Tetrahedral Complexes Research Articles

Investigation of Magnetic and Dielectric Properties of Cobalt Cubic Spinel Ferrite Nanoparticles Synthesized by CTAB-Assisted Co-precipitation Method

In this research work, a novel surfactant (CTAB)-assisted co-precipitation method has been developed for controlled synthesis of CoFe2O4 nanoparticles by using cobalt nitrate, iron nitrate, sodium hydroxide, and CTAB (cetyltrimethylammonium bromide) as reactants. Nanoparticles of CoFe2O4 were synthesized with varying molar amounts of CTAB (0.1M, 0.2M, 0.35M, and 0.4M CTAB). A sample without CTAB (0.0M CTAB) was also synthesized for comparison of properties. Crystal structural, morphological, vibrational spectral, magnetic, and dielectric characterization of synthesized CoFe2O4 nanoparticles were carried out using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), and precision impedance analyzer (LCR meter), respectively. XRD results revealed that single-phase pure spinel CoFe2O4 owing to Fd-3m group was synthesized with improved crystallinity for all samples. It was confirmed by SEM analysis that spherical nanoparticles of CoFe2O4 have been synthesized with an average particle size of 25nm. FTIR analysis revealed that absorption peaks observed at 587–583 cm−1and 377–375 cm−1 referred to the tetrahedral complexes and octahedral complexes, respectively. Dielectric properties which were measured between 100Hz and 5MHz using precision impedance analyzer showed that first dielectric constant and dielectric loss decrease rapidly with increase in frequency, and on further increase in frequency, they decrease slowly and become independent of the frequency, which is a characteristic behavior of magnetic spinel ferrites. VSM analysis which was carried out at maximum magnetic field of 8000 Oe at room temperature and pressure showed that all the specimens showed ferrimagnetic behavior with improvement in magnetic properties originating from the use of surfactant in the synthesis procedure.

Halogenation of Diphosphorus Complexes.

A systematic study of diverse halogenation reactions of the tetrahedral Mo2P2 ligand complex [{CpMo(CO)2}2(μ,η2:η2-P2)] (1) is reported. By reacting 1 with different halogenating agents, a series of complexes such as [(CpMo)4(μ4-P)(μ3-PI)2(μ-I)(I)3(I3)] (2), [{CpMo(CO)2}2(μ-PBr2)2] (3a), [{CpMo(CO)2}(CpMoBr2)(μ-PBr2)2] (4a), [{CpMo(CO)2}2(μ-PCl2)2] (3b), and [{CpMo(CO)2}(CpMoCl2)(μ-PCl2)2] (4b) were obtained. Whereas the reaction of 1 toward various bromine and chlorine sources leads to similar results, a different behavior is observed in the reaction with iodine in which 2 is formed. The products were comprehensively characterized by spectroscopic methods and single crystal X-ray diffraction, and the electronic structures of 2, 3a, and 4a were elucidated by DFT calculations.

Computational study of the structure of ternary ionic liquid/salt/polymer electrolytes based on protic ionic liquids

The stability of binary mixtures of several protic ionic liquids (ethylammonium nitrate, ethylammonium acetate and ethylammonium tetrafluoroborate) with polyethylene oxide is studied by means of molecular dynamics simulations. The solubility range is seen to be wider for ethylammonium acetate, and the structure and single-particle dynamics of its ternary mixtures with lithium acetate are then studied. The structure of liquid mixtures of lithium acetate with the ionic liquid is seen to be seldom modified by the addition of the polymer, with very limited hydrogen bonding between the ionic liquid and the polymer taking place. Moreover, lithium is seen to be solvated in the liquid phase forming [Li(ACE)4]−3 tetrahedral complexes irrespective of the presence of the polymer, with very limited binding of metal cations to oxygen atoms in the polymer backbone. Hence, the registered single particle dynamics and lithium transport takes place in practically the same way as in the liquid phase with almost no interference of the polymer, contrarily to previously reported results for other ionic liquids.

The role of monodentate tetrahedral borate complexes in boric acid binding to a soil organic matter analogue

Boron is an essential plant micronutrient responsible for several important functions. Boron availability in soils may be influenced by binding with soil organic matter (SOM), particularly with aromatic diol and polyphenol groups on SOM. The mechanism by which aromatic diols bind boron, however, remains unclear. The objective of this work is to further investigate interaction between boric acid and varying concentrations of an aromatic, polyphenolic SOM analogue (tannic acid at 5, 10 and 20 g L−1) from pH = 5–9. UV/Visible spectroscopy showed boric acid enhanced tannic acid deprotonation at pH = 7.0 and 9.0, resulting in singly deprotonated tannic acid subunits. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) showed boric acid/tannic acid binding for all concentrations at pH = 7 and 9, whereas binding at pH = 5.0 was observed only at 20 g L−1 tannic acid. Uncomplexed boron species were not evident at pH = 9.0, but were detectable at pH = 7.0 at lower tannic acid concentrations and prevalent at pH = 5.0, qualitatively indicating binding affinity increases from pH = 5.0 to 9.0. ATR-FTIR results indicated tetrahedral coordination of boron upon complexation to tannic acid with a monodentate mechanism. These results collectively highlight a transition of solution planar boric acid to a tetrahedral, monodentate coordination with a single phenol group in tannic acid polyphenols. This contrasts with previous spectroscopic studies, which indicated bidentate tetrahedral or monodentate trigonal planar orientations prevail at aromatic diol sites. This work presents a previously unobserved boric acid coordination mechanism to an SOM analogue and, therefore, may better inform prediction and modeling of boron behavior in soils.

Structural and electrical properties of La3+ ions substituted MnFe2O4 ferrite nanoparticles synthesized via cost-effective reverse micelles strategy

La3+ ions substituted manganese ferrite (MnFe2-x La x O4) nanoparticles via reverse micelles strategy were synthesized and their structural and electrical properties are discussed in this article. Using low-cost precursors, mono-dispersed, and well crystalline MnFe2-x La x O4 nanoparticles were prepared at low temperature. X-ray diffraction (XRD) explored cubic spinel structure with minute secondary phase as LaFeO3. The crystallite size of MnFe2-x La x O4 was found to increase from 12.82 nm to 15.95 nm with increased La3+ ions contents. The room temperature Fourier transform infrared (FTIR) spectra were recorded in the wavenumber range 1000–400 cm−1 that showed the vibrational bands of octahedral and tetrahedral complexes. These bands are the fingerprints of spinel ferrites. Surface morphology characterized by field emission scanning electron microscopy (FESEM) revealed the relative spherical morphology of prepared spinel ferrite particles. The elemental composition analysis from Energy-dispersive x-ray (EDX) spectroscopy confirmed the presence of expected elements in the samples. The modification in resistivity and the enhancement in the dielectric parameters suggested the possible utilization of these soft ferrite nanoparticles in advanced electronics, especially the devices that are required to operate at high frequencies.

Asymmetric Hetero-Michael Additions to α,β-Unsaturated Carboxylic Acids by Multifunctional Boronic Acid Catalysts

Several direct asymmetric Michael additions to α,β-unsaturated carboxylic acids with integrated catalysts comprising chiral bifunctional thiourea and arylboronic acid were developed. First, the asymmetric aza-Michael addition of hydroxylamine derivatives efficiently afforded a variety of optically active β-amino acid derivatives. Furthermore, upon detailed investigation of the reaction, tetrahedral borate complexes, comprising two carboxylate molecules, were found to serve as reaction intermediates. Based on this observation, a drastic improvement in product enantioselectivity was achieved upon benzoic acid addition. Second, on merely changing the solvent, the asymmetric thia-Michael addition of arylthiols afforded both enantiomers of the adducts, which are important building blocks for biologically active compounds.

Structurally Modelling the 2-His-1-Carboxylate Facial Triad with a Bulky N,N,O Phenolate Ligand.

We present the synthesis and coordination chemistry of a bulky, tripodal N,N,O ligand, ImPh2NNO tBu (L), designed to model the 2‐His‐1‐carboxylate facial triad (2H1C) by means of two imidazole groups and an anionic 2,4‐di‐tert‐butyl‐subtituted phenolate. Reacting K‐L with MCl2 (M = Fe, Zn) affords the isostructural, tetrahedral non‐heme complexes [Fe(L)(Cl)] (1) and [Zn(L)(Cl)] (2) in high yield. The tridentate N,N,O ligand coordination observed in their X‐ray crystal structures remains intact and well‐defined in MeCN and CH2Cl2 solution. Reacting 2 with NaSPh affords a tetrahedral zinc thiolate complex, [Zn(L)(SPh)] (4), that is relevant to isopenicillin N synthase (IPNS) biomimicry. Cyclic voltammetry studies demonstrate the ligand's redox non‐innocence, where phenolate oxidation is the first electrochemical response observed in K‐L, 2 and 4. However, the first electrochemical oxidation in 1 is iron‐centred, the assignment of which is supported by DFT calculations. Overall, ImPh2NNO tBu provides access to well‐defined mononuclear, monoligated, N,N,O‐bound metal complexes, enabling more accurate structural modelling of the 2H1C to be achieved.

Cytotoxicity, anti-microbial studies of M(II)-dithiocarbamate complexes, and molecular docking study against SARS COV2 RNA-dependent RNA polymerase.

Ten transition metal dithiocarbamate (DTC)complexes of the type [M(κ 2‐Et2DT)2] (1–5), and [M(κ 2‐PyDT)2] (6–10) (where M = Co, Ni, Cu, Pd, and Pt; Et2DT = diethyl dithiocarbamate; PyDT = pyrrolidine dithiocarbamate) were synthesized and characterized by different methods. The dithiocarbamate acted as bidentate chelating ligands to afford a tetrahedral complexes with Co(II) ion and square planner with other transition metal ions. The dithiocarbamate complexes showed good activity against the pathogen bacteria species. The results showed the Pt‐dithiocarbamate complexes are more active against all the tested bacteria than the Pd‐dithiocarbamate complex. The dithiocarbamate complexes displayed the maximum inhibition zone against E. coli bacteria, whereas the lowest activity of the dithiocarbamate against Salmonella typhimurium bacteria. The cytotoxicity of the Pd(II) and Pt(II) complexes was screened against the MCF‐7 breast cancer cell line and the complexes showed moderate activity compared with the cis‐platin. The results indicated that the MCF7 cells treated with 500 μg\\ml of ligands and Pd(II) and Pt(II) complexes after 24 hr exposure showed intercellular space and dead cells. Finally, molecular docking studies were carried out to examine the binding mode of the synthesized compounds against the proposed target; SARS COV2 RNA‐dependent RNA polymerase.

Speciation and determination of iron in aqueous solution and river water by high-resolution electrospray ionization mass spectrometry

Characterization and determination of Fe2+ co-existing with Fe3+ using a simple method of electrospray ionization mass spectrometry (ESI-MS) is employed. We attempted to characterize Fe2+ species in aqueous solution in combination with various inorganic salts of iron, such as chloride, sulfate, and cyanide salts, using two kinds of detection systems (a quadrupole mass spectrometer and a high-resolution magnetic mass spectrometer), to establish the stability of the complexes formed. The study further extended to the determination of Fe2+ concentration, and we expect that ESI-MS will be a new method to determine Fe2+. Among the inorganic salts studied, 1,10-Phenanthroline forms stable tetrahedral complexes with Fe2+ in the gas phase of ESI-MS which is observed in a high-m/z region and are well separated. The method is extended for determining Fe2+ concentration in natural river water samples by measuring the peak intensity of [Fe(phen)2]2+ (m/z 208) and obtaining a calibration curve (R2 = 0.9992) of the peak intensity determined by HR-ESI-MS. The Fe2+ concentrations in Tama River samples were obtained by the standard addition method (Fe2+ 0.23 μmol/L, R2 = 0.9998), and total concentration of iron in Tama River sample was 0.59 μmol/L (ICP-MS), thus about 40% of iron is present as Fe2+.

Widening the Window of Spin-Crossover Temperatures in Bis(formazanate)iron(II) Complexes via Steric and Noncovalent Interactions

Bis(formazanate)iron(II) complexes undergo a thermally induced S = 0 to S = 2 spin transition in solution. Here we present a study of how steric effects and π-stacking interactions between the triarylformazanate ligands affect the spin-crossover behavior, in addition to electronic substituent effects. Moreover, the effect of increasing the denticity of the formazanate ligands is explored by including additional OMe donors in the ligand (7). In total, six new compounds (2–7) have been synthesized and characterized, both in solution and in the solid state, via spectroscopic, magnetic, and structural analyses. The series spans a broad range of spin-crossover temperatures (T1/2) for the LS ⇌ HS equilibrium in solution, with the exception of compound 6 which remains high-spin (S = 2) down to 210 K. In the solid state, 6 was shown to exist in two distinct forms: a tetrahedral high-spin complex (6a, S = 2) and a rare square-planar structure with an intermediate-spin state (6b, S = 1). SQUID measurements, 57Fe Mössbauer spectroscopy, and differential scanning calorimetry indicate that in the solid state the square-planar form 6b undergoes an incomplete spin-change-coupled isomerization to tetrahedral 6a. The complex that contains additional OMe donors (7) results in a six-coordinate (NNO)2Fe coordination geometry, which shifts the spin-crossover to significantly higher temperatures (T1/2 = 444 K). The available experimental and computational data for 7 suggest that the Fe···OMe interaction is retained upon spin-crossover. Despite the difference in coordination environment, the weak OMe donors do not significantly alter the electronic structure or ligand-field splitting, and the occurrence of spin-crossover (similar to the compounds lacking the OMe groups) originates from a large degree of metal–ligand π-covalency.

Synthesis, structural and magnetic properties of Ni2+and In3+ doped cobalt ferrite and application as catalyst for synthesis of Bis-(Indolyl) methane derivatives

The Ni2+ and In3+ substituted cobalt ferrites were prepared having the chemical composition NixCo1-xInyFe2-yO4 (x = 0.0, 0.25, 0.5, 0.75, 1.0 and y = 0.0, 0.03, 0.06, 0.08, 0.1) by sol–gel auto-combustion method. The precursors were calcinated at temperature 500 °C. The EDAX pattern confirmed stoichiometric composition of elements of synthesized ferrite nano particles. The XRD pattern confirms single phase cubic spinel structure. Lattice constants increase as increase in In+3 ions content. X–ray density increases whereas bulk density decreases. Infrared spectroscopy of synthesized samples shows absorption bands ‘ν2’ around 400 cm−1 and ‘ν1’ at 600 cm−1 are allocated to the intrinsic stretching vibrations of octahedral and tetrahedral complexes respectively. Scanning electron microscopy was applied to study the surface characteristics and uniform distribution of particle size and also prepared samples are porous in nature. Transmission electron microscopy carried out to know the particle size of synthesized ferrite samples and selected area electron diffraction pattern clearly shows that particles were well crystalline in nature. Magnetic measurements of ferrite nanoparticles were done by vibrating sample magnetometer (VSM). Bis-(indolyl) methane derivatives efficiently prepared from Indole and aromatic aldehydes using NixCo1-xInyFe2-yO4 nano particles as catalyst.

Slow magnetic relaxation in distorted tetrahedral Dy(III) aryloxide complexes.

Three distorted tetrahedral Dy(iii) aryloxide complexes, [Na(THF)6][Dy(OArAd2tBu)2Cl2] (1) (OArAd2tBu = OC6H2Adamantyl2-2,6-tBu-4) and [Na(THF)6][Dy(OMes*)3X] (X = Cl, 2; BH4, 3), (OMes* = OC6H2tBu3-2,4,6) exhibit easy axis magnetic anisotropy and slow magnetic relaxation at zero field, with relaxation rates 1 < 2 < 3.

Facile co-precipitation route for magnesium ferrites nanostructure: Synthesis, influence of pH variation on structural properties

This report presents the synthesis of magnesium ferrite (MgFe2O4) by coprecipitation method and its subsequent characterization by using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) techniques. XRD results confirm the formation of single phase cubic spinel structure, having lattice constant from 8.3216 ? to 8.3252 ?. An infrared spectroscopy study confirms the presence of two main absorption bands indicating tetrahedral and octahedral group complexes, within the spinel lattice. We also report hopping length (LA and LB), strain (?) and dislocation density (?D) of ferrite sample.

Pseudo-tetrahedral vs. pseudo-octahedral ErIII single molecule magnets and the disruptive role of coordinated TEMPO radical

Tetrahedral ErIII complexes are potential candidates for high-performance single molecule magnets (SMMs).

Highly Selective and Label-Free AuNPs Based Optical Sensor Development Significant in Smartphone Sensing of L-Lactate in Food Samples

L-lactate is an essential organic chemical in food processing, clinical, chemical, and fermentation industries. AuNPs were synthesized by chemical reduction reaction method and functionalized with 3-aminophenylboronic acid (3-APBA). The structural, morphological, FTIR, DLS, zeta potential characterization studies were performed to optimize the sensing mechanism. First time reporting facile enzyme-free sensor for the detection of L-lactate content in milk. Initially, the sensor has been optimized for nano reagent concentration, pH and time. 3-APBA@AuNPs showed a stable SPR intensity and forms a reversible tetrahedral ester complex with the analyte L-lactate (100 mM) resulting the NPs aggregation and revealing the blue shift of UV-VIS absorption wavelength (λ = 300 nm to 288 nm). Nestle- Lactogen, an India commercial milk powder has been used for the standardization study of lactate sensing. The milk samples spiked with L-Lactate (1-20mM) showed an increase in UV-VIS absorption peak intensity with concentration, and estimated the lower detection limit (LOD) = 1.1 mM using the calibration graphs. The optical sensing mechanism is explained may be due to π-π* transition of AuNPs stabilized by tetragonal complex of L-lactate bonded to 3-boronate via nucleophilic attack on boron atom. The nanosensor data was validated with commercial Megazyme kit and conventional HPLC technique. In commercial product Amul-India milk, the L-lactate value estimated as 0.678Mm with 95% correlation. Hence, the proposed sensor technique could be an alternate to the high cost conventional methods and at next level, it can be interfaced to smart phone to develop an onsite food, pharma and clinical device applications.

A Lower Bound for Splines on Tetrahedral Vertex Stars

A tetrahedral complex all of whose tetrahedra meet at a common vertex is called a vertex star. Vertex stars are a natural generalization of planar triangulations, and understanding splines on vertex stars is a crucial step to analyzing trivariate splines. It is particularly difficult to compute the dimension of splines on vertex stars in which the vertex is completely surrounded by tetrahedra---we call these closed vertex stars. A formula due to Alfeld, Neamtu, and Schumaker gives the dimension of $C^r$ splines on closed vertex stars of degree at least $3r+2$. We show that this formula is a lower bound on the dimension of $C^r$ splines of degree at least $(3r+2)/2$. Our proof uses apolarity and the so-called Waldschmidt constant of the set of points dual to the interior faces of the vertex star. We furthermore observe that arguments of Alfeld, Schumaker, and Whiteley imply that the only splines of degree at most $(3r+1)/2$ on a generic closed vertex star are global polynomials.

Reactivity of a T-shaped cobalt(I) pincer-complex.

The reactivity of a paramagnetic T-shaped cobalt(i) complex, [(iPrboxmi)Co], stabilised by a monoanionic bis(oxazolinylmethylidene)-isoindolate (boxmi) NNN pincer ligand is described. The exposure to carbon monoxide as an additional neutral ligand resulted in the square-planar species [(iPrboxmi)Co(CO)], accompanied by a change in the electronic spin state from S = 1 to S = 0. In contrast, upon treatment with trimethylphosphine the formation of the distorted tetrahedral complex [(iPrboxmi)Co(PMe3)] was observed (S = 1). Reacting [(iPrboxmi)Co] with iodine (I2), organic peroxides (tBu2O2, (SiMe3)2O2) and diphenyldisulphide (Ph2S2) yielded the tetracoordinated complexes [(iPrboxmi)CoI], [(iPrboxmi)Co(OtBu)], [(iPrboxmi)Co(OSiMe3)] and [(iPrboxmi)Co(SPh)], respectively, demonstrating the capability of the boxmi-supported cobalt(i) complex to homolytically cleave bonds and thus its distinct one-electron reactivity. Furthermore, a square-planar cobalt(ii) alkynyl complex [(iPrboxmi)Co(CCArF)] was identified as the main product in the reaction between [(iPrboxmi)Co] and a terminal alkyne, 4-fluoro-1-ethynylbenzene. Putting such species in the context of the previously investigated hydroboration catalysis, its stoichiometric reaction with pinacolborane revealed its potential conversion into a cobalt(ii) hydride complex, thus confirming its original attribution as off-cycle species.

Crystal Packing Studies, Thermal Properties and Hirshfeld Surface Analysis in the Zn(II) Complex of 3-Aminopyridine with Thiocyanate as Co-Ligand

Reaction of zinc acetate, potassium thiocyanate and the ligand 3-ampy gave the discrete tetrahedral complex [Zn(NCS)2(3-ampy)2] in which 3-ampy chelates in a monodentate fashion through its pyridine-N atom. It was characterized by single crystal X-ray diffraction, infrared, and elemental analysis. Density Functional Theory calculations were performed in order to gain insights into the role of weak molecular interactions in the complex that influence the self-assembly process and crystal packing. X---H (X = H, C, N and S) inter-actions. S-H interactions (30.2%) were found to be the main interactions that hold the molecules in the crystal structure. Furthermore, the thermolysis of the complex was studied in order to evaluate whether it was suitable as a precursor for zinc sulphide.

Multiple Transformations among Anion-based A2nL3n Assemblies: Bicapped Trigonal Antiprism A8L12, Tetrahedron A4L6, and Triple Helicate A2L3 (A = Anion).

The construction of sophisticated, high-nuclearity polyhedral cages is an attractive yet challenging task in supramolecular chemistry. Herein we report the anion-coordination-driven assembly (ACDA) of a series of A2nL3n architectures ("A" denotes anion, L is ligand, n = 1, 2, 4) with a biphenylene-spaced bis-bis(urea) ligand including triple helicate A2L3 (H), tetrahedron A4L6 (T), and the octanuclear, bicapped trigonal antiprism (or parallelepiped) A8L12 (P). Among them, P is held by 96 hydrogen bonds, the largest number ever reported in a discrete polyhedron, and encapsulates multiple guests (three tetramethylammonium cations) in three compartments. Remarkably, multiple reversible transformations of these dynamic assemblies have been realized by alternation of the template guest, solvent, and concentration. Furthermore, a chiral ligand (L2S) with carbon stereocenters at both termini of the bis-bis(urea) backbone was designed and assembled with phosphate to form the enantio-pure triple helicate or tetrahedron. The chiral amplification effect in the tetrahedral complex is significantly larger than that in the triple helicate as a function of the point chirality.

A Mononuclear and High-Spin Tetrahedral TiII Complex.

A high-spin, mononuclear TiII complex, [(TptBu,Me)TiCl] [TptBu,Me– = hydridotris(3-tert-butyl-5-methylpyrazol-1-yl)borate], confined to a tetrahedral ligand-field environment, has been prepared by reduction of the precursor [(TptBu,Me)TiCl2] with KC8. Complex [(TptBu,Me)TiCl] has a 3A2 ground state (assuming C3v symmetry based on structural studies), established via a combination of high-frequency and -field electron paramagnetic resonance (HFEPR) spectroscopy, solution and solid-state magnetic studies, Ti K-edge X-ray absorption spectroscopy (XAS), and both density functional theory and ab initio (complete-active-space self-consistent-field, CASSCF) calculations. The formally and physically defined TiII complex readily binds tetrahydrofuran (THF) to form the paramagnetic adduct [(TptBu,Me)TiCl(THF)], which is impervious to N2 binding. However, in the absence of THF, the TiII complex captures N2 to produce the diamagnetic complex [(TptBu,Me)TiCl]2(η1,η1;μ2-N2), with a linear Ti=N=N=Ti topology, established by single-crystal X-ray diffraction. The N2 complex was characterized using XAS as well as IR and Raman spectroscopies, thus establishing this complex to possess two TiIII centers covalently bridged by an N22– unit. A π acid such as CNAd (Ad = 1-adamantyl) coordinates to [(TptBu,Me)TiCl] without inducing spin pairing of the d electrons, thereby forming a unique high-spin and five-coordinate TiII complex, namely, [(TptBu,Me)TiCl(CNAd)]. The reducing power of the coordinatively unsaturated TiII-containing [(ΤptBu,Me)TiCl] species, quantified by electrochemistry, provides access to a family of mononuclear TiIV complexes of the type [(TptBu,Me)Ti=E(Cl)] (with E2– = NSiMe3, N2CPh2, O, and NH) by virtue of atom- or group-transfer reactions using various small molecules such as N3SiMe3, N2CPh2, N2O, and the bicyclic amine 2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene.