Astrid Malassa

Friedrich-Schiller-University Jena, Jena, Thuringia, Germany

Are you Astrid Malassa?

Claim your profile

Publications (16)30.56 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Carbon monoxide (CO) is a toxic gas for mammals and despite this fact, it is naturally produced in these organisms and has been proven to be beneficial in medical treatments, too. Therefore CO-releasing molecules (CORMs) are intensively developed to administer and dose CO for physiological applications. Nearly all of these compounds are metal carbonyl complexes, which have been synthesized and investigated. However, for most of these CORMs the exact reaction mechanisms of CO release is not completely elucidated, although it is of utmost importance. The widely used myoglobin assay for testing the CO release has several disadvantages and therefore, different methods have to be applied to characterize CORMs. In this work different setups of IR absorption spectroscopy are used to analyze and quantify the CO release during the decay of various CORMs: IR spectroscopy of the gas phase is applied to follow the CO liberation and attenuated total reflection (ATR) IR spectroscopy is used to record the decay of the metal carbonyl. IR spectroscopy supported by DFT calculations yields valuable insights in the CO release reaction mechanism. The focus is set on two different CORMs: CORM-2 (Ru2(CO)6Cl4) and on the photoactive CORM-S1 (photoCORM [Fe(CO)2(SCH2CH2NH2)2]). Our results indicate that the CO liberation from CORM-2 strongly depends on sodium dithionite, which is required for the commonly applied myoglobin assay, and that CORM-S1 loses all its bound CO molecules upon irradiation with blue light.
    The journal of physical chemistry. A. 06/2014;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The green title complex, [Co(2)(CH(3))(2)(C(12)H(21)N(2)Si)(2)], was obtained from bis-{[μ-N-tert-butyl-dimethyl-silyl-N-(pyridin-2-ylmeth-yl)amido]-chloridocobalt(II)} and methyl-lithium in diethyl ether at 195 K via a metathesis reaction. The dimeric cobalt(II) complex exhibits a crystallographic center of inversion in the middle of the Co(2)N(2) ring (average Co-N = 2.050 Å). The Co(II) atom shows a distorted tetra-hedral coordination sphere. The exocyclic Co-N bond length to the pyridyl group shows a similar value of 2.045 (4) Å. The exocyclic methyl group has a rather long Co-C bond length of 2.019 (5) Å.
    Acta Crystallographica Section E Structure Reports Online 09/2012; 68(Pt 9):m1167-8. · 0.35 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: [Fe(CO)2(SCH2CH2NH2)2] (1, CORM-S1), [Fe(CO)2(SC6H4-2-NH2)2] (2, CORM-S2), [Ru(CO)2(SCH2CH2NH2)2] (3), and [Ru(CO)2(SC6H4-2-NH2)2] (4) were prepared from the corresponding metal carbonyl compounds and cysteamine (deprotonation of the thiol functionality) or cystamine (oxidative addition of the S–S bond). They crystallized from donor solvents, such as tetrahydrofuran and dimethylformamide, as adducts with the bases bound by hydrogen bridges to the amino functionalities. Although the iron derivatives proved to be valuable photosensitive CO-releasing molecules (CORMs), CO was not released from the ruthenium analogs with visible light.
    Berichte der deutschen chemischen Gesellschaft 03/2012; 2012(7). · 2.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The reaction of (thf)Fe[N(SiMe3)2]2Cl with (2-pyridylmethyl)(diphenylphosphanyl)amine (1) in hot tetrahydrofuran (THF) yields dinuclear [(ClFe)2{μ-N(SiMe3)2}{Ph2P(NCH2Py)2}] (2) and [ClFe{Ph2P(O)-NCH2Py}]2 (3) with the oxygen atom stemming from THF degradation. The formation of 2 requires a P–N bond cleavage and reformation leading to the tetradendate diphenyl-bis(2-pyridylmethylamido)phosphonium ion. If this reaction of (thf)Fe[N(SiMe3)2]2Cl with 1 is performed at room temperature, no P–N bond cleavage is observed. Instead of that, ether degradation occurs yielding [Fe4(μ4-O)(μ2-Cl)2(Ph2P-NCH2Py)4] (4) with a central oxygen-centered iron tetrahedron as well as complex 3. Recrystallization of 3 from dichloromethane leads to addition of HCl and to the formation of [FeCl2·{Ph2P(O)-N(H)-CH2Py}] (5). The phosphonium ion of 2 is isoelectronic to the corresponding diphenyl-bis(2-pyridylmethylamino)silane (6). Lithiation of 6 followed by a metathetical reaction with (thf)2FeCl2 yields the trinuclear complex [Fe3Cl2{Ph2Si(NCH2Py)2}2] (7) with antiferromagnetic interactions.
    Berichte der deutschen chemischen Gesellschaft 04/2011; 2011(10). · 2.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The reaction of di(2-pyridylmethyl)amine with FeCl2 yields [Fe{HN(CH2Py)2}2]Cl2 (1) with the tridentate amines coordinating in a facial manner at the iron(II) center. Transamination of this amine with [M{N(SiMe3)2}2] in an equimolar ratio leads to the formation of heteroleptic [(Me3Si)2N-M{μ-N(CH2Py)2}]2 [M = Mn (2a), Fe (2b), and Zn (2c)]. The metallation of di(2-pyridylmethyl)amine with dimesityl iron(II) gives [Mes-Fe{μ-N(CH2Py)2}]2 (3). At temperatures below −30 °C the transamination reaction of [Fe{N(SiMe3)2}2] with di(2-pyridylmethyl)amine in a molar ratio of 1:2 yields [Fe{N(CH2Py)2}2] (4). The reaction of [Co{N(SiMe3)2}2] with HN(CH2Py)2 leads to the formation of [Co{N(CHPy)2}2] (5b) with 1,3-di(2-pyridyl)-2-azaallyl ligands, regardless of the employed stoichiometry. The compounds 2b, 2c, 3, and 4 have to be handled and manipulated at low temperatures because they degrade already at room temperature whereas the manganese(II) derivative 2a is stable under these conditions. The degradation products [M{N(CHPy)2}2] [M = Fe (5a), Zn (5c)] contain the 1,3-di(2-pyridyl)-2-azaallyl ligands and can be considered as the dehydrogenation products of [M{N(CH2Py)2}2]. A metathetical approach via the reaction of lithium di(2-pyridylmethyl)amide with FeCl2 did not give the desired product 4 but a mixture of 1 and 5a. A 1H NMR and EPR spectroscopic pursuit of the degradation of [(Me3Si)2N-Zn{μ-N(CH2Py)2}]2 (2c) in tetrahydrofuran at temperatures between 253 and 328 K showed diminishing amounts of 2c and the appearance of 1,3-di(2-pyridyl)-2-azaallyl anions whereas the EPR experiments clearly verify the presence of di(2-pyridylmethyl)aminyl radicals in solution.Graphical abstractThe di(2-pyridylmethyl)amides show a rather unique redox chemistry in the vicinity of late transition metals. These ligands can be deprotonated at the methylene fragments, initiating the formation of 1,3-di(2-pyridyl)-2-azaallyl anions.
    Journal of Organometallic Chemistry 06/2010; 695:1641-1650. · 2.00 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The deprotonation of (2-pyridylmethyl)(triorganylsilyl)amines of the type Py-CH(2)-N(H)-SiR(3) with SiR(3) = SiMe(2)tBu (1a), SiMe(2)(CMe(2)iPr) (1b), SiiPr(3) (1c) and SiPh(3) (1d) with (thf)Fe[N(SiMe(3))(2)](2)Cl in THF is accompanied by redox reactions and leads to the formation of iron(II) compounds. The products with lower solubility precipitated first and are the pale yellow and paramagnetic complexes chloro-(2-pyridylmethyl)(triorganylsilyl)amido iron(ii) [SiR(3) = SiMe(2)tBu (2a), SiMe(2)(CMe(2)iPr) (2b), SiiPr(3) (2c), and SiPh(3) (2d)]. These complexes crystallized dimeric with Fe(2)N(2) rings with different Fe-N bond lengths (average values of 211.1 and 203.2 pm). The Fe-Cl distances vary around an average value of 225.6 pm. Another isolated product consists of orange to blue crystals of dichloro-(2-pyridylmethylidene)(triorganylsilyl)amino iron(II) [SiR(3) = SiMe(2)tBu (3a), SiMe(2)(CMe(2)iPr) (3b), SiiPr(3) (3c), and SiPh(3) (3d)] which are obtained from very concentrated reaction solutions. These (2-pyridylmethylidene)(triorganylsilyl)amino ligands (imines) act as bidentate bases at FeCl(2) with average Fe-N and Fe-Cl bond lengths of 211.8 and 223.5 pm, respectively. The metallation of the (2-pyridylmethyl)(triorganylsilyl)amines with dimeric Fe[N(SiMe(3))(2)](2) yields homoleptic iron(II) bis[(2-pyridylmethyl)(triorganylsilyl)amides] (4) with distorted tetrahedrally coordinated iron centers. Metathesis reactions of FeCl(3) with lithium (2-pyridylmethyl)(triorganylsilyl)amide as well as employing a mixture of Fe[N(SiMe(3))(2)](2) and FeCl(3) with (2-pyridylmethyl)(triorganylsilyl)amine give similar results and the formation of chloro-(2-pyridylmethyl)(triorganylsilyl)amido iron(II) (2) and dichloro-(2-pyridylmethylidene)(triorganylsilyl)amino iron(II) (3) are observed.
    Dalton Transactions 06/2010; 39(22):5356-66. · 4.10 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The transamination of 8-(tert-butyldimethylsilylamino)quinoline with (thf)2Cr[N(SiMe3)2]2 yields monomeric bis[8-(tert-butyldimethylsilylamido)quinoline]chromium(II) (1). Similar reactions of M[N(SiMe3)2]2 (M = Mn, Fe, Co) with 8-(trialkylsilylamino)quinoline lead to the formation of monomeric bis[8-(trialkylsilylamido)quinoline]metal(II) [M = Mn, SiR3 = SiMe2tBu (2a), SiiPr3 (2b); M = Fe, SiR3 = SiMe2tBu (3a),SiiPr3 (3b); M = Co, SiR3 = SiMe2tBu (4a), SiiPr3 (4b)]. The transamination of 8-aminoquinoline with M[N(SiMe3)2]2 (M = Mn, Fe, Co) allows the isolation of the heteroleptic 1:1 and homoleptic 2:1 products. The 1:1 complexes bis[8-amidoquinoline metal(II)bis(trimethylsilyl)amide] [M = Mn (5), Fe (6), Co (7)] are dimeric with bridging 8-amidoquinoline moieties. The 2:1 complexes of Mn and Fe, bis(8-amidoquinoline)manganese(II) (8) and bis(8-amidoquinoline)iron(II) (9), form hexamers with wheel-like molecular structures consisting of metal-centered nitrogen octahedra interconnected by common N···N edges. The cobalt complex, bis(8-amidoquinoline)cobalt(II) (10), precipitates as a microcrystalline powder. Investigations of the magnetic properties by DFT corroborate the experimental data for the Mn derivative 8, where an antiferomagnetic coupling is observed. By contrast, calculations on the Fe6-wheel 9 yield very close-lying ferromagnetically and antiferromagnetically coupled states.
    Berichte der deutschen chemischen Gesellschaft 03/2010; 2010(12):1777 - 1790. · 2.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A series of nickelacyclic carboxylates of the general formula [Ni(CH2CH2COO)(L2)] with p-substituted pyridine ligands (2: L = 4-picoline; 3: L = 4-MeO2C-C4H4N; 4: 4-Me2N-C4H4N) was synthesized and characterized by NMR spectroscopy. A correlation between the shift of the CH2 groups of the nickelacycle in the 1H NMR spectra and basicity of the used pyridine ligand was observed. Furthermore, amino-substituted pyridine derivatives were used in ligand-exchange reactions leading to supramolecular assemblies via H-bond formation between the amino function and the carboxylate group. Depending on the ligand used, discrete dimers [5: L2 = (tBu)(Me)2Si-aminomethylpyridine], chains [6: L2 = 2-(aminomethyl)pyridine] or layers (7: L = 4-H2N-C4H4N) were observed. The molecular structures of all new compounds 2–7 were determined by X-ray measurement.
    Berichte der deutschen chemischen Gesellschaft 11/2009; 2010(2):275 - 281. · 2.94 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The reddish-brown title complex, [Ni(C(18)H(27)N(2)Si)(2)], was prepared via the salt-metathesis reaction of N-triisopropyl-silyl-8-amido-quinoline lithium with nickelocene (NiCp(2)). The asymmetric unit contains two symmetry-independent mol-ecules with the Ni atoms in distorted tetra-hedral environments.
    Acta Crystallographica Section E Structure Reports Online 01/2009; 66(Pt 1):m6. · 0.35 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Local properties, such as partial charges or local spins, are an important concept in chemistry. In this work, two alternative local decomposition schemes for molecular total spin expectation values View the MathML source〈S^2〉 are compared for Kohn–Sham density functional theory calculations on polynuclear transition-metal clusters. It is confirmed that the scheme proposed by Mayer resolves the problem of the non-zero local spins View the MathML source〈S^A2〉 which arise in the first approach of this kind suggested by Clark and Davidson. Furthermore, it is demonstrated that Mayer’s View the MathML source〈S^A2〉 expectation values can be interpreted as SA(SA+1)SA(SA+1). The cross-terms, View the MathML source〈S^A·S^B〉A≠B, are very similar in both schemes when calculated for two metal atoms in polynuclear clusters, whereas they differ for small open-shell molecules such as NO. Overall, Mayer’s approach is more consistent for the local decomposition of View the MathML source〈S^2〉.
    Chemical Physics Letters 01/2008; 451:301-308. · 2.15 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 2-Aminomethylpyridine (Amp) substitutes the bis(dimethylamino)ethane ligand (TMEDA) of [(tmeda)NiMe2] leading to the formation of N,N′-(2-aminomethylpyridine)dimethylnickel (1). The reaction of bulkier N-diphenylphosphanyl-2-aminomethylpyridine with [(tmeda)NiMe2] yields tetrakis(N-diphenylphosphanyl-2-aminomethylpyridine)nickel(0) (2), ethane and TMEDA. The nickel(II) complex 1 shows a distorted square planar environment for the metal center, whereas nickel(0) in 2 displays a distorted tetrahedral coordination sphere with an average Ni–P bond length of 217.35 pm.
    Inorganic Chemistry Communications - INORG CHEM COMMUN. 01/2008; 11(6):612-615.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Transamination of Zn[N(SiMe3)2]2 with 8-(triisopropylsilylamino) (1a) and 8-(tert-butyldimethylsilylamino)quinoline (1b) yields monomeric heteroleptic bis(trimethylsilyl)amido zinc 8-(trialkylsilylamido)quinoline (2a, 2b). The reaction of Zn[N(SiMe3)2]2 with 8-aminoquinoline leads to the formation of heteroleptic dimeric 8-amidoquinoline zinc bis(trimethylsilyl)amide (3). This compound shows fluxionality on the NMR time scale due to a transannular trans–cis isomerization process and also a strong temperature dependency of the ratio of these two isomers. Variation of the stoichiometry allows the synthesis and isolation of homoleptic zinc bis(8-amidoquinoline) (4) with the zinc atoms in a distorted tetrahedral environment. The metallation of 8-aminoquinoline with (tmeda)NiMe2 yields diamagnetic nickel bis(8-amidoquinoline) (5) with a nickel center showing a distorted square planar coordination sphere. Dinuclear zinc complexes are accessible employing tetra-dentate di(8-aminoquinolyl)diphenylsilane (6). The metallation of 6 with dimethylzinc yields dimeric zinc di(8-amidoquinolyl)diphenylsilane (7) with tetrahedrally coordinated zinc atoms. A comparison of the molecular structures of 1a, 2b, 3, 4, 5, 6, and 7 shows nearly no dependency of the structural data of the quinolyl unit on the substitution pattern of the amino function. The metal–nitrogen bond lengths depend on the coordination numbers of the metal and the nitrogen atoms (terminal or bridging position) as well as the electrostatic attraction between the metal cations and the amino bases.
    Inorganica Chimica Acta. 01/2008; 361(5):1405-1414.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Copper(II) and nickel(II) complexes with the new Schiff-base ligands N-salicylidene-3-(2-pyridyl)-propionic acid hydrazide (H2salhypyp) and the newly synthesized N-Salicylidene-3-(1-benzylimidazol-2-yl)-propionic acid hydrazide (H2salhyimp) have been synthesized and structurally characterized. The crystal structure analysis of the metal complexes reveals two fundamentally different structural motifs. Cationic di-μ-phenolate-bridged dimers are observed for the complexes with the H2salhypyp ligand, [{Cu(H2salhypyp)(MeOH)(ClO4)}2](ClO4)2 (1) and [{Ni(H2salhypyp)Cl(MeOH)}2]Cl2(MeOH)2 (2), whereas neutral dimeric units aggregated via the side chain nitrogen donors are observed for the complexes with the H2salhyimp ligand, [{Ni(salhyimp)}2](H2O)4 (4) and [{Cu(salhyimp)}2](MeOH)4 (3). The formation of either motif depends on the charge of the ligand species and consequently on the pH-value of the reaction solution. For the complexes 1 and 2 extensive hydrogen-bonding networks are observed which involve the perchlorate (N–H···O–Cl) and chloride anions (N–H···Cl), respectively. The M2O2 core unit of complexes 1 and 2 facilitates the formation of intramolecular M–(Me)O–H···X–M hydrogen-bonding interactions . The copper complex 3 exhibits an unusual one-dimensional coordination polymer which is linked through the axial coordination of phenolate oxygen atoms of adjacent dimeric units. Complex 4 exhibits a layered structure with each layer composed of hydrophobic π-stacks of the dimeric complex units which are interlaced by hydrogen-bonded chains of water molecules. The supramolecular structures of 3 and 4 are governed by π-π-stacking interactions. For 4 additional CH/π interactions are found within and between individual sheets of the layered structure.
    Zeitschrift für anorganische Chemie 08/2007; 633(11‐12):2009 - 2018. · 1.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The transamination reaction of M[N(SiMe3)2]2 with (2-pyridylmethyl)(tert-butyldimethylsilyl)amine yields the corresponding homoleptic metal bis[(2-pyridylmethyl)(tert-butyldimethylsilyl)amides] of Mg (1), Mn (2), Fe (3), Co (4) and Zn (5). All these compounds crystallize from hexane isotypic in the space group C2/c. From toluene the zinc derivative precipitates as toluene solvate 5·toluene. The molecular structures of these compounds are very similar with large NMN angles to the amide nitrogen atoms with NMN values of 148° (1) and 150° (5) for the diamagnetic compounds and 156° for the paramagnetic derivatives 2 and 3. The Co derivative 4 displays a rather small NCoN angle of 142°. Different synthetic routes have been explored for compound 3 which is also available via the metallation reaction of bis(2,4,6-trimethylphenyl)iron with (2-pyridylmethyl)(tert-butyldimethylsilyl)amine and via the metathesis reaction of lithium (2-pyridylmethyl)(tert-butyldimethylsilyl)amide with [(thf)2FeCl2]. In course of the metathesis reaction, an equimolar amount of lithium (2-pyridylmethyl)(tert-butyldimethylsilyl)amide and [(thf)2FeCl2] yields heteroleptic (2-pyridylmethyl)(tert-butyldimethylsilyl)amido iron(II) chloride (6) which crystallizes as a centrosymmetric dimeric molecule. The oxidative C-C coupling reaction of 5 with Sn[N(SiMe3)2]2 leads to the formation of tin(II) 1,2-bis(2-pyridyl)-1,2-bis(tert-butyldimethylsilylamido)ethane, tin metal and Zn[N(SiMe3)2]2.
    Zeitschrift für anorganische Chemie 02/2007; 633(3):375 - 382. · 1.16 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: 2-Pyridylmethylamine (amp) and 8-aminochinoline (ach) readily form the following complexes with iron halides in methanol: [(amp)2FeCl2] (1a), [(amp)2FeBr2] (1b), [(ach)2Fe(MeOH)2]Br2 (1c), and [(amp)FeCl2(μ-OMe)]2 (2). Methanol was chosen as a solvent because these reactions are rather complex in ether. For example, FeCl3 forms the ionic complex pair [(dme)2FeCl2] [FeCl4] (3) with 1,2-dimethoxyethane (dme). The reaction of FeBr2 with tridentate di(2-pyridylmethyl)amine (dpa) and tetradentate 1,2-dipyridyl-1,2-diaminoethane (dpdae) yields the complexes [(dpa)2Fe]Br2·2 MeOH (4) and [(dpdae)2Fe] [FeBr4] (5), respectively. Crystallographic and magnetochemical investigations show the high-spin configuration for the complexes 1 and 2, whereas the short Fe-N distances of 4 clearly indicate a low-spin state. Compound 2 exhibits an antiferromagnetic exchange interaction with a coupling constant J = −29.4 cm−1 (H;af = −J S;afA·S;afB).
    Zeitschrift für anorganische Chemie 10/2006; 632(14):2355 - 2362. · 1.16 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The reaction of a nickelalactone with dppm, resulting in the formation of a stable binuclear Ni(I) complex with an acrylate, a Ph2P- and a dppm bridge, models a key step in the formation of acrylic acid from CO2 and ethylene.
    Chemical Communications 07/2006; · 6.38 Impact Factor