Reaction of iron(II) thiocyanate with an excess of trans-1,2-bis(4-pyridyl)-ethylene (bpe) in acetonitrile at room temperature leads to the formation of Fe(NCS)2(bpe)2·(bpe) (1), which is isotypic to ...its Co(II) analogue. Using slightly different reaction conditions the literature known compound Fe(NCS)2(bpe)2(H2O)2 (2) was obtained as a phase pure material. Simultaneous differential thermoanalysis and thermogravimetry prove that the hydrate 2 transforms into the anhydrate Fe(NCS)2(bpe)2 (3), that decomposes on further heating into the new ligand-deficient 1:1 compound of composition Fe(NCS)2(bpe) n (4), which can also be obtained directly by thermal decomposition of 1. Further investigations reveal that 4 can also be prepared under solvothermal conditions, and single crystal structure analysis shows that the iron(II) cations are linked via μ-1,3 bridging thiocyanato anions into chains, that are further connected into layers by the bpe ligands. Magnetic measurements, performed on powder samples, prove that 1 and 2 show only Curie–Weiss behavior, whereas in 4 antiferromagnetic ordering with a Néel temperature of 5.0 K is observed. At T < 4.0 K a two-step metamagnetic transition occurs at applied magnetic fields of 1300 and 1775 Oe. The magnetic properties are discussed and compared with those of related compounds.
Self-assembly of Fe2+ ions and the rigid ditopic ligand 1,4-bis(2,2′:6′,2′′-terpyridin-4′-yl)benzene results in metallo-supramolecular coordination polyelectrolytes (MEPE). Sequential self-assembly ...of MEPE and dialkyl phosphoric acid esters of varying chain length via electrostatic interactions leads to the corresponding polyelectrolyte−amphiphile complexes (PAC), which have liquid−crystalline properties. The PACs have a stratified architecture where the MEPE is embedded in between the amphiphile layers. Upon heating above room temperature, the PACs show either a reversible or an irreversible spin-crossover (SCO) in a temperature range from 360 to 460 K depending on the architecture of the amphiphilic matrix. As the number of amphiphiles per metal ion is increased in the sequence 1:2, 1:4, and 1:6, the temperature of the SCO is shifted to higher values whereas the amphiphile chain length does not have a significant impact on the SCO temperature. In summary, we describe in this article how the structure and the magnetic response function of PACs can be tailored through the design of the ligand and the composition. To investigate the structure and the magnetic behavior, we use X-ray scattering, X-ray absorption spectroscopy, differential scanning calorimetry, faraday-balance, and superconducting quantum interference measurements in combination with molecular modeling.
Herein, we report the synthesis and characterization of the new di-iron(III) complex (bbpmp)(H2O)(Cl)FeIII(μ-Ophenoxo)FeIII(H2O)Cl)Cl (1), with the symmetrical ligand ...2,6-bis{(2-hydroxybenzyl)(pyridin-2-yl)methylaminomethyl}-4-methylphenol (H3bbpmp). Complexes 2 with the unsymmetrical ligand H2bpbpmp — {2-(2-hydroxybenzyl)(2-pyridylmethyl)aminomethyl-6-bis(pyridylmethyl) aminomethyl}-4-methylphenol and 3 with the ligand L1=4,11-dimethyl-1,8-bis{2-N-(di-2-pyridylmethyl)aminoethyl}cyclam were included for comparison purposes. Complex 1 was characterized through elemental analysis, X-ray crystallography, magnetochemistry, electronic spectroscopy, electrochemistry, mass spectrometry and potentiometric titration. The magnetic data show a very weak antiferromagnetic coupling between the two iron centers of the dinuclear complex 1 (J=−0.29cm−1). Due to the presence of labile coordination sites in both iron centers the hydrolysis of both the diester model substrate 2,4-BDNPP and DNA was studied in detail. Complex 1 was also able to catalyze the oxidation of the substrate 3,5-di-tert-butylcatechol (3,5-DTBC) to give the corresponding quinone, and thus it can be considered as a catalytically promiscuous system.
The synthesis, X-ray structure and catalytic promiscuity (diesterase and catecholase activity) of a new dinuclear FeIII complex are here reported. Display omitted
•Dinuclear Iron(III) complex using a symmetric ligand•Synthesis, X-ray structure, magnetic properties and solution studies of the dinuclear catalyst•Ability of the complex to catalyze different reactions (catalytic promiscuity)
Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and ...magnetochemistry, of two dinuclear copper(II) complexes, using the unsymmetrical ligands N′,N′,N-tris(2-pyridylmethyl)-N-(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L1) and N′,N′-bis(2-pyridylmethyl)-N,N-(2-hydroxybenzyl)(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L2). The structures of the complexes Cu2(L1)(μ-OAc)(ClO4)2·(CH3)2CHOH (1) and Cu2(L2)(μ-OAc)(ClO4)·H2O·(CH3)2CHOH (2) were determined by X-ray crystallography. The complex Cu2(L3)(μ-OAc)2+ 3; L3 = N-(2-hydroxybenzyl)-N′,N′,N-tris(2-pyridylmethyl)-1,3-propanediamin-2-ol was included in this study for comparison purposes only (Neves et al. Inorg. Chim. Acta 2005, 358, 1807–1822). Magnetic data show that the CuII centers in 1 and 2 are antiferromagnetically coupled and that the difference in the exchange coupling J found for these complexes (J = −4.3 cm–1 for 1 and J = −40.0 cm–1 for 2) is a function of the Cu–O–Cu bridging angle. In addition, 1 and 2 were tested as catalysts in the oxidation of the model substrate 3,5-di-tert-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal CuII-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis(dinitrophenyl)phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the CuII center that contains the phenol group with tert-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (K ass. and k cat.) of 1 and 2 in comparison with that found for complex 3. In fact, complexes 1 and 2 show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity.
Molecular chains of antiferrimagnetically coupled MnIII-ion (S 2) and TCNE (tetracyanoethylene) radical moments (s ½) show different behaviour depending on group R substituted to TPP ...(tetraphenylporphyrin) and on the substitution site. The compound with R F in Ortho position is a Single-Chain Magnet (SCM) with blocking temperature Tb 6.6K, while that with R F in Meta position shows both blocking (Tb 5.4 K) and magnetic ordering transition (Tc 10 K). For bulky groups R OCnH2n+1, the magnetically ordered phase is observed (Tc ≈ 22 K), which does not however prevent slow relaxation at T <8 K. Magnetic hysteresis with coercive field Hc of 2 T at 2.3 K is like that of SCM. The frequency dependent AC susceptibility in the superimposed DC field reveals common features of all systems. The energy of intrachain ferromagnetic coupling between effective spin units 3/2, relevant at low temperatures, is determined for all compounds and the interchain dipolar coupling is estimated. It is concluded that slow relaxation is inherent for all quasi one-dimensional compounds and for the magnetically ordered ones shows up in the high enough magnetic field.
The liquid-crystalline rare-earth complexes of the type Ln(LH)3(DOS)3where Ln is Tb, Dy, Ho, Er, Tm, or Yb; LH is the Schiff base N-octadecyl-4-tetradecyloxysalicylaldimine; and DOS is ...dodecylsulfateexhibit a smectic A phase. Because of the presence of rare-earth ions with a large magnetic anisotropy, the smectic A phase of these liquid crystals can be easier aligned in an external magnetic field than smectic A phases of conventional liquid crystals. The magnetic anisotropy of the Ln(LH)3(DOS)3 complexes was determined by measurement of the temperature-dependence of the magnetic susceptibility using a Faraday balance. The highest value for the magnetic anisotropy was found for the dysprosium(III) complex. The magnetic alignment of these liquid crystals was studied by time-resolved synchrotron small-angle X-ray scattering experiments. Depending on the sign of the magnetic anisotropy, the director of the liquid-crystalline molecules was aligned parallel or perpendicular to the magnetic field lines. A positive value of the magnetic anisotropy (and parallel alignment) was found for the thulium(III) and the ytterbium(III) complexes, whereas a negative value of the magnetic anisotropy (and perpendicular alignment) was observed for the terbium(III) and dysprosium(III) complexes.
Rare-Earth-Containing Magnetic Liquid Crystals Binnemans, Koen; Galyametdinov, Yury G; Van Deun, Rik ...
Journal of the American Chemical Society,
05/2000, Volume:
122, Issue:
18
Journal Article
Peer reviewed
Open access
Rare-earth-containing metallomesogens with 4-alkoxy-N-alkyl-2-hydroxybenzaldimine ligands are reported. The stoichiometry of the complexes is Ln(LH)3(NO3)3, where Ln is the trivalent rare-earth ion ...(Y, La, and Pr to Lu, except Pm) and LH is the Schiff base. The Schiff base ligands are in the zwitterionic form and coordinate through the phenolic oxygen only. The three nitrate groups coordinate in a bidentate fashion. The X-ray single-crystal structures of the nonmesogenic homologous complexes Ln(LH)3(NO3)3, where Ln = Nd(III), Tb(III), and Dy(III) and LH = CH3OC6H3(2-OH)CHNC4H9, are described. Although the Schiff base ligands do not exhibit a mesophase, the metal complexes do (SmA phase). The mesogenic rare-earth complexes were studied by NMR, IR, EPR, magnetic susceptibility measurements, X-ray diffraction, and molecular modeling. The metal complexes in the mesophase have a very large magnetic anisotropy, so that these magnetic liquid crystals can easily be aligned by an external magnetic field.
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