Syntheses, Structures, and Characterization of Two Manganese(II)-Aminobenzoic Complexes

Synthesis, Crystal Structure, and Magnetic Properties of a New Mixed Metal (Co(II), Ni(II)) Cubane

The mixed Co(II)/Ni(II) complex, [Co_2.67Ni_1.33L₄(CH₃COO)₂][BPh₄]₂·0.75H₂O where HL = 4-(salicylaldimine)antipyrine, was isolated as an orange solid from the reaction of 4-(salicylaldimine)antipyrine, with mixed cobalt(II) acetate and nickel(II) acetate in ethanol. The complex was characterized by Frustrated Total Internal Reflection (FTIR), UltraViolet Visible spectroscopy (UV-Vis), X-ray single crystal diffraction, and by elemental analysis. The complex is composed of two symmetry independent cationic units, A and B. The two units are essentially isostructural; nevertheless, small differences exist between them. The units contain four metal atoms, arranged at the corners of a distorted cubane-like core alternately with phenoxy oxygen of the Schiff base. The overall eight corners occupied by metal ions in the asymmetric unit are shared between cobalt and nickel in a 5.33:2.67 ratio. Each metal divalent cation binds three coordinated sites from the corresponding tridentate Schiff base ligand, the fourth one is bound by the acetate oxygen, the fifth and the sixth donor sites come from the phenolate oxygens of other Schiff base ligands. Intermolecular hydrogen bonds join the complexes to the water molecules present in the crystal packing. The magnetic characterization was carried out for this new complex and for its isostructural counterpart containing only cobalt ions. The magnetic measurements for the cobalt(II)/nickel(II) mixed compound indicate either antiferromagnetic interactions among the two cubanes or an anisotropic contribution, whereas a ferromagnetic interaction is observed within the cubane, for both the complexes, as expected by geometrical considerations. A comparison between the magnetic properties of the pure cobalt(II) derivative and similar systems discussed in literature, is presented.

Crystal structure of trans-bis-(di-ethano-lamine-κ(3) O,N,O')manganese(II) bis-(3-amino-benzoate)

Reaction of m-amino-benzoic acid (MABA), di-ethano-lamine (DEA) and MnCl2·4H2O led to the formation of the title salt, [Mn(C4H11NO2)2](C7H6NO2)2. In the complex cation, the Mn(2+) ion is located on an inversion centre and is coordinated by two symmetry-related tridentate DEA mol-ecules, leading to the formation of a slightly distorted MnN2O4 octa-hedron. The MABA(-) counter-anions are connected to the complex ion by a pair of rather strong O-H⋯O hydrogen bonds, yielding a 1:2 supra-molecular aggregate. Much weaker N-H⋯O hydrogen bonds connect neighbouring aggregates into a three-dimensional network structure.

Synthesis, Crystal Structure and Magnetic Properties of a Dinuclear Mn(II) Complex with two syn–Anti Bridging Carboxylate Groups

The dinuclear Mn(II) complex [Mn2(L)2(bipy)4]·(ClO4)2·3H2O (HL = 2-benzothiazolylthioacetic acid; bipy = 2,2'-bipyridine) has been synthesised and characterised by single crystal X-ray diffraction, IR and elemental analysis. In the dimeric, cationic complex with a crystallographic centre of symmetry, two bipy molecules chelate each Mn atom. These two metal fragments are then bridged by two L groups in a syn–anti conformation with a Mn···Mn distance of 4.767 Å. The arrangement of these dimers allows the formation of tunnels that host the ClO4- anions and lattice water molecules through hydrogen bonds. Magnetic susceptibility measurement revealed antiferromagnetic coupling between the metal centres.

Structural and magnetic studies of two-dimensional solvent-free manganeseII complexes prepared via ligand exchange reaction under solvothermal conditions

Systematic investigation of the ligand exchange reactions between manganese(II) acetate and benzoic acid under solvothermal conditions led to the isolation of crystalline complexes {Mn5(OC(O)CH3)6(OC(O)C6H5)4}(infinity) ( 1) and {Mn5(OC(O)CH3)4(OC(O)C6H5)6}}(infinity) ( 2) in high (i.e., >90%) yields. The complexes are characterized structurally as 2-D honeycomb-like sheets comprised of edge-shared Mn 12 loops with some noteworthy differences as follows. First, buckling of the 2-D sheet in 1 is not observed for 2, presumably as a consequence of additional intersheet phenyl groups in the latter. Second, complex 1 is comprised of only six-coordinate MnII, while 2 has both pseudo-octahedral and distorted trigonal bipyramidal coordinate metal ions. Third, while complex 2 exhibits pi-stacking interactions with intersheet phenyl-phenyl contacts of 3.285 and 3.369 A, 1 exhibits no such bonding. Antiferromagnetic exchange is observed with Weiss constants (theta) of -28 and -56 K and Neel temperatures of 2.2 and 8.2 K for complexes 1 and 2, respectively. The paramagnetic transition at higher temperatures for complex 2 may be attributed to pi-pi exchange through phenyl groups in adjacent layers. Preliminary gas sorption studies (76 K) indidate preferential adsorption of H2 versus N2 for complex 1 only.

Two Multi-Copper-Containing Heteropolyoxotungstates Constructed from the Lacunary Keggin Polyoxoanion and the High-Nuclear Spin Cluster

Two novel high-nuclear copper-substituted polyoxometalates, Na16[Cu14(OH)4(H2O)16(SiW8O31)4].20.5H2O (1) and K10Na14[Cu10(H2O)2(N3)4(GeW9O34)2(GeW8O31)2].30H2O (2), containing 14 Cu2+ ions and 10 Cu2+ ions, respectively, have been obtained in aqueous solution and characterized by IR, UV, TG, element analysis, electrochemistry, and single-crystal X-ray analyses. The polyoxoanion framework of 1 is composed of four [beta-SiW8O31] units connected by 14 Cu2+ ions to constitute a tetrameric compound. In 2, two [beta-GeW8O31] anions and two [B-alpha-GeW9O34] anions are connected together by a [Cu10(N3)4O32(H2O)2] {Cu10(N3)4} cluster to construct a novel tetrameric compound. The results of the electrocatalytic experiments reveal that the reduced species of 1 and 2 have electrocatalytic activities for nitrate reduction.