Hydride ion as a two-electron donor in a nanoporous crystalline semiconductor 12CaO.7Al2O3

The 12CaO.7Al2O3 (C12A7) crystal with a nanoporous lattice framework exhibits high electrical conductivity with an activation energy of approximately 1.5 eV when equilibrated in a hydrogen atmosphere above approximately 800 degrees C. The high conductivity is preserved in a quenched state below approximately 600 degrees C with a reduced activation energy of approximately 0.8 eV. Such complex behavior in electrical conductivity is associated with incorporation of hydride ions (H-) in cages of the lattice framework. Electromotive force measurements reveal that the major carrier for the conductivity is electron with a small contribution by proton (H+), ruling out the possibility of direct intercage migration of the H- ion. A combination of these observations with the ab initio calculations leads to the conclusion that the electrons are thermally generated from the H- ion by the dissociation into two electrons and an proton, which is further converted to an OH- ion via reaction with an extraframework oxide ion (O2-). The energy difference between the initial (H- + O2-) and the final (2e- + OH-) states as evaluated by the theoretical calculation is as small as approximately 1 eV, which agrees well with an experimentally obtained enthalpy change, approximately 1.4 eV. Thus, internal equilibration between the extraframework hydrogen and the oxygen species is responsible for the thermal generation of the carrier electron. It is also suggested that the same conductive (2e- + OH-) state is reached by the photoirradiation of H- -containing C12A7. In this case the photoionization of H- forms an electron and an Ho atom, which then forms an OH- ion and another electron with thermal assistance. The persistence of photoinduced conductivity is explained by the slow kinetics of the reverse process at room temperature.     

Hydride ion as photoelectron donor in microporous crystal

Atomic hydrogen (H0) and trapped electrons generated by UV illumination (lambda approximately 330 nm) at 4 K were observed using electron paramagnetic resonance (EPR) in a 12CaO.7Al2O3 (C12A7) crystal heated in a hydrogen atmosphere. The concentration ratio of generated H0 to the electrons encaged in the subnanometer-sized cages of C12A7 (F+ centers) is almost 1:1, providing direct evidence that a hydride ion, H-, accommodated in the cage by the heat treatment was dissociated to a pair of an H0 and an electron by a UV photon: H- --> H0 + e- (F+). After annealing at 300 K, H0 was completely annihilated, while approximately 60% of the trapped electrons survived. The remaining electrons can hop between neighboring cages and give electrical conductivity to C12A7. The hyperfine splitting of the EPR spectrum of H0 in C12A7 (48.6 mT) is 4% smaller than that of the neutral hydrogen atom (50.6 mT), implying that H0 is trapped at the interstitial sites among the cages.     

Polyhedral boranes and elemental boron: direct structural relations and diverse electronic requirements.

Details of the electronic and structural connections between macropolyhedral boranes and elemental boron are reported. The nature of electron deficiency in the beta-rhombohedral polymorph of boron is analyzed by using a molecular fragments approach with boranes as model systems. The B57H36 molecule constructed from such an approach has three more electrons than mandated by the electron-counting rules (Balakrishnarajan, M. M.; Jemmis, E. D. J. Am. Chem. Soc. 2000, 122, 456. Jemmis, E. D.; Balakrishnarajan, M. M.; Pancharatna, P. D. J. Am Chem. Soc. 2001, 123, 4313-4323.) devised for macropolyhedral boranes. This is also confirmed by electronic structure calculations at the extended Hückel and B3LYP/6-31G levels. The aromaticity of this B57H36(3+) molecule is on par with the most stable B12H12(2-) itself, as revealed by nuclear independent chemical shift calculations. The B57 skeleton can be made electron precise by adopting a nido arrangement by eliminating an atom from the closo skeleton, so that three valence electrons will be removed. The exact site of elimination, governed by thermodynamic factors, necessitates the removal of a boron atom from any of the six symmetrically equivalent B[13] sites in the unit cell. This leads to partial occupancies, which causes disorder in packing, as revealed by X-ray structure studies. The rest of the boron atoms are distributed in icosahedral B12 fragments, whose two-electron deficiency is satisfied by the capping of extra atoms, distributed statistically in the interstitial sites. These results show that the three-dimensional network of the idealized beta-rhombohedral unit cell is not stable, unlike the electron-precise carbon polymorphs such as diamond and graphite. Thus, disorder in the form of partial occupancies, interstitial atoms, alien atoms, etc., is necessary for electron sufficiency and hence for the stability of this polymorphic form. Through these ingenious steps, all components of the unit cell attain electron sufficiency, which explains the high thermodynamic stability of the polymorph. The connection established between boranes and elemental boron in terms of their structure and distribution of electrons has important implications in understanding the structure of boron-rich solids and new strategies to utilize their diverse and technologically important properties.     

Light-induced charge separation in anatase TiO2 particles

Ultraviolet light-induced electron-hole pair excitations in anatase TiO(2) powders were studied by a combination of electron paramagnetic resonance and infrared spectroscopy measurements. During continuous UV irradiation in the mW.cm(-2) range, photogenerated electrons are either trapped at localized sites, giving paramagnetic Ti(3+) centers, or remain in the conduction band as EPR silent species which may be observed by their IR absorption. Using low temperatures (90 K) to reduce the rate of the electron-hole recombination processes, trapped electrons and conduction band electrons exhibit lifetimes of hours. The EPR-detected holes produced by photoexcitation are O(-) species, produced from lattice O(2-) ions. It is found that under high vacuum conditions, the major fraction of photoexcited electrons remains in the conduction band. At 298 K, all stable hole and electron states are lost from TiO(2). Defect sites produced by oxygen removal during annealing of anatase TiO(2) are found to produce a Ti(3+) EPR spectrum identical to that of trapped electrons, which originate from photoexcitation of oxidized TiO(2). Efficient electron scavenging by adsorbed O(2) at 140 K is found to produce two long-lived O(2)(-) surface species associated with different cation surface sites. Reduced TiO(2), produced by annealing in vacuum, has been shown to be less efficient in hole trapping than oxidized TiO(2).     

Modification of mesoporous TiO2 electrodes with cross-linkable B12 derivatives

The modification of mesoporous TiO2 film electrodes with vitamin B12 derivatives (e.g., 1, 2, or 3) yields electrodes with interesting sensing and electrocatalytic properties. So far, only coordinative bonding between the B12 derivatives and the metal oxide surface was used, and B12 was lost under conditions of extended electrocatalysis [1. Schulthess, P.; Ammann, D.; Simon, W.; Caderas, C.; Stepanek, R.; Krautler, B. Helv. Chim. Acta 1984, 67 (4), 1026-1032. 2. Mayor, M.; Scheffold, R.; Walder, L. Helv. Chim. Acta 1997, 80 (4), 1183-1189. 3. Stepanek, R. Ph.D.; ETH: Zürich, 1987]. (1-3) We report here on a procedure that yields highly improved stabilities of the electrocatalysts toward reductive expulsion from the mesopores. It is based on cross-linking the B12 derivatives (4 or 5) equipped with multiple reaction sites in the TiO2 mesopores. The cross-linkers are multiple functionalized, one of them assisting the electron transfer from TiO2 to the Co centers via redox shuttling. The modified electrodes show high electrocatalytic reactivity toward organic halides and highly improved stability.     

Sudden, "step" electron capture by conjugated polymers

Data showing significant time-resolution-limited "step" capture of electrons following radiolysis by 7 - 10 ps electron pulses in a series of different length and different concentration conjugated polyfluorene polymers in tetrahydrofuran (THF) are presented. At the highest concentration, ～48 mM in repeat units for lengths from 20 to 133 fluorenes, ～30% of the electrons formed during pulse radiolysis were captured in the step, with a constant efficiency per repeat unit. Step capture per repeat unit (q = 6.9 M(-1)) is 60% of the presolvated electron capture efficiency previously reported for biphenyl in THF, giving capture per polymer molecule 12-80 times larger than that for biphenyl at the same concentration. This increase in capture efficiency is large compared to the rate constant per repeat unit for diffusion-limited electron attachment to the same molecules, which is 13% of that of a single unit of fluorene. Plausible mechanisms of this fast capture are explored. It is shown that both capture of quasi-free and localized presolvated electrons can adequately explain the observations. The large yield of radical anions at low concentration of polyfluorene enables observation of subsequent chemistry on the picosecond time scale in these systems, which would otherwise been limited by diffusional attachment to the nanosecond regime.     

Low-energy electron diffraction and induced damage in hydrated DNA

Elastic scattering of 5-30 eV electrons within the B-DNA 5'-CCGGCGCCGG-3' and A-DNA 5'-CGCGAATTCGCG-3' DNA sequences is calculated using the separable representation of a free-space electron propagator and a curved wave multiple scattering formalism. The disorder brought about by the surrounding water and helical base stacking leads to a featureless amplitude buildup of elastically scattered electrons on the sugar and phosphate groups for all energies between 5 and 30 eV. However, some constructive interference features arising from diffraction are revealed when examining the structural waters within the major groove. These appear at 5-10, 12-18, and 22-28 eV for the B-DNA target and at 7-11, 12-18, and 18-25 eV for the A-DNA target. Although the diffraction depends on the base-pair sequence, the energy dependent elastic scattering features are primarily associated with the structural water molecules localized within 8-10 A spheres surrounding the bases and/or the sugar-phosphate backbone. The electron density buildup occurs in energy regimes associated with dissociative electron attachment resonances, direct electronic excitation, and dissociative ionization. Since diffraction intensity can be localized on structural water, compound H2O:DNA states may contribute to energy dependent low-energy electron induced single and double strand breaks.     

Electron pairing in one‐dimensional anharmonic crystal lattices

We show that when anharmonicity is added to the electron–phonon interaction it facilitates electron pairing in a localized state. Such localized state appears as singlet state of two electrons bound with the traveling local lattice soliton distortion, which survives when Coulomb repulsion is included. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Electron-rich rods as building blocks for Sb strips and Te sheets.

We analyze the bonding in a number of networks of heavy main group elements comprised of finite-length linear chains fused at right angles. Isolated linear chain building blocks may be understood easily by analogy with three-orbital four-electron "hypervalent" bonding picture in such molecules as I(3)(-) and XeF(2). After deriving the appropriate electron-counting rules for such linear units, we proceed in an aufbau to fuse these chains into simple (and not so simple) infinite networks. It is proposed that (a) infinite Sb(3) ribbons of vertex sharing squares are stable for an electron count of 20 electrons per three atoms (i.e., ); (b) sidewise fused Sb double ribbons are stable for an electron count of 38 electrons per six atoms (i.e., ); (c) Sb(4) strips cut from a square lattice are stable at the electron count of 24 electrons per four atoms (i.e., ); (d) Te(6) defect square sheets are stable at the electron count of 40 electrons per six atoms (i.e., ). The electronic structures of the solid-state compounds containing these networks, namely La(12)Mn(2)Sb(30), alpha-ZrSb(2), beta-ZrSb(2), Cs(3)Te(22), and Cs(4)Te(28), are elaborated. We propose preferred electron counts for two hypothetical Sb ribbons derived from the Sb(3) ribbon in La(12)Mn(2)Sb(30). A possibility of geometry distortion modulation by excess charge in lattices comprised of even-membered linear units is suggested.     

Crystal structures and in-situ formation study of mayenite electrides

Mayenite inorganic electrides are antizeolite nanoporous materials with variable electron concentration [Ca12Al14O32]2+ square5-deltaO1-delta2-e2delta- (0 < delta < or = 1), where square stands for empty sites. The oxymayenite crystal structure contains positively charged cages where loosely bounded oxide anions are located. These oxygens can be removed to yield electron-loaded materials in which the electrons behave like anions (electrides). Here, a new preparation method, which allows synthesizing powder mayenite electrides easily, is reported. Accurate structural data for the white (delta = 0) and green electride (delta approximately 0.5) are reported from joint Rietveld refinements of neutron and synchrotron X-ray powder diffraction data and also from single-crystal diffraction. The electride formation at high temperature under vacuum has been followed in-situ by neutron powder diffraction. The evolution of mayenite crystal structure, including the changes in the key occupation factor of the intracage oxide anions, is reported. Furthermore, the stability of mayenite framework in very low oxygen partial pressure conditions is also studied. It has been found that C12A7 decomposes, at 1373 K in reducing conditions, to give Ca5Al6O14 (C5A3) and Ca3Al2O6 (C3A). The kinetics of this transformation has also been studied. The fit of the transformed fraction to the classic Avrami-Erofe'ev equation gave an "Avrami exponent", n = 2, which indicates that nucleation is fast and the two-dimensional linear growth of the new phases is likely to be the limiting factor.     

Electron magnetic resonance and density functional theory study of room temperature X-irradiated β-D-fructose single crystals

Stable free radical formation in fructose single crystals X-irradiated at room temperature was investigated using Q-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR induced EPR (EIE) techniques. ENDOR angular variations in the three main crystallographic planes allowed an unambiguous determination of 12 proton HFC tensors. From the EIE studies, these hyperfine interactions were assigned to six different radical species, labeled F1-F6. Two of the radicals (F1 and F2) were studied previously by Vanhaelewyn et al. [Vanhaelewyn, G. C. A. M.; Pauwels, E.; Callens, F. J.; Waroquier, M.; Sagstuen, E.; Matthys, P. J. Phys. Chem. A 2006, 110, 2147.] and Tarpan et al. [Tarpan, M. A.; Vrielinck, H.; De Cooman, H.; Callens, F. J. J. Phys. Chem. A 2009, 113, 7994.]. The other four radicals are reported here for the first time and periodic density functional theory (DFT) calculations were used to aid their structural identification. For the radical F3 a C3 carbon centered radical with a carbonyl group at the C4 position is proposed. The close similarity in HFC tensors suggests that F4 and F5 originate from the same type of radical stabilized in two slightly different conformations. For these radicals a C2 carbon centered radical model with a carbonyl group situated at the C3 position is proposed. A rather exotic C2 centered radical model is proposed for F6.     

Antiferromagnetic phase of a 2‐D Wigner crystal

The antiferromagnetic phase of a 2‐D Wigner crystal is investigated, using a localized representation for electrons. In our model, the electrons are located at the lattice sites of a face‐centered square lattice (corresponding to bcc in the 3‐D case). This lattice may be thought of as consisting of two equivalent interpenetrating sublattices. The ground‐state energies of the antiferromagnetic phase of a 2‐D Wigner electron crystal are computed with uniform neutralizing, Gaussian‐type, and Yukawa‐type positive backgrounds in the range of r_s = 5 to 130. The role of correlation energy is suitably taken into account. The possibility of the antiferromagnetic phase of the 2‐D Wigner crystal having a square or circle as the region of occupation in momentum space is also analyzed. The low‐density region favorable for the antiferromagnetic phase of Wigner crystallization is found to be at r_s = 7.0. Our results agree well with experimental and other theoretical results for the 2‐D Wigner crystal. The structure‐dependent Wannier functions, which give proper localized representation for Wigner electrons, are constructed and employed in the calculation for the first time. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Vibrational analysis of mononitrosyl complexes in hemerythrin and flavodiiron proteins: relevance to detoxifying NO reductase

Flavodiiron proteins (FDPs) play important roles in the microbial nitrosative stress response in low-oxygen environments by reductively scavenging nitric oxide (NO). Recently, we showed that FMN-free diferrous FDP from Thermotoga maritima exposed to 1 equiv NO forms a stable diiron-mononitrosyl complex (deflavo-FDP(NO)) that can react further with NO to form N(2)O [Hayashi, T.; Caranto, J. D.; Wampler, D. A; Kurtz, D. M., Jr.; Mo?nne-Loccoz, P. Biochemistry 2010, 49, 7040-7049]. Here we report resonance Raman and low-temperature photolysis FTIR data that better define the structure of this diiron-mononitrosyl complex. We first validate this approach using the stable diiron-mononitrosyl complex of hemerythrin, Hr(NO), for which we observe a ν(NO) at 1658 cm(-1), the lowest ν(NO) ever reported for a nonheme {FeNO}(7) species. Both deflavo-FDP(NO) and the mononitrosyl adduct of the flavinated FPD (FDP(NO)) show ν(NO) at 1681 cm(-1), which is also unusually low. These results indicate that, in Hr(NO) and FDP(NO), the coordinated NO is exceptionally electron rich, more closely approaching the Fe(III)(NO(-)) resonance structure. In the case of Hr(NO), this polarization may be promoted by steric enforcement of an unusually small FeNO angle, while in FDP(NO), the Fe(III)(NO(-)) structure may be due to a semibridging electrostatic interaction with the second Fe(II) ion. In Hr(NO), accessibility and steric constraints prevent further reaction of the diiron-mononitrosyl complex with NO, whereas in FDP(NO) the increased nucleophilicity of the nitrosyl group may promote attack by a second NO to produce N(2)O. This latter scenario is supported by theoretical modeling [Blomberg, L. M.; Blomberg, M. R.; Siegbahn, P. E. J. Biol. Inorg. Chem. 2007, 12, 79-89]. Published vibrational data on bioengineered models of denitrifying heme-nonheme NO reductases [Hayashi, T.; Miner, K. D.; Yeung, N.; Lin, Y.-W.; Lu, Y.; Mo?nne-Loccoz, P. Biochemistry 2011, 50, 5939-5947 ] support a similar mode of activation of a heme {FeNO}(7) species by the nearby nonheme Fe(II).     

Dependence of electron transfer among alpha cages on the chemical compositions of zeolite LTAs including K clusters

K atoms are loaded in diluted amount into K-form LTA zeolites whose framework compositions are Al(x)Si(24-x)O(48) (6相似文献   

A bioinspired construct that mimics the proton coupled electron transfer between P680*+ and the Tyr(Z)-His190 pair of photosystem II

A bioinspired hybrid system, composed of colloidal TiO2 nanoparticles surface modified with a photochemically active mimic of the PSII chlorophyll-Tyr-His complex, undergoes photoinduced stepwise electron transfer coupled to proton motion at the phenolic site. Low temperature electron paramagnetic resonance studies reveal that injected electrons are localized on TiO2 nanoparticles following photoexcitation. At 80 K, 95% of the resulting holes are localized on the phenol moiety and 5% are localized on the porphyrin. At 4.2 K, 52% of the holes remain trapped on the porphyrin. The anisotropic coupling tensors of the phenoxyl radical are resolved in the photoinduced D-band EPR spectra and are in good agreement with previously reported g-tensors of tyrosine radicals in photosystem II. The observed temperature dependence of the charge shift is attributed to restricted nuclear motion at low temperature and is reminiscent of the observation of a trapped high-energy state in the natural system. Electrochemical studies show that the phenoxyl/phenol couple of the model system is chemically reversible and thermodynamically capable of water oxidation.     

DFT+U study of defects in bulk rutile TiO(2)

We present a systematic study of electronic gap states in defected titania using our implementation of the Hubbard-U approximation in the grid-based projector-augmented wave density functional theory code, GPAW. The defects considered are Ti interstitials, O vacancies, and H dopants in the rutile phase of bulk titanium dioxide. We find that by applying a sufficiently large value for the Hubbard-U parameter of the Ti 3d states, the excess electrons localize spatially at the Ti sites and appear as states in the band gap. At U=2.5?eV, the position in energy of these gap states are in fair agreement with the experimental observations. In calculations with several excess electrons and U=2.5?eV, all of these end up in gap states that are spatially localized around specific Ti atoms, thus effectively creating one Ti(3+) ion per excess electron. An important result of this investigation is that regardless of which structural defect is the origin of the gap states, at U=2.5?eV, these states are found to have their mean energies within a few hundredths of an eV from 0.94 eV below the conduction band minimum.     

Structure and electrons in mayenite electrides

One major goal in materials chemistry is to find inexpensive compounds with improved capabilities. Stable inorganic electrides, derived from nanoporous mayenite [Ca12Al14O32]O, are a new family that has very interesting properties such as electronic conductivity combined with transparency. However, an intriguing fundamental problem is to understand the structures of these cubic materials and to characterize their free-electron loadings. Here we report an accurate structural study for three members of the series [Ca12Al14O32]O(1-delta)e(2delta) (delta = 0, 0.15, and 0.45), from single-crystal low-temperature synchrotron X-ray diffraction. The complex structural disorder imposed by the presence of the oxide anions into the mayenite cages has been unravelled. Furthermore, the final electron density map for delta = 0.45 black mayenite has shown electron density localized into the center of the cages, which is the first experimental proof of their electride nature. The reported structural findings challenge theorists to improve predictive models in this new family of materials.     

Salt-inclusion synthesis of two new polar solids, Ba6Mn4Si12O34Cl3 and Ba6Fe5Si11O34Cl3

A new family of salt-containing, mixed-metal silicates (CU-14), Ba6Mn4Si12O34Cl3 (1) and Ba6Fe5Si11O34Cl3 (2), was synthesized via the BaCl2 salt-inclusion reaction. These compounds crystallize in the noncentrosymmetric (NCS) space group Pmc2(1) (No. 26), adopting 1 of the 10 NCS polar, nonchiral crystal classes, mm2 (C2v). The cell dimensions are a = 6.821(1) A, b = 9.620(2) A, c = 13.172(3) A, and V = 864.4(3) A3 for 1 and a = 6.878(1) A, b = 9.664(2) A, c = 13.098(3) A, and V = 870.6(3) A3 for 2. The structures form a composite framework made of the (M(4+x)Si(12-x)O34)9- (M = Mn, x = 0; M = Fe, x = 1) covalent oxide and (Ba6Cl3)9+ ionic chloride sublattices. The covalent framework exhibits a pseudo-one-dimensional channel where the extended barium chloride lattice (Ba3Cl1.5)(infinity) resides, and it consists of fused eight-membered meta-silicate rings propagating along [100] via sharing two opposite [Si2O7]6- units to form an acentric lattice. Single-crystal structure studies also reveal the ClBa4 unit adopting an interesting seesaw configuration, in which the lone pair electrons of chlorine preferentially face the oxide anions of the transition metal silicate channel, thus forming the observed polar frameworks. Similar to the synthesis of organic-inorganic hybrid materials, the salt-inclusion method facilitates a promising approach for the directed synthesis of special framework solids, including NCS compounds, via composite lattices.     

Hypervalent Bonding in One, Two, and Three Dimensions: Extending the Zintl-Klemm Concept to Nonclassical Electron-Rich Networks

We construct a theory for electron-rich polyanionic networks in the intermetallic compounds of heavy late main group elements, building a bonding framework that makes a connection to well-understood hypervalent bonding in small molecules such as XeF(4), XeF(2), and I(3)(-). What we do is similar in spirit to the analogy between the Zintl-Klemm treatment of classical polyanionic networks and the octet rule for molecules. We show that the optimal electron count for a linear chain of a heavy main group element is seven electrons per atom, six electrons per atom for a square lattice, and five electrons per atom for a simple cubic lattice. Suggestions that these electron counts are appropriate already exist in the literature. We also derive electron counts for more complicated topologies, including one-dimensional ladders and one dimensional strips cut from a square lattice. We also study pairing (Peierls) distortions from these ideal geometries as well as other deformations. The presence of s-p mixing (or its absence) plays a critical role in the propensity for pairing and, in general, in determining the geometrical and electronic structure of these phases. Hypervalent bonding goes along with the relative absence of significant s-p interaction; there is a continuum of such mixing, but also a significant difference between the second-row and heavier elements. We attribute the existence of undistorted metallic networks of the latter elements to diminished s-p mixing, which in turn is due to the contraction of less-screened s orbitals relative to p orbitals down the groups in the Periodic Table. The number of electrons in the polyanionic network may be varied experimentally. An important general principle emerges from our theoretical analysis: upon oxidation a hypervalent structure transforms into a classical one with the same lattice dimensionality, while upon Peierls distortion the hypervalent structures transform into classical ones with the lattice dimensionality reduced. Dozens of crystal structure types, seemingly unrelated to each other, may be understood using the unifying concept of electron-rich multicenter bonding. Antimonides, which are explored in great detail in the current work, conform particularly well to the set of electron counting rules for electron-rich nonclassical networks. Some deviation up and down from the ideal electron count is exhibited by known stannides and tellurides. We can also make sense of the bonding in substantially more complicated alloys, including La(12)Mn(2)Sb(30) and Tl(4)SnTe(3). The hypervalent electron counting scheme developed in this paper, along with the classical Zintl-Klemm electron counting rules, gives an easy qualitative understanding of bonding in a wide variety of intermetallic compounds of heavy main group elements.     

A "sea urchin" family of boranes and carboranes: the 6m + 2n electron rule

A new family of related borane and carborane cages has been designed computationally. These compounds obey a new electron counting rule (6m + 2n rule) rather than Wade's rule. The structures of these cages can be conceived by combining m aromatic pyramidal and n aromatic triangular units. The interstitial electrons from the m pyramids (six electrons for each unit) and the n triangles (two electrons for each unit) constitute the total 6m + 2n skeletal electrons. The greater number of skeletal electron pairs in large closo-borane cages (e.g., B32H328- or C8B24H32) achieves stabilization through the optimal occupancy of all bonding orbitals. The favorable electronic structure, the large HOMO-LUMO gaps, the large lowest positive frequencies, and the local aromaticity of the pyramidal and triangular units (as demonstrated by the large negative NICS values) of the new large closo-cages auger well for their eventual experimental realization.