Mohammed Mbarki

Unexpected Synergy between Magnetic Iron Chains and Stacked B6 Rings in Nb6Fe1−xIr6+xB8

The synergistic combination of experiment and density functional theory has led to the discovery of the first ferromagnetic material, Nb6Fe(1-x)Ir(6+x)B8, containing in its crystal structure iron chains embedded in stacked B6 rings. The strong ferromagnetic Fe-Fe interactions found in the iron chains induce an unexpected strengthening of the B-B interactions in the B6 rings. Beside these strong B-B interactions, strong interlayer metal-boron bonds (Ir-B and Nb-B) ensure the overall structural stability of this phase, while the magnetic Fe-Fe interactions are mainly responsible for the observed ferromagnetic ordering below T(C)=350 K.

Chemical Tuning of Magnetic Properties through Ru/Rh Substitution in Th7Fe3-type FeRh6–nRunB3 (n = 1–5) Series

The new quaternary boride series FeRh6-nRunB3 (n = 1-5) was synthesized by arc melting and characterized by powder and single-crystal X-ray diffraction (XRD), energy-dispersive X-ray analysis, and superconducting quantum interference device magnetometry. Single-crystal structure refinement showed the distribution of the iron atoms in two of three possible crystallographic 4d metal sites in the structure (Th7Fe3-type, space group P63mc). Rietveld refinements of the powder XRD data indicated single-phase synthesis of all the members. A linear decrease of the lattice parameters and the unit cell volume with increasing Ru content was found, indicating Vegards behavior. Susceptibility measurements show decreasing Curie temperature and magnetic moment (μa5T) recorded at 5 T with increasing Ru content from TC = 295 K and μa5T = 3.35 μB (FeRh5RuB3) to TC = 205 K and μa5T = 0.70 μB (FeRhRu5B3). The measured coercivities lie between 1.0 and 2.2 kA/m indicating soft to semihard magnetic materials.

A Dimeric Copper(II) Complex of Oxalate and Oxamide Dioxime Ligands: Synthesis, Crystal Structure, Thermal Stability, and Magnetic Properties

The dimeric copper(II) complex [Cu(C2O4)(H2oxado)(H2O)]2 (1), where H2oxado=oxamide dioxime, has been synthesized in water and characterized by elemental and thermal analyses, IR spectroscopy, and single-crystal X-ray diffraction. Complex 1 is composed of two neutral [Cu(C2O4)(H2oxado)(H2O)] entities connected by Cu-O bonds between oxalate oxygen atoms and copper(II) ions, thereby producing a centrosymmetric dimer, with the Cu(II) centers exhibiting a strongly distorted octahedral coordination. Neighboring dimers are hydrogen-bonded through O- H···O interactions leading overall to a layer structure. Thermal analyses of complex 1 showed two significant weight losses corresponding to the coordinated water molecules, followed by the decomposition of the network. Variable-temperature (10 - 300 K) magnetic susceptibility measurements revealed very weak antiferromagnetic interactions (θ = 0:86 K from Curie-Weiss law behavior) within the dinuclear unit Graphical Abstract A Dimeric Copper(II) Complex of Oxalate and Oxamide Dioxime Ligands: Synthesis, Crystal Structure, Thermal Stability, and Magnetic Properties

Quantum-chemical Ab Initio Calculations on the Donor–Acceptor Complex Pyridine–Borabenzene (C5H5N–BC5H5)

The adduct of borabenzene (C5H5B) and pyridine (C5H5N) was studied by means of quantum-chemical ab initio and time-dependent density functional theory calculations at different levels of theory. In the fully optimized structure (MP2/6-311++G**) of the free donor–acceptor complex (C2), the C–B–C angle amounts to 120.6°. The planes of the two aromatic rings enclose a torsion angle of ~40° with a barrier to rotation about the B–N bond of less than 3 kcal mol–1 (1 kcal mol–1 = 4.186 kJ mol–1). The highest computational level applied in this study (complete basis set limit, coupled cluster with single and double excitations (CCSD)) results in an energy associated with the reaction of borabenzene with pyridine of –52.2 kcal mol–1. Natural bond orbital analyses were performed to study the bond between the borabenzene and the pyridine unit of the adduct. The UV-vis spectrum of the adduct was calculated employing time-dependent density functional theory methods and the symmetry-adapted cluster-configuration interaction method. Our calculated electronic excitation spectrum of the pyridine adduct as well as its spectrum of the normal modes qualitatively reproduce the characteristic features of the IR and the UV-vis spectra described by experimentalists and thus allows assignment of the observed absorption bands, which in part agree with those by other authors.

2-Amino­pyridinium trans-diaqua­bis­(oxalato-κ2O,O)chromate(III)

In the title hybrid salt, (C5H7N2)[Cr(H2O)2(C2O4)2], the CrIII ion is coordinated in a slightly distorted octahedral environment by four O atoms from two oxalate ligands in the equatorial plane and by two water O atoms in the axial sites. The 2-aminopyridinium cation is disordered over two sets of sites in a 0.800 (7):0.200 (7) ratio. In the crystal, N—H⋯O and O—H⋯O hydrogen bonds connect the components into a three-dimensional network. The crystal studied was an inversion twin with components in a ratio 0.75 (2):0.25 (2).

Pyridinium trans-di­aqua­bis­[oxalato(2−)-κ2O1,O2]chromate(III) urea monosolvate

The asymmetric unit of the title solvated molecular salt, (C5H6N)[Cr(C2O4)2(H2O)2]·CO(NH2)2, contains half a formula unit. Each component is completed by crystallographic twofold symmetry: in the cation, one C and the N atom lie on the rotation axis; in the anion, the CrIII ion lies on the axis; in the solvent molecule, the C and the O atom lie on the axis. The aqua ligands are in a trans disposition in the resulting CrO6 octahedron. In the crystal, the components are linked by O—H⋯O, N—H⋯O and N—H⋯(O,O) hydrogen bonds, generating a three-dimensional network.

Pyridinium cis-diaqua­bis­(oxalato-κ2O,O′)chromate(III)

The title compound, (C5H6N)[Cr(C2O4)2(H2O)2], contains one protonated pyridine molecule and one [Cr(C2O4)2(H2O)2]− complex anion in the asymmetric unit. The CrIII in the complex anion is coordinated in a distorted octahedral environment by two O atoms from two cis water molecules and four O atoms from two chelating oxalate dianions. The crystal packing is stabilized by intermolecular N—H⋯O(oxalate) and O—H⋯O(oxalate) hydrogen bonds and by π–π stacking interactions (centroid–centroid distance = 3.602 Å) between pyridine rings, thereby building up a three-dimensional network.

Corrigendum to: Quantum-chemical Ab Initio Calculations on the Donor–Acceptor Complex Pyridine–Borabenzene (C5H5N–BC5H5)

The adduct of borabenzene (C5H5B) and pyridine (C5H5N) was studied by means of quantum-chemical ab initio and time-dependent density functional theory calculations at different levels of theory. In the fully optimized structure (MP2/6-311++G**) of the free donor–acceptor complex (C2), the C–B–C angle amounts to 120.6°. The planes of the two aromatic rings enclose a torsion angle of ~40° with a barrier to rotation about the B–N bond of less than 3kcalmol–1 (1kcalmol–1=4.186kJmol–1). The highest computational level applied in this study (complete basis set limit, coupled cluster with single and double excitations (CCSD)) results in an energy associated with the reaction of borabenzene with pyridine of –52.2kcalmol–1. Natural bond orbital analyses were performed to study the bond between the borabenzene and the pyridine unit of the adduct. The UV-vis spectrum of the adduct was calculated employing time-dependent density functional theory methods and the symmetry-adapted cluster-configuration interaction method. Our calculated electronic excitation spectrum of the pyridine adduct as well as its spectrum of the normal modes qualitatively reproduce the characteristic features of the IR and the UV-vis spectra described by experimentalists and thus allows assignment of the observed absorption bands, which in part agree with those by other authors.

Synthesis, crystal structure investigation and magnetism of the complex metal-rich boride series Cr{sub x}(Rh{sub 1-y}Ru{sub y}){sub 7-x}B{sub 3} (x=0.88-1; y=0-1) with Th{sub 7}Fe{sub 3}-type structure

Abstract Powder samples and single crystals of the new complex boride series Crx(Rh1−yRuy)7−xB3 (x=0.88–1; y=0–1) have been synthesized by arc-melting the elements under purified argon atmosphere on a water-cooled copper crucible. The products, which have metallic luster, were structurally characterized by single-crystal and powder X-ray diffraction as well as EDX measurements. Within the whole solid solution range the hexagonal Th7Fe3 structure type (space group P63mc, no. 186, Z=2) was identified. Single-crystal structure refinement results indicate the presence of chromium at two sites (6c and 2b) of the available three metal Wyckoff sites, with a pronounced preference for the 6c site. An unexpected Rh/Ru site preference was found in the Ru-rich region only, leading to two different magnetic behaviors in the solid solution: The Rh-rich region shows a temperature-independent (Pauli) paramagnetism whereas an additional temperature-dependent paramagnetic component is found in the Ru-rich region.