A self-assembled octanuclear complex bearing the uncommon close-packed {Fe4Mn4(µ4-O)4(µ-O)4} molecular core.

A one-pot open-air reaction of manganese powder with iron(ii) chloride in DMF solution of the Schiff base (H2L) formed in situ from salicylaldehyde and hydroxylamine hydrochloride yields the heterometallic complex [Fe4(µ4-O)4Mn4(L)8(DMF)4]·2DMF (). Single crystal X-ray analysis shows that its molecular structure is based on the octanuclear core {Fe4Mn4(µ4-O)4(µ-O)4} with a quite rare molecular structure type {M8(µ4-X)4(µ-X)4}, where the central cube-like iron motif is modified with four terminal manganese fragments, the whole core being presented as the {Fe4(µ4-O)4} + 4{Mn(µ-O)} combination. Using the data from the Cambridge Structural Database (CSD), an analysis of the octanuclear structures with similar central {M4(µ4-X)4} fragments was performed. The hierarchical order of molecular structure types with the general formula M8Xn for such compounds was proposed and the topological features as well as the factors that influence the molecular type formation are discussed. Variable-temperature (1.8-300 K) magnetic susceptibility measurements reveal an antiferromagnetic coupling among the magnetic centres in .

Direct synthesis of a {Co6(III)Fe6(III)} dodecanuclear complex, revealing an unprecedented molecular structure type.

A novel heterometallic Co6Fe6 Schiff base complex, possessing an unprecedented {M12(µ-X)22} branched structure (according to the search via the Cambridge Structural Database), has been prepared using the "direct synthesis" approach and characterized by single crystal X-ray diffraction and magnetometry.

Tetra-kis(µ3-2-{[1,1-bis-(hy-droxy-meth-yl)-2-oxidoeth-yl]imino-meth-yl}-6-nitro-pheno-lato)tetra-copper(II).

The title cluster, [Cu4(C11H12N2O6)4], was obtained from the Cu(0)-FeCl2·4H2O-H4 L-Et3N-DMF reaction system (in air), where H4 L is 2-hy-droxy-methyl-2{[(2-hy-droxy-3-nitro-phen-yl)methyl-idene]amino}-propane-1,3-diol and DMF is di-methyl-formamide. The asymmetric unit consists of one Cu(2+) ion and one dianionic ligand; a -4 symmetry element generates the cluster, which contains a {Cu4O4} cubane-like core. The metal ion has an elongated square-based pyramidal CuNO4 coordination geometry with the N atom in a basal site. An intra-molecular O-H⋯O hydrogen bond is observed. The solvent mol-ecules were found to be highly disordered and their contribution to the scattering was removed with the SQUEEZE procedure in PLATON [Spek (2009 ▶). Acta Cryst. D65, 148-155], which indicated a solvent cavity of volume 3131 Å(3) containing approximately 749 electrons. These solvent molecules are not considered in the given chemical formula.

Magnetic, high-field EPR studies and catalytic activity of Schiff base tetranuclear CuII2FeIII2 complexes obtained by direct synthesis.

Two novel heterometallic complexes [Cu2Fe2(HL(1))2(H2L(1))2]·10DMSO (1) and [Cu2Fe2(HL(2))2(H2L(2))2]·2DMF (2) have been prepared using the open-air reaction of copper powder, iron(II) chloride and DMSO (1) or DMF (2) solutions of the polydentate Schiff base (H4L(1), 1; H4L(2), 2) formed in situ from salicylaldehyde (1) or 5-bromo-salicylaldehyde (2) and tris(hydroxymethyl)aminomethane. Crystallographic analysis revealed that both compounds are based on the centrosymmetric tetranuclear core {Cu(II)2Fe(III)2(µ-O)6} where metal centres are joined by µ-O bridges from the deprotonated ligands forming a nonlinear chain-like arrangement. Variable-temperature (1.8-300 K) magnetic susceptibility measurements of 1 and 2 showed a decrease of the effective magnetic moment value at low temperature, indicative of antiferromagnetic coupling (JCu-Fe/hc = -10.2 cm(-1), JFe-Fe/hc = -10.5 cm(-1) in 1, JCu-Fe/hc = -10.5 cm(-1), JFe-Fe/hc = -8.93 cm(-1) in 2) between the magnetic centres in both compounds. They reveal an exceptionally high catalytic activity in the oxidation of cyclohexane with hydrogen peroxide under mild conditions, with the best observed yield/TON combined values of 36%/596 and 44%/1.1 × 10(3) for 1 and 2, respectively.

Heterometallic Co(III)4Fe(III)2 Schiff base complex: structure, electron paramagnetic resonance, and alkane oxidation catalytic activity.

The heterometallic complex [Co(4)Fe(2)OSae(8)]·4DMF·H(2)O (1) was synthesized by one-pot reaction of cobalt powder with iron chloride in a dimethylformamide solution of salicylidene-2-ethanolamine (H(2)Sae) and characterized by single crystal X-ray diffraction analysis, magnetic measurements, high frequency electron paramagnetic resonance (HF-EPR), and Mössbauer spectroscopies. The exchange coupling in the Fe(III)-Fe(III) pair is of antiferromagnetic behavior with J/hc = -190 cm(-1). The HF-EPR spectra reveal an unusual pattern with a hardly detectable triplet signal of the Fe(III) dimer. The magnitude of D (ca. 13.9 cm(-1)) was found to be much larger than in related dimers. The catalytic investigations disclosed an outstanding activity of 1 toward oxidation of cycloalkanes with hydrogen peroxide, under mild conditions. The most efficient system showed a turnover number (TON) of 3.57 × 10(3) with the concomitant overall yield of 26% for cyclohexane, and 2.28 × 10(3)/46%, respectively, for cyclooctane. A remarkable turnover frequency (TOF) of 1.12 × 10(4) h(-1) (the highest initial rate W(0) = 3.5 × 10(-4) M s(-1)) was achieved in oxidation of cyclohexane. Kinetic experiments and selectivity parameters led to the conclusion that hydroxyl radicals are active (attacking C-H bonds) species. Kinetic and electrospray ionization mass spectrometry (ESI-MS) data allowed us to assume that the trinuclear heterometallic particle [Co(2)Fe(Sae)(4)](+), originated from 1 in solution, could be responsible for efficient generation of hydroxyl radicals from hydrogen peroxide.

Bis(µ-4-nitro-2-{[2-(oxidometh-yl)phen-yl]imino-meth-yl}phenolato)bis-[chlorido(dimethyl sulfoxide)-iron(III)] dimethyl sulfoxide disolvate.

In the centrosymmetric dimeric title complex, [Fe(2)(C(14)H(10)N(2)O(4))(2)Cl(2)(C(2)H(6)OS)(2)]·2C(2)H(6)OS, two {Fe(L)Cl(DMSO)} units (L is the tridentate ligand 4-nitro-2-{[2-(oxidometh-yl)phen-yl]imino-meth-yl}phenolate; DMSO is dimethyl sulfoxide) are bridged by two O atoms, with an Fe⋯Fe separation of 3.1838 (8) Å. The coordination polyhedron of the Fe(III) atoms can be described as distorted octa-hedral, with four Fe-O, one Fe-N and one Fe-Cl coordination bonds. The L ligand is not planar, the dihedral angle between the 2-(oxidometh-yl)phen-yl]imino and 4-nitro-2-(imino-meth-yl)phenolate planes being 48.54 (9)°. The solvent DMSO molecule is disordered over two orientations with equal occupancy.

Tris(2,2'-bipyridine-κN,N')cobalt(III) tris-(oxalato-κO,O)ferrate(III) mono-hydrate.

The title compound, [Co(C(10)H(8)N(2))(3)][Fe(C(2)O(4))(3)]·H(2)O, con-sists of two discrete tris-(chelate) metal ions (Co(III)N(6) and Fe(III)O(6) chromophores) and a water mol-ecule. The structure is highly symmetrical; the Co(III) and Fe(III) ions occupy positions with site symmetry 3.2. The coordination polyhedra of the metal atoms have a nearly octa-hedral geometry with noticeable trigonal distortions. The Co-N and Fe-O bond lengths are equal by symmetry, viz. 1.981 (2) and 1.998 (4) Å, respectively. The cations and anions are arranged alternately along their threefold rotation axes parallel to [001], forming chains that are packed in a hexa-gonal manner. The water mol-ecules occupy voids between the chains. The crystal under investigation was an inversion twin.

Novel heterometallic Schiff base complexes featuring unusual tetranuclear {Co(III)2Fe(III)2(µ-O)6} and octanuclear {Co(III)4Fe(III)4(µ-O)14} cores: direct synthesis, crystal structures, and magnetic properties.

A one-pot reactions of cobalt powder with iron(II) chloride in dimethylformamide (DMF; 1) or dimethyl sulfoxide (DMSO; 2) solutions of polydentate salicylaldimine Schiff base ligands (H(2)L(1), 1; H(4)L(2), 2) based on 2-aminobenzyl alcohol (1) or tris(hydroxymethyl)aminomethane (2), formed in situ, yielded two novel heterometallic complexes, [Co(III)(2)Fe(III)(2)(L(1))(6)]·4DMF (1) and [Co(III)(4)Fe(III)(4)(HL(2))(8)(DMSO)(2)]·18DMSO (2). Crystallographic investigations revealed that the molecular structure of 1 is based on a tetranuclear core, {Co(III)(2)Fe(III)(2)(µ-O)(6)}, with a chainlike metal arrangement, while the structure of 2 represents the first example of a heterometallic octanuclear core, {Co(III)(4)Fe(III)(4)(µ-O)(14)}, with a quite rare manner of metal organization, formed by two pairs of {CoFe(HL(2))(2)} and {CoFe(HL(2))(2)(DMSO)} moieties, which are joined by O bridges of the Schiff base ligands. Variable-temperature (1.8-300 K) magnetic susceptibility measurements showed a decrease of the µ(B) value at low temperature, indicative of antiferromagnetic coupling (J/hc = -32 cm(-1) in 1; J/hc = -20 cm(-1) in 2) between the Fe(III) magnetic centers in both compounds. For 2, three J constants between Fe(III) centers were assumed to be identical. High-frequency electron paramagnetic resonance spectra allowed one to find spin Hamiltonian parameters in the coupled-spin triplet and quintet states of 1 and estimate them in 2. The "outer" and "inner" Fe atoms in 2 appeared separately in the Mössbauer spectra.

Triethyl-ammonium bis-{2-[(2-oxido-5-nitro-benzylidene)amino]-benzoato}ferrate(III) monohydrate.

In the title compound, [NH(C(2)H(5))(3)][Fe(C(14)H(8)N(2)O(5))(2)]·H(2)O, the iron(III) ion is hexa-coordinated by four O atoms in the basal plane [Fe-O distances in the range 1.904 (4)-1.909 (4) Å] and two N atoms in the axial plane [Fe-N = 1.981 (4) and 1.985 (4) Å] of two tridentate fully deprotonated 2-{[(2-oxido-5-nitro-phen-yl)methyl-ene]amino}-benzoato (H(2)L) ligands, forming a tetra-gonally elongated octa-hedral geometry. The triethyl-ammonium cations and complex anions are linked by N-H⋯O hydrogen bonds into chains parallel to [100]. Disordered water mol-ecules (occupancy ratio 0.6:0.4) occupy the voids in the crystal structure.

Hexa-kis-(dimethyl-formamide-κO)manganese(II) µ-oxido-bis-[trichlorido-ferrate(III)].

The title compound, [Mn(C(3)H(7)NO)(6)][Fe(2)Cl(6)O], was obtained unintentionally as a product of an attempted synthesis of heterometallic complexes with Schiff base ligands using manganese powder and FeCl(3)·6H(2)O as starting materials. In the [Fe(2)OCl(6)](2-) anion, the O atom and the Fe atom occupy positions with site symmetry [Formula: see text] and 3, respectively, resulting in a linear Fe-O-Fe angle and a staggered conformation. The octa-hedrally surrounded cation (site symmetry [Formula: see text]) and the [Fe(2)Cl(6)O](2-) anion are alternately stacked along [001].