Hexamethylenetetramine Complexes Research Articles

Well-defined ruthenium-hexamethylenetetramine complex: Synthesis, characterization, and catalytic activity towards base and acceptor free oxidation of alcohols and amines

A ruthenium hexamethylenetetramine complex [RuCl2(p-cym)HMTA] was prepared in quantitative yield at room temperature for 30 m. NMR and fluorescence spectroscopic studies revealed that the complex is unstable in solution resulting in the decomposition of HMTA unit with the elimination of p-cymene moiety. The newly synthesized complex is very efficient for the conversion of amines and alcohols into imines and ketones, respectively, in the absence of any base/additive/acceptor. The synthetic viabilty of the catalyst was successfully tested for the gram scale synthesis of industrially important product bis(4-chlorophenyl)methanone. The spectroscopic and experimental studies showed that ruthenium-hydride species was formed as active catalyst during the catalytic reactions and oxidation of alcohols and amines follows a dehydrogenative oxidation mechanism. The amount of hydrogen gas evolved during the ruthenium complex catalysed oxidation of diphenylmethanol was estimated to be 92%, implies the potential usage of catalyst in the field of liquid organic hydrogen storage.

Hexamethylenetetramine Complexes as Easy-to-Handle and Efficient Lewis Acid–Base Heterogeneous Catalysts for Coupling of CO2 under Mild Conditions

Hexamethylenetetramine Complexes as Easy-to-Handle and Efficient Lewis Acid–Base Heterogeneous Catalysts for Coupling of CO₂ under Mild Conditions

Hexamethylenetetramine-derived pyridinic N abundant porous carbon-supported Co/Co-Nx nanoparticles as highly efficient oxygen reduction catalyst and zinc-air battery cathode

Fuel cells and metal-air batteries attracted extensive research attention owing to high power density, renewability, and environmental friendliness. Hence, developing heteroatom-doped pyridinic N abundant porous carbon materials with large surface area have an extensive effect on oxygen reduction reaction (ORR) for fuel cell and metal-air battery. Herein, high content of pyridinic N porous carbon-supported Co/Co-Nx nanoparticles were synthesized as ORR catalysts by carbonizing complexes of hexamethylenetetramine (HMT) and Co(NO3)2·6H2O with silica template. The HMT-Co@SiO2-900 with high content of pyridinic N, large specific surface area, and porous structure exhibits a more positive half-wave potential (0.85 V) than 20% Pt/C and the outstanding performance oxygen evolution reaction behavior. The low Tafel slope of HMT-Co@SiO2-900 revealed the faster reaction kinetics during ORR. The HMT-Co@SiO2-900 zinc-air battery showed a high excellent cyclic stability in continuous charge/discharge cycles for 420 times at 10 mA/cm2. This research provides an efficient strategy for the preparation of pyridinic N porous electrocatalyst by the reduction of diffusion restriction and exposure of active sites.

Characterisation of Zinc Oxynitride Thin Films Prepared Using Zinc(II) Complex of Hexamethylenetetramine as the Precursor

A Zinc(II) complex of hexamethylenetetramine was prepared as a single source precursor and used to deposit zinc oxynitride thin films. The thin films were deposited on soda-lime glass substrates using the Metal Organic Chemical Vapour Deposition (MOCVD) technique at the deposition temperature of 370°C and 390°C, respectively. The Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the functional groups in the precursor, with stretching frequency for O-H, N-H, and C-H observed. The deposited films were characterized using UV-Visible Spectroscopy, Scanning Electron Microscopy (SEM), Elemental diffraction X-ray (EDX), and X-ray Diffractometer (XRD). A direct bandgap of 3.15 eV and 3.18 eV was obtained from the film deposited at 370°C and 390°C, respectively, using the Envelope Method. In comparison, a bandgap of 3.19 eV and 3.21 eV was obtained using the absorption spectrum fitting (ASF) method. The SEM revealed that the film is homogeneous, dense, and compact, composed of cluster grains. The EDX confirmed the presence of Zinc, Nitrogen and Oxygen. The X-ray Diffraction indicated the polycrystalline nature of the film.

One-step synthesis of pure γ-FeNi alloy by reaсtive sol–gel combustion route: mechanism and properties

A pure crystalline γ-FeNi alloy powder was fabricated through the one-step process of sol–gel combustion. An experiment was conducted in inert atmosphere with the hexamethylenetetramine (HMTA) used as an oxygen-free fuel and metal nitrites as oxidizers. It was demonstrated that fuel-to-oxidizer ratio is a critical parameter to produce pure γ-FeNi alloy. A concentration of the fuel necessary for the alloy synthesis is three times higher (φ = 3) than at the stochiometric molar ratio. The ~1100 K maximum temperature, 830 K/s heating and 170 K/s cooling rates and the total reaction time of ~3 s are characteristics of the optimized sol–gel combustion synthesis of the γ-FeNi alloy powder. A mechanism of the alloy formation through the coordination metals—HMTA complex was proposed and experimentally verified. Microstructural and magnetic properties of the synthesized material are also investigated and discussed.

Fast production of zinc–hexamethylenetetramine complex microflowers as an advanced sulfur reservoir for high-performance lithium–sulfur batteries

Hierarchical zinc–hexamethylenetetramine complex microflowers were developed to establish a multifunctional interlayer towards high-capacity and durable lithium–sulfur batteries.

Utilization of CO2 and N2 for selective synthesis of styrene from ethylbenzene over high surface area γ-Al2O3 supported molybdenum nitride catalysts

The present work highlights the synthesis of styrene from ethylbenzene dehydrogenation by coupling with reverse water gas shift reaction (RWGSR) and ammonia synthesis reactions over high surface area Al2O3 supported molybdenum nitride (γ-Mo2N) catalyst. γ-Mo2N was prepared by in-situ thermal decomposition of molybdenum hexamethylenetetramine complex and the support high surface area Al2O3 (HSA) was prepared by sol-gel method. Different weight loadings of γ-Mo2N (10, 20 and 30) supported on HSA catalysts were systematically characterized by using powder XRD, N2 physisorption, H2 - TPR, XPS and TEM analysis. XRD, TEM and normalized BET surface area analysis reveal highly dispersed nitride species over HSA surface. The synthesized catalysts have been studied for ethylbenzene dehydrogenation reaction using CO2 and N2 as feed gases with different percentage compositions. It was found that CO2 rich N2 feed gas favors higher ethylbenzene conversion due to RWGSR and N2 rich CO2 favors higher selectivity to styrene due to ammonia synthesis. EB dehydrogenation along with RWGSR and ammonia synthesis reactions come along and privileged the formation of higher styrene yields.

Structural variations in self-assembled coordination complexes of hexamethylenetetramine, zinc(II) and carboxylates (RCOO−, R = –CH3/−C6H5): Encapsulation of the water hexamer in benzoate assembly

Two new zinc(II) complexes [Zn2(ac)3(hmt)2(OH)]·H2O (1) and [{Zn5(Obz)8(H2O)2(μ3-OH)2}(μ2-hmt){Zn2(Obz)4}·6H2O]n (2) have been synthesized using two different carboxylate salts (acetate (ac) for 1 and benzoate (Obz) for 2) and hexamethylenetetramine (hmt). Both the complexes have been structurally characterized by X-ray crystallography. Their identities have also been established by elemental analysis and IR spectral studies. Complex 1 is a dimer in which two zinc atoms contain equivalent four-coordinate tetrahedral environments. On the other hand, complex 2 is a 1D zig-zag coordination polymer containing alternative zinc pentamers and zinc dimers separated by bridging μ2-hmts. The centrosymmetric pentamer unit contains three independent zinc atoms, one being four-coordinate with a tetrahedral environment and other two being six-coordinate with octahedral geometries whereas the centrosymmetric dimer unit contains two five-coordinate Zn atoms with square pyramidal geometries. H-bonding interactions play a key role in stabilizing the observed structures. In complex 1, the water molecule is held within the dimer and in 2, a rare water hexamer is encapsulated in the supramolecular assembly by hydrogen bonds. The DFT calculations reveal that inter- and outer-cluster H-bond stabilization energies of water hexamer are −29.99 and −15.93 kcal/mol respectively. Lower stabilization energy from the ideal hexamer of chair conformer is attributed to the deformation of H-atoms as well as longer hydrogen bonded O⋯O distances. Additionally, the extra stability due to outer-cluster H-bonds is responsible for significant deformation from ideal chair conformer of hexamer cluster.

Complex of hexamethylenetetramine with magnesium-tetraphenylporphyrin: Synthesis, structure, spectroscopic characterizations and electrochemical properties

A new crystalline material of a magnesium (II)–porphyrin complex was prepared and characterized by single crystal X-ray diffraction. The molecular structure is made by (5,10,15,20-tetraphenylporphyrinato-κ4N)bis(hexamethylenetetramine) magnesium dichloromethane disolvate. The title compound crystallizes in the orthorhombic system, space group Pbcn, with a = 19.2932 (6) Å, b = 10.4878 (4) Å, c = 26.0025 (14) Å, V = 5261.4 (4) Å3 and Z = 4. The supramolecular architecture includes weak C__H⋯N hydrogen bond. This magnesium-porphyrin species was also characterized by UV–visible, IR and fluorescence spectroscopy and a cyclic voltammetry investigation was also carried out on this species.

ChemInform Abstract: Sponge‐Like Silver Obtained by Decomposition of Silver Nitrate Hexamethylenetetramine Complex.

AbstractDecomposition of AgNO3·hexamethylenetetramine (obtained from an aqueous mixture of AgNO3 and hexamethylenetetramine) under N2 above 200 °C leads to the formation of sponge‐like silver with pore sizes from 10 μm to 10 nm.

Sponge-like silver obtained by decomposition of silver nitrate hexamethylenetetramine complex

Silver nitrate hexamethylenetetramine [Ag(NO3)·N4(CH2)6] coordination compound has been prepared via aqueous route and characterized by chemical analysis, XRD and electron microscopy. Decomposition of [Ag(NO3)·N4(CH2)6] under hydrogen and under inert has been studied by thermal analysis and mass spectrometry. Thermal decomposition of [Ag(NO3)·N4(CH2)6] proceeds in the range 200–250°C as a self-propagating rapid redox process accompanied with the release of multiple gases. The decomposition leads to formation of sponge-like silver having hierarchical open pore system with pore size spanning from 10µm to 10nm. The as-obtained silver sponges exhibited favorable activity toward H2O2 electrochemical reduction, making them potentially interesting as non-enzyme hydrogen peroxide sensors.

Cobalt(II) and Zinc(II) Complexes of Hexamethylenetetramine as Single Source Precursors for their Metal Oxide Nanoparticles

Co3O4 and ZnO nanoparticles with different morphologies were synthesised by the thermal decomposition of single source precursors obtained from readily available and eco-friendly starting materials (hexamethylenetetramine and metal nitrates). The precursors, which were characterized by elemental analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction and thermal gravimetric analysis, were calcined at 500oC for 2 h, and the oxide samples obtained were characterized by FTIR, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and nitrogen physisorption. XRD showed that the oxides obtained were crystalline and free of extraneous impurity phases. The morphology of the nanoparticles obtained changed from cube-like (Co3O4) to hexagonal-prism like morphology (ZnO), while the particle size increased from 19.6 to 64.5 nm, respectively. The method used simple and cheap precursors, which should make it suitable for large-scale synthesis.

Kinetics of thermolysis of lanthanum nitrate with hexamethylenetetramine: Crystal structure, TG–DSC, impact and friction sensitivity studies, Part-96

The development of high energetic materials includes process ability and the ability to attain insensitive munitions (IM). This paper investigates the preparation of lanthanum metal nitrate complex of hexamethylenetetramine in water at room temperature. This complex of molecular formulae [La (NO3)2(H2O)6] (2HMTA) (NO3−) (H2O) was characterized by X-ray crystallography. Thermal decomposition was investigated using TG, TG–DSC and ignition delay measurements. Kinetic analysis of isothermal TG data has been investigated using model fitting methods as well as model free isoconversional methods. The sensitivity measurements towards mechanical destructive stimuli such as impact and friction were carried out and the complex was found to be insensitive. In order to identify the end product of thermolysis, X-ray diffraction patterns of end product was carried out which proves the formation of La2O3.

CdO Nanoparticles by Thermal Decomposition of a Cadmium- Hexamethylenetetramine Complex

CdO nanoparticles have been prepared by the thermal decomposition of a precursor complex. A simple and cost effective room temperature synthetic technique allows the preparation of the precursor complex from hexamethylenetetramine and cadmium nitrate in ethanol. The precursor, characterized by elemental analysis, mass spectrometry, Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis, had the composition [{Cd(HMTA)(NO3)2(H2O)2}n]. It was calcined at 500 oC for 2 h, and the cadmium oxide nanoparticles obtained was characterized by X-ray diffraction (XRD), scanning electron microscopy, high resolution transmission electron microscopy (HRTEM), Nitrogen adsorption and physisorption, and Selected Area Electron Diffraction (SAED). XRD shows that the CdO obtained is pure and crystalline. The particles obtained had a cubic morphology and are mesoporous.

HDS and HDN activity of (Ni,Co)Mo binary and ternary nitrides prepared by decomposition of hexamethylenetetramine complexes

Highly dispersed pure phases of binary and ternary nitrides (Co,Ni)Mo were prepared using decomposition of hexamethylenetetramine (HMTA) complexes. Their catalytic activity was evaluated in the HDS of thiophene and HDN of quinoline. Three different pre-treatment modes were applied, including direct in situ preparation of nitrides in the catalytic reactor; pre-sulfidation with hydrogen sulfide and soft oxidation in air followed by sulfidation. Pure bimetallic nitrides are highly active HDN catalysts in the absence of sulfur and show substantial synergy effect between Ni or Co and Mo. By contrast, no synergy was observed for thiophene HDS, specific surface rates for binary and ternary nitrides being similar to that of unsupported MoS 2. Transmission microscopy, XRD and XPS studies showed that MoS 2 segregation on the surface occurs during HDS reaction or sulfidation with H 2S. As a result bimetallic catalysts contained nitride particles covered with MoS 2 layers and VIII group metal sulfide crystalline particles in the subsurface layer. The introduction in the preparation sequence of an additional step of oxidation–sulfidation led to a considerable increase of HDS catalytic activity of bimetallic catalysts. Pre-sulfidation of nitrides with H 2S/H 2 mixture resulted in a drastic decrease of specific surface area (Ssp) and very low HDS activity. Soft sulfidation with thiophene under reaction conditions led to high Ssp and high HDS activity per unit of mass.

Seven hexamethylenetetramine (HMTA) complexes with mono- and dicarboxylic acids: analysis of packing modes of HMTA complexes in the literature

The crystal structures of seven hexamethylenetetramine (HMTA) complexes, or co-crystals, with carboxylic acid donor molecules are reported to explain the link between the molecular structure of HMTA and the crystal structure of the co-crystals, i.e. the dimension and shape of their hydrogen-bonded assembly. A comprehensive and detailed literature survey of HMTA complexes (38), be they neutral co-crystals or salts, with molecules containing carboxylic acid and phenol functional groups reveals that in general two N acceptors are used for strong O-H···N interactions. Owing to the relative arrangement of two of the four N atoms, the most common type of assembly features one-dimensional zigzag chains. Weak interactions of the C-H···N type are formed by N atoms not involved in strong interactions. These chains also form the basis of two-dimensional assemblies. These one- and two-dimensional assemblies feature either two or three functional groups. If only one functional group is on the donor molecule, then wing or V-shaped zero-dimensional assemblies are formed, which can be considered to be the building blocks for one- and two-dimensional assemblies. In general, the HMTA molecules form two-dimensional layers which are stabilized by weak hydrogen bonds. Co-crystals with cyclohexylcarboxylic acid (I), 4-fluorobenzoic acid (II), 4-methylbenzoic acid (III) and cinnamic acid (IV) all feature the V-shaped zero-dimensional assemblies. Co-crystals with cis-1,4-cyclohexyldicarboxylic acid (VI) and trans-1,4-cyclohexylcarboxylic acid (VII) feature the zigzag chains and can be structurally derived from co-crystal (I). Co-crystal (V), with 4-nitrobenzoic acid, has solvent water included and features hydrogen bonding to all four N atoms of the HMTA molecule.

Simultaneous determination of Pt and Rh by catalytic adsorptive stripping voltammetry, using hexamethylene tetramine (HMTA) as complexing agent

Characteristics of the adsorption/electro-reduction of Pt/Rh hexamethylene tetramine (HMTA) complex on static mercury drop electrode surface were studied. Cyclic voltammetry was carried out to get the insight about the mechanistic behaviour of the catalytic current obtained in the voltammetric scan of Pt/Rh HMTA complex in acidic solution. Adsorptive stripping voltammetry using HMTA as the complexing agent was found to be highly sensitive method for the determination of Pt/Rh. Voltammetric measurements were carried out using hanging mercury drop electrode (HMDE) as the working electrode, a glassy carbon rod as the counter and an Ag/AgCl/KCl saturated as the reference electrode. Various electrochemical parameters like deposition potential, deposition time, concentration of the ligand, supporting electrolyte etc. were optimized. The detection limit of Pt and Rh was found to be 4.38 pML −1 and 2.80 pML −1, respectively for the deposition time of 30 s. Simultaneous determination of Pt(II) and Rh(III) in water samples was possible. The method was found to be free from the commonly occurring interfering ions such as Cu(II), Cd(II), Zn(II), Pb(II), Cr(III), Cr(VI), Fe(III), Fe(II), Ni(II) and Co(II). Spike recovery tests for both Pt and Rh in tap water and sea water samples were also carried out. The method has been verified by analyzing certified reference material (WMG-1).

Preparation, X-ray Crystallography, and Thermal Decomposition of Some Transition Metal Perchlorate Complexes of Hexamethylenetetramine

The perchlorate complexes of manganese, nickel, and zinc with hexamethylenetetramine (HMTA) of the general formula [M(H2O-HMTA-H2O)2(H2O-ClO4)2(H2O)2] (where M=Mn, Ni, and Zn) have been prepared and characterized by X-ray crystallography. Thermal studies were undertaken using thermogravimetry (TG), differential thermal analysis (DTA), and explosion delay (DE) measurements. The kinetics of thermal decomposition of these complexes was investigated using isothermal TG data by applying isoconversional method. The decomposition pathways of the complexes have also been proposed. These were found to explode when subjected to higher temperatures.

The synthesis, crystal structure and thermal studies of a mixed-ligand 1,10-phenanthroline and hexamethylenetetramine complex of lanthanum nitrate. Insight into coordination sphere geometry changes of lanthanide(III) 1,10-phenanthroline complexes

The structure of tetraaqua-bis(nitrato-O,O′)-(1,10-phenanthroline-N,N′)-lanthanum(III) 1,3,5,7-tetraazatricyclo[3.3.1.13,7]decane nitrate dihydrate, [La(NO3)2 · phen · (H2O)4]+ · hmt · NO3− · 2H2O, is presented. The lanthanum ion exhibits tenfold coordination and the polyhedron can be described as tetradecahedron. The complex cations, nitrate ions, water and hexamethylenetetramine molecules are assembled via hydrogen bonds, H–π rings and π–π stacking interactions into 3D supramolecular network. The bond strength of coordination sphere was calculated by means of the bond-valence method. The influence of La:phen stoichiometry and additional ligand on the changes of lanthanum(III) coordination sphere geometry in ten-coordinated complexes with 1,10-phenanthroline was discussed. The infrared spectrum of structure optimised by means of quantum mechanical calculations was analysed and compared with measured one. The obtained compound was characterised by thermogravimetric analysis in conjunction with evolved gases in the air atmosphere.

Preparation, structure and properties of nitrile–butadiene rubber–organoclay nanocomposites by reactive mixing intercalation method

AbstractThe nanocomposites of nitrile–butadiene rubber (NBR) and organo‐montmorillonite modified by hexadecyltrimethyl ammonium bromide (HMMT) were prepared by the reactive mixing intercalation method in the presence of the resorcinol and hexamethylenetetramine complex (RH). The structure of the NBR–RH–HMMT nanocomposites was characterized by XRD, TEM, FTIR, determination of crosslinking density, and so on. The results showed that the d‐spacing of HMMT increased substantially with RH addition and the layers of HMMT were dispersed in rubber matrix on a nanometer scale. The mechanical properties of the NBR–RH–HMMT nanocomposites were far superior to those of NBR–HMMT composites, and the glass transition temperature of NBR–RH–HMMT nanocomposite was higher than that of NBR. The reactive mixing intercalation method by introducing RH could enhance the interface combination between the rubber and the organoclay through the interactions of RH with NBR and modified clay. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1905–1913, 2006