Probing the Electronic Structure and Aromaticity of Pentapnictogen Cluster Anions Pn5- (Pn = P, As, Sb, and Bi) Using Photoelectron Spectroscopy and ab Initio Calculations

Reactivity of Sodium Pentaphospholide Na[cyclo-P5 ] towards C≡E (E=C, N, P) Triple Bonds

A diglyme solution of Na[cyclo-P5 ] (1) reacts with alkynes and isolobal nitriles and phosphaalkynes to afford the otherwise elusive (aza)phospholide anions 2 a-c, 4 a,b, and 6. The reaction of Na[cyclo-P5 ] with alkynes and nitriles was studied by means of DFT methods, which suggested a concerted mechanism for the formation of 2 a and 4 b. The anions 2 a-c, 4 a,b, and 6 coordinate in an η5 -fashion towards FeII to give the sandwich (aza)phosphametallocenes 3 a-c, 5 a,b and 7 in moderate to good yields. The new compounds were characterized by means of multinuclear NMR spectroscopy, single-crystal X-ray diffraction and cyclic voltammetry.

Spherical Aromaticity of Tetrahedral Pnictogens through Off-Nucleus Isotropic Magnetic Shielding

This work revealed the spherical aromaticity of some inorganic E₄ cages and their protonated E₄ H⁺ ions (E=N, P, As, Sb, and Bi). For this purpose, we employed several evaluations like (0D-1D) nucleus independent chemical shift (NICS), multidimensional (2D-3D) off-nucleus isotropic shielding σ_iso (r), and natural bond orbital (NBO) analysis. The magnetic calculations involved gauge-including atomic orbitals (GIAO) with two density functionals B3LYP and WB97XD, and basis sets of Jorge-ATZP, 6-311+G(d,p), and Lanl2DZp. The Jorge-ATZP basis set showed the best consistency. Our findings disclosed non-classical aromatic characters in the above molecules, which decreased from N to Bi cages. Also, the results showed more aromaticity in E₄ than E₄ H⁺ . The NBO analysis attributed the aromaticity in the above molecules to the residual density of the overlapping σ-bonding orbitals. So, the aromaticity in these molecules is unlike the classical aromaticity that is associated with electron delocalization. Scanning 1D σ_iso (r) variation along E-E bonds indicated a lowering in the shielding trend from N to Bi cages. The 3D results showed a similar decrease in the relative volumetric diffusion of the magnetic activity, whereas the volumetric ratio of V_1ppm /V_2ppm is almost constant for all the E₄ cages.

Structural Uniqueness of the [Nb(As5)2]5- Cluster in the Zintl Phase Cs5NbAs10

The structure of the novel Zintl phase, Cs₅NbAs₁₀, is reported for the first time. This compound crystallizes in the monoclinic P2₁/c space group (no. 14) with eight formula units per cell. The structure represents a unique atomic arrangement, constituting a new structure type with Wyckoff sequence e32. The most important structural element is the unprecedented [Nb(As₅)₂]^5- cluster anion, formed by a Nb atom enclosed between two As₅ rings. These nonaromatic cyclic species, formally [As₅]^5-, adopt an envelope conformation similar to that of cyclopentane. To date, it is only the second example of an [As₅]^5- ring with this conformation, reported in an inorganic solid-state compound. The bonding characteristics of the [Nb(As₅)₂]^5- cluster and the [As₅]^5- rings are thoroughly investigated using first-principles methods and discussed. Electronic band structure calculations on Cs₅NbAs₁₀ suggest that this compound is a semiconductor with an estimated band gap of ca. 1.4 eV.

Laser Ablation Generation of Antimony Selenide Clusters: Laser Desorption Ionization (LDI) Quadrupole Ion Trap Time of Flight Mass Spectrometry

The binary system Sb-Se was studied via laser ablation using antimony-selenium mixtures made from powdered elements in various ratios generating new Sb_mSe_n clusters. The results show that in addition to Sb_m⁺ (m = 1-8) and Se_n⁺ (n = 2-9) clusters, a series of Sb_mSe_n⁺ clusters such as SbSe_1-8⁺, Sb₂Se_1-6⁺, Sb₃Se_1-5⁺, Sb₄Se_1-3⁺, and Sb₅Se_1,2⁺ is generated. In addition, some low intensity oxidized clusters like Se₆O₂⁺, Se₇O₂⁺, and SbSe_2-6O₅⁺ and partially hydroxylated clusters (SbSeO₂H₇⁺, SbSe₅O₄H⁺) are also formed. In total, 24 new antimony selenide clusters were generated. The knowledge gained can contribute to the elucidation of the structure of Sb_mSe_n glasses. Graphical Abstract.

Brimstone chemistry under laser light assists mass spectrometric detection and imaging the distribution of arsenic in minerals

Singly charged As2n+1 ion clusters (n = 2-11) were generated from elemental arsenic by negative-ion laser-ablation mass spectrometry. The overall abundance of the gaseous As ions generated upon laser irradiation was enhanced nearly a hundred times when As-bearing samples were admixed with sulfur. However, sulfur does not act purely as an inert matrix: irradiating arsenic-sulfur mixtures revealed a novel pathway to generate and detect a series of [AsSn]- clusters (n = 2-6). Intriguingly, the spectra recorded from As2O3, NaAsO2, Na3AsO4, cacodylic acid and 3-amino-4-hydroxyphenylarsonic acid together with sulfur as the matrix were remarkably similar to that acquired from an elemental arsenic and sulfur mixture. This result indicated that arsenic sulfide cluster-ions are generated directly from arsenic compounds by a hitherto unknown pathway. The mechanism of elemental sulfur extracting chemically bound arsenic from compounds and forming [AsSn]- clusters is enigmatic; however, this discovery has a practical value as a general detection method for arsenic compounds. For example, the method was employed for the detection of As in its minerals, and for the imaging of arsenic distribution in minerals such as domeykite. LDI-MS data recorded from a latent image imprinted on a piece of paper from a flat mineral surface, and wetting the paper with a solution of sulfur, enabled the localization of arsenic in the mineral. The distribution of As was visualized as false-color images by extracting from acquired data the relative intensities of m/z 139 (AsS2-) and m/z 171 (AsS3-) ions.

Long-lived excited states in metal clusters

Long-lived excited states may exist only in metal clusters with a weak coupling between the electronic and geometric structure.

Joint experimental and theoretical studies of the surprising stability of the aryl pentazole upon noncovalent binding to β-cyclodextrin

Large enhancement in the thermal stability of aryl pentazole is confirmed experimentally and theoretically through the formation of a host–guest complex with β-cyclodextrin

Negative ion photoelectron spectroscopy of P2N3-: electron affinity and electronic structures of P2N3˙

We report here a negative ion photoelectron spectroscopy (NIPES) and ab initio study of the recently synthesized planar aromatic inorganic ion P2N3-, to investigate the electronic structures of P2N3- and its neutral P2N3˙ radical. The adiabatic detachment energy of P2N3- (electron affinity of P2N3˙) was determined to be 3.765 ± 0.010 eV, indicating high stability for the P2N3- anion. Ab initio electronic structure calculations reveal the existence of five, low-lying, electronic states in the neutral P2N3˙ radical. Calculation of the Franck-Condon factors (FCFs) for each anion-to-neutral electronic transition and comparison of the resulting simulated NIPE spectrum with the vibrational structure in the observed spectrum allows the first four excited states of P2N3˙ to be determined to lie 6.2, 6.7, 11.5, and 22.8 kcal mol-1 above the ground state of the radical, which is found to be a 6π-electron, 2A1, σ state.

Search for aromatic anions in the P2E3− (E = N, P, As, Sb, Bi) series

Nine aromatic five-membered rings were computationally characterized in the P₂E₃⁻ (E = N, P, As, Sb, Bi) series of anions.

Adding a new dimension to the chemistry of phosphorus and arsenic

We predict two novel highly stable free-standing 2D monolayers of P and As alloyed with Cu (Cu₂X) that have exotic hypercoordination motifs. These are the first predicted hexacoordinate P and planar hexacoordinate As extended alloy sheets.

Study on electronic structures and properties of neutral and charged arsenic sulfides [As n S3 ((-1,0,+1)), n =1-6] with the Gaussian-3 scheme

The structures and energies of neutral and charged arsenic sulfides As n S3 ((-1,0,+1)) (n = 1-6) were studied systematically with the G3 method. The ground-state structures of these species are reported. The ground-state structures of As n S3 with n ≥ 4 can be considered as resulting from the replacement of an As atom of the ground-state structure of neutral As n+1S2 by an S atom. In neutral As n S3, the character of sulfur bonding is edge-bridging. The ground-state structures of anion As n S3 (-) sometimes differ from their corresponding neutral structures. In such case, they exhibit a terminal sulfur atom. The ground-state structures of cationic As n S3 (+) are also sometimes different from the corresponding neutral ones. There, sulfur bonding can exhibit face-capping and arsenic can be four-fold coordinated. The potential energy surfaces of As4S3 (+) and As5S3 (+) are very flat and co-existence of various isomers of As4S3 (+) and As5S3 (+) is possible. Reliable adiabatic electron affinities (AEAs) and adiabatic ionization potentials (AIPs) of As n S3 are predicted. There are odd-even alternations in both AEAs and AIPs as a function of size. In addition, the reliable vertical detachment energies (VDEs) and vertical ionization potentials (VIPs) are presented. The dissociation energies (DEs) of S (and/or its ion S((-/+))) from As n S3 species and their ions were calculated to examine relative stabilities. The hardnesses and HOMO-LUMO gaps of As n S3 (n = 1-6) were evaluated and used to discuss relative chemical reactivity.

Experimental and theoretical investigation on binary anionic clusters of Al(m)Bi(n)(-)

Al(m)Bi(n)(-) (m = 1-12; n = 1-4) binary cluster anions are generated by laser ablation of a sample composed of Al and Bi, and studied by reflectron time-of-flight mass spectrometry (RTOF-MS) in the gas phase. Some clusters with magic numbers are present in the mass spectrum. The structures of Al(m)Bi(n)(-) (m + n <or=7) clusters are investigated with the density functional theory (DFT) method and the most likely structures are obtained. The calculations of the binding energy (BE), energy gain (Delta) and HOMO-LUMO gaps confirm that the Al(2)Bi(3)(-) cluster has a very stable structure, which agrees well with the experimental results. It is further established that Al(2)Bi(3)(-) can be considered as a gas-phase Zintl analogue that follows Wade's rules and is the analogue of Ga(2)Bi(3)(-) and Sn(5)(2-) Zintl ions.

Electronic structure and bonding in neutral and dianionic boradiphospholes: R'BC2P2R2 (R = H, tBu, R' = H, Ph)

Classical and non-classical isomers of both neutral and dianionic BC(2)P(2)H(3) species, which are isolobal to Cp(+) and Cp(-), are studied at both B3LYP/6-311++G(d,p) and G3B3 levels of theory. The global minimum structure given by B3LYP/6-311++G(d,p) for BC(2)P(2)H(3) is based on a vinylcyclopropenyl-type structure, whereas BC(2)P(2)H(3)(2-) has a planar aromatic cyclopentadienyl-ion-like structure. However, at the G3B3 level, there are three low-energy isomers for BC(2)P(2)H(3): 1) tricyclopentane, 2) nido and 3) vinylcyclopropenyl-type structures, all within 1.7 kcal mol(-1) of each other. On the contrary, for the dianionic species the cyclic planar structure is still the minimum. In comparison to the isolobal Cp(+) and H(n)C(n)P(5-n)(+) isomers, BC(2)P(2)H(3) shows a competition between pi-delocalised vinylcyclopropenyl- and cluster-type structures (nido and tricyclopentane). Substitution of H on C by tBu, and H on B by Ph, in BC(2)P(2)H(3) increases the energy difference between the low-lying isomers, giving the lowest energy structure as a tricyclopentane type. Similar substitution in BC(2)P(2)H(3)(2-) merely favours different positional isomers of the cyclic planar geometry, as observed in 1) isoelectronic neutral heterodiphospholes EtBu(2)C(2)P(2) (E = S, Se, Te), 2) monoanionic heterophospholyl rings EtBu(2)C(2)P(2) (E = P(-), As(-), Sb(-)) and 3) polyphospholyl rings anions tBu(5-n)C(n)P(5-n) (n = 0-5). The principal factors that affect the stability of three-, four-, and five-membered ring and acyclic geometrical and positional isomers of neutral and dianionic BC(2)P(2)H(3) isomers appear to be: 1) relative bond strengths, 2) availability of electrons for the empty 2p boron orbital and 3) steric effects of the tBu groups in the HBC(2)P(2)tBu(2) systems.

Theoretical study on structures and aromaticities of P5(-) anion, [Ti (eta(5)-P5)]- and sandwich complex [Ti(eta(5)-P5)2]2-

The equilibrium geometries, energies, harmonic vibrational frequencies, and nucleus independent chemical shifts (NICSs) of the ground state of P5(-) (D(5h)) anion, the [Ti (eta(5)-P5)]- fragment (C(5v)), and the sandwich complex [Ti(eta(5)-P5)2]2- (D(5h) and D(5d)) are calculated by the three-parameter fit of the exchange-correlation potential suggested by Becke in conjunction with the LYP exchange potential (B3LYP) with basis sets 6-311+G(2d) (for P) and 6-311+G(2df) (for Ti). In each of the three molecules, the P-P and Ti-P bond distances are perfectly equal: five P atoms in block P5(-) lie in the same plane; the P-P bond distance increases and the Ti-P bond distance decreases with the order P5(-), [Ti(eta(5)-P5)2]2-, and [Ti (eta(5)-P5)]-. The binding energy analysis, which is carried out according to the energy change of hypothetic reactions of the three species, predicts that the three species are all very stable, and [Ti (eta(5)-P5)]- (C(5v)), more stable than P5(-) and [Ti(eta(5)-P5)2]2- synthesized in the experiment, could be synthesized. NICS values, computed for the anion and moiety of the three species with GIAO-B3LYP, reveal that the three species all have a larger aromaticity, and NICS (0) of moiety, NICS (1) of moiety, and minimum NICS of the inner side of ring P5 plane in magnitude increase with the order P5(-), [Ti(eta(5)-P5)2]2-, and [Ti (eta(5)-P5)]-. By analysis of the binding energetic and the molecular orbital (MO) and qualitative MO correlation diagram, and the dissection of total NICS, dissected as NICS contributions of various bonds, it is the main reason for P5(-) (D(5h)) having the larger aromaticity that the P-P sigma bonds, and pi bonds have the larger diatropic ring currents in which NICS contribution are negative, especially the P-P sigma bond. However, in [Ti (eta(5)-P5)]- (C(5v)) and [Ti(eta(5)-P5)2]2- (D(5h), and D(5d)), the reason is the larger and more negative diatropic ring currents in which the NICS contributions of P-P pi bonds and P5-Ti bonds including pi, delta, and sigma bonds, especially P5-Ti bonds, are much more negative and canceled the NICS contributions of P and Ti core and lone pair electrons.