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Two new dinuclear nickel(II) complexes, [(H2O)Ni(N3)(L1)(μ1,1-N3)Ni(L1)] and [(H2O)Ni(N3)(L2)(μ1,1-N3)Ni(L2)]·MeOH, derived from two isomeric Schiff base ligands, HL1 [2-{(2-(ethylamino)ethylimino)methyl}-6-ethoxyphenol] and HL2 [2-{(2-(dimethylamino)ethylimino)methyl}-6-ethoxy-phenol], have been synthesized and characterized. Variable temperature (2–300 K) magnetic susceptibility measurements indicate the presence of moderate ferromagnetic exchange coupling between nickel(II) centers. In each complex, antiferromagnetic exchange takes place through the phenoxido bridge and ferromagnetic through the μ1,1-azido bridge. The competitive interactions therefore reduce the overall magnetic coupling. In a theoretical complex, where the bridging azido ligand has been eliminated and the rest of the geometry is kept frozen, the magnetic coupling becomes antiferromagnetic which suggests that the ferromagnetic exchange occurs via the μ1,1-azido bridge. Mulliken population analysis and spin density plots clearly show that the spin distributed spherically in the Ni centers is due to the presence of one unpaired electron in both the and orbitals. The shape of the spin density at the bridging O-atom and azide evidences the participation of their p orbitals in the magnetic coupling. The SOMO is basically constituted by the orbital of one nickel(II) center with the participation of the azide π-system. The SOMO−1 is constituted by the orbital of the other nickel(II), an oxygen atom and the azide π-system. [ABSTRACT FROM AUTHOR]

Microwave and solvothermal activation processes have been explored as tools for the preparation of various nickel and ruthenium complexes. Different reaction conditions are tested using ethanol or water as solvents. Three nickel derivatives, [Ni(9-atc) 2 (OH 2 ) 2 (py) 2 ]·2EtOH ( 1 ), [Ni 2 (9-atc) 4 (OH 2 )(py) 4 ]·2H 2 O ( 2 ·2H 2 O), and [Ni 2 (9-atc) 4 (py) 2 ] ( 3 ), and two diruthenium compounds, {[Ru 2 Cl(9-atc) 4 ]·2H 2 O} n ( 4 ) and [Ru 2 (9-atc) 4 (EtOH) 2 ]·2EtOH ( 5 ), are obtained. The crystal structure determination of complexes 1 – 3 and 5 is also described. Compound 1 displays a 1D extended supramolecular structure with hydrogen bonds involving crystallization solvent molecules. Compound 2 is dimetallic, and both nickel centers show an octahedral coordination environment, whereas complexes 3 and 5 display a typical carboxylate-bridged paddlewheel-type structure with two metal atoms connected by four bridging carboxylate ligands. All compounds show weak antiferromagnetic interactions except 3 , where a strong intra-dimer antiferromagnetic coupling is observed. Compound 4 also shows a strong zero field splitting. [ABSTRACT FROM AUTHOR]

A one-dimensional coordination polymer [Ni(tp)(OH2)4] ( 1) (tp = -O2CC6H4CO2-; terephthalate) has been synthesized under environmentally friendly conditions. It has been characterized by elemental analysis, infrared spectroscopy, thermogravimetry, single-crystal and powder X-ray diffraction, and magnetic measurements. Compound 1 is a rare example of 1D polymeric NiII dicarboxylate that shows ferromagnetic interactions through hydrogen bonds. The zigzag arrangement of the NiII octahedral units connected by hydrogen bonds distinguishes compound 1 from other [Ni(dicarboxylate)(OH2)4] compounds, in which the interactions are antiferromagnetic. [ABSTRACT FROM AUTHOR]

Several metal-organic frameworks of nickel(II) were obtained starting from the molecular complex 1, [Ni(OH2)4(4-pyc)2] (4-pyc = 4-pyridinecarboxylate or isonicotinate). By using different reaction conditions, two polymorphs of the anhydrous complex [Ni(4-pyc)2] n ( 2a and 2b) and the polynuclear compound [Ni5(OH2)3(4-pyc)10] n ( 3) were obtained in very high yield. All of the compounds were characterized by elemental analysis and spectroscopic data. The crystal structure determination of compounds 2b and 3 was also carried out. Structural and topological analysis of these new structural types and other related ones were performed. It was found that compounds 2a and 2b are a rare case of coordination framework isomers. Thermogravimetric studies indicate that compounds 2b and 3 lose the pore-allocated solvent molecules at moderate temperatures without any significant structural change, and at higher temperatures, compounds 1 and 3 are transformed into 2a. Textural parameters that characterize the microporous networks for 2b and 3 were obtained by nitrogen-adsorption measurements. For both samples, the micropore size distribution indicates cylindrical pores with diameters of 0.85 ( 2b) and 0.90 nm ( 3). The values of Brunauer-Emmett-Teller and Langmuir surface areas are 178 and 185 m2 g-1 for compound 2b, and 995 and 982 m2 g-1 for compound 3. Micropore volumes are 0.065 and 0.350 cm3 g-1 for 2b and 3, respectively. The magnetic properties of compounds 1, 2a, and 2b are consistent with the presence of zero-field splitting and a small antiferromagnetic coupling between the metal atoms. The magnetic properties of the pentanuclear compound 3 were analyzed by considering one monomer with zero-field splitting caused by axially distorted NiII octahedral compounds, and two dimeric fragments with magnetic interactions within each dimetallic unit. [ABSTRACT FROM AUTHOR]