Spin-crossover complexes in solution,II solvent effects on the high spin-low spin-equilibrium of [Fe(bzimpy)2](ClO4)2

Summary The influence of the solvent on the spin-equilibrium of [Fe(bzimpy)₂](ClO₄)₂ (bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) has been investigated in several nonaqueous solvents by means of UV-Vis spectroscopy and magnetic susceptibility measurements. In methanol, a bis-tris ligation equilibrium is found. Both, the FeL ₂ ²⁺ and FeL ₃ ²⁺ species show spin-crossover behaviour in solution. Photometric and magnetic properties of the complex in various solvents are related. The spin-equilibrium of [Fe(bzimpy)₂](ClO₄)₂ shows the strongest sensitivity towards changes of the solvent that has ever been observed for spin-crossover compounds. Increase in solvent donor number (DN) from DN=14.1 (Acetonitril) to DN=19.1 (Methanol) causes a shift from _exp=4.21 (78% High-Spin (HS)) to _exp=3.0 (56% HS). In solvents with DN 30 deprotonation of the complex occurs yielding a low-spin species. The solvent effects are discussed in terms of the donor-acceptor concept.Dedicated to Professor Harry J. Emeléus with heartiest congratulations to his 90^th birthday on 22^th June 1993.     

Investigations on the spin-crossover complex [Fe(bzimpy)2](ClO4)2 and its Mn2+, Co2+, Ni2+ and Zn2+ analogues

Summary A series of transition metal complexes [M(bzimpy)₂](ClO₄)₂ (M=Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺;bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) was synthesized and characterized by elemental analysis, UV-Vis and far-IR spectroscopy. The electronic spectra of [Ni(bzimpy)₂](ClO₄)₂ in solution and solid state reveal a ligand field splitting parameter ₀ in the range of 11470 cm^–1 to 11840 cm^–1. The simultaneous existence of two species with distinct spin state is found for [Fe(bzimpy)₂](ClO₄)₂ by means of variable temperature far-IR measurements. Assignments of the observed far-IR bands are given on the basis of the investigations of the variation of the metal ion in [M(bzimpy)₂](ClO₄)₂.This paper is dedicated to Professor Ulrich Wannagat on the occasion of his 70^th birthday with warmest personal wishes.     

PROTONATION CONSTANTS AND SOLVENT DEPENDENT SPIN-CROSSOVER BEHAVIOUR OF IRON(II)-2-(2′-PYRIDYL)BENZIMIDAZOLE COMPLEXES

Abstract

2-(2′-Pyridyl)benzimidazole (pybzim = LH) coordinates to iron(II) as a bidentate and forms the tris-ligated complex, [Fe(pybzim)₃]²⁺ as isolated in the solid. Titration of [Fe(pybzim)₃]²⁺ with base demonstrates the successive deprotonation of the imino hydrogens of the coordinated ligands. Protonation constants for the free ligand, pybzim (Iog₁₀ K ^H = 11.33) and the complex, [Fe(pybzim)₃]²⁺ (log₁₀ K ^H ₁ = 9.58, log₁₀ K ^H ₂ = 8.13 and log₁₀ K ^H ₃ = 6.97) were measured in 30% (v/v) H₂O/EtOH. Results show that coordination to iron(II) increases the acidity of the imino hydrogen of the ligand. Spin-crossover behaviour of the complex were studied in different solvents ME, AC, AN, NM, NB, DMF, DMSO and ANL. The complex shows strong spin-crossover behaviour which is solvent dependent. Values of the spin-equilibrium constant (K _sc) and the associated thermodynamic parameters (ΔH _sc = 18.1–21.3 kJ mol^?1 and δS _sc = 69.6–84.4JK^?1 mol^?1) were calculated. An increase of the enthalpy is observed with increasing donor number (DN) of the solvent.     

Spin-transition behaviour of transition metal complexes with 2,6-bis-(benzimidazol-2′-yl)-pyridine induced by deprotonation of the complex

Summary 2,6-bis-(Benzimidazol-2-yl)-pyridine (bzimpy = H₂ L) acts as a bidentate ligand when combining with transition metal ions. The complexes [M(bzimpy)₂](ClO₄)₂ (M = Fe²⁺, Mn²⁺, Zn²⁺, Co²⁺, and Ni²⁺) were obtained as solids. The protonation constants (logK) for the ligand and the complexes were evaluated in 30:70 (v/v) H₂O:EtOH at 293 K and at constant ionic strength of 0.12M KCl. Coordination of the ligand to the metal ions leads to an increase of acidity of the imino-hydrogen of the benzimidazole group of the ligand as a function of the complex stability. Deprotonation leads to a spin-state transition (intermediate spin-state low-spin) of the iron(II)-complex, followed by a shift of the metal-to-ligandcharge transfer band (MLCT) to lower energies (_max=563 to 580 nm). The d-d absorption bands are found to shift to higher energies and the low-spin isomer is favoured at room temperature. An opposite shift of theMLCT band (_max=563 to 557 nm) is observed when HClO₄ is added to the complex solution, rendering the high-spin state of the complex more favourable.On leave from the Chemistry Department, Jahangirnagar University, Dhaka, Bangladesh     

Spin-crossover complexes in solution. III. Substituent- and solvent effects on the spin-equilibrium of 4-substituted iron(II)-2,6-bis-(benzimidazol-2′-yl)-pyridine systems

Summary Transition metal complexes of the composition [Fe(4-X-bzimpy)₂](ClO₄)₂ [bzimpy = 2,6-bis-(benzimidazol-2-yl)pyridine and X=H, OH, Cl] show thermally accessible spin-crossover behaviour in solution that depends on both the ligand and the solvent.¹H-NMR spectroscopy and UV-visible spectroscopy measurements suggest that ligand substituent effects, solvent donor-acceptor properties and hydrogen-bonding may be employed to fine-tune the ligand field strength and hence to affect the spin-crossover behaviour. The ligand substitution changes in solution are reflected by the magnetic data (X=H:_exp=2.50 _B; X=OH:_exp=4.20 _B and X=Cl:_exp=4.30 _B at 294 K in MeOH), and by the shift of metal-to-ligandcharge-transfer band (X=H, =557 nm; X=OH, =520 nm; X=Cl, =500 nm). [Fe(bzimpy)₂](ClO₄)₂ exhibits a pronounced spin-crossover equilibrium (¹A₁ ⁵T₂) in solution (K _sc=0.26 at 293 K; _exp=1.30 3.40 _B for 213 328 K in MeOH). A small variation of magnetic moments of [Fe(4-OH-bzimpy)₂](ClO₄)₂ (_exp=3.77 4.73 _B at 220 332 K) might indicate either the existence of (temperature dependent) hydrogen bonding between the ligand and solvent molecules or a temperature dependent variation in the population of the⁵E_g sublevel. The presence of strong donor solvents (DN 30) shifts the spin-state of the complexes.In course of absence from the Chemistry Department, Jahangirnagar University, Dhaka, Bangladesh     

Cyclic Voltammetry of 1,1′-bis(Diarylphosphino)metallocenes and Their Complexes with Palladium(II)

Cyclic voltammetry is used to study 1,1-bis(diarylphosphino)metallocenes (PP) [M(⁵-C₅R₄PAr₂)₂] (M = Fe; R = H; Ar = Ph, o-MeOC₆H₄, o-PrOC₆H₄, C₆F₅; M = Fe, R = Me, Ar = Ph; M = Ru, Os; R = H, Ar = Ph) and such Pd(II) complexes with these as neutral dichlorides [(PP)PdCl₂], dication solvates [(PP)Pd(L) _n ]²⁺ (L = H₂O, MeCN), and dication triphenylphosphines containing metal–Pd bond (PP)Pd(PPh₃)]²⁺. The nature of the metallocene metal atom and aryl substituents at phosphor atoms and the formation of a metal–Pd bond affect redox potentials of these compounds. 1,1-bis(Diphenylphosphino)metallocenes [M(⁵-C₅H₄PPh₂)₂] (M = Fe, Ru, Os) feature similar electron-donating properties. Oxidation potentials of Pd(II) complexes can serve as a criterion indicating the formation of a metal–Pd bond.     

Deprotonation energetics of adenine,adenosine, 5′-adenosine monophosphate and adenosine triphosphate in water from EMF and spectrophotometric measurements

The deprotonation constants of adenine (ADE) [K₁ and K₂], adenosine (ADO) [K₁ and K₂], 5-adenosine monophosphate (5-AMP) [K₁, K₂ and K₃] and adenosine triphosphate (ATP) [K₃ and K₄] have been obtained for aqueous soutions from emf measurements on cells such as Pt, H₂ (g, 1 atm)/HA(m₁), NaA(m₂), KI(m₃)/AgI-Ag (where HA is the corresponding acid of ADE, ADO, 5-AMP and ATP) at different temperatures. The pK values were fitted by the temperature equation: pK=AT¹+B+CT by the least squares method and the related thermodynamic quantities viz. G ^o , TS ^o and H ^o were calculated from the coefficients A, B and C.     

Structural Dynamics of Isomorphic Substitution in N,N′-Diallylbenzimidazolium Copper Halide π-Complexes [C7H5N2(C3H5)2]+[Cu2Cl3?xBrx]? (x=0, 1.60, 2.33, 3)

Two new -complexes of copper(I) halides with the 1,3-diallylbenzimidazolium cation, [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl_1.40Br_1.60]^– and [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Br₃]^–, have been synthesized and structurally defined (space group P2 ₁/c for both; a = 22.094(6), b = 9.272(8), c = 9.22(1) , = 118.26(4)° and a = 22.267(5), b = 9.311(3), c = 9.263(2) , = 117.51(2)°). The mutual effects of chlorine–bromine substitution and the efficiency of -interactions are discussed based on XRD data for these two compounds and for the compounds [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl₃]^– and [C₇H₅N₂(C₃H₅)₂]⁺[Cu₂Cl_0.67Br_2.33]^– studied previously.     

DSC Monitoring of the Spin Crossover in Fe(II) Complexes

Heat flow to [Fe(bzimpy)²](ClO₄)₂⋅0.25H₂O complex (bzimpy=2,6-bis(benzimidazol-2-yl)pyridine) (I) was measured between 300 and 460 K by differential scanning calorimetry. This exhibits a well-developed peak characteristic of the first-order phase transitions at temperature 403 K. The enthalpy and entropy of transition from low-spin to high-spin state has been determined to be ΔH=17 kJ mol⁻¹ and ΔS=43.0 Jmol⁻¹ K⁻¹. Heat flow to [Fe(bzimpy_−1H)₂]⋅H₂O complex (bzimpy _−1H=deprotonated bzimpy) (II) was measured between 300 and 580 K. The spin crossover in this system is accompanied with liberation of crystal water on the first heating. To monitor the structural changes during the spin crossover, powder diffraction data have been collected as a function of temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Studies on the equilibria in Ag(I) - 1,4,8,11-tetraazacyclotetradecane and Ag(I) - 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane systems in water

Summary Protonation constants of 1,4,8,11-tetraazacyclotetradecane (T ACT) and 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (TMT ACT) (=0.1) were determined bypH-metry. The values are logK ₁=10.922, logK ₂=10.511, logK ₃=2.646, logK ₄=1.620 forT ACT, and logK ₁=9.387, logK ₂=9.050, logK ₃=2.491, logK ₄=1.380 forTMTACT. Absorption maxima of the complexes AgTA CT(NO₃)₂ and AgTMTACT(NO₃)₂ were found to be ₁=280 nm, ₂=350 nm, and ₁=290 nm, ₂=400 nm, respectively. The disproportionation constants of Ag(I) ions in the presence of the amines were determined by potentiometry: forTA CT logK _d =12.778, and forTMT ACT logK _d =11.778. The mechanisms of the electrode processes taking place in solutions of the complexes under investigation were examined by means of chronovoltamperometric and coulometric measurements. The formal potential,E _f ⁰ , of the system: AgTMT ACT ²⁺+e AgTMT ACT ⁺ is +0.450 V vs. NHE.

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Untersuchungen zu den Gleichgewichten Ag(I) -1,4,8,11-Tetraazacyclotetradekan und Ag(I) -1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradekan in Wasser

Zusammenfassung Die Protonierungskonstanten von 1,4,8,11-Tetraazacyclotetradekan (TACT) und 1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradekan (TMT ACT) wurdenpH-metrisch bei =0.1 bestimmt. Folgende Werte wurden ermittelt: logK ₁=10.922, logK ₂=10.511, logK ₃=2.646, logK ₄=1.620 fürTACT und logK ₁=9.387, logK ₂=9.050, logK ₃=2.491, logK ₄=1.380 fürTMT ACT. Die Absorptionsmaxima der Komplexe AgTACT(NO₃)₂ und AgTMTACT(NO₃)₂ waren ₁=280 nm, ₂=350 nm, bzw. ₁=290 nm, ₂=400 nm. Die Disproportionierungskonstanten der Ag(I)-Ionen in Gegenwart der Amine wurden potentiometrisch bestimmt: logK _d =12.778 fürTACT und logK _d =11.778 fürTMTACT. Der Mechanismus des Elektrodenprozesses in den Komplexlösungen wurde mittels Chronovoltamperometrie und Coulometrie überprüft. Das formale PotentialE _f ⁰ des Systems AgTMT ACT ²⁺+eAgTMT ACT ⁺ ist +0.450 V gegenüber NHE.

     

Application of solvent extraction and synchronous spectrofluorimetry to the determination of the formation constant for a 1:1 complex of carbazole withβ-cyclodextrin in water-dimethyl sulfoxide medium

Extraction of carbazole in heptane was performed at 25±1°C with an aqueous dimethyl sulfoxide (DMSO) medium containing -cyclodextrin (CD) at consecutive concentrations in the range of 0–10 mM. The fluorescence intensity of carbazole remaining in the heptane phase was measured by synchronous scanning fluorimetry. The apparent formation constant (K _f) for a 1:1 carbazole: CD inclusion complex in water-DMSO medium was determined by using a linear plot of the distribution ratio calculated from the fluorescence intensities vs. the -CD concentration. The values thus obtained ranged from 477 M^–1 in a 10% v/v DMSO medium to 12.1 M^–1 in a 60% v/v medium. Good linear relationships were observed between logK _f and the DMSO concentration ([DMSO]), and also between logK _f and the logarithm of the distribution coefficient (K _d) for carbazole. The formation constant in 100% water was estimated to be approximately 1.0×10³ M^–1 on the basis of the logK _f vs. [DMSO] and the logK _f vs. logK _d correlations.     

Kinetics and mechanism of the hydrolysis of sodium carboxymethylcellulose (Na-CMC) by a cellulase complex

TheSomogyi-Nelson colorimetric method is applied in a new manner more suitable for evaluating the kinetics of the enzyme hydrolysis of sodium carboxymethylcellulose (Na-CMC) catalyzed by the cellulase complex. By means of selective inhibition of a chosen enzyme from the cellulase complex it became possible to trace the effect of the other enzymes included in its composition.

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Kinetik und Mechanismus der Hydrolyse von Natriumcarboxymethylcellulose (Na-CMC) durch einen Cellulase-Komplex

Zusammenfassung Die kolorimetrische Methode nachSomogyi undNelson wird nach einem neuen Verfahren zur Verfolgung der Kinetik der hydrolytischen Spaltung von Natriumcarboxymethylcellulose (Na-CMC), katalysiert durch den Cellulase-Komplex, angewandt. Durch selektive Inhibierung eines bestimmten Enzyms des Cellulase-Komplexes kann man die Wirkung der anderen zu seiner gesamten Zusammensetzung gehörenden Enzyme verfolgen.

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Symbols Used E enzyme (E—cellulase;E—exo-cellobiohydrolase;E—-glucosidase) - [E] _w weight concentration of enzymeE - S substrate (Na-CMC—sodium carboxymethylcellulose) - [S]₀ weight concentration of substrateS - I inhibitor (I—lactose;I—calcium chloride;I—condurrite-B-epoxide) - P product (P—oligosaccharides;P—cellobiose;P—D-glucose) - P end product (K , K , K ) - DP degree of polymerization - DS degree of substitution - ES enzyme-substrate complex (E S, E S, E S) - EP enzyme-product complex (E P, E P) - EI enzyme-inhibitor complex (E I, E I, E I) - M _s molecular mass of substrateS - K _s substrate constant (K _s , K _s , K _s ) - K _I inhibitor constant (K _I , K _I , K _I ) - K _m Michaelis-Menten constant - k ₊₁,k ₊₂ (k ₊₂ ,k ₊₂ ,k ₊₂ ) forward rate constants - k _–1 reverse rate constant - ₀ initial rate of reaction - V maximal reaction rate - A change in absorbance - molar absorption coefficient - wavelength Herrn Prof. Dr.Hans Tuppy zum 60. Geburtstag herzlichst gewidmet.     

Photoredox properties of Kojic acid and its derivatives complexed to Iron(III)

Summary Iron(III) complexes of the formcis-[Fe(SB(X - K)] in whichSB ^2– are open-chain tetradentateSchiff base N₂O₂-ligands ofacacen,benacen orsalen type, andX - K ^– are bidentate anions of kojic acid (5-hydroxy-2-hydroxymethyl-4H-pyran-4-one) or other -pyranones undergo photoredox transformations when being irradiated in methanol into intraligand orLMCT bands. The quantum yields of the photoredox reactions depend on the peripheral constitution of the N₂O₂ ligands, the substituentsA andB of the ligandsX - K ^–, and the wavelength of irradiation _irr. The proposed mechanism involves the population of photoredox reactiveLMCT states by photophysical deactivation steps, primary photoredox formation ofX - K radicals and Fe(II), and subsequent dark redox processes giving back the anionsX - K ^– and the final products Fe(II) and formaldehyde formed in the molar ratio 2:1.

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Photoredoxeigenschaften von Fe(III)-Komplexen von Kojic Acid und ihren Derivaten

Zusammenfassung Eisen(III)-Komplexe der Formcis-[Fe(SB)(X - K)] mitSB ^2–=offenkettige tetradentateSchiff-Basen-N₂O₂-Liganden undX - K ^–=bidentate Anionen von 5-Hydroxy 2-hydroxymethyl-4H-pyran-4-on oder andere -Pyranone unterliegen bei Bestrahlung in Methanol Photoredoxumwandlungen, was durch Intraligand- oderLMCT-Banden belegt wird. Die Quantenausbeuten der Reaktionen hängen von der Konstitution der N₂O₂-Liganden, den SubstituentenA undB und dem LigandenX - K ^– sowie der Anregungswellenlänge _irr ab. Der vorgeschlagene Mechanismus beinhaltet die Population photoredoxreaktiverLMCT-Zustände durch photophysikalische Deaktivierungsschritte, die Bildung vonX - K*-Radikalen und Fe(II) und-Über Dunkelprozesse — die Rückbildung der AnionenX - K ^– sowie die Reaktion zu den Endprodukten Fe(II) und Formaldehyd im molaren Verhältnis 2:1.

     

Study on complex formation equilibria of tervalent lanthanons with fluorinated β-ketoesters in aqueous dioxane medium

Summary The thermodynamic stepwise formation constants (log ^T K _n) of nine tervalent lanthanons (La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Dy³⁺, Er³⁺ and Lu³⁺) with three fluorinated -ketoesters (methyltrifluroacetoacetate, ethyltrifluoroacetoacetate, and ethylpentafluoropropionylacetate) have been evaluated potentiometrically in a 50% dioxane-water mixture at 25 and 35 ± 0.01 °C. The values of log ^T K _n do not follow a linearity when plotted againstZ/r and invariably obey the sequence: La³⁺ < Nd³⁺ < Pr³⁺ < Sm³⁺ < Gd³⁺ < Eu³⁺ < Dy³⁺ Er³⁺ Lu³⁺ in all instances. The standard thermodynamic parameters (G ₁ ⁰ , H ₁ ⁰ , S ₁ ⁰ ) associated with log ^T K _n have also been calculated. The validity of the chosen equilibrium model was examined by an error analysis usingS _min values (sum of the squared residuals), scatter plots, and slopes and intercepts of Abrahams-Kave type normal probability plots.

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Komplexbildungsgleichgewichte von dreiwertigen Lanthanoiden mit fluorierten -Ketoestern in wäßrigem Dioxanmedium

Zusammenfassung Es wurden die thermodynamischen stufenweisen Komplexbildungskonstanten (log ^T K _n) von 9 dreiwertigen Lanthanoiden (La³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, Gd³⁺, Dy³⁺, Er³⁺ und Lu³⁺) mit drei fluorierten -Ketoestern (Methyltrifluoracetoacetat, Ethyltrifluoracetoacetat und Ethylpentafluopropionylacetat) in 50% Dioxan-Wasser bei 25 und 35±0.01 °C potentiometrisch bestimmt. Die Werte für log ^T K _n ergeben keine lineare Abhängigkeit gegenüberZ/r, sie gehorchen stets der Reihenfolge: La³⁺ < Nd³⁺ < Pr³⁺ < Sm³⁺ < Gd³⁺ < Eu³⁺ < Dy³⁺ Er³⁺ Lu³⁺. Die thermodynamischen Standardparameter G ₁ ⁰ , H ₁ ⁰ und S ₁ ⁰ wurden ebenfalls berechnet. Die Gültigkeit des gewählten Gleichgewichtsmodells wurde unter Verwendung der Summe der Quadratreste (S _min), von Streukurven und Steigung/Ordinatenabschnitt der Normalwahrscheinlichkeitsdarstellung nach Abrahams-Kave untersucht.

     

Synthesis and characterization of the complexes of lanthanide(III) chlorides and nitrates with the tetradentate schiff base diethyl(ethylenebis-β-aminocrotonate)

Summary The Schiff base ligand diethyl(ethylenebis--aminocrotonate) (LH₂) reacts with lanthanide(III) chlorides and nitrates in various solvents to give solid complexes of the stoichiometriesLn(LH₂)Cl₃ (Ln=La–Yb),Ln(LH₂)₂Cl₃ (Ln=La–Sm),Ln ₂(LH₂)₃Cl₆(Ln=Eu–Yb) andLn(LH₂)(NO₃)₃ (Ln=La–Yb). Properties, conductivity measurements, X-ray powder patterns, thermal data, magnetic moments and spectroscopic (IR,¹H-NMR, electronic diffuse reflectance and solid state emission f-f spectra) are discussed in terms of the nature of the bonding and the possible structural types.

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Synthese und Charakterisierung der Komplexe von Lanthanid(III)chloriden und -nitraten mit der vierzähnigen Schiff-Base Diethyl(ethylenbis--aminocrotonat)

Zusammenfassung Der Schiffbasen-Ligand Diethyl(ethylenbis--aminocrotonat) reagiert mit Lanthanid(III)chloriden und -nitraten in verschiedenen Lösungsmitteln unter der Bildung von festen Komplexen der StöchiometrienLn(LH₂)Cl₃ (Ln = La – Yb),Ln(LH₂)₂Cl₃ (Ln = La – Sm),Ln(LH₂)₃Cl₆ (Ln = Eu – Yb) undLn(LH₂)(NO₃)₃ (Ln = La – Yb). Die allgemeinen Eigenschaften, Leitfähigkeitsmessungen, Röntgen-Pulverdiagramme, thermische Daten, magnetische Momente und spektroskopische Daten (IR,¹H-NMR, Elektronenreflexionsspektren und Festkörperemissions-f-f-Spektren) werden im Hinblick auf die Bildungsverhältnisse im Komplex und strukturelle Möglichkeiten diskutiert.

     

Discrete Variational (DV)-Xα Calculations of Incomplete Cubane-Type Molybdenum Clusters [Mo3X4(H2O)9]4+ (X= O,S)1

Electronic structures of two incomplete cubane-type clusters [Mo₃X₄(H₂O)₉]⁴⁺ (X =O, S) have been calculated by the discrete-variational (DV)-X method. The calculations explain the experimental results of valence-band X-ray photoelectron spectra, electronic spectra, and reactivity difference toward acetylene. The net charge of Mo in [Mo₃S₄(H_2O)₉]⁴⁺(S) is more negative than that of Mo in [MO₃O₄H₂O)⁴⁺] (O), and the bridging sulfur atoms are the main negative charge-source for the molybdenum atoms in the cluster S. As for S,levels of HOMO (45e) and LUMO (46e) consist mainly of Mo 4d and-S 3p atomic orbitals, and contribution of ₃-S 3p to the orbitals is not large. The existence of Mo-Mo, Mo--S, and Mo- ₃-S bounds is clear from the contour maps of the orbitals. As for O levels of HOMO (40e) and LUMO (41c) consist mainly of Mo 4d and-O 2p atomic orbitals. Contribution of ₃-O 2p to the orbitals is not large except in the orbital 30a₁,. The existence of Mo-Mo, Mo--O, and MO- ₃-O bonds also is appreciable from the contour maps of the orbitals.Dedicated to Professor Jiaxi Lu on the occasion of his 80th birthday.     

peri-Naphthylenediamines. 33. Further studies of the reactions of 1,8-bis(dimethylamino)naphthalene with trifluoroacetic anhydride

The reaction of 1,8-bis(dimethylamino)naphthalene (1) (proton sponge) with a large excess of trifluoroacetic anhydride in the absence of a solvent afforded a complex mixture of products among which were trans- (2) and cis-diols (3) of the naphtho[1,8-c,d]pyran series, the double proton sponge (4), its di- (5) and tetrafluoroacetyl (6) derivatives, and compound 7. These results differ substantially from those obtained previously in the reactions performed in various solvents. Some conversions of compounds 4 and 7 were investigated. The ¹⁹F NMR spectra of the compounds synthesized are discussed.     

Spectroscopic and thermodynamic studies on solvatochromic nickel(II) complexes

Summary The solvatochromic and thermochromic behaviour of a series of mixed Ni(II) complexes with unsubstituted and substituted -diketones and diamines in the solvents 1,2-dichloroethane (DCE), acetonitrile (An), acetone (AC),n-butanol (n-BuOH), formamide (FA), N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO) and pyridine (PY) has been studied and characterized on the basis of electronic spectra. Spectrophotometric methods have been used to evaluate equilibrium constants and their enthalpic and entropic terms for the formation of Ni(-dik)(diam)L ⁺ and Ni(-dik)(diam)L ₂ ⁺ . Increasing donor strength of the donor-solvents (L) and (or) increasing electronwithdrawing parameters of the substituents at the -diketone and the diamine ligands lead to increasing formation constants, paralleled by relative increase in the stability of the five-coordinated species Ni(-dik)(diam)L ⁺. The results are discussed in terms of the extended donor-acceptor concept.On leave of absence from the Faculty of Education, Ain Schams University, Roxy, Cairo, Egypt     

Ruthenium carbene complexes containing bidentate and tridentate PO ligands

Treatment of [Ru(CHR)Cl₂(PCy₃)₂] (Cy = cyclohexyl) with Tl[N(Pr₂ⁱPO)₂] and AgL_OEt (L_OEt⁻ = [CpCo{P(O)(OEt)₂}₃]⁻) afforded the Ru carbene complexes [Ru(CHPh)(PCy₃)Cl{N(Pr₂ⁱPO)₂}] (1) and [L_OEtRu(CHR)(PCy₃)Cl] (2), respectively. Chloride abstraction of complex 2 with TlPF₆ in MeCN afforded [L_OEtRu(CHPh)(PCy₃)(MeCN)][PF₆] (3). Complexes 1 and 2 are capable of catalyzing ring-closing metathesis of diethyl 1,2-diallylmalonate. The crystal structure of complex 2 has been determined.     

The molecular complex of dibenz[a,c]anthracene and trinitrobenzene

The crystal structure of the complex between the polycyclic aromatic hydrocarbon di-benz[a,c]anthracene and 1,3,5-trinitrobenzene is reported. The crystals are triclinic, space group P¯1 with unit cell dimensionsa=7.277(2) å,b=11.237(6) å, andc=13.902(5) å,= 104.13(4),=96.04(3), and =95.15(2). Diffraction data were measured at 121(2) K. The structure was determined and refined toR ₁=0.046. The structure consists of layers containing both dibenz[a,c]anthracene and 1,3,5-trinitrobenzene molecules, interconnected within a layer by C-H O interactions. Layers stack on one another so that dibenz[a,c]anthracene molecules are sandwiched between 1,3,5-trinitrobenzene molecules and vice versa. The average distance between molecules in these sandwiches is 3.23 å.