Anisotropic exchange interactions in dinuclear systems (Ln = Dy, Tm, Yb): Magnetometry and Dual Mode X-band Electron Paramagnetic Resonance spectroscopic study

A recently developed experimental and theoretical procedure is used in order to calculate the magnitude and anisotropy of interaction between a lanthanide and a 3d-metal ion. The general formula of the molecular compounds is [Ln(H₂O)₃(dmf)₄(μ-CN)Fe–(CN)₅] · nH₂O where 1  n  1,5 and dmf = N,N′-dimethylformamide, abbreviated as [LnFe] from now on. The main parts of this procedure are (a) the evaluation of the effective g-parameters of the lanthanide ion with the help of EPR measurements. (b) The use of dual mode EPR spectroscopy to define the anisotropic exchange interactions with the help of an anisotropic Hamiltonian model. (c) Use of the same magnetic model to fit magnetization and susceptibility data in order to verify the EPR findings.It was possible to define some trends concerning the exchange components of the [DyFe] dimer according to which the antiferromagnetic isotropic exchange constant is smaller than 4 cm⁻¹ and the anisotropic components are [D_exc, E_exc] = [6(1), 0.0] cm⁻¹. Also for the case of [TmFe] and [YbFe] dimers the antiferromagnetic isotropic exchange constant is smaller than 0.3 cm⁻¹ while the anisotropic components are [D_exc, E_exc] = [12.0, 0.0] cm⁻¹ and [D_exc, E_exc] = [0.4(1), 0.0] cm⁻¹, respectively.     

Synthesis of new condensed heterocyclic systems

Two new diamines — [1,3-bis(5-phenyl-1,2,4-triazol-3-yl)-4,6-diamino]benzene and [1,3-di-(2-benzimldazolyl)-4,6-diamino]benzene — were synthesized from 4,6-dinitroisophthalic acid. Newheterocyclic systems — 3,5,9,11-tetraphenyl[benzo[1,2-a; 4,5-a]bis(1,2,4-triazolo[4,3-c]pyrimidine)] and 2,16-diphenyl[benzo[1,2-a;4,5-a']bis(pyrimido[1,6-a]benzimidazole)]—were obtained by reaction of the diamines with benzoyl chloride and subsequent cyclization.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1274–1277, September, 1977.     

Investigations in the imidazole series

The reactions of 2-mercaptonaphth[1,2-d]imidazole with 1,2-dichloro- and 1,2-dibromoethanes and the cyclization of 3-(-hydroxyethyl)- and 2-(-hydroxyethyl)mercaptonaphth[1,2-d]imidazoles were studied. 2,3-Dihydro derivatives of naphth[1,2-d]imidazo[1,2-b]thiazole and naphth[1,2-d]imidazo[3,2-b]thiazole were obtained.See [1] for communication LXX.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 257–259, February, 1972.     

Monte—Carlo model of the diffusion-limited reaction kinetics in microheterogeneous media. Comparison with the experimental plots of the forward and backward electron phototransfer kinetics on the pore diameter in silica gel

The kinetics of the diffusion-limited decay reaction A + B B was simulated by the Monte—Carlo method on a two-dimensional square lattice with defects presented by randomly distributed sites. The cases were considered where [B] [A] at the random initial distribution (quenching reaction) and [B] = [A] with the initial distribution of the A and B particles on neighboring sites (geminate recombination). The kinetic curves were approximated by the simplest analytical equation [A]/[A]₀ = (1 – )exp[–(kt)^1–h ] + (where k and are constants). The plots of the heterogeneity parameter (h) and time-averaged first-order rate constant vs. concentration of defects (p) or B particles (in the case of quenching) were obtained and compared with similar correlations obtained earlier by the experimental study of the kinetics of forward (quenching reaction) and backward (geminate recombination) electron phototransfer on the surface of different porous silica gels. The experimental plots of h vs. silica gel porosity are in satisfactory agreement with the plots of h vs. p in the model space, if the fraction of volume inaccessible for reactants, calculated from the free silica gel volume, is chosen as the p parameter for silica gel.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1536–1541, August, 2004.     

New unsymmetrical μ-phenoxo bridged binuclear copper(II) complexes

A series of binuclear Cu^II complexes [Cu₂XL] ⁿ⁺ having two copper(II) ions bridged by different motifs (X = OH^–, MeCO₂ ^–, or Cl^–) have been prepared using the ligands: H₂L¹ = 4-methyl-2-[N-(2-{dimethylamino}ethyl-N-methyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol, H₂L² = 4-nitro-2-[N-(2-{dimethylamino}ethyl-N-methyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol, H₂L³ = 4-methyl-2-[N-(2-{diethylamino}ethyl-N-ethyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol and H₂L⁴ = 4-nitro-2-[N-(2-{diethylamino}ethyl-N-ethyl)aminomethyl]-6-[(prolin-1-yl)methyl]phenol. The complexes have been characterized by spectroscopic, analytical, magnetic and electrochemical measurements. Cryomagnetic investigations (80–300 K) revealed anti-ferromagnetic exchange between the Cu^II ions (–2J in the range –50 to –182 cm^–1). The strength of anti-ferromagnetic coupling lies in the order: OAc > OH > Cl. Cyclic voltammetry revealed the presence of two redox couples, assigned to Cu^II/Cu^II/Cu^II/Cu^I/Cu^I/Cu^I. The first reduction potential is sensitive to electronic effects from the aromatic ring substituents and steric effect on the donor nitrogens (side arm) of the ligand systems.     

Determination of copper(I)-ethylene complexes, [Cu(C2H4)]+ and [Cu(C2H4)2]+, with aid of EDTA titration of copper(I) and copper(II) ions

Summary Volumetric measurements of ethylene and simple EDTA titration of copper(I) and copper(II) ions confirm that [CuL]⁺ and [CuL₂]⁺ are formed when an aqueous solution of copper(II) is reduced by copper metal in the presence of ethylene, (L). The formation constants,K ₁=[CuL⁺]²[Cu²⁺]^–1[L]^–2 andK ₂=[CuL ₂ ⁺ ]^–1[L]^–1, have been estimated. The formation of [CuL]⁺ is accompanied by an enthalpy change, H, of –25 kJ mol^–1, and a positive entropy change, S, of 13 J mol^–1 K^–1.     

Regioselective Synthesis of Thieno[3,2-<Emphasis Type="Italic">c</Emphasis>][1]benzopyran-4-ones by Thio-<Emphasis Type="Italic">Claisen</Emphasis> Rearrangement

Summary. A number of thieno[3,2-c][1]benzopyran-4-ones, potential antiinflamatory, antipyretic, and antiallergic drugs, are synthesized in 65–80% yield by thermal thio-Claisen rearrangement of 4-allylthio[1]benzopyran-2-ones in refluxing quinoline for 0.5–8.0h. The 4-allylthio[1]benzopyran-2-ones are in turn prepared in 75–85% yield from 4-mercaptocoumarin and different allylic halides by phase-transfer-catalysed alkylation with TBAB or BTEAC catalyst in chloroform-aq. NaOH at room temperature.     

Syntheses,crystal structures and magnetic properties of two cyano-bridged two-dimensional assemblies [Fe(salpn)]2 [Fe(CN)5NO] and [Fe(salpn)]2[Ni(CN)4]

Two cyano-bridged assemblies, [Fe^III(salpn)]₂[Fe^II(CN)₅NO] (1) and [Fe^III (salpn)]₂[Ni^II(CN)₄] (2) [salpn = N, N-1,2-propylenebis(salicylideneiminato)dianion], have been prepared and structurally and magnetically characterized. In each complex, [Fe(CN)₅NO]^2– or [Ni(CN)₄]^2– coordinates with four [Fe(salpn)]⁺ cations using four co-planar CN^– ligands, whereas each [Fe(salpn)]⁺ links two [Fe(CN)₅NO]^2– or [Ni(CN)₄]^2– ions in the trans form, which results in a two-dimensional (2D) network consisting of pillow-like octanuclear [—M^II—CN—Fe^III—NC—]₄ units (M = Fe or Ni). In complex (1), the NO group of [Fe(CN)₅NO]^2– remains monodentate and the bond angle of Fe^II—N—O is 180.0°. The variable temperature magnetic susceptibilities, measured in the 5–300 K range, show weak intralayer antiferromagnetic interactions in both complexes with the intramolecular iron(III)iron(III) exchange integrals of –0.017 cm^–1 for (1) and –0.020 cm^–1 for (2), respectively.     

Behavior of rifampicin in association with<Emphasis Type="Italic"> β</Emphasis>-cyclodextrin in aqueous media: a spectroscopic and conductometric study

The behavior of rifampicin (D) with -cyclodextrin (-CyD) in aqueous media (W) has been examined by means of UV-vis spectroscopy and conductivity measurements over the temperature range 15–30 °C. The UV-vis study has been used to characterize the systems. The estimated molar absorption coefficient for D/CyD/W system was 10757±280 M^–1 cm^–1 in comparison to the value of 6133±99 M^–1 cm^–1 for D/W system. The conductivity was measured (i) as a function of [D] for binary D/W systems, (ii) as a function of [CyD], keeping the concentration of drug constant, for D/CyD/W system, and (iii) as a function of [D] in the presence of a constant cyclodextrin concentration. Two transition points were observed for D/CyD/W system at constant [CyD], which were assigned as cac-1 and cac-2. The stoichiometry of the association was estimated from the conductivity data. This was obtained from [drug] value at which the change in slope of occurs. The standard free energy change, of aggregation was also calculated from the critical concentration data. An attempt has also been made to estimate the stoichiometry of -cyclodextrin:rifampicin association.     

Reductive cyclization of o-cyanocinnamic acids and their analogs

The hydrogenation of esters of o-cyanocinnamic acid or -(o-cyanoaryloxy)carboxylic acids over Raney nickel leads to the corresponding seven-membered lactams. Subsequent reduction of these with lithium aluminum hydride gives 2,3,4,5-tetrahydro[1H]benzo[c]azepine and 1,2,3,5-tetrahydro[4H]benzo[f]-1,4-oxazepine.Communication VI of the series Nitrosophenols and Their Rearrangement Products. See [1] for communication V.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1288–1292, September, 1971.     

Kinetische Untersuchungen der Essigsäureanhydrid—Methanol-Reaktion mit Hilfe der Kernresonanzspektroskopie

Zusammenfassung Die Veresterung des Essigsäureanhydrids (I) mit Methanol (II) ohne zusätzliches Lösungsmittel wurde bei 20 und 30°C mit Hilfe der Kernresonanzspektroskopie kinetisch untersucht. Aus der durch elektronische Integration bestimmten Intensitätszunahme des Ester-Methoxy-Protonensignals wurden die Konzentrationen im Verlauf der Reaktion bestimmt. Das Geschwindigkeitsgesetz:RG=k·[(CH₃CO)₂O]·[CH₃OH] wird bei den Konzentrationsverhältnissen [I]:[II]=11 bis 16,7 erfüllt;k=7,17·10^–5 (20°C) bzw. 15,30·10^–5 (30°C) mol^–1·l·min^–1; S ^*=–42Cl. Diese Befunde führten uns zu dem Schlusse, daß I und II zunächst unter Bildung von protoniertem Essigsäuremethylester und Acetat-Anion reagieren, und daß dieser protonierte Ester rasch das Proton abspaltet.

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Kinetics of the esterification of aceticanhydride (I) with methanol (II) without any solvent were investigated by means of nuclear magnetic resonance spectroscopy. Increasing of the methoxyproton-signal intensity of the ester was evaluated by electronic integration and thus the kinetic run was determined. The law: rate=k·[I]·[II] is satisfied by the experimental data from the concentration range [I][II]=11 up to 16,7;k=7,17·10^–5 (20°C), and 15,30·10^–5 (30°C) mol^–1·l·min^–1; S ^*=–42Cl. From these results we concluded that first I and II react, forming protonized methyl acetate and acetate-anion, and that this protonized ester rapidly delivers the proton.

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Dem lieben Kollegen Herrn Prof. Dr.Leopold Schmid zum 70. Geburtstag herzlichst gewidmet.

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Referat bei der Vortragstagung des Vereins Österreichischer Chemiker in Wien am 6. Oktober 1967.     

Synthesis,crystal structure and magnetic properties of the first dinuclear copper(II)–iron(II) complex [Cu(L)Fe(CN)5NO] based on nitroprusside

The nitrosyl cyanide [Cu(L)Fe(CN)₅NO] was prepared by the reaction of [Cu(L)]Cl₂ [L = 3, 10-bis(2-hydroxymethyl)-1,3,5,8,10,12-hexaazacyclotetradecane] with Na₂[Fe(CN)₅NO]·2H₂O in aqueous solution. Single-crystal analysis revealed that the title complex is the first structurally characterized dinuclear copper(II)–iron(II) complex based on the nitroprusside. Variable temperature magnetic susceptibility measurements (4.0–180.0 K) show the occurrence of very weak antiferromagnetic interactions between the copper(II) ions with zJ = –0.410 cm^–1.     

Reactivity of tungsten(0) and molybdenum(0) pentacarbonyl thiobenzoate anions: thiobenzoate as a cis-CO labilizing ligand

The [Et₄N][M(CO)₅SCOPh] complexes (1a, M = Mo; 2a, M = W) have been prepared at ambient temperatures by reacting the photogenerated M(CO)₅ THF intermediate with [Et₄N][SCOPh] in THF. Kinetic studies of the reactions of the anions [M(CO)₅SCOPh]^– with the tri(iso-propyl)phosphite (L) ligand under pseudo-first-order conditions indicate that these reactions are first-order in substrate and are independent of the P(OPr-i)₃ concentration. It is thus envisaged that these CO substitutions proceed via a mechanism which involves initial cis-M—CO bond-breaking, followed by fast attack of the incoming nucleophile on the resulting intermediate to give [cis-M(CO)₄{P(O-Pri)₃}SCOPh]^–. This facile displacement of cis-CO indicates the labilizing nature of the thiobenzoate ligand, most probably by virtue of distal oxygen atom participation. Activation parameters for the reactions are: [M(CO)₅SCOPh]^– + L cis-[M(CO)₄(L)SCOPh]^– + CO M = Mo, H = 24.6(2) kcal mol^–1, S = 8.2(6) eu; M = W, H = 28.4(2) kcal mol^–1, S = 11.3(5) eu. Kinetic data and the mechanism of these ligand-substitutions are discussed.     

Investigations in the imidazole series

2,3-Dihydro derivatives of naphth[1,2-d]imidazo[3,2-b]imidazole were synthesized by the reaction of 2-chloro-3-(-haloalkyl)naphth[1,2-d]imidazole with ammonia and primary amines and by the reaction of 2-chloro-3-(-hydroxyaIkyl)naphth[1,2-d]imidazole with ammonia and amines with subsequent cyclization of the resulting 2-amino(alkylamino, arylamino)-3-(-hydroxyalkyl)naphth[1,2-d]imidazoles under the influence of thionyl chloride or phosphorus oxychloride. Dihydro derivatives of the condensed naphth[1,2-d]imidazo[3,2-b]imidazole system have not been described in the literature.See [1] for communication LX.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1125–1127, August, 1971.     

Die Kristallstruktur von Li4SiO4

Zusammenfassung Die Kristallstruktur des Lithiumorthosilicats wurde mittels dreidimensionaler Fourier-Synthesen und nach der Methode der kleinsten Quadrate bestimmt. Die Gitterparameter der monoklinen Elementarzelle (C _2h ² –P2₁/m) betragen:a=5,14;b=6,10;c=5,30 Å und =90,5°. Die Struktur enthält isolierte [SiO₄]-Tetraeder, welche durch [LiO _n ]-Polyeder (n=4, 5, 6) verknüpft sind. Hervorzuheben ist, daß sämtliche Lithiumlagen nur partiell besetzt sind. Als mittlerer Si–O-Abstand wurde 1,632 Å erhalten; als Mittelwerte der Li–O-Abstände für die verschiedenen Koordinationszahlen ergeben sich: 1,975 [4]; 2,099 [5] und 2,247 [6] Å.

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The crystal structure of lithium orthosilicate has been determined by means of three-dimensional Fourier syntheses and the least squares method. The lattice parameters of the monoclinic unit cell (P2₁/m–C _2h ² ) are:a=5.14;b=6.10;c=5.30 Å and =90.5°. The crystal structure contains isolated [SiO₄]-tetrahedra being connected by [LiO _n ]-polyhedra (n=4, 5, 6). The positions of the lithium atoms are partially occupied only. The average interatomic Si–O distance is found to be 1.632 Å. The averaged values for Li–O distances given for the different coordination numbers are: 1.975 [4]; 2.099 [5] and 2.247 [6] Å.

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Synthese von [1]Benzothieno[2,3—d]isoxazol-Derivaten

Derivatives of [1]benzothieno[2.3—d]isoxazole, a new heterocyclic ring system, were synthesized by 1.3-dipolar cyclisations: benzo[b]thiophene-1.1-dioxide and its 3-methyl derivative reacted with nitrile oxides and nitrones to the corresponding substituted [1]benzothieno[2.3—d]isoxazolines and-isoxazolidines. Hydrogenolysis of the latter cleaved the isoxazolidine ring, yielding the corresponding 2-(-phenylamino-benzyl)-3-hydroxy-2.3-dihydro-benzo[b]thiophene-1.1-dioxides.

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Herrn Prof. Dr.E. Hardegger zum 60. Geburtstag gewidmet.     

Ab initio study of oxaphosphaalkyne P=C-OH and its isomers

Anab initio study on HP=C=O PC-OH isomerization has been performed at the 3-21G(d(P)), 4–31G(d(P)) and 6–31G** levels. In contrast to analogous transformation of 1-aza-3-phosphaallene, this process is endothermic in the gas phase. It proceedsvia a [1,3]H shift without an intermediate. The route, including two subsequent [1,2]H shifts, leads to phosphinidene.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 172–173, January, 1994.     

Solid-solute phase equilibria in aqueous solutions,VIII: The standard gibbs energy of La2(CO3)3·8H2O

The solubilities of lanthanum carbonate La₂(CO₃)₃·8H₂O in solutionsS ₀([H⁺]=H mol kg^–1, [Na⁺]=(I–H) mol kg^–1, [ClO ₄ ^– ]=I mol kg^–1) at various fixed partial pressures of CO₂ have been investigated at 25.0 °C. The hydrogen ion molality and the total molality of La(III) ion in equilibrium with the solid phase were determined by e.m.f. and analytical methods, respectively. The stoichiometric solubility constants