Polycyano Anions Research Articles

Synthesis and Characterization of a Dinuclear Nitrogen‐Rich Ferrocenyl Ligand and Its Ionic Coordination Compounds and Their Catalytic Effects During Combustion

Alkylferrocene‐based burning‐rate catalysts (BRCs) exhibit distinct migration tendency and high volatility and thus result in inferior performance of composite solid propellants during their combustion processes. To deal with these drawbacks, a novel dinuclear nitrogen‐rich ferrocene derivative, 4‐amino‐3,5‐bis(4‐ferrocenyl‐1,2,3‐triazolyl‐1‐methyl)‐1,2,4‐triazole (BFcTAZ) and its twenty seven ionic coordination compounds, [M2(BFcTAZ)2(H2O)4]mXn·xH2O (M = Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2; X = polycyano anions), were synthesized and characterized by FT‐IR, UV/Vis, and elementary analysis. Crystal structure of BFcTAZ was further confirmed by single‐crystal X‐ray diffraction and a general molecular structure of the new complexes was proposed. Their high thermal stability was verified by TG technique. Cyclic voltammetry studies suggested that the new compounds are diverse redox systems. Their effects on the thermal degradation of some common oxidizers were measured by DSC technique. The results indicated that most of the new complexes exert great effects on the thermal decomposition of AP, RDX, and 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7) and some of them are more active than catocene. The Cu2+ complexes are among the excellent ones. However, only six compounds have appreciable catalytic activity in the thermal degradation of HMX.

Dinuclear (Ferrocenylmethyl)imidazolium Ionic Compounds with Polycyano Anions. Characterization, Migration, and Effects during Combustion

Alkyl‐substituted ferrocene‐based burning rate catalysts exhibit high migration and volatility during curing process and prolonged storage of the composite solid propellants. To deal with the drawbacks twenty‐one dinuclear (ferrocenylmethyl)imidazolium compounds paired with polycyano anions, were synthesized and characterized by 1H NMR, 13C NMR, UV/Vis, elementary analysis, and both 2 and 11 were further characterized by single‐crystal X‐ray diffraction. The migration test revealed that the compounds have excellent anti‐migration ability. The cyclic‐voltammetry results suggested that they are quasi‐reversible or irreversible redox systems. The TG/DSC analyses showed that the compounds are highly thermal stable. Their effects on the thermal decomposition of ammonium perchlorate (AP) and 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX) were additionally examined. The results showed that the new compounds have strong effects on the thermal decomposition of both AP and RDX during combustion. Both 13 and 21 are more excellent than catocene for increasing the released heats of AP and can be used as alternatives of catocene in the composite solid propellants.

Coordination abilities of polycyano anions in the solid state: coordination geometries and d–d transition energies of mixed-ligand solvatochromic copper(ii) complexes with B(CN)4, C(CN)3, and N(CN)2 anions

B(CN)4-, C(CN)3-, and N(CN)2- are highly versatile polycyano anions that produce various functional compounds. To investigate the coordination abilities of these anions in the solid state quantitatively, we synthesized mixed-ligand Cu(ii) complexes: [Cu(R-acac)(tmen)X] (X = polycyano anion, R-acac = acetylacetonate or butyl-acetylacetonate, tmen = tetramethylethylenediamine). The coordination abilities of the anions, increasing in the order B(CN)4- < C(CN)3- < N(CN)2-, result in a decrease in the d-d transition energies of the complexes and the shortening of the axial coordination distance. The influence of crystal packing on the coordination geometries and d-d transition energies of the complexes was also demonstrated. The donor numbers of the anions were determined from the d-d transition energies in solution.

Mono‐ and Dinuclear Ferrocenyl Ionic Compounds with Polycyano Anions. Characterization, Migration, and Catalytic Effects on Thermal Decomposition of Energetic Compounds

AbstractNeutral ferrocene‐based burning rate (BR) catalysts show strong migration trends and volatility during long‐time storage and curing of the composite solid propellants. To reduce these disadvantages thirty‐two ferrocenyl quaternary ammonium compounds, paired with polycyano anions, were synthesized and characterized by 1H NMR, 13C NMR, and UV/Vis spectroscopy, as well as elemental analysis. Additionally, crystal structures of eight compounds were confirmed by single‐crystal X‐ray diffraction. TG and DSC analyses indicated that the compounds containing 1,1,2,3,3‐pentacyanopropenide anions show high thermal stability. Cyclic voltammetry studies suggested that they are quasi‐reversible or irreversible redox systems. Anti‐migration tests verified that the tested compounds show very low migration tendency and some of them exhibit no migration after 30 days aging at 70 °C. Their catalytic efficiency in the thermal decomposition of ammonium perchlorate (AP), 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX), and 1,2,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane (HMX) were examined by DSC analyses. The results revealed that most of the compounds exhibit distinct effects on the thermal degradation of AP and RDX. Two compounds have good catalytic ability in the thermal decomposition of HMX, representing rare examples of the reported ferrocenyl ionic compounds, which display catalytic property during combustion of HMX.

Ionic Ferrocene‐Based Burning‐Rate Catalysts with Polycyano Anions: Synthesis, Structural Characterization, Migration, and Catalytic Effects during Combustion

AbstractInvited for the cover of this issue is the group of Guofang Zhang from Shaanxi Normal University, China. The cover image shows how to develop low‐migratory ferrocene‐based burning‐rate catalysts (BRCs) for the next generation of rocket propellants.

Ionic Ferrocene‐Based Burning‐Rate Catalysts with Polycyano Anions: Synthesis, Structural Characterization, Migration, and Catalytic Effects during Combustion (Eur. J. Inorg. Chem. 9/2015)

Ionic Ferrocene‐Based Burning‐Rate Catalysts with Polycyano Anions: Synthesis, Structural Characterization, Migration, and Catalytic Effects during Combustion (Eur. J. Inorg. Chem. 9/2015)

Ionic Ferrocene‐Based Burning‐Rate Catalysts with Polycyano Anions: Synthesis, Structural Characterization, Migration, and Catalytic Effects during Combustion

AbstractAlkylferrocene‐based burning‐rate (BR) catalysts, have a high tendency to migrate during curing and storage due to their neutral and nonpolar nature. To overcome these drawbacks, fifteen novel ionic compounds, 1‐(ferrocenylmethyl)imidazolium paired with polycyano anions, were synthesized and characterized. The structures of eleven of the compounds were confirmed by single‐crystal X‐ray diffraction. Compound 1 crystallizes in the tetragonal space group I4(1)/a; 2, 12 and 15 crystallize in the monoclinic space group P21/c, and 3 in the monoclinic space group P21/n; 4, 6–8, 13 and 14 crystallize in the triclinic space group P$\bar {1}$. Cyclic voltammetry investigations suggested that most of the compounds exhibit quasireversible redox systems. Compounds 1–10 have high thermal stability (&gt; 190 °C). Migration studies revealed that these compounds are low‐migratory materials. The thermal degradation of ammonium perchlorate (AP), hexogen (RDX), and octogen (HMX) catalyzed by these compounds was evaluated by differential scanning calorimetry (DSC) and by thermogravimetric (TG) techniques. The results show that the decomposition peak temperature of AP shifts downwards dramatically and that the released heat of AP increases significantly with the new compounds as additives (5 wt.‐%). Moreover, the ionic compounds exhibit significant effects on the thermal decomposition of RDX. The catalytic activities of the new compounds are higher than those of their nitrate and picrate analogues, which supports the conclusion that high nitrogen content in a ferrocene‐based BR catalyst is favorable for its combustion catalytic activity.

Ionic Ferrocenyl Compounds Containing Polycyano Anions. Synthesis, Structures, and Effects on Thermal Decomposition of Core Components of Solid Propellants

AbstractFor lowering high migration tendency of alkyl‐substituted ferrocenes as burning‐rate catalysts in composite solid propellants, eight new ionic ferrocenyl compounds, [FcCH2N(CH3)2(CnH2n+1]+X– (Fc = ferrocenyl; X– = 1,1,3,3‐tetracyanopropenide; n = 3–10; consequently numbered as 1–8), were synthesized and characterized by 1H NMR, 13C NMR, FT‐IR and UV/Vis spectroscopy as well as elementary analysis. In addition, the structures of 1, 3, and 5 were confirmed by single‐crystal X‐ray diffraction analysis and their cations were studied by density functional theory calculations (DFT). 1, 3, and 5 crystallize in the triclinic space group P$\bar{1}$. 1–6 show highly thermal stability (&gt;166 °C), whereas compounds 7 and 8 exhibit volatility to a certain degree. Cyclic voltammetry studies suggested that each salt exhibits a quasi‐reversible redox wave of the ferrocenyl group. The effects of the new compounds on thermal decomposition of ammonium perchlorate (AP), 1,3,5‐trinitro‐1,3,5‐triazacyclohexane (RDX), and 1,2,5,7‐tetranitro‐1,3,5,7‐tetraazacyclooctane (HMX) were investigated by DSC technique. The results show that all the new compounds can catalyze thermal degradation of AP and RDX effectively and are higher in catalytic activity than the corresponding nitrates and picrates, verifying the prospect that relatively high nitrogen content in an ionic ferrocenyl compound is able to enhance its combustion catalytic efficiency.

Polymorphism and Metallic Behavior in BEDT-TTF Radical Salts with Polycyano Anions

Up to five different crystalline radical salts have been prepared with the organic donor BEDT-TTF and three different polynitrile anions. With the polynitrile dianion tcpd2− (=C[C(CN)2]32−), two closely related radical salts: α'-(ET)4tcpd·THF (1) (THF = tetrahydrofurane) and α'-(ET)4tcpd·H2O (2) have been prepared, depending on the solvent used in the synthesis. With the mono-anion tcnoetOH− (=[(NC)2CC(OCH2CH2OH)C(CN)2]−) two polymorphs with similar physical properties but different crystal packings have been synthesized: θ-(ET)2(tcnoetOH) (3) and β''-(ET)2(tcnoetOH) (4). Finally, with the mono-anion tcnoprOH− (=[(NC)2CC(OCH2CH2CH2OH)C(CN)2]−) we have prepared a metallic radical salt: β''-(ET)2(tcnoprOH)(CH2Cl2CH3Cl)0.5 (5). Salts 1‑4 are semiconductors with high room temperature conductivities and activation energies in the range 0.1–0.5 eV, whereas salt 5 is metallic down to 0.4 K although it does not show any superconducting transition above this temperature.

Ionic Liquids Formed with Polycyano 1,1,3,3-Tetracyanoallyl Anions: Substituent Effects of Anions on Liquid Properties

A series of ionic liquids based on five kinds of polycyano 1,1,3,3-tetracyanoallyl anions with 2-substituents having different electron-withdrawing or -donating abilities were prepared. The influence of the chemical modification on their thermal properties, viscosity, ionic conductivity, ion association, and solvatochromic shifts was characterized and compared with the case of previously reported polycyano anions, N(CN)(2)(-) and C(CN)(3)(-). Among the 1-butyl-3-methylimidazolium (BMI) salts, cyano-substituted (i.e., 1,1,2,3,3-pentacyanoallyl anion) salt has the highest melting point (42 degrees C), possibly indicating the importance of high local symmetry over decreased interionic CN...cation interactions due to the limited electron densities on terminal nitrogens of the anions, predicted by ab initio calculations. In the liquid state, methoxy-substituted (i.e., 2-methoxy-1,1,3,3-tetracyanoallyl anion) salt has the highest fluidity and ionic conductivity, associated with the significant conformational degree of freedom in the methoxy group. Although the ion diffusivity has no definite correlation with the Hammett parameter of the substituents, the introduction of electron-withdrawing cyano or cyanomethyl (i.e., 2-cyanomethyl-1,1,3,3-tetracyanoallyl anion) groups leads to the decrease in the degree of ion association and solvent donor ability, which were manifested in the Walden rule deviation and solvatochromic shift, respectively.

Polycyano‐Anion‐Based Energetic Salts

Energetic salts based on polycyano anions and cations with a high nitrogen content tend to have extensive hydrogen bonding and exhibit heats of formation up to DeltaH(f)=1579.1 kJ mol(-1). Based on theoretical calculations, some of the new salts may be considered to be low-energy monopropellants. One of the salts can be used as a precursor to a carbon nitride.

Variety of BEDT-TTF salts with organic polycyano anions

Cation radical salts based on BEDT-TTF (ET) with 1,1,2,4,5,5-hexacyano-3-azapentadienide (HCAPD −) and a series of 2-alkyl-1,1,3,3-tetracyanoallyl anions (R–TCA −; R=MeS, MeNH, NH 2) were investigated. HCAPD − provided 1:1 (D:A) ( 1) and 2:1:0.5 (THF) ( 2) salts. Although 1 consists of ladder-like structures, the strong dimerization of ET + molecules results in a non-magnetic state. 2 shows a semiconductor–semiconductor transition near 200 K. Magnetic susceptibility of 2 shows a peculiar behavior. R–TCA − anions provided 2:1 salts. MeS– and MeNH–TCA − salts are metallic, though NH 2–TCA − salt is regarded as a Mott insulator.

Cation Radical Salts with Flexible Polycyano Anions having Tetracyanoallyl Skeleton

Cation radical salts of BEDO-TTF (BO) with six kinds of polycyano counter anions of tetracyanoallyl derivatives (R-TCA; R: substituent) were investigated. Although the stoichiometries of the salts are different from salt to salt, the degree of charge transfer on BO molecules ranges from +0.4 to +0,5. 2-propoxy-TCA anion (PrO-TCA − ) provides a semiconducting salt, while the other anions afford metallic ones. The EtO-TCA − salt exibits successive metal-semiconductor and semiconductor-metal transitions near 150 K and 40 K, respectively. Magnetic susceptibility of this salt shows slight decrease near 100 K and it keeps non-zero value even at 1.9 K. The crystal structures of three kinds of the salts were solved. The salts of EtO-TCA − and cyanomethyl(CM)-TCA − have I 3 -type packing motifs of the BO molecules. The salt of DHCP 2− (R=C(CN)C(CN)C(CN) 2 − ) has a similar packing motif to I 3 -type, however, the stacking direction of the BO molecules varies par five BO molecules.

Metallic and Mott insulating BEDT-TTF salts with polycyano anions

Stable and flexible organic anions, RO-TCA . (R = Me, Et, Pr, Bu; TCA = tetracyanoallylide) afford a variety of cation radical salts having varied structures and physical properties. BEDT-TTF (ET) salts with them are classified into two groups based on packing motives of donor molecules; β- and a'-type. The β-type salts are highly conductive compared to the a'-type ones, especially the β-type salt of MeO-TCA (1) is metallic down to 2.5 K. The a'-type salts are Mott insulators, which show semiconducting behavior and have large magnetic susceptibility. The insulating α'-type salts of MeO-TCA transform into metallic β-type one by losing solvent of crystallization.

A new approach to the generation of metal-bearing, medium-pore, shape-selective zeolites for fischer-tropsch catalysis: spectroscopic studies of zeolites

We have combined two recent developments in zeolite synthesis and modification to demonstrate a new approach to the generation of metalbearing, medium-pore, shape-selective zeolites for use as catalysts in Fischer-Tropsch conversions. The sequence of steps is: (1) synthesis of an alumino-ferrisilicate zeolite having the ZSM-5-type structure; (2) removal of the organic base template incorporated in the channel system during synthesis; (3) formation of a polycyano inclusion compound in the AFS zeolite; and (4) reduction of the inclusion compound by hydrogen at ~ 400 °C. PAS and EPR spectroscopy have been used to establish that the as-synthesized AFS zeolite contains Fe3+ ions in both framework and non-framework sites. Estimates of the orthorhombic crystal field interaction parameters for the two kinds of Fe3+ are obtained from the EPR spectra. The non-framework Fe3+ ions react with complex polycyano anions in solution to precipitate the inclusion compounds in the zeolite. PAS has been used to monitor the reaction chemistry and establish the formation of the following inclusion compounds in the AFS zeolite: (1) KFeIII[RuII(CN)6]; (2) KFeIII[CoII(CN)6]; and (3) FeIII[FeII(CN)5(NO)]. The latter two compounds are the products of slow, secondary one-electron reductions of the starting anionic complex. It is shown that these inclusion compounds must occur in grain boundaries of the AFS zeolite microcrystallites, rather than in the intracrystalline channel structure. FMR spectroscopy has been used to confirm the formation of the metallic (Fe) and bimetallic (Fe/Ru and Fe/Co) particles as products of the reduction of the inclusion compounds by hydrogen.The application of some other spectroscopic techniques in recent studies of cations, complexes, and metal particles in zeolites is reviewed in a brief appendix. The examples cited illustrate the use of high-resolution solid-state NMR, nuclear spin relaxation studies, FMR, EXAFS, and XANES.