C-S bond cleavage of 2-methoxythiophene by Ir-TMEDA complex (TMEDA = N,N,N’,N’-tetramethylethylenediamine). Formation of novel dinuclear iridathiacyclohexenyl complex

The Ir-TMEDA complex [Ir(C₂H₄)₂(TMEDA)(MeCN)][BF₄] (TMEDA = Me₂NCH₂CH₂NMe₂) was treated with 2-methoxythiophene in MeCN at 70 °C in the presence of H₂O to afford the novel dinuclear iridathiacyclohexenyl complex [Ir₂{C(OMe)CHCHCH(CMeNH)S}(MeCONH)(TMEDA)₂][BF₄]₂ in 42% yield, in which two Ir(TMEDA) fragments, one 2-methoxythiophene, and two MeCN molecules are incorporated together with one H₂O molecule. The mechanism that involves the insertion of the Ir center into the thiophenic S-C(OMe) bond followed by the π-coordination of the second Ir center to the thiametallacycle has been proposed.     

Retention and Thermodynamic Studies of Piperazine Diastereomers in Reversed-Phase Liquid Chromatography

The effect of organic modifier concentration on retention and selectivity of two piperazine diastereomers in a typical n-octadecyl-bonded silica (ODS) column was investigated at pH 6.4 and pH 3.0 using phosphate-buffered acetonitrile (MeCN/H₂O) and methanol (MeOH/H₂O) mobile phases. The results show the logarithmic retention factors decrease with increasing organic concentration in a less rectilinear fashion in the MeCN/H₂O system than in the MeOH/H₂O system at high organic concentrations at both pHs. At pH 6.4, the MeOH/H₂O system provided significantly higher diastereomer selectivity than the MeCN/H₂O system, which can be ascribed to the hydrogen bonding interaction of methanol (as a hydrogen donor) with the piperazine amine moiety of the solute (as a hydrogen acceptor). At pH 3.0, both mobile phases provided high selectivity, in which both acetonitrile and methanol acted as hydrogen acceptors, while the protonated amine acted as the hydrogen donor. The effect of temperature on retention and selectivity was also studied in the two mobile phase systems at both pHs. It was found that at pH 6.4 the retention and selectivity were enthalpically driven in the MeOH/H₂O system, while entropically driven in the MeCN/H₂O system. However, the retention was entropically driven and the selectivity enthalpically driven in both systems at pH 3.0. Locally preferential solvating and hydrogen bonding effects are proposed to explain the anomalous retention and selectivity behaviors.     

Heteromolecular insertion of EtNCX (X = O, S) and RCN (R = CH3, C6H5) into tungsten hexachloride

The interactions of tungsten hexachloride with EtNCX (X = O, S) and RCN (R = CH₃, C₆H₅) were studied. In the case of E = CH₃, heterocumulenes are inserted at the W-Cl bond, while in the case of R = C₆H₅, they were inserted at a multiple tungsten-nitrogen bond of an intermediate imido complex [WCl₄(NCPh)(CNCl₂Ph)]. The IR, MALDI TOFF mass spectroscopy, and elemental analysis data confirmed that these interactions yielded the products of heteromolecular insertion, namely, [WCl₄{(EtNCO)₂(MeCN)Cl}], [WCl₄(EtNCS)₂(MeCN)Cl], [WCl₄N(CCl₂Ph)C(=NEt)O}], and WCl₄N(CCl₂Ph)C(=NEt)S}], whose compositions and structures were determined by the nature of the organic nitrile radical.     

Photochemical water reduction by molybdenum tetrachloride

The photolysis of MoCl₄(MeCN)₂ in MeCN in the presence of small amounts of H₂O proceeds according to the equation Mo^IVCl₄·H₂OMo^VIOCl₄ + H₂. It is suggested that a ligand field excited state of MoCl₄(H₂O) _n , which is initially populated by light absorption, is deactivated to a reactive metal-to-ligand (Mo^IVH₂O) charge transfer state.     

Sodium dithionite initiated addition of CF2Br2 to β-pinene and reactions of the adduct: Synthesis and the reactivity of new 1,1-difluorodienes

Sodium dithionite effectively promotes the addition of dibromodifluoromethane to the exocyclic double bond of β-pinene. The reaction proceeded in a MeCN/H₂O system to give almost quantitatively an adduct, 1-(2-bromo-2,2-difluoroethyl)-4-(2-bromoisopropyl)-cyclohexene, as the sole product. On treatment of the adduct with 2,2,6,6-tetramethylpiperidine elimination of HBr only from the (CH₃)₂CHBr group occurred to give a mixture of regioisomeric dienes, while treatment with 50% KOH under phase transfer catalysis conditions or with K₂CO₃ in DMF resulted in total dehydrobromination to give trienes possessing an exocyclic CHCF₂ group. Surprisingly, the main course of the reactions of the adduct with DBU (1,8-diazabicyclo[5.4.0]undece-7-ene) and also with t-BuOK in THF was elimination of HBr only from the CH₂CF₂Br group to afford 1-(2,2-difluorovinyl)-4-(2-bromoisopropyl)cyclohexene as the main product. Catalytic hydrogenation of the adduct followed by treatment with DBU afforded a conjugated diene, 1-(2,2-difluorovinyl)-4-isopropylcyclohexene. Compounds bearing the CHCF₂ group are new 1,1-difluorodienes which readily reacted with 4-phenyl-3H-1,2,4-triazoline-3,5-dione to give cycloadducts, derivatives of triazolo[1,2-α]cinnoline.     

The kinetics of radiation-induced hydrogen abstraction by CCl3 radicals in the liquid phase: Cyclohexene

The kinetics of hydrogen abstraction from cyclohexene by CCl₃ radicals were studied in CCl₄ solution as a function of cyclohexene concentration and temperature in the range of 26–140°C. The CCl₃ radicals were produced both by radiolysis of CCl₄ and by photolysis of CCl₃Br. The rate constant for the reaction was found to be given by the equation where θ = 2.303 RT kcal/mol. This activation energy leads to C? H bond strength for the allylic hydrogen of 85 ± 1 kcal/mol, which means a resonance stabilization energy of 11 ± 1.5 kcal/mol for the C-C₆H₁₁ radical.     

Solid state and solution study of some phosphoramidate derivatives containing the P(O)NHC(O) bifunctional group: Crystal structures of CCl2HC(O)NHP(O)(NCH3(CH2C6H5))2, p-ClC6H4C(O)NHP(O)(NCH3(CH2C6H5))2, CCl2HC(O)NHP(O)(N(CH2C6H5)2)2 and p-BrC6H4C(O)NHP(O)(N(CH2C6H5)2)2

Synthetic methods for several novel phosphoramidate compounds containing the P(O)NHC(O) bifunctional group were developed. These compounds with the general formula R₁C(O)NHP(O)(N(R₂)(CH₂C₆H₅))₂, where R₁ = CCl₂H, p-ClC₆H₄, p-BrC₆H₄, o-FC₆H₄ and R₂ = hydrogen, methyl, benzyl, were characterized by several spectroscopic methods and analytical techniques. The effects of phosphorus substituents on the rotation rate around the P–N_amine bond were also investigated. ¹H NMR study of the synthesized compounds demonstrated that the presence of bulky groups attached to the phosphorus center and electron withdrawing groups in the amide moiety lead to large chemical-shift non-equivalence (Δδ_H) of diastereotopic methylene protons. The crystal structures of CCl₂HC(O)NHP(O)(NCH₃(CH₂C₆H₅))₂, p-ClC₆H₄C(O)NHP(O)(NCH₃(CH₂C₆H₅))₂, CCl₂HC(O)NHP(O)(N(CH₂C₆H₅)₂)₂ and p-BrC₆H₄C(O)NHP(O)(N(CH₂C₆H₅)₂)₂ were determined by X-ray crystallography using single crystals. The coordination around the phosphorus center in these compounds is best described as distorted tetrahedral and the P(O) and C(O) groups are anti with respect to each other. In the compound Br-C₆H₄C(O)NHP(O)(N(CH₂C₆H₅)₂)₂ (with two independent molecules in the unit cell), two conformers are connected to each other via two different N–H?O hydrogen bonds forming a non-centrosymmetric dimer. In the crystalline lattice of other compounds, the molecules form centrosymmetric dimers via pairs of same N–H?O hydrogen bonds. The structure of CCl₂HC(O)NHP(O)(N(CH₂C₆H₅)₂)₂ reveals an unusual intramolecular interaction between the oxygen of CO group and amine nitrogen.     

Der unterschiedliche Charakter von Wasserstoffbindungen in Komplexen zwischen Wasser und organischen Basen

Zusammenfassung Die 11-Komplexe von H₂O mit Dioxan (als Beispiel einer schwachen Base) und Triäthylamin (Et ₃N) (als Beispiel einer starken Base) werden in verd. Lösung in nichtpolaren Lösungsmitteln (CCl₄, Benzol) untersucht. Wie erwartet, ist im Vergleich zu H₂O:Et ₃N die Komplexbildungskonstante von H₂O: Dioxan kleiner, die Frequenzverschiebung der OH-Fundamentalschwingung geringer und die Veränderung der chemischen Verschiebung des OH-Protons schwächer ausgeprägt. Auch ist die Volumenkontraktion im System H₂O+Dioxan weniger bedeutend als im System H₂O+Et ₃N. Andererseits vermag H₂O in verd. Lösungen in Dioxan beide H-Atome unter H-Brückenbildung zu einem 2 Dioxan: 1 H₂O-Komplex zu betätigen, während H₂O in verd. Lösungen inEt ₃N lediglich den 11-Komplex ergibt. Dieses Verhalten kann erklärt werden durch die unterschiedliche Polarität der 11-Komplexe. Während der H₂O: Dioxan-Komplex keine Erhöhung des Dipolmoments erkennen läßt, weist der H₂O:Et ₃N-Komplex infolge der Polarisierung der O–H...N-Bindung ein Inkrement des Momentes von ca. 0,4 D auf. Durch diese zusätzliche Polarisierung des H₂O-Moleküls wird die Ausbildung einer zweiten H-Bindung gehemmt.

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The different character of hydrogen bonds in complexes of water with organic bases

The 11 complexes of H₂O with 1.4-dioxane (as an example of a weak base) and triethylamine (Et ₃N) (as an example of a strong base) have been investigated in dilute solutions of non-polar solvents (CCl₄, benzene). Compared with the H₂O:Et ₃N complex, the complex H₂O: dioxane has a smaller complex formation constant, a smaller frequency shift of the OH fundamental, and the change of the chemical shift of the OH proton due to complex formation is less pronounced. The volume contraction of mixing in the system H₂O+dioxane is also smaller than in the system H₂O+Et ₃N. On the other hand, in dilute solutions of H₂O in dioxane a H₂O: (dioxane)₂ complex is formed in which both water protons are involved in H-bonds to a dioxane molecule, whereas in dilute solutions of H₂O inEt ₃N only the 11 complex exists. This behaviour can be explained by the difference in polarity of the 11 complexes. The H₂O: dioxane does not show an increment of the dipole moment, but the H₂O:Et ₃N complex shows an increment of ca. 0.4 D, due to the polarization of the O–H...N bond. This polarization of the H₂O-molecule hinders the formation of a second H-bond.

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Mit 8 Abbildungen

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Herrn Univ.-Prof. Dr.O. Kratky gewidmet.     

Seeking new metalloligands: Synthesis and reactivity of palladacycles with pyridine and pyrimidine rings

Treatment of the Schiff base ligands 4-(NC₅H₄)C₆H₄C(H)N[2′-(OH)C₆H₄] (a), 3,5-(N₂C₄H₃)C₆H₄C(H)N[2′-(OH)-C₆H₄] (b) and 3,5-(N₂C₄H₃)C₆H₄C(H) N[2′-(OH)-5′-^tBuC₆H₃] (c) with palladium (II) acetate in toluene gave the poly-nuclear cyclometallated complexes [Pd{4-(NC₅H₄)C₆H₃C(H)N[2′-(O)C₆H₄]}]₄ (1a), [Pd{3,5-(N₂C₄H₃)C₆H₃C(H)N[2′-(O)-C₆H₄]}]₄ (1b) and [Pd{3,5-(N₂C₄H₃)C₆H₃C(H)N[2′-(O)-5′-^tBuC₆H₃]}]₄ (1c) respectively, as air stable solids, with the ligand acting as a terdentate [C,N,O] moiety after deprotonation of the –OH group. Reaction of the cyclometallated complexes with triphenylphosphine gave the mononuclear species [Pd{4-(NC₅H₄)C₆H₃C(H) N[2′-(O)C₆H₄]}(PPh₃)], (2a), [Pd{3,5-(N₂C₄H₃)C₆H₃C(H) N[2′-(O)C₆H₄]}(PPh₃)], (2b) and [Pd{3,5-(N₂C₄H₃)C₆H₃C(H)N[2′-(O)-5′-^tBuC₆H₃)}(PPh₃)], (2c) in which the polynuclear structure has been cleaved and the coordination of the ligand has not changed [C,N,O]. When the cyclometallated complexes 1b and 1c were treated with the diphosphines Ph₂P(CH₂)₄PPh₂ (dppb), Ph₂PC₅H₄FeC₅H₄PPh₂ (dppf) and Ph₂P(CH₂)₂PPh₂ (t-dppe) in a 1:2 molar ratio the dinuclear cyclometallated complexes [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H)N{2′-(O)C₆H₄}]}₂(μ-Ph₂P(CH₂)₄PPh₂)], (3b), [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H) N{2′-(O)-5′-^tBuC₆H₃}]}₂(μ-Ph₂P(CH₂)₄PPh₂)], (3c), [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H)N{2′-(O)C₆H₄}]}₂(μ-Ph₂P(η⁵-C₅H₄)Fe(η⁵-C₅H₄)PPh₂)], (4b), [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H) N{2′-(O)-5′-^tBuC₆H₃}]}₂(μ-Ph₂P(η⁵C₅H₄)Fe(η⁵C₅H₄)P-Ph₂)], (4c) and [{Pd[3,5-(N₂C₄H₃)C₆H₃C(H)N{2′-(O)-5′-^tBuC₆H₃}]}₂(μ-Ph₂P(CHCH)PPh₂)], (5c) were obtained as air stable solids.     

Study on H-bond patterns in phosphoric triamides having a P(O)NHC(O) skeleton, a gauche orientation of P(O) vs C(O) in new compounds

The crystal and packing structures of new phosphoric triamides, in a rare gauche orientation of P(O) versus C(O), with the formula (CCl₂HC(O)NH)X₂P(O), X = NC₄H₈ (1), N(C₂H₅)₂ (2), N(CH₃)(C₆H₁₁) (3) and (CCl₂HC(O)NH)(Y)P(O), Y = NHCH₂C(CH₃)₂CH₂NH (4) have been investigated. This article also reviews 91 similar structures deposited in the CSD aiming to classify hydrogen bond patterns in this category of phosphorus compounds. The present X-ray structural analysis shows that the H-bond pattern in the studied structures strongly depends on the conformation in the P(O)NHC(O) skeleton and the kind of amide linked to the P atom. The spectroscopic features (³¹P{¹H}, ¹H and ¹³C NMR, IR) of the new compounds have been investigated.     

Crystal structure and FT-IR study of aqualithium 1-naphthylmethyl ester of monensin A perchlorate

The crystal [MON8LiClO₄H₂O] containing the neutral molecule of 1-naphthylmethyl ester of monensin A (MON8), lithium perchlorate and one water molecule was obtained and its structure was examined using X-ray diffraction and discussed in detail. The MON8LiClO₄H₂O supramolecular complex is crystallized in the non-centrosymmetric space group of the orthorhombic system (P2₁2₁2₁) with four molecules in the unit cell. Within MON8LiClO₄H₂O complex the Li⁺ cation is square-pyramidally coordinated by four oxygen atoms of the MON8 molecule and by the oxygen atom of the water molecule. The oxygen atoms (O9 and O14) of the two OH groups are involved in two intramolecular O(14)H?O(9) and O(9)H?O(14) hydrogen bonds of similar strength stabilizing a pseudo-cyclic structure of MON8. Additionally the coordinated water molecule acts as proton donor in the two hydrogen bonds. The FT-IR spectrum of the crystal provides spectroscopic evidence for the complex formation and it is discussed in detail.     

Synthesis,crystal structure and thermal stability of new copper(II) trichloroacetate complexes

We have synthesized two novel complexes of copper(II) trichloro acetate, Cu₂(CCl₃COO)₃(OH)(H₂O)₄·H₂O and Cu(CCl₃COO)₂(MeCN), and determined their crystal structures and thermal stability. While the complex with acetonitrile has a discrete binuclear paddle-wheel structure, typical of copper carboxylates, the aqua-hydroxo complex belongs to a novel unique chain–molecular type of basic copper complexes.     

NMR study of the interaction between water and tributyl phosphate in the TBP-CCl4-H2O system

Hydrogen bonding between water and tributyl phosphate (TBP) in TBP? CCl₄? H₂O system has been studied by ¹H NMR. A new model and an empirical equation have been established on the basis of Li's model and the parameters of hydrogen bond between water and TBP are determined by nonlinear optimization method. In TBP? CCl₄? H₂O system change of ¹H chemical shift of water can be satisfactorily explained by the new model and the empirical equation in the whole concentration range. When the concentration of water in the organic phase is very low, the main existing forms of water are H₂O · TBP and H₂O · 2TBP. When the concentration of water reaches saturation, the main existing form is associated water, but there are still about 20% of water existing in the forms of H₂O · TBP and H₂O · 2TBP.     

Synthesis and characterization of new heterocyclic Schiff base palladacycles: Ring activation through N-oxide formation

Reaction of the Schiff base ligand derived from 4-pyridinecarboxaldehyde NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂], (1), with palladium(II) acetate in toluene at 60 °C for 24 h gave [Pd{NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂]}₂(OCOCH₃)₂], (2), with two ligands coordinated through the pyridine nitrogen. Treatment of the Schiff base ligand derived from 4-pyridinecarboxaldehyde N-oxide, 4-(O)NC₅H₄C(H)N[2′,4′,6′-(CH₃)C₆H₂], (4), with palladium(II) acetate in toluene at 75 °C gave the dinuclear acetato-bridged complex [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(OCOCH₃)]₂, (5) with metallation of an aromatic phenyl carbon. Reaction of complex 5 with sodium chloride or lithium bromide gave the dinuclear halogen-bridged complexes [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Cl)]₂, (6) and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Br)]₂, (7), after the metathesis reaction. Reaction of 6 and 7 with triphenylphosphine gave the mononuclear species [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(Cl)(PPh₃)], (8) and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}-(Br)(PPh₃)], (9), as air stable solids. Treatment of 6 and 7 with Ph₂P(CH₂)₂PPh₂ (dppe) in a complex/diphosphine 1:2 molar ratio gave the mononuclear complexes [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(PPh₂(CH₂)₂PPh₂)][Cl], (10), and [Pd{4-(O)NC₅H₃C(H)N[2′,4′,6′-(CH₃)C₆H₂]}(PPh₂(CH₂)₂PPh₂)][PF₆], (11), with a chelating diphosphine. The molecular structure of complex 9 was determined by X-ray single crystal diffraction analysis.     

Synthesis and crystal structures of cyclodiazastannoxides fused cyclopentadienyl M-Sn (M = Mo, W) bonded organometallic heterocycle

The condensation reaction of CH₃COC₅H₄M(CO)₃SnCl₃ (M = Mo or W) with PyCONHNH₂ (Py = 2,3,4-pyridyl or 2-pyridylmethyl) in mild conditions yields cyclodiazastannoxides fused cyclopentadienyl M-Sn bonded organometallic heterocycle {μ-[C₅H₄(CH₃)CN-NC(O)PyH]M(CO)₃SnCl₃}. The similar reaction of CH₃COC₅H₄M(CO)₃SnCl₃ with ArCONHNH₂ (Ar = 2-furanyl) gives complexes μ-[C₅H₄(CH₃)CN-NC(O)Ar]M(CO)₃SnCl₂(H₂O), in which the water molecule can be replaced by other N-donor ligands, such as pyridine or 4,4-bipyridine. Arene-bridged organometallic heterocyclic complexes μ-{[C₅H₄(CH₃)CN-NC(O)]₂C₆H₄}{M(CO)₃SnCl₂(Solvent)}₂ have also been prepared by the reaction of CH₃COC₅H₄M(CO)₃SnCl₃ with terephthaloyl hydrazine. In these new organometallic heterocyclic complexes, it seems that the tin atom prefers to be six-coordinate through absorbing the chloridion or solvent molecules.     

Aldol condensation reactions of [Co(η-C4Ph4){η-C5H4C(O)CH3}]

The aldol condensation reaction between [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] and a range of aromatic aldehydes [RCHO] and [RCHCH-CHO] gives a series of α,β-unsaturated ketones [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-R}] and [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-CHCH-R}] (3). The reaction is promoted by various bases: NaH proved to be the most effective whilst ⁿBuLi gave [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(OH)(ⁿBu)CH₃}] as the major product. NaOH was ineffective, perhaps indicating that that the methyl protons in [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] are less acidic than those in [Fe(η⁵-C₅H₅){η⁵-C₅H₄C(O)CH₃}]. Compounds 3 were characterised spectroscopically. Their ¹H NMR spectra are consistent with a trans configuration about their CC bond, and this was confirmed by X-ray crystallography in five cases, which showed that all have the same basic structure with parallel cyclobutadiene and cyclopentadienyl ligands, but they are not identical. The C₅H₄C(O)(CHCH)_n-R (n = 1 or 2) moieties show little evidence for delocalisation and often deviate from planarity. The UV/Vis spectra of those 3 with smaller aromatic rings (R = C₆H₅, 4-C₆H₄NMe₂, 2-C₄H₃S and 1-C₁₀H₇) suggest that these are donor-π-acceptor systems, but as the annellation of R increases (R = 9-C₁₄H₉, 1-C₁₆H₉ and 1-C₂₀H₁₁) the spectra increasingly resemble those of the parent polycyclic aromatic hydrocarbon, RH. Reduction of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CHCH-C₁₀H₇-1}] with DIBAL gives a mixture of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₂CH₂-C₁₀H₇-1}] and [Co(η⁴-C₄Ph₄){η⁵-C₅H₄CH(OH)CHCH-C₁₀H₇-1}]. A minor product from the preparation of [Co(η⁴-C₄Ph₄){η⁵-C₅H₄C(O)CH₃}] was shown by X-ray crystallography to be the η⁴-butadiene complex [Co{η⁴-Ph(H)CC(Ph)-C(Ph)C(H)Ph}{η⁵-C₅H₄C(O)CH₃}].     

Synthesis, thermal behavior, and other properties of Y(III) and La(III) complexes with 4,4′-bipyridine and trichloro- or dibromoacetates

New Y(III) and La(III) complexes with 4-bpy (4,4??-bipyridine) and trichloro- or dibromoacetates with the formulae: Y(4-bpy)₂(CCl₃COO)₃·H₂O I, La(4-bpy)_1.5(CCl₃COO)₃·2H₂O II, Y(4-bpy)_1.5(CHBr₂COO)₃·3H₂O III, and La(4-bpy)(CHBr₂COO)₃·H₂O IV were prepared and characterized by chemical, elemental analysis, and IR spectroscopy. Conductivity studies (in methanol, dimethyloformamide, and dimethylsulfoxide) were also described. They are small, crystalline substances. The way of metal?Cligand coordination was discussed. The thermal properties of complexes in the solid state were studied by TG-DTG techniques under dynamic flowing air atmosphere. TG-FTIR system was used to analyze principal volatile thermal decomposition and fragmentation products evolved during pyrolysis in dynamic flowing argon atmosphere for La(III) compounds.     

Charging and Release Mechanisms of Flexible Macromolecules in Droplets

We study systematically the charging and release mechanisms of a flexible macromolecule, modeled by poly(ethylene glycol) (PEG), in a droplet by using molecular dynamics simulations. We compare how PEG is solvated and charged by sodium Na⁺ ions in a droplet of water (H₂O), acetonitrile (MeCN), and their mixtures. Initially, we examine the location and the conformation of the macromolecule in a droplet bearing no net charge. It is revealed that the presence of charge carriers do not affect the location of PEG in aqueous and MeCN droplets compared with that in the neutral droplets, but the location of the macromolecule and the droplet size do affect the PEG conformation. PEG is charged on the surface of a sodiated aqueous droplet that is found close to the Rayleigh limit. Its charging is coupled to the extrusion mechanism, where PEG segments leave the droplet once they coordinate a Na⁺ ion or in a correlated motion with Na⁺ ions. In contrast, as PEG resides in the interior of a MeCN droplet, it is sodiated inside the droplet. The compact macro-ion transitions through partially unwound states to an extended conformation, a process occurring during the final stage of desolvation and in the presence of only a handful of MeCN molecules. For charged H₂O/MeCN droplets, the sodiation of PEG is determined by the H₂O component, reflecting its slower evaporation and preference over MeCN for solvating Na⁺ ions. We use the simulation data to construct an analytical model that suggests that the droplet surface electric field may play a role in the macro-ion–droplet interactions that lead to the extrusion of the macro-ion. This study provides the first evidence of the effect of the surface electric field by using atomistic simulations.

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Graphical Abstract ?

     

Reaction Mechanisms in Both a CCl2F2/O2/Ar and a CCl2F2/H2/Ar RF Plasma Environment

Decomposition of dichlorodifluoromethane (CCl₂F₂ or CFC-12) in aradiofrequency (RF) plasma system is demonstrated. The CCl₂F₂decomposition fractions _{CCl 2 F 2} and mole fractionsof detected products in the effluent gas stream of CCl₂F₂/O₂/Ar andCCl₂F₂/H₂/Ar plasma, respectively, have been determined. The experimentalparameters including input power wattage, O₂/CCl₂F₂ or H₂/CCl₂F₂ ratio,operational pressure, and CCl₂F₂ feeding concentration wereinvestigated. The main carbonaceous product in the CCl₂F₂/O₂/Arplasma system was CO₂, while that in the CCl₂F₂/H₂/Ar plasma systemwas CH₄ and C₂H₂. Furthermore, the possible reaction pathways werebuilt-up and elucidated in this study. The results of the experimentsshowed that the highly electronegative chlorine and fluorine wouldeasily separate from the CCl₂F₂ molecule and combine with the addedreaction gas. This led to the reactions terminated with the CO₂,CH₄, and C₂H₂ formation, because of their high bonding strength. Theaddition of hydrogen would form a preferential pathway for the HCland HF formations, which were thermodynamically stable diatomicspecies that would limit the production of CCl₃F, CClF₃, CF₄, andCCl₄. In addition, the HCl and HF could be removed by neutral orscrubber method. Hence, a hydrogen-based RF plasma system provideda better alternative to decompose CCl₂F₂.