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The fragmentation of metastable and collisionally activated ions as well as different experimental techniques which can be used to record daughter, parent and neutral loss spectra are discussed in the first part of this review. Advanced MS/MS methods are represented by the Neutralization Reionisation Mass Spectrometry (NRMS) which allows the characterization of neutral species and the angular resolution of the ion beam emerging from a collision cell, lending to Angle Resolved Mass Spectrometry (ARMS). Typical applications of the tandem mass spectrometry are given by the determination of ion structures, the gas phase reactions of ions and the analysis of compounds in complex mixtures.

Positive ion mobility spectra of n -alkanes ( n -C 5 to n -C 19 ), branched chain alkanes (C 5 to C 9 ) and aromatic compounds (benzene and alkylated benzenes) were acquired with an ion mobility spectrometer equipped with a corona discharge ionization source. Reduced mobilities and mass-to-mobility correlation curves were determined for these compounds. Depending on their concentration, the n -alkanes form one or two product ion peaks. The mobilities of product ion peaks regularly decrease with increasing chain length. The same behavior was observed for branched chain alkanes. However, characteristic fragment ions are additionally formed in comparison with n -alkanes. The investigated aromatic hydrocarbons show simple spectra consisting of up to three characteristic product ion peaks. The obtained mass-to-mobility correlation curve differs from that determined using photoionization.

The gas-phase complexes HCN/Cu and HNC/Cu seem to exist only in a linear end-on coordinated structure. No other minima could be localized on the UHF potential surface. The electron-rich copper does not act as a π donor but as a σ acceptor. A slight but significant charge transfer from the ligand lone pair into the copper 4p σ orbital is responsible for the bonding interaction.

A large number of emission sources contribute to the contamination of ecosystems in the Bitterfeld area. Flood-plains are a special sink of anthropogenic emmissions because they are able to store substances stemming from different sources and matter flows for, at least, a while. In the flood-plain of the river Mulde, at positions both near and far from the chemical industrial complex of Bitterfeld-Wolfen, soil profiles under wood, meadow and arable land were investigated. The differently used soils are located only some metres apart from each other and the soil-genetic features of the test sites are comparable with one another. Both near the emitters and far from them, the highest heavy-metal concentrations (Cu, Zn, Pb) were observed in the wood profile and the lowest values in the arable land. In some cases, limit values of the German sewage sludge regulation (Klarschlammverordnung) were exceeded. The topsoil of the wood profile taken near the emitters contained the highest copper concentrations observed. The highest zinc and lead contents, however, were observed in the topsoil of the wood profile far from the emitters. Because of the better sorption features of the subsoils situated far from the emitters, Cu, Zn and Pb values are higher here than at positions near the emitters.

Synthesis of N-[2(1H-pyrolylmethyl)]-N′-(4-pentene-3-one-2)ethane-1, 2-diamine has been effected and the compound characterised by X-ray diffraction. Crystal data for C12H19N3O: space group P21/c: a=10.358(3), b=7.953(1), c=15.640(4) A, β=101.63(1)°, V=1261(2) A3 to give Z=4 for D=1.165 g cm−3. Structure solution and refinement based on 2114 reflections converged at R=0.064, Rw=0.079. Reaction of this molecule with Bu4N[TcO(ethylene glycolate)2] results in the formation of a neutral technetium(V) complex [TcOL]. The X-ray structure of this complex confirms a five-coordinate, square based pyramidal geometry with no crystallographic axes of symmetry. Crystal data: orthorhombic space group P212121; a=11.701(1), b=14.949(2), c=7.516(1) A, V=1314.6 A3 to give Z=4 for D=1.68 g cm−3. Structure resolution and refinement based on 2115 reflections converged at R=0.037, Rw=0.033. Reaction of N-[2(1H-pyrolylmethyl)]-N′-(4-pentene-3-one-2)ethane-1,2-diamine with rhenium(V) oxotrichlorobistriphenylphosphine [ReOCl3(PPh3)2] or a rhenium(V) glycolato precursor yields the [ReOL] complex. The compounds have been studied by NMR, UVVis, IR spectroscopy as well as by mass spectrometry. The obtained results have been discussed in terms of the complex formation and the different transition metals.

Bis(tetrabutylammonium)bis( 1,1 -dicyanoethene-2,2-diselenolato)nitridotechnetate( V), (Bu4N)2[TcN(i-mns)2] has been prepared by the reaction of (Bu4N)TcNCl4 with the potassium salt of the ligand and Bu4NBr. The compound forms yellow crystals which were characterized by elemental analysis, IR and UV/VIS spectrometry, mass spectroscopy as well as X-ray structure determination. The compound crystallizes triclinic in the space group P 1̄ with Z = 2. The final R value is 0.045. In the complex anion the five-coordinate technetium atom exhibits a square pyramidal environment with the selenium donors in the basal plane and the nitrido ligand in the apical position. The bond length Tc≡=N = 161(1) pm is within the normal range of TcN triple bonds.

Bis-bidentate Isophthaloyl-bis(selenoharnstoffe) bilden mit Nickel(II)-Ionen unter deprotonierenden Bedingungen makrocyclische Zweikernchelate. Dies wurde durch Rontgenkristallstrukturanalyse des cyclo-Di[nickel-μ-[1,1,1,′,1′-tetraisobutyl-3,3′-iso-phthaloyl-bisselenoureaoto(2−)-Se, O:O′, Se′]], 2, bestatigt. Die Verbindung 2 kristallisiert monoklin in der Raumgruppe P 21/c mit den Gitterkonstanten a = 11,673 (1); b = 19,834 (2); c = 13,606 (1) A; β = 107,45 (1)° und Z = 2. Der abschliesende R-Wert betrug R = 0,081 fur 3049 beobachtete Reflexe. Bis-bidentate Terephthaloyl-bis(selenoharnstoffe) ergeben unter den gleichen Bedingungen makrocyclische Dreikernnickel(II)-chelate. Beide Komplextypen wurden durch FAB-Massenspektren charakterisiert. Di- and Trinuclear Nickel(II) Chelates of Bis-bidentate N-Acylselenoureas Bis-bidentate isophthaloyl-bis(selenoureas) form with nickel(II) ions under deprotonating conditions macrocyclic dinuclear metal chelates. This was confirmed by X-ray crystal structure analysis of the cyclo-di[nickel-μ-[1,1,1′,1′-tetraisobutyl-3,3′-iso-phthaloyl-bis-selenoureato(2−)Se,O:O′, Se′]], 2. The compound 2 crystallizes in the monoclinic space group P 21/c with a = 11.673 (1); b = 19.834 (2); c = 13.606 (1) A; β = 107.45 (1)° and Z = 2. The final R value was R = 0.081 for 3049 observed reflections. Bis-bidentate terephthaloyl-bis(selenoureas) give under the same conditions macrocyclic trinuclear nickel(II) chelates. Both types of the complexes are characterized by FAB mass spectra.

Der Titelkomplex entsteht in guten Ausbeuten bei der Umsetzung von (Bu4N)ReOBr4 oder ReOCl3(Ph3P)2 mit der triphenylmethyl-geschutzten Form des vierzahnigen Liganden. Die Struktur des Chelats als neutrale Oxoverbindung des Rheniums (V) wird durch analytische sowie 1H-, 13C-NMR, IR-, UV/Vis- und massenspektrometrische Untersuchungen gestutzt. Synthesis and Characterization of [N-(2-Mercaptoacetyl)-N′ -4-(penten-3on-2)ethylen-1,2-diaminato]oxorhenium(V), ReO(MRP 40) The title complex is obtained in good yields from the reaction of the triphenylmethyl-protected ligand with (Bu4N)ReOBr4 or ReOCl3(Ph3P)2. The structure of the compound as neutral oxorhenium(V) complex is confirmed by analytical, 1H-, 13C-NMR, IR, UV/Vis as well as mass spectrometric studies.

Diamagnetic nitridotechnetium(V) complexes with tri- and tetradentate azomethine ligands which possess electron withdrawing groups in their periphery can be prepared starting from TcNCl 2 (Ph 3 P) 2 or (in the case of the tetradentate ligands) TcNX 4 − (X = Cl, Br). The products are air stable compounds which have been characterized by elemental analysis, infrared and UV-Vis spectroscopy, NMR and mass spectrometry. The mixed-ligand complex [ N -(2-Ethoxycarbonyl-3-oxo-but-l-en(1)yl)-2-aminophen- olato](triphenylphosphine)nitridotechnetium(V) (C 31 H 28 N 2 O 4 PTc, M r = 622.5) crystallizes monoclinic in the space group C 2/ c . The coordination geometry is a distorted square pyramid with the nitrido ligand at the apex.

{ N-(2-Mercaptoacetyl)-N′-[4-(pentene-3-one-2)]ethane-1,2-diaminato} oxotechnetium(V) has been prepared by the reaction of (Bu4N)TcOX4 complexes (X = Cl, Br) with N-(mercaptoacetyl)-N′-[4-(pentene-3-one-2)]ethane-1,2-diamine in methanolic solution. The compound forms dark red crystals which were characterized by elemental analysis, IR and 1H NMR spectroscopy, mass spectrometry, as well as an X-ray structure determination. The compound crystallizes triclinic in the centrosymmetric space group PĪ with a = 776.50(3), b = 819.69(6), c = 1040.43(7) pm, α = 92.944(6)°, β = 110.805(5)° and γ = 109.957(5)°. The final R value is 0.023. In the monomeric complex the five coordinate technetium atom exhibits a square pyramidal environment with the donors of the tetradentate ligand in the basal plane and the oxo ligand in the apical position. The bond length Tc–O = 165.7(2) is within the normal range of Tc=O double bonds.

Some partial synthetic amino acid ((S)-alanine, (S)-leucine, (S)-isoleucine, (S)-aspartic acid, (S)-glutamic acid, (S)-phenylalanine, (S)- and (R)-valine) conjugates of the plant growth regulator (-)-jasmonic acid (JA) were investigated as methyl esters by capillary gas chromatography/mass spectrometry. By gas chromatographic data (retention indices) as well as by mass spectral behaviour all these substances can be differentiated unequivocally. In addition, the distinction between the leucine and isoleucine JA conjugates was carried out by mass-analysed ion kinetic energy spectroscopy (tandem mass spectrometry). Based on this some naturally occurring (S)-isoleucine conjugates of (-)-JA, (+)-7-iso-JA and related compounds as well as the (S)-leucine and (S)-phenylalanine conjugates of (-)-JA could be identified from extracts of the broad bean Vicia faba L.

Es wurden Losungen mit Vanadium(IV) sowie Vanadium(V) bei Anwesenheit eines hohen Uberschusses an Hydrogencarbonat bzw. Carbonat voltammetrisch und spektroskopisch untersucht. In 1 M KHCO3 trifft man im pH-Bereich 7–8 auf eine reversible Elektrodenreaktion VV/VIV, die von der Anlagerung eines Carbonatliganden beim Ubergang VV VIV begleitet wird. Auf der Basis der bei Raumtemperatur und 77 K erhaltenen ESR-Parameter wird die Existenz eines VIV-Carbonatokomplexes postuliert. Durch Vergleich der ESR-Parameter dieses Komplexes mit denen analoger VIV-Komplexe werden Schlusfolgerungen hinsichtlich seiner Struktur gezogen. Dieser Strukturvorschlag last sich durch die Tatsache stutzen, das VIV und VV im HCO3−/CO2-Medium (pH = 7,5) ein gemischtvalentes Dimer bilden. Solche Dimere treten nur auf, wenn eines der beiden Oxo-Sauerstoffatome der VVO2+-Gruppierung des VV-Komplexes an einer vakanten Koordinationsstelle in cis-Position zur VIV-Sauerstoff-doppelbindung im VIV-Komplex koordinieren kann. In diesem Zusammenhang ergibt sich auch die Moglichkeit, Schlusfolgerungen bezuglich der Anordnung der Carbonatliganden im monomeren VV-Komplex zu ziehen. Eine vergleichende Betrachtung der Komplexe, die VIV und VV mit Carbonat bilden und den Assoziaten des VIV als VV mit Transferrin last die Ahnlichkeiten dieser beiden korrespondierenden Redoxpaare deutlich werden. Voltammetric and Spectroscopic Investigation of Complexation of Vanadium(IV) and Vanadium(V) by Carbonate Solutions which contain in addition to vanadium(IV) or vanadium(V), respectively, a high excess of bicarbonate or carbonate were studied by voltammetric and spectroscopic methods. A reversible electrode reaction occurs in the pH range 7–8 in 1 M KHCO3. While generating VIV from VV electrochemically a carbonate ligand is added to VIV. Based on ESR parameter recorded at room temperature and 77 K the existence of a VIV carbonato complex is suggested. A comparison of these ESR parameter with those of analogous VIV complexes leads to conclusions in view of the structure of the VIV carbonato complex. These structural suggestions are supported by the fact that VIV and VV form a mixed valent dimer in HCO3−/CO2-buffer of pH 7.5. Such dimers can be formed only when one of the oxygens of the VVO2+ cis-dioxo unit is able to coordinate at a basal site in the VIV-complex. Thus, conclusions regarding the arrangement of the carbonato ligands in the monomeric VV complex are possible too. A comparison of the complexes which are formed by VIV and VV with carbonate and the adducts arising from the interaction of VIV and VV with transferrin reveals the similarities of the both redox couples.

Synthesis, Coordination Chemistry and Mass Spectrometric Fragmentation of New N-(Thiocarbamoyl)-benzamidines Syntheses of N-(thiocarbamoyl)benzamidines from benzimidoylchlorides and aromatic amino acids as starting materials are reported. The prepared compounds were used as ligands for complexing nickel(II) and copper(II)ions. The benzamidines were characterized by mass spectrometric methods. The fragmentation pattern of the benzamidines was derived from the corresponding MIKE-spectra.

Die Benzoylthioharnstoff-Derivate 1–3 reagieren mit konz. H2SO4 zu 2-Amino-4-oxo-4H-3,1-benzothiazinen 4a–c. Entgegen Literaturangaben geben 1 oder 2 unter anderen Reaktionsbedingungen durch Cyclokondensation die 2-Benzoylamino-4-oxo-4H-3,1-benzothiazine 6a–c. Dimroth-Umlagerung von 4 fuhrt zu den 2-Thioxochinazolinen 5. Die ms Fragmentierung von 4, 5 und 6 wird diskutiert. Polycyclic Azines, XXV: Benzoylthiourea derivatives 1–3 react on treatment with conc. H2SO4 to give 2-amino-3,1-benzothiazin-4-ones 4a–c. In contrast to lit. data 1 or 2 undergo cyclocondensation under modified conditions to give 2-benzoylamino-3,1-benzothiazin-4-ones 6a–c. Dimroth-Rearrangement of 4 affords quinazolin-2-thiones 5. The mass spectral fragmentation of 4, 5 and 6 is discussed.

Obwohl erste Untersuchungen zur Ionenbildung in Luft seit den 80er Jahren des vorigen Jahrhunderts bekannt sind [1–3] und grundlegende Arbeiten zur Mobilitat von Ionen in elektrischen Feldern durch Langevin bereits um 1905 publiziert wurden [4], gehort die Ionenmobilitatsspektrometrie (IMS) zu den vergleichsweise jungen analytischen Methoden. Fast 100 Jahre liegen zwischen den Anfangen und den erfolgreichen analytischen Anwendungen, die in Verbindung mit ersten kommerziellen Geraten [5–7] hauptsachlich den umfangreichen Arbeiten von F.W. Karasek [8–34] zu verdanken sind. Freilich sind mit dieser Feststellung wichtige Entwicklungsetappen nicht berucksichtigt. Hierzu gehoren die weiterfuhrenden Arbeiten von Hasse zur Ionenmobilitat [35, 36] ebenso wie grundlegende Untersuchungen zu Ionen-Molekul-Reaktionen [37–40] oder Experimente mit Drift-Rohren, die in den 60er Jahren publiziert wurden [41–43].

The yeast Torulopsis apicola produces a microcrystalline mixture of glycolipids, the major component of which has been identified as the novel 16-(2′- O -β- d -glucopyranosyl-β- d -glucopyranosyloxy)hexadecanoic acid 1′,4″-lactone 6′,6″-diacetate ( 2 ) by spectroscopic methods.

The crystal and molecular structure of bis(tetraphenylarsonium) bis(maleonitriledithiolato)tellurate(II), a new tellurium(II) compound containing dithiolene ligands, and the single-crystal e.s.r. spectra of the system [AsPh4]2[63Cu/Te(mnt)2] are reported. [AsPh4]2[Te(mnt)2] crystallises in the triclinic space group P, with a= 10.211 (2), b= 14.460(2)A, c = 18.583(3)A, α = 105.95(2), β = 95.60(2), γ = 77.67(2)°, and Z = 2; R= 0.047 for 7749 observed reflections. The tellurium atoms have trapezoid planar co-ordination with Te–S bond distances of 2.501(1), 2.482(2), 2.971(2), and 3.104(2) A. In the single-crystal e.s.r. spectra the signals of two Cu sites with somewhat different spin-Hamiltonian parameter sets are observed. The and the 63Cu hyperfine tensors are rhombic symmetric. The planar [Cu(mnt)2]2– anions are considerably distorted but do not adopt the structure of the tellurium host.

Ausgehend von Selenkohlenstoff und Selenschwefelkohlenstoff wird die elektrochemische Darstellung heterocyclischer Dichalkogenolate C3X52− (X = Se: dsis; X = S/Se: C3SxSey2−), die als Dibenzoylverbindungen isoliert und charakterisiert werden, beschrieben. Aus den mit Alkalimethanolat erhaltenen Verseifungslosungen dieser Dibenzoylverbindungen sind Metall-bis- und -tris-Chelate der heterocyclischen 1, 2-Dichalkogenolate vom Typ Am[M(C3X5)n] (A = Bu4N+, Ph4As+; M = ZnII, PtII, PdII, NiIII, CuIII, AuIII, InIII; X = Se, S/Se; m = 1, 2, 3; n = 2, 3) unmittelbar zuganglich. Cyclovoltammetrisch und mittels EPR werden die Nickel(III)-Verbindungen Bu4N[Ni(C3X5)2] (X = Se, S/Se) charakterisiert und der analogen Schwefelverbindung Bu4N[Ni(dmit)2] (X = S) gegenubergestellt. Fur die bei der Chelatisierung mit dsis (X = Se) beobachtete Metall(II)-Metall(III)-Oxydation bei Kupfer und Nickel werden Argumente erortert. Electrochemical Reduction of CSSe and CSe2 in Dimethylformamide: Heterocyclic 1,2-Dichalcogenolates and their Coordination Chemistry Starting from carbon diselenide or carbon selenidesulfide the electrochemical preparation (electrosynthesis) of heterocyclic dichalcogenolates C3X52− (X = Se: dsis; X = S/Se: C3SxSey2−) is outlined. The 1,2-dichalcogenolate compounds were isolated and characterized as dibenzoyl derivatives. Bis- or tris-chelates of general type Am[M(C3X5)n] (with A = Bu4N+, Ph4As+; M = ZnII, PtII, PdII, NiIII, CuIII, AuIII, InIII; X = Se, S/Se; m = 1, 2, 3; n = 2, 3, respectively) are available directly from methanolic solutions of the dibenzoylates after hydrolytic cleavage of the latter with sodium methanolate. In addition bis-chelates Bu4N[Ni(C3X5)2] (X = Se, S/Se) have been characterized by cyclovoltammetry and epr spectroscopy and compared with the corresponding all-sulfur ligand compound Bu4N[Ni(dmit)2] (X = S). Arguments are given for the fact that the allselenium ligand dsis (X = Se) yields the CuIII or NiIII chelate at once whereas with dmit using identical conditions the metal(II) compounds are formed.

By oxidation of nitridotechnetate(V) complexes of the type [TcN( parSS ) 2 ] 0,2− ( parSS = diethyldithiocarbamate, diphenyldithiophosphinate and maleonitrile-dithiolate) with chlorine the Tc 6+ complex anion [TcNCl 5 ] 2− was created and studied by EPR in liquid and frozen solutions. The EPR spectra are in agreement with a d 1 ( S = 1/2) system. The hyperfine interactions are used to characterize the bonding properties in the molecular orbital of the unpaired electron.

Von den beiden isosteren Dithioesterliganden Benzoyldithioessigsaure-methylester (1) und N-Benzoylamino-dithiokohlensaureethylester (2) werden Bis-Komplexe mit NiII, PdII, CuII, ZnII und PbII und der Tris-Komplex mit CoIII (alle von 1, deprotoniert) bzw. die Bis-Komplexe mit NiII und PbII (von 2, deprotoniert) dargestellt und ihre IR-, ESCA- und EPR-Daten (CuII/1) interpretiert. Es stellt sich heraus, das die deprotonierten Liganden als 1,3-(S, O)-Chelat-bildner fungieren. Einzige Ausnahme ist der PbII-Komplex von 1, der den Liganden einzahnig uber O koordiniert enthalt. Metal Complexes of the Methylester of Benzoyldithioacetic Acid and the Ethylester of N-Benzoylamino-dithiocarbonic Acid: Preparation and Characterization, ESCA and EPR Investigations Neutral bis-complexes of the methylester of benzoyldithioacetic acid (1) with NiII, PdII, CuII, ZnII and PbII were prepared as well as the tris-complex with CoIII. They are compared with corresponding complexes of the aza-isosteric ester ligand N-benzoylamino-dithiocarbonic acid ethylester (NiII, PbII). It turns out from IR, ESCA and (CuII/1)-EPR data that both ligands chelate via O and S of its deprotonated forms with the exception of the lead complex of 1, which contains the ligand monodentate and O-bound.

Es wird uber EPR-Untersuchungen an den Nitrosyl-Eisen-Chelaten [FeNO(mnt)(diphos)] und {FeNO(mnt)[P(C6H5)3]2} (mnt = Maleonitrildithiolat, diphos = Tetraphenylethylendiphosphin) berichtet. Die verbindungen wurden in polykristallinen Proben diamagnetisch verdunnt mit den entsprechenden Cobalt-Chelaten untersucht. Das Eisen-Chelat{FeNO(mnt) [P(C6H5)3]2} ist nur im wirtsgitter des analogen Cobalt-Komplexes bestandig. Die aus den EPR-Spektren der polykristallinen Proben abgeleiteten Parameter ergeben fur das ungepaarte Elektron in [FeNO(mnt)(diphos)] ein MO, das aus dem Metall-dz2- und entsprechenden Liganden-Orbitalen besteht. Demgegenuber wird fur {FeNo(mnt)[P(C6H5)3]2} anhand der EPR-Parameter ein MO fur das ungepaarte Elektron diskutiert, das sich aus dem Metall-dyz- und entsprechenden Liganden-Orbitalen zusammensetzt. Die Ursache hierfur ist in starken Strukturunterschieden zu sehen. EPR Investigations on Nitrosyl Iron Chelates of the Type [FeNO(S, S)(P, P)] The EPR powder spectra of [FeNO(mnt)(diphos)] and {FeNO(mnt)[P(C6H5)3]2} (mnt = maleonitriledithiolate, diphos = tetraphenylethylenediphosphine), diamagnetically diluted in the corresponding cobalt chelates, are reported. The nitrosyl iron chelate {FeNO(mnt)[P(C6H5)3]2} could, However, be only isolated in the host chelate. According to the EPR parameters obtained for [FeNO(mnt)(diphos)] the MO of the unpaired electron consists of the metal dz2 and the corresponding ligand orbitals. The g tensor components and the ligand hyperfine structure coupling constants found for {FeNO(mnt)[P(C6H5)3]2} are more in agreement with an MO for the unpaired electron consisting of the metal dyz and the corresponding ligand orbitals. Large structural deviations are responsible for this difference.

Das Spin-Trap-Reagenz Nitrosoduren reagiert mit σ-Alkyl, σ-Aryl, π-Allyl, σ-Allyl und π-Cyclopentadienylverbindungen des Nickel(II) unter Bildung von Nitrosodurylradikalen, die ESR-spektroskopisch nachweisbar sind. Nickel-Olefin- und -Heteroolefin-Komplexe reagieren normalerweise nicht unter Bildung von Radikalen. Die Spin-Trap-Methode kann allgemein als Indikatormethode zur Bestimmung von Strukturelementen an Nickelorganoverbindungen und zur Bestimmung der relativen Reaktivitaten von σ- und π-gebundenen Gruppen verwendet werden. Investigations to the Reactivity of Organonickel Compounds – “Spin Trapping” as an Indicator Method for the Relative Reactivity of Nickel-Carbon Bonds The spin trap nitrosodurene reacts with σ-alkyl, σ-aryl, π-allyl, σ-allyl, and π-cyclopentadienyl compounds of nickel(II) to form nitrosoduryl radicals which can be detected by ESR spectroscopy. Nickelolefine and nickel heteroolefine complexes do not react by formation of radicals. The spin trapping method can be generally used as an indicator for determination of structure elements in organonickel compounds and for determination of the relative reactivity of σ- and π-bonded groups.

Es wird uber ESR-Untersuchungen an V(N⌢N)3 und Co(N⌢N)2 (N⌢N: Benzil-bis-N-phenylimin) berichtet. Die ESR-Parameter — g, AV — zeigen fur V(N⌢N)3 eine schwach gestorte trigonale Koordinationsgeometrie (D3) an. Ihre Interpretation im Rahmen der Ligandenfeldtheorie fur eine Niedrigspin-d5-Elektronenkonfiguration ergibt fur den Grundzustand des ungepaarten Elektrons einen 2A1-Bahnsingulett-Zustand und einen grosen Wert fur den trigonalen Ligandenfeldparameter K. Das ESR-Spektrum von Co(N⌢N)2 konnte nur bei 4,2 K erhalten werden. Seine rhombische Symmetrie und das Fehlen von Hyperfeinstrukturwechselwirkungen mit den Kernen 59Co und 14N ist auf der Basis einer rhombisch verzerrten, gestauchten Tetraedersymmetrie (D2) fur Co(N⌢N)2 erklarbar. Ausgehend von den Parametern des Spin-Hamiltonoperators wird der Charakter der Metall-Ligand-Bindung und das Elektronenspektrum diskutiert. Interaction of Hetero-π-Systems with Central Metal Atoms in Low Oxidation States. ESR Investigations on Structure and Bonding in Low Spin d5-(S = 1/2)-Tris(benzil-bis-N-phenylimine)vanadium(0) and Bis(benzil-bis-N-phenylimine)cobalt(0) ESR investigations on V(N⌢N)3 and Co(N⌢N)2(N⌢N: Benzil-bis-N-phenylimine) are reported. The ESR parameters — g, AV — indicate trigonal coordination geometry (D3) for V(N⌢N)3 disturbed by a small lower-symmetric ligand-field component. Interpretation of these parameters in terms of a ligand-field model for a low-spin d5 electronic configuration shows the electronic ground state to be 2A1 and yields a large value for the trigonal field splitting parameter K. The ESR spectrum of Co(N⌢N)2 could be obtained at 4.2 K only. Its rhombic symmetry and the absence of hyperfine interactions with the nuclei 59Co and 14N is consistent with a rhombically distorted, compressed tetrahedral symmetry (D2) for Co(N⌢N)2. The spin-Hamiltonian parameters are discussed in terms of the metal-ligand bond character and the electronic spectrum.