Eleanna Diamantopoulou

Synthetic and structural chemistry of nickel(II)/1-methylbenzotriazole complexes

Abstract A systematic investigation of the NiX2/Mebta (X = Cl, Br, NCS, NO3; Mebta = 1-methylbenzotriazole) reaction system in various solvents is described. Particular emphasis has been placed on determining the influence of the Mebta: Ni11 ratio on the identity of the reaction products. In the nitrate case, the influence of the water concentration in the reaction mixture on reaction products has also been investigated. These combined variations have led to the preparation of 14 discrete six-coordinate complexes with the formulae [Ni(NO)3)2(Mebta)2], [Ni(NO3)(H2O)2(Mebta)2]NO3, [Ni(H2O)4 (Mebta)2](NO3)2, [Ni(NO3)2(Mebta)3]·CH3COCH3, [NiX2(Mebta)4](X = ONO2, NCS, Cl, Br), [NiX2(Mebta)2]n (X = Cl, Br), [NiX2(MeOH)2(Mebta)2] (C = Br, NCS) and [NiX2 (Mebta)]n (X = Cl, Br). Four complexes have been structurally characterized by single-crystal X-ray studies: cis-[Ni(NO3)2(Mebta)2] (1), trans-[Ni(H2O)4)Mebta)2](NO3)2 (3), mer-[Ni(NO)3)2((Mebta)3]·CH3COCH3 )4) and trans-[Ni(NCS)2(MeOH)2(Mebta)2] (6). Mebta behaves as a monodentate ligand binding through N(3). The structures of 3and 6 are stabilized by intermolecular hydrogen bonds. The new complexes were studied by thermal techniques, conductivity measurements, magnetic susceptibilities and spectroscopic (IR, ligand field) methods. Monomeric, trans pseudo-octahedral structures are assigned for the complexes [NiX2(Mebta)4] and [NiBr2(MeOH)2(Mebta)2] in the solid state. Polymeric structures are suggested for [NiX2(Mebta)2]n and [NIX2(Mebta)]n with NiX4N2 and NiX5N coordination spheres, respectively.

Heptanuclearity in nickel(II) chemistry: preparation, characterization, crystal structure and magnetic properties of [Ni7(OH)2(acac)8(btaO)4(H2O)2] (btaO−=the 1-hydroxybenzotriazolate ion)

Abstract The use of the substituted benzotriazole ligand btaOH (1-hydroxybenzotriazole) in nickel(II) chemistry has yielded a structurally and magnetically interesting polynuclear complex. The [Ni(acac)2(H2O)2]–btaOH·H2O (4:1, 3:1, 7:4) reaction system in refluxing MeCN gives light green–blue [Ni7(OH)2(acac)8(btaO)4(H2O)2] (4) in good yield (∼75%). The structure of 4·MeCN·0.9H2O was determined by single-crystal X-ray crystallography. The heptanuclear assembly is held together by two μ3 hydroxo ligands, two terminal H2O molecules, four chelating acac− groups, two μ2 acac− groups, two μ3 acac− groups, two μ4 btaO− ligands and two μ2 btaO− ligands. The Ni(II) atoms have distorted octahedral geometries. The IR and UV–Vis data of 4 are discussed in terms of the nature of bonding and the known structure. Variable-temperature magnetic susceptibility data (3–300 K), fitted with a 3-J model, show ferromagnetic and antiferromagnetic interactions. Magnetization data at 4 K are in line with an S=1 ground state for 4. The versatility of the 1-hydroxybenzotriazolate ligand is also discussed.

A novel coordination mode of the 1-hydroxybenzotriazolate (btaO−) ligand: preparation, X-ray crystal structure and spectroscopic characterizationof the trinuclear complex [Ni3(btaO)6(NH3)6]

Reaction of Ni(NO3)2 · 6H2O with 1-hydroxybenzotriazole (btaOH) in DMF/aqueous NH3 and layering of the resulting solution with MeCN yields the complex [Ni3(btaO)6(NH3)6] · 0.47DMF · 0.75MeCN · 1.58H2O, (ca. 80% yield), the structure of which has been determined by single-crystal X-ray crystallography. The asymmetric unit contains two, structurally similar, trinuclear molecules. The six-coordinate NiII atom is linked to each terminal NiII atom by three btaO− ions; three NH3 molecules complete the octahedral coordination at each terminal metal ion. The btaO− ions behave as bidentate bridging ligands, binding through N(3) to the central NiII atom and through N(2) to the terminal NiII atoms, with the deprotonated oxygen atom remaining uncoordinated and participating in hydrogen bonding with the ammine ligand. The complex was also characterized by room-temperature effective magnetic moment and spectroscopic (i.r., ligand field) studies. The data are discussed in terms of the nature of bonding and other known structures.

The case of symmetry-dependent ground-state spin value in Ni(II) clusters of high-nuclearity. Crystal structure and magnetic properties of a pentanuclear and a nonanuclear Ni(II) clusters

Abstract The crystal structures and the magnetic properties of a pentanuclear (1) and a nonanuclear (2) Ni(II) clusters are described. In the former, crystallizing in the cubic I23 space group, the Ni(II) assembly is composed of a regular tetrahedral geometry of four metal ions centered on the fifth. The nonanuclear cluster crystallizes in the hexagonal crystallographic system -R3 space group - the Ni(II) assembly is composed of two regular tetrahedra, like that of the pentanuclear cluster, sharing a common apex. All metal ions in either cluster are six-coordinate. Variable-temperature magnetic susceptibility data show antiferromagnetic interactions for both clusters. Moreover, magnetization data are in line with uneven intermediate-spin ground states [S=1, S=2] and [S=2, S=3] for 1 and 2, respectively. A comparison of both the symmetry and the spin ground state of 1 to those of lower-symmetry pentanuclear Ni(II) clusters, reveals that the ground-state spin value increases with the cluster symmetry.

Benzotriazolate-mediated assembly of the discrete asymmetric pentanuclear nickel complex [Ni5(OH)(bta)5(acac)4(H2O)4](Hbta = benzotriazole, Hacac = pentane-2,4-dione)

Reaction of [Ni(acac)2(H2O)2] with benzotriazole (Hbta) in acetone–n-hexane yields the pentanuclear nickel complex [Ni5(OH)(bta)5(acac)4(H2O)4]1; the novel structure of this compound is described, together with the results of magnetic susceptibility studies which indicate antiferromagnetic coupling between the nickel(II) ions within the complex.