Sandwich-like Complexes Research Articles

Sandwich, Triple-Decker and Other Sandwich-like Complexes of Cyclopentadienyl Anions with Lithium or Sodium Cations.

Density functional theory, DFT, calculations were carried out on complexes containing cyclopentadienyl anions and lithium or sodium cations; half-sandwich, sandwich and sandwich-like complexes (among them triple-decker ones) are analyzed. Searches performed through the Cambridge Structural Database revealed that crystal structures containing these motifs exist, mostly structures with sodium cations. The DFT calculations performed here include geometry optimization and frequency calculations of the complexes at the ωB97XD/aug-cc-pVTZ level, followed by the partitioning of the energy of interaction via the Energy Decomposition Analysis scheme, EDA, at the BP86-D3/TZ2P level. Additional calculations and analyses were performed using both the Quantum Theory of Atoms in Molecules, QTAIM, and the Natural Bond Orbital analyses, NBO. The results of this work show that the electrostatic interaction energy is the most important attractive contribution to the total interaction energy of each of the complex systems analyzed here, and that complexation itself leads to minor electron charge shifts.

Primer Exchange Reaction-Synthesized DNAzyme for the Sensitive Determination of an Oral Cancer Protein Biomarker

A novel biosensing method is reported for the fluorescence determination of an oral cancer protein biomarker using primer exchange reaction (PER)-synthesized DNAzyme. Specifically, the target protein is captured by antibody-functionalized magnetic beads and recruits antibody-nucleic acid probes through immunoreactions to form sandwich-like complexes. After magnetic separation, the nucleic acid part of the antibody-nucleic acid probe participates in the PER as a catalytic hairpin, mediating the extension of primers. The extended primer forms the complete sequence of RNA-cleaving DNAzyme to effectively catalyze the cleavage of molecular beacons and produce a significantly amplified fluorescence signal. Taking interleukin 6 as a model biomarker, the method allows quantitative determination of the target in a wide linear range from 5 fg/mL to 500 pg/mL with a detection limit of 2.3 fg/mL and shows desirable specificity and usability in biological samples. More importantly, the complete DNAzyme is synthesized by the target-powered PER, which not only ensures the detection specificity, but also enables the decrease of background signals, thus greatly improving the sensitivity. Therefore, the method may provide a valuable tool for the determination of oral cancer protein biomarkers and may expand applications of DNAzyme in biosensing.

An electrochemical genosensor for differentiation of fully methylated from fully unmethylated states of BMP3 gene

The methylation state of a part of the BMP3 gene was detected by our genosensor. This epigenetic biomarker is involved in the biomarker panel of the sDNA test, which is an FDA approved test for colorectal cancer screening. In the present genosensor, polyethyleneimine-stabilized silver nanoparticles (PEI-AgNPs) were used as a non-specific nanolabel for signal generation/amplification and lowering the limit of detection. After immobilization of capture probes and mercaptoethanol molecules on the gold electrode, a thermally treated mixture of the BMP3 targets and reporter probes was introduced to the electrode. Because of the specificity of the reporter probes for fully methylated targets, complete sandwich-like complexes are formed only with them. Therefore, such full-length double-stranded hybrids compared to fully unmethylated targets have more negative charges and can more attract positively charged PEI-AgNPs. For discrimination between methylated and unmethylated targets, electroimpedance spectroscopy and cyclic voltammetry were used for electrode modification monitoring and signal measurement. The sharp and narrow anodic peaks of cyclic voltammograms, which resulted from silver oxidation, were utilized for calibration plot analysis. The genosensor showed a linear response for the target concentration range from 1fM to 100 nM, while the detection limit for methylated and unmethylated target discrimination was 1 fM.

Dual boronate affinity nanoparticles-based plasmonic immunosandwich assay for specific and sensitive detection of ginsenosides.

Ginsenoside is a large family of triterpenoid saponins from Panax ginseng with various important biological functions. It is crucial to develop effective analytical approach for qualitative and quantitative analysis of ginsenosides. Herein, a dual boronate affinity nanoparticles-based plasmonic immunosandwich assay has been developed for analysis of ginsenosides. An imprinted Au NPs-coated glass slide was prepared via controllable oriented surface imprinting and used as specific extraction substrate for target molecules. In the meantime, Ag-cored Raman nanotags were used for specific labeling of target molecules. The MIP-based recognitions ensured the specificity of the assay, while enhanced Raman signal derived from the imprinted substrate-target-nanotags sandwich-like complexes provided high sensitivity. The proposed immunosandwich assay exhibited wide linear range (10ng/mL to 10μg/mL), high sensitive (LOD: 1.7ng/mL, LOQ: 5ng/mL) and good reproducibility (RSD: 8.6%). For real-world applications, successful quantitative analysis of ginsenoside Re in ginseng was performed. Therefore, this dual boronate affinity nanoparticles-based plasmonic immunosandwich assay holds great promise in many important applications such as pharmaceutical analysis.

Dual Molecularly Imprinted Polymer-Based Plasmonic Immunosandwich Assay for the Specific and Sensitive Detection of Protein Biomarkers.

Molecularly imprinted polymers (MIPs), which are synthesized in the presence of a template, have been widely used as antibody mimics for important applications. Through the combination with a highly sensitive detection scheme such as chemiluminescence and surface-enhanced Raman scattering (SERS), MIP-based sandwich assays have emerged as promising analytical tools for the detection of disease biomarkers. However, so far, MIPs have been used only as target-capturing probes, whereas labeling by other means was needed, which limits the application range. Herein, we present a new approach, called a dual MIP-based plasmonic immunosandwich assay (duMIP-PISA), for the specific and sensitive detection of protein biomarkers in complex biological samples. A C-terminal epitope-imprinted self-assembled gold nanoparticle monolayer-coated glass slide was prepared as a plasmonic substrate for the specific extraction of target protein, while N-terminal epitope-imprinted Raman-responsive Ag@SiO2 nanoparticles were prepared as nanotags for the specific labeling of captured protein. The formed MIP-protein-MIP sandwich-like complexes could produce a significantly enhanced SERS signal. The dual MIP-based recognitions ensured high specificity of the assay, while SERS detection provided ultrahigh sensitivity. The duMIP-PISA of neuron-specific enolase (NSE) in human serums was demonstrated, which permitted the differentiation of small cell lung cancer patients from healthy individuals. As compared to regular ELISA, the duMIP-PISA exhibited multiple merits including a simpler procedure, faster speed, lower sample volume requirement, and wider linear range. The approach well demonstrated the great potentials of MIPs and can be easily modified and extended to other protein biomarkers. Therefore, the duMIP-PISA approach holds great promise in many important applications such as disease diagnosis.

Polyazamacrocyclic copper based cyanide-bridged bimetallic sandwich-like complexes: Synthesis, crystal structure and magnetic properties

By employing three dicyanometallates as building blocks, K[Fe(bpb)(CN)2], K[Cr(bpb)(CN)2] (bpb2– = 1,2-bis(pyridine-2-carboxamido)benzenate), K[Fe(bpmb)(CN)2] (bpmb2– = 1,2-bis(pyridine-2-carboxamido)-4-methyl-benzenate) and one 14-membered polyazamacrocycle Cu(II) compound as assembling segment, three cyanide-bridged complexes {[Cu(6,13-Dihydroxylcyclam)][Fe(bpb)(CN)2]2}·2CH3OH·H2O (1), {[Cu(6,13-Dihydroxylcyclam][Cr(bpb)(CN)2]2}·2CH3OH (2) and {[Cu(6,13-Dihydroxylcyclam)][Fe(bpmb)(CN)2]2}·2H2O (3) (6,13-Dihydroxylcyclam = 6,13-Dihydroxyl-1,4,8,11-tetraazacyclotetradecane) have been successfully prepared and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis shows that all the three complexes containing the M2Cu (M = Fe, Cr) core present the neutral trinuclear sandwich-like structures, in which the central Cu(II) ion was coordinated face-to-face to the two Fe or Cr ions of the cyanide precursors functioning as a monodentate ligand through one of its two cyanide groups. Investigation over their magnetic properties reveals the antiferromagneitic and ferromagnetic coupling between the cyanide-bridged Fe(III)—Cu(II) and Cr(III)—Cu(II) ions, respectively.

Stabilization of non-standard conformations of the annulene rings in cyclobutadiene-framed [n]annulenes (n = 8, 10, 12, 14) and their beryllium sandwich-like complexes: a quantum chemical study

The structures of a series of polycyclic derivatives of [n]annulenes (n = 8, 10, 12, 14) functionalized with peripheral cyclobutadiene rings were studied using the DFT B3LYP/6-311+G(3df,2p) and M062X/6-311+G(3df,2p) methods. The compounds with n = 8 and 10 have the planar and those with n = 12, 14 saddle-shaped conformations of the central rings. Stabilization of non-standard planar forms of the hydrocarbons with central 12- and 14-membered conjugated rings may be achieved through π-complexation of C=C bonds of the cyclobutadiene fragments with beryllium atoms to afford the sandwich-like complexes with circular arrangement of beryllium centers around the perimeter of a ligand.

Vibrio parahaemolyticus detection aptasensor using surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) is a flexible tool for biological analysis due to its excellent properties for detecting wide varieties of target biomolecules including pathogenic bacteria. In the present work, a highly selective and sensitive SERS-based aptasensor for the detection of Vibrio parahaemolyticus has been developed. An effective SERS substrate was designed and fabricated by synthesis of SiO2@Au core/shell nanoparticles (NPs). To selectively detect V. parahaemolyticus, we employed aptamer 1 (apt 1) immobilized on the surface of SiO2@Au core–shell NPs. The Raman signal intensity is from a cyanine dye 3 (Cy3) modified aptamer 2 (apt 2), which binds to the target the same as SiO2@Au-apt 1. In the presence of the target, SiO2@Au-apt 1-target-apt 2-Cy3 sandwich-like complexes form due to the high affinity and specificity of the aptamer for V. parahaemolyticus. Under optimal conditions, the correlation between the SERS signal and the V. parahaemolyticus concentration is linear within a range of 10–106 cfu mL−1, with a limit of detection of 10 cfu mL−1. This technique enables a straightforward SERS-based bioassay for quantitative detection of other pathogenic bacteria.

Salmonella typhimurium detection using a surface-enhanced Raman scattering-based aptasensor

Surface-enhanced Raman spectroscopy (SERS) has been used in a variety of biological applications due to its high sensitivity and specificity. Here, we report a SERS-based aptasensor approach for quantitative detection of pathogenic bacteria. A SERS substrate bearing Au@Ag core/shell nanoparticles (NPs) is functionalized with aptamer 1 (apt 1) for the capture of target molecules. X-rhodamine (ROX)-modified aptamer 2 (apt 2) is used as recognition element and Raman reporter. Salmonella typhimurium specifically interacted with the aptamers to form Au@Ag-apt 1-target-apt 2-ROX sandwich-like complexes. As a result, the concentration of S. typhimurium was determined using this developed aptasensor structure, and a calibration curve is obtained in the range of 15 to 1.5×106cfu/mL with a limit of detection of 15cfu/mL. Our method was successfully applied to real food samples, and the results are consistent with the results obtained using plate counting methods. We believe that the developed method shows potential for the rapid and sensitive detection of pathogenic bacteria in food safety assurance.

Solvatochromic and application in dye-sensitized solar cells of sandwich-like Cd(II) complexes: supramolecular architectures based on N(1),N(3)-bis[(6-methoxypyridin-2-yl)methylene]benzene-1,3-diamine.

A novel polydentate Schiff base ligand N(1),N(3)-bis[(6-methoxypyridin-2-yl)methylene]benzene-1,3-diamine (L) and its two dinuclear sandwich-like complexes {[CdL(NO3)(H2O)]·NO3}2 (1) and {[CdL(CH3CN)(H2O)]·(ClO4)2·(CH3CN)2}2 (2) were synthesized. Both C-H∙∙∙O, C-H∙∙∙N and π-π non-covalent interactions had essential roles in constructing the resulting three-dimensional supramolecular networks. L emits a more intense blue-green fluorescence emission around 493 nm than in dilute solution, exhibiting stacking-induced emission properties. Complexes 1 and 2 exhibited the dual properties of exceptional solvatochromism and fluorescence quenching towards CH3OH molecules. As these compounds could overcome the absent absorption of ruthenium complex N719 in the low wavelength region of the visible spectrum, offset the competitive visible light absorption of I3(-) and reduce the charge recombination of injected electrons, the Schiff base ligand l and complexes 1 and 2 were used as co-sensitizers in combination with N719 to investigate their effect on enhancing the performance of dye-sensitized solar cells. A short circuit current density of 14.37 mA cm(-2), an open-circuit voltage of 0.71 V and a fill factor of 0.61 corresponding to an overall conversion efficiency of 6.17% under AM 1.5 G solar irradiation were achieved when 1 was used as a co-sensitizer, which are much higher than the results obtained for dye-sensitized solar cells sensitized by N719 alone (5.06%).

Darstellung und strukturelle und spektroskopische Charakterisierung der Triiodide [M(12-Krone-4)2]I3 mit M = Na und Rb / Preparation and Structural and Spectroscopic Characterization of Triiodides [M(12-Crown-4)2]I3 with M= Na and Rb

Abstract Reddish-brown crystals of [Na(12-crown-4)2]I3 (1) and [Rb(12-crown-4)2]I3 (2) were formed through the reaction of NaI or RbI, I2 and 12-crown-4 in ethanol. Both structures are triclinic, space group P1 with Z = 2. The lattice parameters are a = 8:505(2), b = 14:280(3), c = 10:695(2) Å and α = 89:86(2)°, β = 80:00(2)° and γ = 85:90(2)°; and a = 10:694(2), b = 11:598(2), c = 12:718(2) Å and α = 71:00(2)°, β = 86:97(2)° and γ = 67:710(10)° for 1 and 2, respectively. Both crystal structures contain one independent complex cation without crystallographic symmetry. The anionic parts of both structures consist of two crystallographically independent, isolated, triiodide anions I3 - with crystallographic inversion symmetry. The cations are distorted sandwich-like complexes with two 12-crown-4 molecules surrounding the alkali metal atom in the center.

Theoretical study of the effect of resonance on π–π stacked firefly oxyluciferin dimers

Abstract Firefly oxyluciferin is a prime example in which π–π stacking interactions play an important role, by being the basis for the formation of sandwich-like oxyluciferin complexes. In the present study, we have used a theoretical methodology to further understand the effect of π–π stacking interactions in the properties of oxyluciferin molecule. More specifically, we have analysed the effect of resonance changes in oxyluciferin π–π stacking dimers. We have found that resonance changes have little effect on the ground state properties of the dimmers. More interestingly, by modulating the resonance of the dimmers we can obtain different transition energies and efficiencies. This results in changes in the degree of contributions made by the different orbital excitations that compose the excitation transition.

Synthesis, crystal structures and NIR luminescence of sandwich-like tetradentate salophen phenoxo-bridged heterotrinuclear metal complexes

Six phenoxo-bridged tetradentate salophen heterotrinuclear Zn2Ln complexes, [Ln(ZnL)2(NO3)3(CH3OH)2]·CH3OH·CH2Cl2 [Ln = Pr (1), Nd (2)] and [Ln(ZnL)2(NO3)3(CH3OH)]·CH3OH·CH2Cl2 [Ln = Eu (3), Ho (4), Er (5), and Yb (6)], have been isolated from reactions of N,N′-bis(salicylidene)-1,2-(phenylene-diamine) with Ln(NO3)36H2O and Zn(OAc)22H2O. X-ray diffraction analysis reveals that 1–6 are isomorphic with phenoxo-bridged, sandwich-like {Zn2Ln} core. Near infrared (NIR) luminescence spectra show that 6 exhibits typical emission of Yb3+ upon excitation at the ligand-centered absorption band at 357 nm.

Design and Synthesis of Enantiomerically Pure Chiral Sandwichlike Lamellar Structure: New Explorations from Molecular Building Blocks to Three-Dimensional Morphology

This article reports a pair of novel chiral sandwichlike complexes for the first time. In the two complexes, lanthanide Eu3+ ions and Na+ ions are sandwiched between Schiff base ligands, resulting in a two-dimensional plane. For both of the complexes, the intraplane and interplane interactions are utterly different. The adjacent planes are held together by weak van der Waals forces, while the single plane is formed by covalently bonded intraplane N–Eu–O, O–Eu–O, and O–Na–O atoms. On the basis of this characteristic information derived from their molecular building blocks, we studied three-dimensional morphology which has good agreement with expected lamellar morphology. Furthermore, to examine the chiroptical and stable activities, the CD spectra were investigated in the solution of methanol and five different solid forms.

Which kind of binuclear sandwich-like compound is more stable in M2(η4 − E4)2 (M = B, Al, Ga; E = XYZ = BCO, BNN, CBO), the metal centered or the non-metal centered sandwich-like complex?

To investigate the difference between the non-metal centered and metal centered binuclear sandwich-like compounds, a series of novel non-metal centered and metal centered binuclear sandwich-like complexes M2(η4−E4)2 (M=B, Al, Ga; E=XYZ=BCO, BNN, CBO) have been studied by the density functional theory (DFT). The bonding characters of each species are discussed by the natural bond orbital (NBO), atoms in molecules (AIM) and molecular orbitals (MO) analysis. The aromaticity of the stable structures is analysized by the criterion of the nucleus-independent chemical shifts (NICS). The thermodynamic stabilities of M2(η4−E4)2 are investigated by the dissociation reactions and isomerization reactions. It is found that the E42- rings as the ligands can form the stable binuclear sandwich-like complexes, and the synthesis of M2(η4−E4)2 in future is desirable. Moreover, the non-metal centered sandwich-like compounds are more stable than the metal centered ones and the CBO-based compounds are energetically favored than their BCO-based isomers. The main difference of the bonding nature between the non-metal centered and metal centered binuclear sandwich-like complex is the interaction between the centered atoms and the ligands: one is predominantly covalent and the other is mainly ionic.

Synthesis, Properties of Gadolinium Double-Decker Sandwich-Type Complex Containing Tetrabenzoporphyrin Ligand

A novel gadolinium double-decker sandwich-type complex with tetrabenzoporphyrin (TBP) ligands-Gd(TBP)2 was synthesized by the reaction of porphyrin 1 with Gd(acac)3. nH2O in boiling 1, 2, 4-Tcb for 15~17 h under Ar. Its structure is characterized byUv-Vis-NIR and HR-MS. The spectroscopic properties show that the longest-wavelength visible band (600-800 nm) and the strong near-IR absorption band centered near 1340 nm of Gd (TBP)2 complex are obviously red-shifted due to the extension of the π conjugated systems derived from the linear benzoannulation in the TBP ring. The magnetic studies also indicate that the observed value of χMT of Gd(TBP)2 complex is close to the combined value of Gd(III) and porphyrin radical anion at room temperature, and antiferromagnetic interaction that possibly results from the intramolecular spin exchange between the porphyrin π-radical electron, and the gadolinium f unpaired electrons dominates its magnetic properties over the whole temperature range. Since the first report of bis(porphyrinato) metal complexes M(Por)2 such as a cerium(IV) bisporphyrinate, Ce(TPP)2 and hydrogen praseodymium(III), PrH(TPP)2 in 1983[1], sandwich-type rare earth complexes with porphyrin ligands have received increasing attentions due to the unusual physical, spectroscopic, redox, electron transfer, and/or conductivity properties resulting from their strong π-π interactions[2-4]. Whereas the chemistry and properties of homoleptic sandwich complexes containing the same pophyrinato ligands of various lanthanide, actinides and group 4 transition metals have been extensively studied[5-6], actually all of them are confined to the sandwich-type complexes containing meso-substituted porphyrin ligands except for octaethylporphyrin (OEP) or octamethylporphyrin (OMP). Little is known about sandwich-like complexes with aromatic ring-fused porphyrin ligands that contain a more delocalized π system. In this paper, we will describe the preparation of a novel gadolinium homoleptic double-decker sandwich-type complex with tetrabenzoporphyrin (TBP) ligand (see Fig.1) as well as their spectroscopic characterization and magnetic studies.

Theoretical studies on all-metal binuclear sandwich-like complexes M2(η4-E4)2 (M=Al, Ga, In; E=Sb, Bi)

A series of all-metal binuclear sandwich-like complexes with the formula M(2)(η(4)-E(4))(2) (M=Al, Ga, In; E=Sb, Bi) was studied by density functional theory (DFT). The most stable conformer for each of the M(2)(η(4)-E(4))(2) species is the staggered one with D (4d) symmetry. The centred metal-metal bond in each M(2)(η(4)-E(4))(2) species is a covalent single bond, with the main contributors to these covalent bonds being the a(1) and e orbitals. For all these species, the interactions between the centred metal atoms and the all-metal ligands are covalent; η(4)-Sb (4) (2-) has a stronger ability to stabilize metal-metal bonds than η(4)-Bi (4) (2-). Nucleus-independent chemical shifts (NICS) values and molecular orbital (MO) analysis reveal that the all-metal η(4)-Sb (4) (2-) and η(4)-Bi (4) (2-) ligands in M(2)(η(4)-E(4))(2) possess conflicting aromaticity (σ antiaromaticity and π aromaticity), which differs from the all-metal multiple aromatic unit Al (4) (2-). In addition, all of these M(2)(η(4)-E(4))(2) species are stable according to the dissociation energies of M(2)(η(4)-E(4))(2) → 2 M(η(4)-E(4)) and M(2)(η(4)-E(4))(2) → 2 M + 2E(4), and these stable species can be synthesized by two-step substitution reactions: CpZnZnCp + 2E (4) (2-) → [E(4)ZnZnE(4)](2-) + 2Cp(-) and [E(4)ZnZnE(4)](2-) + 2 M (2) (+) → E(4)MME(4) + 2Zn(+).

The first nonmetal-centered binuclear sandwich-like complexes based on the tetraatomic species E2−4 (E = N, P, As, Sb, Bi) and boron atoms

The first nonmetal-centered binuclear sandwich-like complexes, B2(η4-E4)2 (E = CMe, N, P, As, Sb, Bi; Me = CH3), have been investigated by density functional theory (DFT) to explore whether the nonmetal element can be at the center to form stable sandwich-like complexes. The stable conformer for each species is the D4d staggered one, in which there exists strong interaction between the two boron atoms. Natural bonding orbital (NBO) analysis indicates that the boron–boron bonds are all σ single bonds, which are predicted to be derived mostly from the s and pz orbitals of the boron atoms. The boron–boron bond dissociation energies are higher than that of the Zn–Zn bond in the synthesized complex Cp*ZnZnCp* (Cp* = C5Me5; Me = CH3) suggesting that these nonmetal-centered sandwich-like complexes may be synthesized in future experiments. According to the energy decomposition analysis (EDA), the boron–boron bond is much weaker than the boron–ligand bond and the ability of the E2−4 ligands to stabilize the boron–boron bonds is in the order of N2−4 > P2−4 > As2−4 > Sb2−4 > Bi2−4. Nucleus-independent chemical shift (NICS) values reveal that E2−4 (E = CMe, N, P, As, Sb) rings of B2(η4-E4)2 exhibit characteristics of π aromaticity at 1.0 A above the ring center, whereas Bi2−4 rings of B2(η4-Bi4)2 possess antiaromaticity. In addition, the differences in the bonding nature between the nonmetal-centered and metal-centered binuclear sandwich-like complexes were also investigated. In these nonmetal-centered complexes B2(η4-E4)2, the interactions between the boron atoms and the E2−4 ligands are more than half covalent, while in the metal-centered binuclear sandwich-like complexes, the metal–ligand interactions are mainly ionic.

The first binuclear sandwich-like complexes based on the aromatic tetraatomic species

The first binuclear sandwich-like complexes based on the aromatic tetraatomic species with formula M(2)(η(4)-E(4))(2) (M = Al, Ga; E = N, P, As) have been studied by density functional theory (DFT). The stable conformer for each M(2)(η(4)-E(4))(2) is the staggered one with D(4d) symmetry except for Ga(2)(η(2)-N(4))(2) with C(2v) symmetry. Natural bonding orbital (NBO) analysis indicates that the metal-metal bonds of Al(2)(η(4)-E(4))(2) (E = N, P, As) and Ga(2)(η(4)-E(4))(2) (E = P, As) are all σ single bonds, which are derived mostly from the s and p(z) orbitals of the metal atoms by molecular orbital (MO) analysis. For M(2)(η(4)-E(4))(2) (M = Al, Ga; E = P, As), the metal-ligand interactions are covalent, while for Al(2)(η(4)-N(4))(2) the interactions between the Al atoms and the N(4)(2-) ligands are ionic. According to the calculated dissociation energies for breaking metal-metal bonds, the Al-Al and Ga-Ga bonds are very strong indicating that these stable sandwich-like compounds Al(2)(η(4)-E(4))(2) (E = N, P, As) and Ga(2)(η(4)-E(4))(2) (E = P, As) may be synthesized in future experiments. The nitrogen-rich compounds Al(2)(η(4)-N(4))(2) and Ga(2)(η(2)-N(4))(2) may be used as potential candidates of high energy density materials (HEDMs). Nucleus-independent chemical shifts (NICS) values reveal that the E(4)(2-) rings in the Al(2)(η(4)-E(4))(2) (E = N, P, As) and Ga(2)(η(4)-E(4))(2) (E = P, As) species possess conflicting aromaticity (σ antiaromaticity and π aromaticity) and with the same ligands, the E(4)(2-) ligands in Ga(2)(η(4)-E(4))(2) have more aromaticity than those in Al(2)(η(4)-E(4))(2).

N3MN5]q: A Type of Low-Lying Sandwich-like Isomer on [N8M]q Hypersurface with (M, q) = (Ni, 0), (Co, −1), and (Fe, −2)

Recently, design and assembly of small, high-energy-density, all-nitrogen units into more complex sandwich-like forms have received growing attention. In this paper, we report a type of heterodecked sandwich-like structures [N(3)MN(5)](q) containing two odd-membered all-nitrogen rings (N(3) and N(5)) on the hypersurface of [N(8)M](q) [(M, q) = (Ni, 0), (Co, -1), (Fe, -2)]. At the B3LYP/6-311+G(d) level, the new isomers are energetically more stable than the previously reported homodecked sandwich-like isomers [N(4)MN(4)](q) based on the even-membered all-nitrogen ring N(4)(2-). In particular, the eta(3)-eta(2) (eta(3)-eta(1)) isomers of [N(3)MN(5)](q) [(M, q) = (Ni, 0), (Co, -1), (Fe, -2)] possess considerable kinetic stability for laboratory characterization. The bond length and natural charge analysis of [N(3)MN(5)](q) [(M, q) = (Ni, 0), (Co, -1), (Fe, -2)] indicate that each complex possesses the smallest triplet all-nitrogen ring (3)N(3)(-). The unique stability of the presently designed heterodecked sandwich-like complexes await future laboratory investigations.