Iron-Promoted Nucleophilic Additions to Diimine-Type Ligands: A Synthetic and Structural Study

We report here three examples of the reactivity of protic nucleophiles with diimine-type ligands in the presence of FeII salts. In the first case, the iron-promoted alcoholysis reaction of one nitrile group of the ligand 2,3-dicyano-5,6-bis(2-pyridyl)-pyrazine (L1) permitted the isolation of an stable E-imido−ester, [Fe(L1‘)2](CF3SO3)2 (1), which has been characterized by spectroscopic studies (IR, ES-MS, Mössbauer), elemental analysis, and crystallographically. Compound 1 consists of mononuclear octahedrally coordinated FeII complexes where the FeII ion is in its low-spin state. The iron-mediated nucleophilic attack of water to the asymmetric ligand 2,3-bis(2-pyridyl)pyrido[3,4-b]pyrazine (L2) has also been studied. In this context, the crystal structures of two hydration−oxidation FeIII products, [Fe(L2‘)2](ClO4)3·3CH3CN (2) and trans-[FeL2‘‘Cl2] (3), are described. Compounds 2 and 3 are both mononuclear FeIII complexes where the metals occupy octahedral positions. In principle, L2 is expected to coordinate to metal ions through its bipyridine-type units to form a five-membered ring; however, this is not the case in compounds 2 and 3. In 2, the ligand coordinates through its pyridines and through the hydroxyl group attached to the pyrazine imino carbon after hydration, that is, in an N,O,N tridentate manner. In compound 3, the ligand has suffered further transformations leading to a very stable diamido complex. In this case, the metal ion achieves its octahedral geometry by means of two pyridines, two amido N atoms, and two axial chlorine atoms. Magnetic susceptibility measurements confirmed the spin state of these two FeIII species:  compounds 2 and 3 are low-spin and high-spin, respectively

TaFe1.14Te3TaFe_{1.14}Te_3, A New Low-Dimensional Ternary Tantalum Telluride

$TaFe_{1.14}Te_3$ is obtained from the elements in sealed quartz ampoules at 600°C. It crystallizes in the monoclinic space group P21/m with a = 7.4262(8), b = 3.6374(5), c = 9.9925(5) Å, and β = 109.166(8)°. The structure is built up from $TaFeTe_3$ layers. Fe atoms with fractional occupancy are situated at the Te surfaces of the TaFeTe3 slabs giving rise to a 3 D connectivity of the TaFeTe3 layers in space. TaFe1.14Te3 exhibits metallic properties and shows an antiferromagnetic ordering at 215 K. Tight-binding band structure calculations show that Fe–Fe and Ta–Fe interactions are important for the electronic stability of TaFe1.14Te3; replacing Fe by more electron-rich transition metals such as Co or Ni may lead to compounds of composition $TaM2Te_3$. A possible structure is derived from that of $TaFe_{1.14}Te_3$ by filling tetrahedral voids within the $TaMTe_3$ layers with additional 3d metal atoms

An iron-based molecular redox switch as a model for iron release from enterobactin via the salicylate binding mode

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A polymeric two-dimensional mixed-metal network. Crystal structure and magnetic properties of {[P(Ph)4][MnCr(ox)3]}n

The mixed-metal ferromagnet {[P(Ph)4][MnCr(ox)3]}n, where Ph is phenyl and ox is oxalate, has been prepared and a two-dimensional network structure, extended by Mn(II)-ox-Cr(III) bridges, has been determined from single crystal X-ray data. Crystal data: space group R3c, a=b=18.783(3), c=57.283(24) Å, α=β=90, γ=120°, Z=24 (C30H20O12PCrMn). The magnetic susceptibility data obey the Curie-Weiss law in the temperature range 260–20 K with a positive Weiss constant of 10.5 K. The temperature dependence of the molar magnetization exhibits a magnetic phase transition at Tc=5.9 K. The structure is discussed in relation to the strategy for preparing molecular based ferromagnets and, in addition, it is a solution to the question of the dimensionality of the [MM'(ox)3]n network, which in principle can extend two- or three-dimensionally to the crystal lattice. The optical absorption spectra of the single crystals are assigned to the ‘CrO6' chromophores. Their polarization patterns reflect the electric dipole selection rules for D3 symmetry. A strong site selective luminescence from the chromium(III) 2E states is observed at low temperature and the system may be suitable for studying energy transfer mechanisms

Molecule-Based Magnets: Polarized Neutron Ddiffraction and Mössbauer Spectral Study of Short-Range Magnetic Correlations in the Ferrimagnetic Layered Compounds (PPh₄) [Fe\u3csup\u3eII\u3c/sup\u3eFe\u3csup\u3eIII\u3c/sup\u3e(ox)₃] and (NBu₄) [Fe\u3csup\u3eII\u3c/sup\u3eFe\u3csup\u3eIII\u3c/sup\u3e(ox)₃]

Short-range antifemmagnetic correlations have been studied in the layered compounds (PPh4) [FeIIFeIII(ox) 3] and (NBu4) [FeIIFeIII(ox) 3] by neutron polarization analysis and Mössbauer spectroscopy. Polarized neutron diffraction profiles obtained between 2 and 50 K on (d20-, PPh4) [FeIIFeIII(ox) 3] show no magnetic Bragg scattering: The lack of such scattering indicates the absence of long-range magnetic order. However, a broad asymmetric feature observed at a Q of ca. 0.8 8, Å-1 is attributed to two-dimensional shortrange magnetic correlations, which are described by a Warren function. The correlation length is ca. 50 Å, between 2 and 30 K and then decreases to ca. 20 Å, at 50 K. The Mössbauer spectra of (PPh4) [FeIIFeIII(ox) 3] and (NBu4) [FeIIFeIII(ox) 3] have been measured between 1.9 and 293 K and 1.9 and 315 K, respectively, and are very similar. The paramagnetic spectra exhibit both high-spin Fen and Fen’ doublets with relative areas which indicate a 5% and 2% excess, respectively, of FIII. The coexistence in (PPh4) [FeIIFeIII(ox) 3] between 10 and 30 K of broad sextets and doublets in the Mossbauer spectra and the paramagnetic scattering observed in the polarized neutron measurements indicate the coexistence of spin-correlated and spin-uncorrelated regions in the layers of this compound. The polarized neutron scattering profiles and the Mossbauer spectra yield the magnetic exchange correlation length and lifetime, respectively, and the combined results are best understood in terms of layers composed of random frozen, but exchange correlated domains of ca. 50 Å, diameter at the lowest temperatures, of spin-correlated domains and spin-uncorrelated regions at intermediate temperahues, and of largely spin-uncorrelated regions above the N&l temperature as determined from magnetometry. The similarity of the Mossbauer spectra of (PPh4) [FeIIFeIII(ox) 3] and (NBu4) [FeIIFeIII(ox) 3] leads to the conclusion that similar magnetic exchange correlations are present in the latter compound

Polarized Neutron Diffraction and Mössbauer Spectral Study of Short-Range Magnetic Correlations in the Ferrimagnetic Layered Compounds (PPh₄) [Fe\u3csup\u3eII\u3c/sup\u3eFe\u3csup\u3eIII\u3c/sup\u3e(ox)₃] and (NBu₄) [Fe\u3csup\u3eII\u3c/sup\u3eFe\u3csup\u3eIII\u3c/sup\u3e(ox)₃]

Short-range antiferromagnetic correlations have been studied in the layered compounds (PPh4) [FeIIFeIII(ox)3] and (NBu4) [FeIIFeIII(ox)3] by neutron polarization analysis and Mössbauer spectroscopy. Polarized neutron diffraction profiles obtained between 2 and 50 K on (d20-Pph4) [FeIIFeIII(ox)3] show no magnetic Bragg scattering; the lack of such scattering indicates the absence of long-range magnetic order. However, a broad asymmetric feature observed at a Q of ca. 0.8 Å-1 is attributed to two-dimensional short-range magnetic correlations, which are described by a Warren function. The correlation length is ca. 50 Å between 2 and 30 K and then decreases to ca. 20 Å at 50 K. The Mössbauer spectra of (PPh4) [FeIIFeIII(ox)3] and (NBu4) [FeIIFeIII(ox)3] have been measured between 1.9 and 293 K and 1.9 and 315 K, respectively, and are very similar. The paramagnetic spectra exhibit both high-spin FeII and FeIII doublets with relative areas which indicate a 5% and 2% excess, respectively, of FeIII. The coexistence in (PPh4) [FeIIFeIII(ox)3] between 10 and 30 K of broad sextets and doublets in the Mössbauer spectra and the paramagnetic scattering observed in the polarized neutron measurements indicate the coexistence of spin-correlated and spin-uncorrelated regions in the layers of this compound. The polarized neutron scattering profiles and the Mössbauer spectra yield the magnetic exchange correlation length and lifetime, respectively, and the combined results are best understood in terms of layers composed of random frozen, but exchange correlated domains of ca. 50 Å diameter at the lowest temperatures, of spin-correlated domains and spin-uncorrelated regions at intermediate temperatures, and of largely spin-uncorrelated regions above the Néel temperature as determined from magnetometry. The similarity of the Mössbauer spectra of (PPh4) [FeIIFeIII(ox)3] and (NBu4) [FeIIFeIII(ox)3] leads to the conclusion that similar magnetic exchange correlations are present in the latter compound