Nickel and cobalt sulfides are promising materials in different cutting-edge research areas like solar cells, supercapacitors, catalysts, and electrode materials. Nickel and cobalt sulfides with various stoichiometries have been synthesized sonochemically from Ni(CH3COO)2 ∙ 4H2O, Co(CH3COO)2 ∙ 2H2O and different sulfur precursors using a direct immersion ultrasonic probe. The products were characterized by X-ray powder diffraction, transmission electron microscopy (TEM) including EDX analysis, IR and UV–Vis spectroscopy and elemental analysis. Following products have been obtained: NiS, Ni3S4, CoS1.097 and Co9S8, with average crystallite sizes in the range 7−30 nm. Effects of different reaction conditions on the size, morphology and optical band-gap energy were evaluated. Optical band-gap energies in the range 3.3 eV−3.8 eV were observed for the obtained nanoparticles.

Dedicated to the memory of Prof. Dr. Jurij V. Bren~i~. AbstractThe synthesis and characterization of two new zinc(II) coordination compounds with 3-and 4-aminopyridine are reported. They were obtained after adding a water solution of Zn(CH 3 COO) 2 · 2H 2 O or dissolving solid Zn(CH 3 COO) 2 · 2H 2 O in methanol solutions of 3-and 4-aminopyridine. The products were characterized structurally by single-crystal X-ray diffraction analysis. Colourless crystals of the compound synthesized by the reaction of Zn(CH 3 COO) 2 · 2H 2 O and 3-aminopyridine (3-apy), are built of trinuclear complex molecules with the formula [Zn 3 (O 2 CCH 3 ) 6 (3-apy) 2 (H 2 O) 2 ](1). The molecules consists of two terminal Zn atoms, coordinated tetrahedrally, and one central Zn atom, coordinated octahedrally. Colourless crystals, obtained by the reaction of Zn(CH 3 COO) 2 · 2H 2 O with 4-aminopyridine (4-apy), consist of a mononuclear complex [Zn(O 2 CCH 3 ) 2 (4-apy) 2 ](2). Hydrogen-bonding interactions in the crystal structures of both complexes are reported.

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