Binary Adducts Research Articles

Supramolecular Synthons in Bumetanide Cocrystals and Ternary Products

A novel design strategy for cocrystals of the diuretic sulfonamide drug bumetanide (BUM) with carboxamides is reported based on reliable supramolecular synthons. Binary cocrystals of BUM with pyridine carboxamides, pyridones, and cytosine were obtained by solvent-assisted grinding followed by solution crystallization. All cocrystal structures exhibit hydrogen bonding of the coformer with the carboxylic acid group of BUM via heterosynthons which replace the acid homodimer in the drug crystal structure. Pyridones are inserted as N–H···O dimers which are in turn bonded to the acid group of BUM, while the pyridine amide coformers interact via the acid–amide heterosynthon. Cocrystal polymorphs were obtained for bumetanide–isonicotinamide cocrystal structure with the sulfonamide–pyridine and sulfonamide–acid synthons. Careful crystal packing analysis of BUM structure and nine new binary adducts gave an idea for the design ternary cocrystals, and subsequently four new ternary crystalline products were crystalliz...

Order–disorder phase transition induced by proton transfer in a co-crystal of 2,4-dichlorobenzoic acid and trimethylamine N-oxide

A crystalline binary adduct between trimethylamine N-oxide and 2,4-dichlorobenzoic acid was obtained. The molecular system was thermally characterized, subsequently demonstrating an order–disorder transition.

Binary adduct formation of desipramine with dicarboxylic acids

This paper presents the results obtained in a screening study for binary adduct formation of desipramine with three dicarboxylic acids—namely succinic, malonic and glutaric acids. Adduct formation is important because most tricyclic antidepressants show limited water solubility as free bases. Three binary adducts were prepared using a wet kneading method in non-homogenous media in presence of ethanol. Investigations of the solid state (ATR-FTIR, PXRD) and thermal analysis (TG/DTG/HF) were used for characterization of the prepared samples. The corroboration of data from employed instrumental techniques suggests that binary adducts in molar ratio 1:1 were obtained under the used experimental conditions.

Structural similarities and diversity in a series of crystalline solids composed of 2-aminopyridines and glutaric acid

A solvent co-crystallization of three 2-aminopyridine derivatives, 2-aminopyridine (AP), 2-amino-6-methylpyridine (AMP), and 2,6-diaminopyridine (DAP) with the odd-membered propane-1,3-dicarboxylic acid (C5H12O4 = GAH2, glutaric acid) resulted in six ionic crystalline products, (HAP)(GAH) (1), (HAMP)(GAH) (2, 3), (HDAP)(GAH) (4), (HDAP)2(GA) (5), and (HDAP)2(DAP)(GA)(EtOH) (6, EtOH = ethanol). New compounds were characterized by single-crystal and powder X-ray diffraction, melting points, and IR spectra. The proton transfer to the pyridine nitrogen atom in all compounds and the location of H-atom in the carboxylic group in the hydrogen glutarate anion in binary adducts 1–4 was determined reliably from the low-temperature X-ray experiments. All compounds adopt the recurring R22(8) 2-aminopyridine–carboxylic acid heteromeric supramolecular synthon. The aggregation of hydrogen glutarate anions in the C(8) chain motifs in 1–4 occurs via the homomeric COOH···COO− robust pattern. Adducts 2 and 3 represent conformational polymorphs; adducts 4, 5 and 6 reveal the diversity in the components’ forms (ionic and neutral), acid–base ratios (1:1, 1:2, and 1:3), and hydrogen-bonding systems. This work demonstrates the variety of forms of glutaric acid in the H-bonded adducts.

Binary and ternary cocrystals of sulfa drug acetazolamide with pyridine carboxamides and cyclic amides.

A novel design strategy for cocrystals of a sulfonamide drug with pyridine carboxamides and cyclic amides is developed based on synthon identification as well as size and shape match of coformers. Binary adducts of acetazolamide (ACZ) with lactams (valerolactam and caprolactam, VLM, CPR), cyclic amides (2-pyridone, labeled as 2HP and its derivatives MeHP, OMeHP) and pyridine amides (nicotinamide and picolinamide, NAM, PAM) were obtained by manual grinding, and their single crystals by solution crystallization. The heterosynthons in the binary cocrystals of ACZ with these coformers suggested a ternary combination for ACZ with pyridone and nicotinamide. Novel supramolecular synthons of ACZ with lactams and pyridine carboxamides are reported together with binary and ternary cocrystals for a sulfonamide drug. This crystal engineering study resulted in the first ternary cocrystal of acetazolamide with amide coformers, ACZ-NAM-2HP (1:1:1).

Single crystals that spontaneously spawn other single crystals: a ternary and a binary adduct of thiourea and 2,5-dimethylpyrazine

Liquid diffusion of n-pentane into a solution of thiourea in 2,5-dimethylpyrazine led to a crystalline 4 : 3 adduct (1), in which corrugated thiourea layers are crosslinked with pyrazines. Attempts to obtain adducts with other stoichiometries, by crystallizing thiourea from a mixture of 2,5-dimethylpyrazine and methanol, formed the ternary 1 : 1 : 1 adduct 2 instead. Adduct 2 displays a layer structure in which parallel thiourea ribbons are linked on the one side by pyrazines and on the other side by methanol and pyrazines, leading to repeating crosslink sequences (⋯thiourea⋯methanol⋯pyrazine⋯methanol⋯thiourea⋯pyrazine⋯); the ribbons within a layer are thus unequally spaced. In inert oil, individual single crystals of 2 spontaneously convert to several smaller crystals, some single, of 1. The process may be regarded as a single-crystal to single-crystal transformation, although not in the usual sense. The 4 : 3 adduct (3) of thiourea with 2-methylpyrazine is isotypic to 1. In all three structures, the preponderant secondary interactions are classical hydrogen bonds.

Binary supramolecular adduct based upon trimeric perfluoro-ortho-phenylenemercury and 4-chlorobenzaldehyde: Enumerating the strength of perfluorophenyl–perfluorophenyl interactions

Due to its proximity of Hg(II) atoms, electron-withdrawing properties and inherent accessibility to electrophilic sites on the molecular surface, trimeric perfluoro-ortho-phenylenemercury, (o-C6F4Hg)3, has demonstrated a capacity to form supramolecular adducts with a variety of neutral and anionic substrates. Often within these complexes the Lewis acid, (o-C6F4Hg)3, interacts with a Lewis base rather than itself in the solid state via various supramolecular interactions. Among these, perfluorophenyl–perfluorophenyl interactions have been utilized in the construction of various supramolecular materials; however, within these molecular complexes, this category of non-covalent interaction is not often observed. Even though these perfluorophenyl–perfluorophenyl interactions have been used to produce new materials, their overall strength has not been generally reported in the literature. In this contribution, we highlight not only the synthesis, structural and spectroscopic properties of a novel binary supramolecular adduct between (o-C6F4Hg)3 and 4-chlorobenzaldehyde (4-ClBA) [(o-C6F4Hg)3(4-ClBA)] 1, but also report on the overall strength of the perfluorophenyl–perfluorophenyl interaction energies determined by means of computational chemistry. The carbonyl group of the 4-ClBA substrate was found to interact with all three mercury atoms within (o-C6F4Hg)3 via Hg⋯O contacts. An infrared spectroscopic analysis of 1 demonstrated a lower wavenumber for the carbonyl stretching frequency when compared to that for the free substrate confirming the presence of these Hg⋯O interactions.

New organic binary solids with phenolic coformers for NLO applications

Five binary adducts between N,N-dimethyl-4-[(E)-2-(pyridin-4-yl)ethenyl]aniline) 1, N,N-diethyl-4-[(E)-2-(pyridin-4-yl)ethenyl]aniline) 2, N,N-dimethyl-4-[(E)-pyridin-3-yldiazenyl]aniline 3, and coformers that include 4-nitrophenol I, 4-nitrobenzoic acid II, benzene-1,3-diol III, and 2,4-dinitrophenol IV were synthesized to follow the factors influencing the formation of polar crystals. New solids were characterized by melting points and absorption spectra, while their structures were proven by single crystal X-ray diffraction. Adducts differ by the components' ratio and position of the acidic hydrogen atom, thus giving examples of four new cocrystals and one salt. The single crystal X-ray analysis revealed the acentric packing for two compounds, 1 (I) and 3(3) (III) that crystallize in the Pca21 and P1 space groups. The melting point data and the cut-off wavelength from absorption spectra show that these materials are stable till relatively high temperatures and transparent in a wide range of spectrum.

Synthesis, spectroscopic properties, and photoconductivity of black absorbers consisting of pt(bipyridine)(dithiolate) charge transfer complexes in the presence and absence of nitrofluorenone acceptors.

The diimine-dithiolato ambipolar complexes Pt(dbbpy)(tdt) and Pt(dmecb)(bdt) (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine; tdt(2-) = 3,4-toluenedithiolate; dmecb = 4,4'-dimethoxyester-2,2'-bipyridine; bdt(2-) = benzene-1,2-dithiolate) are prepared herein. Pt(dmecb)(bdt) exhibits photoconductivity that remains constant (photocurrent density of 1.6 mA/cm(2) from a 20 nm thin film) across the entire visible region of the solar spectrum in a Schottky diode device structure. Pt(dbbpy)(tdt) acts as donor when combined with the strong nitrofluorenone acceptors 2,7-dinitro-9-fluorenone (DNF), 2,4,7-trinitro-9-fluorenone (TRNF), or 2,4,5,7-tetranitro-9-fluorenone (TENF). Supramolecular charge transfer stacks form and exhibit various donor-acceptor stacking patterns. The crystalline solids are "black absorbers" that exhibit continuous absorptions spanning the entire visible region and significant ultraviolet and near-infrared wavelengths, the latter including long wavelengths that the donor or acceptor molecules alone do not absorb. Absorption spectra reveal the persistence of donor-acceptor interactions in solution, as characterized by low-energy donor/acceptor charge transfer (DACT) bands. Crystal structures show closely packed stacks with distances that underscore intermolecular DACT. (1)H NMR provides further evidence of DACT, as manifested by upfield shifts of aromatic protons in the binary adducts versus their free components, whereas 2D nuclear Overhauser effect spectroscopy (NOESY) spectra suggest coupling between dithiolate donor protons with nitrofluorenone acceptor protons, in correlation with the solid-state stacking. The NMR spectra also show significant peak broadening, indicating some paramagnetism verified by magnetic susceptibility data. Solid-state absorption spectra reveal further red shifts and increased relative intensities of DACT bands for the solid adducts vs solution, suggesting cooperativity of the DACT phenomenon in the solid state, as further substantiated by νC-O and νN-O IR bands and solid-state tight-binding computational analysis.

Structure and tunneling dynamics in a model system of peptide co-solvents: rotational spectroscopy of the 2,2,2-trifluoroethanol⋯water complex.

The hydrogen-bonding topology and tunneling dynamics of the binary adduct, 2,2,2-trifluoroethanol (TFE)⋯water, were investigated using chirped pulse and cavity based Fourier transform microwave spectroscopy with the aid of high level ab initio calculations. Rotational spectra of the most stable binary TFE⋯water conformer and five of its deuterium isotopologues were assigned. A strong preference for the insertion binding topology where water is inserted into the existing intramolecular hydrogen-bonded ring of TFE was observed. Tunneling splittings were detected in all of the measured rotational transitions of TFE⋯water. Based on the relative intensity of the two tunneling components and additional isotopic data, the splitting can be unambiguously attributed to the tunneling motion of the water subunit, i.e., the interchange of the bonded and nonbonded hydrogen atoms of water. The absence of any other splitting in the rotational transitions of all isotopologues observed indicates that the tunneling between g+ and g- TFE is quenched in the TFE⋯H2O complex.

Acemetacin cocrystals and salts: structure solution from powder X-ray data and form selection of the piperazine salt.

Acemetacin (ACM) is a non-steroidal anti-inflammatory drug (NSAID), which causes reduced gastric damage compared with indomethacin. However, acemetacin has a tendency to form a less soluble hydrate in the aqueous medium. We noted difficulties in the preparation of cocrystals and salts of acemetacin by mechanochemical methods, because this drug tends to form a hydrate during any kind of solution-based processing. With the objective to discover a solid form of acemetacin that is stable in the aqueous medium, binary adducts were prepared by the melt method to avoid hydration. The coformers/salt formers reported are pyridine carboxamides [nicotinamide (NAM), isonicotinamide (INA), and picolinamide (PAM)], caprolactam (CPR), p-aminobenzoic acid (PABA), and piperazine (PPZ). The structures of an ACM-INA cocrystal and a binary adduct ACM-PABA were solved using single-crystal X-ray diffraction. Other ACM cocrystals, ACM-PAM and ACM-CPR, and the piperazine salt ACM-PPZ were solved from high-resolution powder X-ray diffraction data. The ACM-INA cocrystal is sustained by the acid⋯pyridine heterosynthon and N-H⋯O catemer hydrogen bonds involving the amide group. The acid⋯amide heterosynthon is present in the ACM-PAM cocrystal, while ACM-CPR contains carboxamide dimers of caprolactam along with acid-carbonyl (ACM) hydrogen bonds. The cocrystals ACM-INA, ACM-PAM and ACM-CPR are three-dimensional isostructural. The carboxyl⋯carboxyl synthon in ACM-PABA posed difficulty in assigning the position of the H atom, which may indicate proton disorder. In terms of stability, the salts were found to be relatively stable in pH 7 buffer medium over 24 h, but the cocrystals dissociated to give ACM hydrate during the same time period. The ACM-PPZ salt and ACM-nicotinamide cocrystal dissolve five times faster than the stable hydrate form, whereas the ACM-PABA adduct has 2.5 times faster dissolution rate. The pharmaceutically acceptable piperazine salt of acemetacin exhibits superior stability, faster dissolution rate and is able to overcome the hydration tendency of the reference drug.

Fourier Transform Infrared Spectroscopic Investigation of the Binary and Ternary Cyanide Adducts of the Oxidized Horseradish Peroxidase: Identification of a Second Stretching Mode for the Carbon-Nitrogen Bond of the Bound Cyanide Ion

ABSTRACT The binary and ternary cyanide adducts of the ferric horseradish peroxidase were investigated by Fourier transform infrared spectroscopy. The carbon-nitrogen bond of the bound cyanide ion in the binary ferric cyanohorseradish peroxidase exhibits two stretching vibrations at 2130 cm−1 and 2127 cm−1 with the latter mode being observed in this work for the first time. This finding supports the results of the resonance Raman study of cyanohorseradish peroxidase, which identified two iron-carbon-nitrogen bending vibrations and two iron-carbon stretching vibrations, proving the existence of two conformational states. The identification of the latter carbon-nitrogen stretching frequency allowed the assignment of all of the vibrational modes of the iron-carbon-nitrogen groups of the two conformational states of the ferric cyanohorseradish peroxidase. The first conformer is characterized by a carbon-nitrogen stretch at 2130 cm−1, an iron-carbon stretch at 453 cm−1, and an iron-carbon-nitrogen bending mode at 405 cm−1. The second state has a carbon-nitrogen stretch at 2127 cm−1, an iron-carbon stretch at 360 cm−1, and an iron-carbon-nitrogen bending mode at 422 cm−1. The iron-carbon stretching band is weakly sensitive to pH changes, but it is sensitive to H2O/D2O substitution, indicating that the bound cyanide ion in cyanohorseradish peroxidase is hydrogen bonded to the surrounding protein. The two states were attributed to variation in the extent of hydrogen bonding of the iron-carbon-nitrogen groups in the two states. The carbon-nitrogen stretching vibrations of the ternary complexes of cyanohorseradish peroxidase with ferulic acid, benzamide, and benzhydroxamic acid have been investigated for the first time. The binding of the substrate to cyanohorseradish peroxidase does not always lead to the vanishing of one of the conformational states as in the carbon monoxide adducts of the ferrous horseradish peroxidase, but can cause shifts in the νC-N frequency and in the relative population of both conformational states.

Nanomedicine: Action of Metal Nanoparticles on Neuronal Nitric Oxide Synthase—Fluorimetric Analysis on the Mechanism for Fibrillogenesis

The incubation of neuronal nitric oxide synthase with the five amyloid peptide fragments [Aβ17-21; Aβ25-29; Aβ29-33; Aβ33-37; Aβ25-37] catalyzed the formation of fibrils. The role of neuronal isomer (nNOS) involved the entrapment of free monomers and seed aggregates to initiate the events of nucleation and elongation, critical for the formation of fibrils. It was evident that the hydrophobic nature of Aβ17-21, the three glycine zipper peptides [Aβ25-29; Aβ29-33; Aβ33-37] and Aβ25-37 was a trigger in the formation of fibrils and was a force critical in the association of the peptides with the enzyme. Gold and silver nanoparticles (average 4.0 nm) inhibited fibril formation when added to the induced fibrils from nNOS-Aβ incubation. The addition of nNOS and/or Aβ to co-incubated solutions of nanoparticle-Aβ or nanoparticle-nNOS respectively did not prevent fibril formation but reversed it. Three mechanisms for this reversal were proposed: (1) depletion of free Aβ monomer in solution and blocking potential aggregation sites on the nNOS molecule due to large surface area of the nanoparticle (2) hydrophobic interaction between the Aβ peptide and nanoparticle (3) disruption of binary adducts between Aβ-peptides and nNOS by nanoparticles.

Phosphoryl chloride–methanol adducts: Matrix isolation infrared and DFT studies

The adducts of phosphoryl chloride (POCl3) and methanol (CH3OH) were studied using matrix isolation infrared spectroscopy and DFT calculations. The 1:1 POCl3:CH3OH binary adduct was generated in a nitrogen matrix at low temperatures and studied using infrared spectroscopy. Formation of the adduct was evidenced by the shifts in the vibrational frequencies of the modes involving POCl3 and CH3OH sub-molecules. The structures, vibrational frequencies and stabilization energies of the adducts were computed at B3LYP/aug-cc-pVDZ level of theory. Our computations located two minima for POCl3:CH3OH adducts on the potential energy surface. However, only one adduct was experimentally identified in the matrix at low temperatures, which was the structure corresponding to the global minimum. The computed vibrational frequencies of the adduct agreed well with the observed experimental frequencies. Atoms In Molecules (AIM) analysis was performed to understand the nature of the interactions in these adducts. Natural Bond Orbital (NBO) analysis was performed to understand the effect of charge-transfer interactions on the stability of adducts.

Norfloxacin salts with benzenedicarboxylic acids: charge-assisted hydrogen-bonding recognition and solubility regulation

The crystallization of norfloxacin, an antibacterial fluoroquinolone compound, with different benzenedicarboxylic acids yields five novel pharmaceutical salts via molecular recognition. X-ray single-crystal diffraction analyses reveal that these pharmaceutical agents present uniform charge-assistant hydrogen-bonding networks, which are in 1 : 1 stoichiometry of norfloxacin and dicarboxylate therein (with the exception of that with terephthalate). Unsubstituted benzenedicarboxylates (phthalate in 1, isophthalate in 2, and terephthalate in 3, respectively) are likely to crystallize with norfloxacin without lattice solvents, while the substituted isophthalate moieties (2-aminoisophthalate in 4 and 5-aminoisophthalate in 5) tend to form supramolecular adducts with the inclusion of water. Aromatic stacking interactions are present in all these structures, occurring between the fluoroquinolone and carboxylate phenyl rings (in 1–4) as well as between the fluoroquinolone planes (in 5). Thermal stability and solubility of all crystalline binary adducts have been determined. The effect of carboxylate counterions, substituents, and hydration states on the solubility and dissolution profile of drug salts 1–5 are investigated in pure water and 0.1 M HCl. After the formation of salts, the solubility increases at near neutral pH in almost all cases (except 3), but the order is changed in acidic medium. Phthalic acid shows evidence of a good candidate to enhance the solubility of fluoroquinolone drugs for the solubility of 1 is approximately 39 times as large as that of norfloxacin in pure water and also larger than that of norfloxacin in acidic system. For the isophthalates series, 2 has very poor solubility in 0.1 M HCl (only 0.06 times as that of Nf), while amino substituted isophthalates result in the enhancement of the solubility. Remarkably, crystal packing analyses of these pharmaceutical salts allow a possible correlation between the H-bonding prototypes and the solubility to be established.

Chirality Recognition in the Glycidol⋅⋅⋅Propylene Oxide Complex: A Rotational Spectroscopic Study

Chirality recognition in the hydrogen-bonded glycidol···propylene oxide complex has been studied by using rotational spectroscopy and ab initio calculations. An extensive conformational search has been performed for this binary adduct at the MP2/6-311++G(d,p) level of theory and a total of 28 homo- and heterochiral conformers were identified. The eight binary conformers, built of the two dominant glycidol monomeric conformers, g-G+ and g+G-, were predicted to be the most stable ones. Jet-cooled rotational spectra of six out of the eight conformers were observed and unambiguously assigned for the first time. The experimental stability ordering has been obtained and compared with the ab initio predictions. The relative stability of the two dominant glycidol monomeric conformers is reversed in some cases when binding to propylene oxide. The contributions of monomeric energy, deformation energy, and binary intermolecular interaction energy to the relative stability of the binary conformers are discussed.

Spectroscopic Investigation and Molecular Modeling on Porphyrin/PAMAM Supramolecular Adduct

Noncovalent adducts (TPPC@PAMAM) between meso-tetrakis(4-carboxyphenyl)porphyrin (TPPC) and polyamidoamine PAMAM dendrimer (generation 2.0) have been obtained by simply mixing the two components at different stoichiometric amount. The resulting species are readily soluble and stable in aqueous solution up to millimolar concentration. Electrostatic interactions between the anionic carboxylate groups of TPPC and the protonated amino groups of the PAMAM dendrimer play an important role in the stabilization of these adducts. UV/Vis absorption, steady state and time-resolved fluorescence emission and anisotropy measurements suggest the presence of equilibria involving different species as function of the [PAMAM]/[TPPC] ratio. At low ratios the observed spectroscopic behavior evidence the presence of H-aggregates, while at higher ratios well-defined species containing monomeric TPPC strongly interacting with the charged dendrimer are formed. Docking of the binary supramolecular adduct further supports the experimental results showing a favorable interaction with the porphyrin being completely included in the dendrimer. The interaction of the binary TPPC@PAMAM adduct (1/1 ratio) with calf-thymus DNA has been investigated through spectroscopic and photophysical techniques. All the experimental results point to the formation of a ternary complex between the binary adduct and the DNA backbone.

Hydrogen bonded binary molecular adducts derived from exobidentate N-donor ligand with dicarboxylic acids: Acid⋯imidazole hydrogen-bonding interactions in neutral and ionic heterosynthons

Four new binary molecular compounds between a flexible exobidentate N-heterocycle and a series of dicarboxylic acids have been synthesized. The N-donor 1,4-bis(imidazol-1-ylmethyl)benzene (bix) was reacted with flexible and rigid dicarboxylic acids viz., cyclohexane-1,4-dicarboxylic acid (H 2chdc), naphthalene-1,4-dicarboxylic acid (H 2npdc) and 1H-pyrazole-3,5-dicarboxylic acid (H 2pzdc), generating four binary molecular complexes. X-ray crystallographic investigation of the molecular adducts revealed the primary intermolecular interactions carboxylic acid⋯amine (via O–H⋯N) as well as carboxylate⋯protonated amine (via N–H +⋯O −) within the binary compounds, generating layered and two-dimensional sheet type H-bonded networks involving secondary weak interactions (C–H⋯O) including the solvent of crystallization. Depending on the differences in p K a values of the selected base/acid (Δp K a), diverse H-bonded supramolecular assemblies could be premeditated. This study demonstrates the H-bonding interactions between imidazole/imidazolium cation and carboxylic acid/carboxylate anion in providing sufficient driving force for the directed assembly of binary molecular complexes. In the two-component solid form of hetero synthons involving bix and dicarboxylic acid, only H 2chdc exist as cocrystal with bix, while all the other three compounds crystallized exclusively as salt, in agreement with the Δp K a values predicted for the formation of salts/cocrystals from the base and acid used in the synthesis of supramolecular solids.

Kinetic parameters for thermal decomposition of supramolecular polymers derived from flunixin-meglumine adducts

Meglumine, (2R,3R,4R,5S)-6-methylaminohexane-1,2,3,4,5-pentol, is a carbohydrate derived from sorbitol in which the hydroxyl group in position one is replaced by a methylamine group. It forms binary adducts with substances having carboxyl groups, which have in common the presence of hydrogen bonding as the main force in the stabilization of these species. During melting, adducts of meglumine with flunixin (2-[[2-methyl-3-(trifluoromethyl)phenyl]amino]pyridine-3-carboxylic acid) polymerize or self-assemble in amorphous supramolecular structures with molecular weights around 2.0 × 105 kDa. DSC curves, in a first heating, show isomorphic transitions where the last one at 137 °C for the flunixin-meglumine adduct originated the supramolecular amorphous polymers with glass transition around 49.5 °C. The kinetic parameters for the thermal decomposition step of the polymers were determined by the Capela-Ribeiro non-linear isoconversional method. From data for the TG curves in nitrogen atmosphere and heating rates of 5, 10, 15, and 20 °C min−1, the E α and B α terms could be determined and, consequently, the pre-exponential factor, Aα, as well as the kinetic model, g(α).

Sensitization of Naphthalene Monomer Phosphorescence in a Sandwich Adduct with an Electron-Poor Trinuclear Silver(I) Pyrazolate Complex

Facial complexation of naphthalene to {[3,5-(CF(3))(2)Pz]Ag}(3) (Ag(3)) gives rise to a stacked binary adduct (1) that exhibits phosphorescence corresponding to T(1) monomer emission of naphthalene. Crystals and powders of 1 exhibit bright-green phosphorescence at room temperature with a 830 mus lifetime, whereas cooling to cryogenic temperatures increases the intensity, lifetime, and vibronic resolution. The binary adduct exhibits a drastically shorter phosphorescence lifetime of 6.7 ms versus free naphthalene (2.4 s) in a frozen dichloromethane matrix, which results from the external heavy-atom effect of silver. Adduct 1 represents a new class of phosphors containing lighter but more benign silver than mercury atoms in trinuclear d(10) pi-acid complexes as arene triplet sensitizers.