Inhibition of [FeFe]-hydrogenase by formaldehyde: proposed mechanism and reactivity of FeFe alkyl complexes

The mechanism for inhibition of [FeFe]-hydrogenases by formaldehyde is examined with model complexes. Key findings: (i) CH₂ donated by formaldehyde covalently link Fe and the amine cofactor, blocking the active site and (ii) the resulting Fe-alkyl is a versatile electrophilic alkylating agent. Solutions of Fe₂[(μ-SCH₂)₂NH](CO)₄(PMe₃)₂ (1) react with a mixture of HBF₄ and CH₂O to give three isomers of [Fe₂[(μ-SCH₂)₂NCH₂](CO)₄(PMe₃)₂]⁺ ([2]⁺). X-ray crystallography verified the NCH₂Fe linkage to an octahedral Fe(ii) site. Although [2]⁺ is stereochemically rigid on the NMR timescale, spin-saturation transfer experiments implicate reversible dissociation of the Fe–CH₂ bond, allowing interchange of all three diastereoisomers. Using ¹³CH₂O, the methylenation begins with formation of [Fe₂[(μ-SCH₂)₂N¹³CH₂OH](CO)₄(PMe₃)₂]⁺. Protonation converts this hydroxymethyl derivative to [2]⁺, concomitant with ¹³C-labelling of all three methylene groups. The Fe–CH₂N bond in [2]⁺ is electrophilic: PPh₃, hydroxide, and hydride give, respectively, the phosphonium [Fe₂[(μ-SCH₂)₂NCH₂PPh₃](CO)₄(PMe₃)₂]⁺, 1, and the methylamine Fe₂[(μ-SCH₂)₂NCH₃](CO)₄(PMe₃)₂. The reaction of [Fe₂[(μ-SCH₂)₂NH](CN)₂(CO)₄]²⁻ with CH₂O/HBF₄ gave [Fe₂[(μ-SCH₂)₂NCH₂CN](CN)(CO)₅]⁻ ([4]⁻), the result of reductive elimination from [Fe₂[(μ-SCH₂)₂NCH₂](CN)₂(CO)₄]⁻. The phosphine derivative [Fe₂[(μ-SCH₂)₂NCH₂CN](CN)(CO)₄(PPh₃)]⁻ ([5]⁻) was characterized crystallographically.

The mechanism for inhibition of [FeFe]-hydrogenases by formaldehyde is examined with model complexes.     

Mixed-Ligand Ruthenium(II) Complexes as Structural Units of Polynuclear Systems

Spectral and kinetic parameters were studied for phosphine-bipyridyl ruthenium(II) complexes, namely, cis-[Ru(Bipy)₂(PPh₃)X](BF₄), cis-[Ru(Bipy)(Dppe)X₂], and cis-[Ru(Bipy)(Dppene)X₂] (where Bipy is 2,2"-bipyridyl, PPh₃is triphenylphosphine, Dppe is 1,2-bis(diphenylphosphino)ethane, and Dppene iscis-1,2-bis(diphenylphosphino)ethylene; X = CN^–, NO₂ ^–), in the frozen (77 K) alcohol glasses (EtOH–MeOH, 4 : 1). The energies of the singlet and triplet metal-to-ligand charge transfer states d(Ru) *(Bipy) were found to increase in the order [Ru(Bipy)₂X₂] < [Ru(Bipy)₂(PPh₃)X]⁺< [Ru(Bipy)(Dppe)X₂] < [Ru(Bipy)(Dppene)X₂]. The luminescence quantum yields and the rate constants of the nonradiative deactivation of the lowest excited state ³MLCT increase in the same order.     

Formation pathways and structure—Property interrelationship of 3-imino-1-methyl-5,5-dialkyl-4,7,7-tricyano-2-oxabicyclo-[2.2.1]heptane derivatives

The problems of the structure—property interrelationship of 3-imino-2-oxabicyclo[2.2.1]heptane derivatives are discussed on the basis of x-ray diffraction studies (XDS). A pathway for the formation of the bicyclic compounds is proposed, and the realization of spirans in the reaction of sym-tetracyanoethane with conjugated cyclic systems containing s-cis C=C and C=O fragments is substantiated. The factors responsible for the syn orientation of the oxygen atom and the N-substituent of the imino group are analyzed. It is shown that a change in the steric hindrance in the bicyclic compounds leads to a change in the conformation of the latter. The reasons for the shortening of the C_sp3-C_sp3, C_sp3-C_sp and C=N exo bonds and the correlation of the XDS and IR spectroscopic data are examined. From the XDS data for N-bromo-substituted imines, a model for Br⁺...NC electrophilic attack was proposedCommunication 16 from the series Chemistry of 1,1,2,2-tetracyanoethane. See [1] for Communication 15.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 519–526, April, 1991.     

Complexation de l'anion fluorure par des tetramines cycliques protonees.

The $\text{s}$ynthesis of the new tetraazamacrocycle [20]N₄ is briefly described; complexation of F by the fully protonated [16]N₄, [18]N₄ and [20]N₄ macrocycles is investigated.     

Mass-spectrometric study of 3,9-diazabicyclo- and 3,9-oxaazabicylo[3.3.1]nonanes

The mass spectra of substituted 3,9-diazabicyclo- and 3,9-oxaazabicyclo[3.3.1]-nonanes were studied as a function of competitive distribution of the charge between the N₃ and N₉ and O₃ and N₉ atoms and the properties of the substituents attached to the heteroatoms. It is shown that a characteristic peculiarity of the fragmentation of 3,9-diazabicyclo[3.3.1]nonanes is fragmentation of the molecular ion with an open structure that is formed by cleavage of the C₁-C₂ bond. The formation of an amine fragment with retention of the bicyclic structure with an exocyclic double bond attached to the quaternary N₉ atom is characteristic for 3,9-oxaazabicyclo[3.3.1]nonanes. It is shown that this sort of behavior of the investigated compounds is determined by their structures and the properties of the heteroatoms in the saturated bicyclic systems.Communication 12 from the series Application of mass spectrometry in structural and stereochemical studies. See [1] for Communication 11.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 229–235, February, 1981.     

Substituted aromatic pentaphosphole ligands – a journey across the p-block

The functionalization of pentaphosphaferrocene [Cp*Fe(η⁵-P₅)] (1) with cationic group 13–17 electrophiles is shown to be a general synthetic strategy towards P–E bond formation of unprecedented diversity. The products of these reactions are dinuclear [{Cp*Fe}₂{μ,η^5:5-(P₅)₂EX₂}][TEF] (EX₂ = BBr₂ (2), GaI₂ (3), [TEF]⁻ = [Al{OC(CF₃)₃}₄]⁻) or mononuclear [Cp*Fe(η⁵-P₅E)][X] (E = CH₂Ph (4), CHPh₂ (5), SiHPh₂ (6), AsCy₂ (7), SePh (9), TeMes (10), Cl (11), Br (12), I (13)) complexes of hetero-bis-pentaphosphole ((cyclo-P₅)₂R) or hetero-pentaphosphole ligands (cyclo-P₅R), the aromatic all-phosphorus analogs of prototypical cyclopentadienes. Further, modifying the steric and electronic properties of the electrophile has a drastic impact on its reactivity and leads to the formation of [Cp*Fe(μ,η^5:2-P₅)SbICp′′′][TEF] (8) which possesses a triple-decker-like structure. X-ray crystallographic characterization reveals the slightly twisted conformation of the cyclo-P₅R ligands in these compounds and multinuclear NMR spectroscopy confirms their integrity in solution. DFT calculations shed light on the bonding situation of these compounds and confirm the aromatic character of the pentaphosphole ligands on a journey across the p-block.

The reactivity of cationic electrophiles towards pentaphosphaferrocene [Cp*Fe(ƞ⁵-P₅)] is explored. We report P–E bond formation for electrophiles across the p-block, producing coordination complexes with unprecedented hetero-bispentaphosphole and hetero-pentaphosphole ligands.     

Yield ratio of [11C]-CO2, [11C]-CO and [11C]-CH4 from the irradiation of N2/H2-mixtures in a gas target

The¹⁴N/p, /¹¹C-reaction was studied in different N₂/H₂-mixtures. The products are [¹¹C]-CO₂, [¹¹C]-CO and [¹¹C]-CH₄. The yield ratio may be controlled by varying the bombardment conditions. High pressure, high H₂-content, high beam current and high proton energy shift the ratio towards [¹¹C]-CH₄. Lower beam current and lower proton energy increase the yield of [¹¹C]-CO₂. The production of [¹¹C]-CO is constant over a wide range of conditions /about 10%/. For the production of [¹¹C]-CH₄ in good yield a target gas holder for high pressures has been developed. Details are given in Fig. 7. This target gas holder was filled with 5% H₂ in N₂ at 3×10⁶ Pa. Proton irradiation of the mixture gives a typical yield of [¹¹C]-CH₄ of 400–500 mCi at a beam current of 15–20 A within 20 min. Only traces of other¹¹C-labelled compounds could be detected under these conditions.     

Chromium carbides and cyclopropenylidenes

Carbon tetrabromide can be reduced with CrBr₂ in THF to form a dinuclear carbido complex, [CrBr₂(thf)₂)][CrBr₂(thf)₃](μ-C), along with formation of [CrBr₃(thf)₃]. An X-ray diffraction (XRD) study of the pyridine adduct displayed a dinuclear structure bridged by a carbido ligand between 5- and 6-coordinate chromium centers. The carbido complex reacted with two equivalents of aldehydes to form α,β-unsaturated ketones. Treatment of the carbido complex with alkenes resulted in a formal double-cyclopropanation of alkenes by the carbido moiety to afford spiropentanes. Isotope labeling studies using a ¹³C-enriched carbido complex, [CrBr₂(thf)₂)][CrBr₂(thf)₃](μ-¹³C), identified that the quaternary carbon in the spiropentane framework was delivered by carbide transfer from the carbido complex. Terminal and internal alkynes also reacted with the carbido complex to form cyclopropenylidene complexes. A solid-state structure of the diethylcyclopropenylidene complex, prepared from 3-hexyne, showed a mononuclear cyclopropenylidene chromium(iii) structure.

Carbon tetrabromide can be reduced with CrBr₂ in THF to form a dinuclear carbido complex, [CrBr₂(thf)₂)][CrBr₂(thf)₃](μ-C), along with formation of [CrBr₃(thf)₃].     

Iodination of B12H11OC(O)CH2–3, B12H11OH2–, and B12H11SCN2–

Reactions of iodination of monosubstituted derivatives of B₁₂H₁₁X^2–anion (X = OC(O)CH₃, OH, SCN) were studied. The reactions were shown to proceed smoothly to give B₁₂H₁₀(OC(O)CH₃)I^2–((carboxy)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion), B₁₂H₁₀(OH)I^2–((hydroxo)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion), and B₁₂H₁₀(SCN)I^2–((thiocyanato)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion) in high yields, irrespective of the solvent used (benzene, H₂O–ROH, where R = C₂H₅, CH₂CH₂CH₃).¹     

Actinide arene-metalates: ion pairing effects on the electronic structure of unsupported uranium–arenide sandwich complexes

Addition of [UI₂(THF)₃(μ-OMe)]₂·THF (2·THF) to THF solutions containing 6 equiv. of K[C₁₄H₁₀] generates the heteroleptic dimeric complexes [K(18-crown-6)(THF)₂]₂[U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]₂·4THF (118C6·4THF) and {[K(THF)₃][U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]}₂ (1THF) upon crystallization of the products in THF in the presence or absence of 18-crown-6, respectively. Both 118C6·4THF and 1THF are thermally stable in the solid-state at room temperature; however, after crystallization, they become insoluble in THF or DME solutions and instead gradually decompose upon standing. X-ray diffraction analysis reveals 118C6·4THF and 1THF to be structurally similar, possessing uranium centres sandwiched between bent anthracenide ligands of mixed tetrahapto and hexahapto ligation modes. Yet, the two complexes are distinguished by the close contact potassium-arenide ion pairing that is seen in 1THF but absent in 118C6·4THF, which is observed to have a significant effect on the electronic characteristics of the two complexes. Structural analysis, SQUID magnetometry data, XANES spectral characterization, and computational analyses are generally consistent with U(iv) formal assignments for the metal centres in both 118C6·4THF and 1THF, though noticeable differences are detected between the two species. For instance, the effective magnetic moment of 1THF (3.74 μ_B) is significantly lower than that of 118C6·4THF (4.40 μ_B) at 300 K. Furthermore, the XANES data shows the U L_III-edge absorption energy for 1THF to be 0.9 eV higher than that of 118C6·4THF, suggestive of more oxidized metal centres in the former. Of note, CASSCF calculations on the model complex {[U(η⁶-C₁₄H₁₀)(η⁴-C₁₄H₁₀)(μ-OMe)]₂}²⁻ (1*) shows highly polarized uranium–arenide interactions defined by π-type bonds where the metal contributions are primarily comprised by the 6d-orbitals (7.3 ± 0.6%) with minor participation from the 5f-orbitals (1.5 ± 0.5%). These unique complexes provide new insights into actinide–arenide bonding interactions and show the sensitivity of the electronic structures of the uranium atoms to coordination sphere effects.

Use of Chatt metal-arene protocols with uranium leads to the synthesis of the first well-characterized, unsupported actinide–arenide sandwich complexes. The electronic structures of the actinide centres show a key sensitivity to ion pairing effects.     

Bivalent 3d-metal complexes of malonyl- and succinyldihydrazide based macrocyclic ligands. Synthesis and characterization

Summary The macrocycles 2,10-dimethyl-3,4,8,9,15-pentaazabicyclo-[9.3.1]-pentadeca-1 (15),2,9,11,13-penta-ene-5,7-dione (L) and 2,11-dimethyl-3,4,8,9,10,16-pentaazabicyclo[10.3.1]-hexadeca-1 (16),2,10,12,14-penta-ene-5,8-dione (L) were prepared and characterized by elemental, i.r. and mass spectral data. The macrocycles react with various metal(II) chlorides to yield complexes of the types [MLCl₂H₂O] (M = Mn, Co, Ni, Cu or Zn), [MLCl₂H₂O] (M = Mn, Ni, Cu or Zn) and [Co₃L₂Cl₄]Cl₂. The complexes were characterized by physico-chemical and spectroscopic methods.     

Direct Electrochemical Synthesis of Diaziridines

The possibility of direct electrosynthesis of mono- and bicyclic diaziridines is studied using, respectively, 1,2-dimethyldiaziridine and 1,5-diazobicyclo[3,1,0]hexane as an example. In either case the process is realized in a galvanostatic electrolysis in the anodic space of a diaphragm cell and proceeds through intermediate formation of alkylchloramines; other electrosynthesis conditions depend on the structure of the source aminoalkane. In the synthesis of monocyclic diaziridines, for the electrolyte, a 4 M solution of NaCl in water was used, which contained high concentrations of 0.5 and 2.0 M of, respectively, CH₂O and MeNH₂, and the amine excess served, in particular, for binding protons in the reaction of diaziridine synthesis. The process occurs in a homogeneous phase, and the current efficiency for 1,2-dimethyldiaziridine amounted to 40–50% in optimum conditions. In the synthesis of bicyclic diaziridines, the electrolyte was a 4 M solution of NaCl in a 20-% aqueous methanol, containing a low—0.1 M concentration of H₂N(CH₂)₃NH₂ and an equimolar quantity of CH₂O, and additives of NaHCO₃ were used for binding protons in the reaction of diaziridine synthesis. The process occurs in a heterophase environment because of an incomplete dissolution in the conditions of experiment of NaCl and intermediately-formed chloraminoalkane. The current efficiency for 1,5-diazobicyclo[3,1,0]hexane reached 80–85% in optimum conditions, but the loads of the source aminoalkane were 20 times lower than in the synthesis of monocyclic diaziridines. Compared are the results of a direct and an earlier-described indirect method of electrosynthesis of mono- and bicyclic diaziridines.     

Cs4[Sc6C]Cl13 und Cs4[Pr6(C2)]I13 — zwei Beispiele für das fehlende Bindeglied bei der Verknüpfung der Baueinheiten [M6Z]XX

Cs₄[Sc₆C]Cl₁₃ and Cs₄[Pr₆(C₂)]I₁₃ — Two Examples for the Missing Link in the Connectivity of [M₆Z]X X Building Units Cs₄[Sc₆C]Cl₁₃ (tetragonal, I4₁/amd, a = 1 540.5(4), c = 1 017.9(7) pm, c/a = 0.661, Z = 4, R = 0.038, R_w = 0.026) and Cs₄[Pr₆(C₂)]I₁₃ (a = 1 804.9(3), c = 1 259.5(3) pm, c/a = 0.698, R = 0.106, R_w = 0.068) are obtained as green-black and blue-black single crystals with brass-like metallic lustre through metallothermic reduction of ScCl₃ and PrI₃, respectively, with cesium in the presence of carbon in sealed tantalum containers. The, overall, isotypic compounds contain isolated [Sc₆C] and [Pr₆(C₂)] clusters, respectively, that are surrounded by 18 halide (X) ligands (12 Xⁱ and 6 X^a; X = Cl or I). The connection is carried out via the motif [M₆Z]XXXX (M = Sc and Pr; Z = C and C₂, respectively) and is thereby the missing link of the motifs of connection for the composition A_x[M₆Z]X₁₃. Analogous interconnection of [TiO₆] octahedra is found in the anatase-type of structure of TiO₂.     

Synthesis,Structural Aspects,Antimicrobial Activity,and Ion Transport Investigations of Four New [1 + 1] Condensed 12‐Membered Cyclophane Amides

Two new diamines ( a , b ) and their four [1 + 1] condensed macrocyclic peptides ( c–f ) were synthesized via dilution method affording the expected dilactams in reasonably high‐yield yields. The compounds were characterized by elemental analyses, mass, FT‐IR, ¹H, and ¹³C NMR spectral data. Mass spectra reveal their [1 + 1] cyclic condensation. The macrocycles having two peptide units in the ring would constitute three configurational isomers: cisoid–cisoid, transoid–transoid, and cisoid–transoid. Their ¹H and ¹³C NMR show one signal for each chemically equivalent SCH₂ and CONH and could be assigned symmetrical structures lacking any configurational isomerism. The ion transport activity of the compounds ( c ) and ( d ) on Na⁺ and K⁺ ions were evaluated by CH₂Cl₂ liquid–liquid membrane method using a U tube system. Slightly higher affinity for potassium than sodium was also observed, which is undoubtedly related to the matching size of the cavity between K⁺ and cyclic peptides. The antimicrobial and antifungal activities of four macrocyclic amides (c , d , e , and f) were illuminated using disk diffusion method in dimethyl sulfoxide as well as the minimal inhibitory concentration dilution method, against several bacteria and yeast cultures. Comparing all methods, in most cases, the ( e ) and ( f ) compound seems to show slightly higher biological activity than the ( c ) and ( d ) macrocycles. This may be because of the presence of extra chlorine atoms on the exterior part of the molecules.     

Beiträge zur Chemie der Elemente Niob und Tantal. 84 Die Niob- und Tantalkomplexe [Me6X] X · n H2O mit Me = Nb,Ta; Xi = Cl,Br; Xa = Cl,Br, J

On the chemistry of the elements niobium and tantalum. 84. The niobium and tantalum complexes [Me₆X]X · n H₂O with Me = Nb, Ta; X¹ = Cl, Br; X^a = Cl, Br, J The known and unknown compounds mentioned in the title were prepared. In this group of compounds four different crystal structures (A, B, C, D) occur. Lattice constants are given of the six compounds with structure C which crystallize in the hexagonal system and are isotypic with Ba₂[Nb₆Cl₁₂]Cl₆. Regarding the IR-spectra and the thermal behaviour, possible principles of structure are discussed.     

Palladium carbene complexes as persistent radicals

A series of palladium(ii) radical carbene complexes, [PC˙(sp²)P]PdI, [PC˙(sp²)P]PdBr, and [PC˙(sp²)P]PdCl (PC(sp³)H₂P = bis[2-(di-iso-propylphosphino)-phenyl]methane), is described. Compound [PC˙(sp²)P]PdI dimerizes to {[PC(sp²)P]PdI}₂ in the solid state, akin to the formation of Gomberg''s dimer. While the bromo and the iodo derivatives could be obtained from the oxidation of [PC(sp²)P]Pd(PMe₃) by the respective dihalogens, a halogen transfer reaction from CH₂Cl₂ was used for the formation of [PC˙(sp²)P]PdCl. The halogen transfer from CH₂X₂ (X = Cl, Br, I) could be used to obtain all three radical carbene palladium complexes and also allowed the isolation of [PC(CH₂)P]Pd(PMe₃), which is the result of methylene group transfer from CH₂X₂. Compound [PC(CH₂)P]Pd(PMe₃) was independently synthesized from [PC(CH₃)HP]PdCl₂, which contains a supporting ligand analogous to that of the radical carbene complexes but has one of the hydrogen atoms replaced by a methyl group. All three carbene radical species abstract a hydrogen from 9,10-dihydroanthracene or ⁿBu₃SnH.     

Synthesis of Co2Pt, Co2Pd and MoPd2 mixed-metal clusters with the P–N–P assembling ligands (Ph2P)2NH (dppa) and (Ph2P)2NMe (dppaMe). Crystal structure of [Co2Pt(μ3-CO)(CO)6(μ-dppa)]

Heterometallic triangular platinum–cobalt, palladium–cobalt and palladium–molybdenum clusters stabilized by one or two bridging diphosphine ligands such as Ph₂PNHPPh₂ (dppa) or (Ph₂P)₂NMe (dppaMe) or by mixed ligand sets Ph₂PCH₂PPh₂ (dppm)/dppa have been prepared with the objectives of comparing the stability and properties of the clusters as a function of the short-bite diphosphine ligand used and of the metal carbonyl fragment they contain. Ligand redistribution reactions were observed during the purification of [Co₂Pd(μ₃-CO)(CO)₄(μ-dppa)(μ-dppm)] (4) by column chromatography with the formation of [Co₂Pd(μ₃-CO)(CO)₄(μ-dppm)₂] and the dinuclear complex [(OC)₂ Cl] (5). The latter was independently prepared by reaction of [Pd(dppa-P,P′)₂](BF₄)₂ with Na[Co(CO)₄]. Attempts to directly incorporate the ligand (Ph₂P)₂N(CH₂)₃Si(OMe)₃ (dppaSi) into a cluster or to generate it by N-functionalization of coordinated dppa were unsuccessful, in contrast to results obtained recently with related clusters. The crystal structure of [Co₂Pt(μ₃-CO)(CO)₆(μ-dppa)] (1) has been determined by X-ray diffraction.     

Synthesis of dibenzo-[b,f][1,5]diazocine-based hosts and their assembly behaviors with C60

Diaryl[b,f][1,5]diazocine-based macrocycles 5 and 6 with inner cavities have been synthesized via Hay coupling method. Single crystal of 5 shows that it forms a dimeric aggregate via the weak intermolecular interactions between two adjacent rings, which is rarely reported in such macrocycles. Moreover, SEM results reveal that both macrocycles 5 and 6 assemble with C₆₀ to form well-ordered fullerene-based nano-rod structures.     

Synthesis of a heterobimetallic actinide nitride and an analysis of its bonding

Reaction of [K(DME)][Th{N(R)(SiMe₂CH₂)}₂(NR₂)] (R = SiMe₃) with 1 equiv. of [U(NR₂)₃(NH₂)] (1) in THF, in the presence of 18-crown-6, results in formation of a bridged uranium–thorium nitride complex, [K(18-crown-6)(THF)₂][(NR₂)₃U^IV(μ-N)Th^IV(NR₂)₃] (2), which can be isolated in 48% yield after work-up. Complex 2 is the first isolable molecular mixed-actinide nitride complex. Also formed in the reaction is the methylene-bridged mixed-actinide nitride, [K(18-crown-6)][K(18-crown-6)(Et₂O)₂][(NR₂)₂U(μ-N)(μ–κ²-C,N–CH₂SiMe₂NR)Th(NR₂)₂]₂ (3), which can be isolated in 34% yield after work-up. Complex 3 is likely generated by deprotonation of a methyl group in 2 by [NR₂]⁻, yielding the new μ-CH₂ moiety and HNR₂. Reaction of 2 with 0.5 equiv. of I₂ results in formation of a U^V/Th^IV bridged nitride, [(NR₂)₃U^V(μ-N)Th^IV(NR₂)₃] (4), which can be isolated in 42% yield after work-up. The electronic structure of 4 was analyzed with EPR spectroscopy, SQUID magnetometry, and NIR-visible spectroscopy. This analysis demonstrated that the energies of 5f orbitals of 4 are largely determined by the strong ligand field exerted by the nitride ligand.

The heterobimetallic actinide nitride [(NR₂)₃U^V(μ-N)Th^IV(NR₂)₃] (R = SiMe₃) has an m_J = 5/2 ground state and its highest energy 5f excited state is primarily 5f-N_nitride σ-antibonding in character.     

Simultaneous thermally stimulated luminescence and depolarization current in low density polyethylene

Thermally stimulated luminescence (TSL) and thermally stimulated depolarization current (TSD) measurements were made simultaneously on low density polyethylene samples 0.175 mm thick, carrying evaporated gold electrodes. The samples were dc-polarized at room temperature at a field strength of 90 kV/cm, cooled to –190°C and X-irradiated with the field still applied, and then heated in short-circuit at 3 deg/min. Comparing the TSL and TSD data, particularly the effects of oxidizing the samples and immersing them in fuming nitric acid, it was shown that (1) the space-charge transport component of the TSD current between –190 and 30°C is negligible, (2) charge injection begins around –10°C (for evaporated gold electrodes) and increases rapidly with increasing temperature, and (3) all the injected charge is transported through the sample to the opposite electrode. Such transport takes place only through the amorphous regions of the sample.

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Zusammenfassung Es wurden simultane TSL- und TSD-Messungen an 0.175 mm starken, über aufgedampfte Goldelektroden verfügende Polyethylenproben geringer Dichte durchgeführt. Die Proben wurden bei Raumtemperatur und einer Feldstärke von 90 kV/cm gleichstrompolarisiert, auf –190°C abgekühlt, bei noch anliegendem Feld röntgenbestrahlt und dann unter Kurzschluß mit 3 Grad/min erhitzt. Durch einen Vergleich der TSL- und TSD-Daten, insbesondere der Wirkung der Oxydation der Proben bzw. des Eintauchens in rauchende Salpetersäure, zeigten, daß (1) die Raumladungstransport-Komponente des TSD-Stromes zwischen –190 und 30°C vernachlässigbar ist, (2) die Ladungsinjektion bei etwa — 10°C beginnt (für aufgedampfte Goldelektroden) und mit steigender Temperatur schnell anwächst und (3) die gesamte injezierte Ladung durch die Probe hindurch an die gegenüberliegende Elektrode transportiert wird. Ein derartiger Transport erfolgt nur in den amorphen Regionen der Probe.

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Dedicated to Professor Dr. H. J. Seifert on the occasion of his 60^th birthday