deposited thin films and dilute solutions of Na+(C222)Na-, as well as the reflectance from 4000 to 25 000 cm-1 of oriented single crystals, were measured. The major common feature is a broad band centered at approximately 15 600 cm-1 (1.94 eV). The film spectra also have a shoulder at 18 900 cm-1 (2.34 eV) and a smaller, broad peak at 24 400 cm-1 (3.03 eV) that are not present in the solution spectra. While the solution peak broadened somewhat and shifted dramatically to lower energy with an increase in temperature, the film peak shifted only slightly because of broadening on the low-energy side, indicative of phonon-assisted excitation. As expected from the anisotropic structure, the features of the reflection spectra at near-normal incidence show major differences for light polarized parallel and perpendicular to the c-axis of single crystals. A Kramers−Kronig analysis of the reflection spectra yields the frequency-dependent optical constants of N...

The use of a novel mixed-valence pentavanadate phosphate cluster as a building block has made possible the low-temperature hydrothermal self-assembly of the new three-dimensional square pyramidal−tetrahedral framework vanadium phosphates [HN(CH2CH2)3NH]K1.35[V5O9(PO4)2]·xH2O (1) and Cs3[V5O9(PO4)2]·xH2O (2), from structurally simple starting materials. These materials possess some of the lowest framework densities and the largest cavities thus far observed in open-framework solid-state materials. The degree of curvature, size, shape, and charge of the mixed valence {V5O9(PO4)2} V(4+/5+) pentameric building block, which resembles a portion of an arc of a circle, favors the formation of very large cavities. Phosphate 1 crystallizes in space group I43m with a = 26.247(3) A and has very large cubic-shaped cavities that display 43m point symmetry, each of which enclose nearly 50 positive charges. These charges are distributed among 12 HN(CH2CH2)3NH2+, 32 K+ cations, and several waters of crystallization. Eac...

The sizes and structures of cavities and channels in the first crystalline mixed crown electride, [Cs{sup +}(18-crown-6)(15-crown-5)e{sup {minus}}]{sub 6}{center_dot}(18C6), are reported and related to its properties. The structure consists of cesium cations complexed by one each of the 18-crown-6 and 15-crown-5 complexants, which pack to leave a remarkable ring of six cavities that are presumed to be the trapping sites of the excess electrons. The sizes and shapes of the cavities and connecting channels are described in detail with the aid of a newly developed computer program. The magnetic susceptibility (corrected for the low-temperature {open_quotes}tail{close_quotes} due to defect electrons) is shown to be consistent with that expected for an antiferromagnetically coupled 6-electron ring and yields an estimate of the coupling strength, J/k, of {approximately}-410K. {sup 133}CsMAS NMR and the temperature dependence of the magnetic susceptibility show that the electron density at the cation nucleus is an order of magnitude smaller than that of either Cs{sup +}(18-crown-6){sub 2}e{sup {minus}} or Cs{sup +}(15-crown-5){sub 2}e{sup {minus}}. The compound is moderately conductive with a lower limit of conductivity at 213 K estimated to be 2 x 10{sup {minus}3}{Omega}{sup {minus}1} cm{sup {minus}1}. The dominant conduction mechanism is probably variable range hopping of defect electrons.

ELECTRIDES are crystalline salts that contain complexed alkali metal cations whose charge is balanced by trapped electrons1. Theory2,3 and experiment4,5 indicate that the excess electron distribution is concentrated in cavities and channels formed by close-packing of the large complexed cations. Thus electrides might serve as models of a confined electron gas. Only three electrides have been structurally characterized previously6–8. Here we report the structure of a new electride, [Cs + (15C5) (18C6).e-]6.(18C6), where 15C5 and 18C6 represent crown ethers with five and six oxygen atoms respectively. The unit cell has threefold symmetry, with a central 18C6 molecule surrounded by six Cs+ cations, each sandwiched between a 15C5 and 18C6 molecule. The six electrons released from the Cs/crown ether interaction seem to be trapped in six cavities which form a puckered ring, three above and three below the plane of the central 18C6 molecule. The ground state is diamagnetic. This ring-like distribution of electrons contrasts with the chain-like connections between electron cavities observed in other electrides6–8. Polycrystalline samples of this new electride have an electrical conductivity about a million times greater than those of the electrides Cs+ (15C5)2.e- and Cs+ (18C6)2.e-. The size, shape and connectivity of the electron-containing cavities and channels evidently exert a critical influence on the properties of electrides.

It is well-known that crown ethers form sandwich complexes with the cations of many metals, but to date, the same crown ether formed both halves of the sandwich. Six new alkalides and an electride have now been synthesized that contain mixed sandwich complexes of alkali metal cations with 18-crown-6 (18C6), 15-crown-5 (15C5), and 12-crown-4 (12C4). The properties of Cs s + (18C6)(15C5)Na - and Cs + (18C6)(15C5)e - demonstrate the existence of these stoichiometric compounds, but single-crystal X-ray diffraction studies yielded only the crystal systems and cell parameters

A few decades ago the phrase organic materials brought to mind only insulating polymers. Organic metals and organic superconductors have dramatically changed that perception and opened the materials science field to the full range of molecular architecture manipulation that is the forte of organic chemists. In a similar vein, the term salts generally con­ veyed a picture of insulating inorganic crystals with simple cations and anions, although many organic ions were known. With the synthesis by Pedersen, Lehn, Cram, and others of large organic complexants for metal cations, new classes of salts with thousands of different complex ions became available ( 1-7). When a suitable non-reducible organic complexant, L, is combined with an alkali metal, M, the formation of the complexed alkali cation, M+L, releases an electron. This electron can either combine with an alkali metal to form the alkali metal anion, M-, or become trapped in the solvent or in the ionic lattice to form the solvated electron, or a crystalline electride, respectively. Crystalline electrides sometimes behave as saits, in which the electrons are localized in the vicinity of the anionic sites, and sometimes as expanded metals (or near metals), in which the electrons are itinerant. This review focuses on the optical, magnetic, and electronic properties of these unusual new compounds (8, 8a-f).

The EPR spectra of polycrystalline samples of Cs+( 18-crown-6)2X-, in which X- = e-, Na-, or Cs-, were studied at both X-band (9 GHz) and at 250 GHz. The high frequency affords much better g-factor resolution and reveals at least two types of asymmetric electron sites in each of these compounds. The defect electrons detected in the alkalides Cs+( 18C6)2Na- and Cs+( 18C6)2Cs-appear to be located at isolated centers in the crystal lattice with the strongest signal originating from electrons trapped at anion vacancies. These species exhibit broadening due to unresolved superhyperfine interactions at the periphery of the trapping site. In contrast, the X-band spectra of the two-electron sites in the electride appear to be exchange-narrowed, indicating that the electron spins have some degree of mobility within the crystal lattice. Comparison of the 9- and 250-GHz spectra of the electride places an upper bound of about 1 X lo7 s-l on the rate of spin exchange. The temperature and saturation behavior of the electride at X-band are consistent with the YF-centern model, in which electrons serve to balance the charge of the complexed cations, with the center of charge of each electron at an anionic site. The strongest signal in Cs+( 18C6)ze- has nearly the sameg-anisotropy as one of the signals from the isostructural sodide, Cs+( 18C6)2Na-, indicating that at least one of the electron-trapping sites detected in the two crystal lattices is the same. The temperature dependence of the two EPR signals from Cs+(18C6)2Cs- at X-band suggests an activated process that populates two types of unpaired electron sites from a common spin-paired precursor.

Structures of (Li+)2(TMTCY)2(CH3NH-)Na-,l, Li+( 18C6)(CH3NH2)2Na-, 2, and Li+( 18C6)(CH3NH2)2Na-.( 18C6)3, 3, are reported. (TMTCY is trimethyl tricyclen and 18C6 is 18-crown-6). 1 and 2 show "normal" four-coordination to Li+ but 3 appzrentfy has Li+ in the center of a nearly planar 18C6 ring with 3 symmetry and short (1.7338,) Li+-N distances to two axial methylamine molecules. An alternative model with static or dynamic disorder, but normal distances, is in poorer agreement with the X-ray diffraction data.

A few decades ago the phrase organic materials brought to mind only insulating polymers. Organic metals and organic superconductors have dramatically changed that perception and opened the materials science field to the full range of molecular architecture manipulation that is the forte of organic chemists. In a similar vein, the term salts generally con­ veyed a picture of insulating inorganic crystals with simple cations and anions, although many organic ions were known. With the synthesis by Pedersen, Lehn, Cram, and others of large organic complexants for metal cations, new classes of salts with thousands of different complex ions became available ( 1-7). When a suitable non-reducible organic complexant, L, is combined with an alkali metal, M, the formation of the complexed alkali cation, M+L, releases an electron. This electron can either combine with an alkali metal to form the alkali metal anion, M-, or become trapped in the solvent or in the ionic lattice to form the solvated electron, or a crystalline electride, respectively. Crystalline electrides sometimes behave as saits, in which the electrons are localized in the vicinity of the anionic sites, and sometimes as expanded metals (or near metals), in which the electrons are itinerant. This review focuses on the optical, magnetic, and electronic properties of these unusual new compounds (8, 8a-f).

Transition-metal nitrides have been synthesized by heating nanoscale metal particles under flowing N2(g) or NH3(g). In some cases reaction temperatures are significantly lower than those required by conventional heating procedures. Nanoscale metal particles of Mo, Nb, Ta, Fe−Mo, Fe−Nb, and Cu−Nb were prepared by reduction of the respective metal chloride or mixture of chlorides with the sodide, [K+(15-crown-5)2]Na-, in dimethyl ether solution. The previously characterized nitrides that were prepared (with synthesis conditions indicated) include γ-Mo2N (800 °C, N2) and Mo2N (720 °C, N2), Ta3N5 (650 °C, NH3), Fe3Mo3N (>650 °C, N2), and a mixture of niobium nitride phases (800 °C, N2). A previously unreported phase has been found in the Ba−Nb−N system.

Electron transfer from an alkali metal to a suitable complexant for the cation can yield crystalline ionic solids that contain the complexed cation and either an alkali metal anion (alkalide) or a trapped electron (electride). The nature and properties of electrides are emphasized in this paper. When the organic complexant contains aromatic groups, the anionic species is an aromatic radical anion. Preliminary work on the addition of alkali metals to LOGEAs (large organic globular electron acceptors) is described and strategies for the synthesis of mixed electride-anion compounds are considered.

Electrides are materials in which alkali metals (Li through Cs) ionize to form bound alkali cations and “excess” electrons. The electrons reside in large cavities or channels or both in the host lattice. We report here the first synthesis of thermally stable inorganic electrides with cation-to-electron ratios of 1:1 as in organic electrides. Although alkali metal adducts to alumino-silicate zeolites are well known, the cation-to-electron ratio is generally 3:1 or greater because these zeolites contain alkali cations prior to incorporation of the alkali metal. In this work, two pure silica zeolites, ITQ-4and ITQ-7, with pore diameters of ∼7 A, absorb up to 40 wt % cesium from the vapor phase (even at room temperature). The other alkali metals (except Li) can also be introduced at elevated temperatures. The optical and magnetic properties of the cesium-loaded samples suggest ionization to form Cs+ and e- with substantial electron-spin pairing. The metal-loaded samples are stable to at least 100 °C and are a...

Electrides are ionic solids with cavity-trapped electrons, which serve as the anions. Localization of electrons in well-defined trapping sites and their mutual interactions provide early examples of quantum confinement, a subject of intense current interest. We synthesized the first crystalline electride, Cs(+)(18-crown-6)(2)e(-), in 1983 and determined its structure in 1986; seven others have been made since. This Account describes progress in the synthesis of both organic and inorganic electrides and points to their promise as new electronic materials. Combined studies of solvated electrons in alkali metal solutions and the complexation of alkali cations by crown ethers and cryptands made electride synthesis possible. After our synthesis of crystalline alkalides, in which alkali metal anions and encapsulated alkali cations are present, we managed to grow crystalline electrides from solutions that contained complexed alkali cations and solvated electrons. Electride research is complicated by thermal instability. Above approximately -30 degrees C, trapped electrons react with the ether groups of crown ethers and cryptands. Aza-cryptands replace ether oxygens with less reactive tertiary amine groups, and using those compounds, we recently synthesized the first room-temperature-stable organic electride. The magnetic and electronic properties of electrides depend on the geometry of the trapping sites and the size of the open channels that connect them. Two extremes are Cs(+)(15-crown-5)(2)e(-) with nearly isolated trapped electrons and K(+)(cryptand 2.2.2)e(-), in which spin-pairing of electrons in adjacent cavities predominates below 400 K. These two electrides also differ in their electrical conductivity by nearly 10 orders of magnitude. The pronounced effect of defects on conductivity and on thermonic electron emission suggests that holes as well as electrons play important roles. Now that thermally stable organic electrides can be made, it should be possible to control the electron-hole ratio by incorporation of neutral complexant molecules. We expect that in further syntheses researchers will elaborate the parent aza-cryptands to produce new organic electrides. The promise of electrides as new electronic materials with low work functions led us and others to search for inorganic electrides. The body of extensive research studies of alkali metal inclusion in the pores of alumino-silicate zeolites provided the background for our studies of pure silica zeolites as hosts for M(+) and e(-) and our later use of nanoporous silica gel as a carrier of high concentrations of alkali metals. Both systems have some of the characteristics of inorganic electrides, but the electrons and cations share the same space. In 2003, researchers at the Tokyo Institute of Technology synthesized an inorganic electride that has separated electrons and countercations. This thermally stable electride has a number of potentially useful properties, such as air-stability, low work function, and metallic conductivity. Now that both organic and inorganic electrides have been synthesized, we expect that experimental and theoretical research on this interesting class of materials will accelerate.