The synthesis, purification, characterization, electrochemical properties, and fluorescence quenching of two new mononuclear Ni(II) complexes, [Ni(tptz) (CH 3 OH)Cl 2 ] (1) and [Ni(tptz) 2 ](PF 6 ) 2 ÁCH 3 CN (2), containing the ligand 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) are described. Solid state structures of both complexes have been determined by single crystal X-ray crystallography. In (1) and (2), the Ni(II) metal centers use the major coordination site of the tptz ligand and the coordination geometry around the Ni(II) is a distorted octahedron. The free tptz ligand has three emission bands that are assigned to the 1 (p-p * ) and 1 (n-p * ) states. The fluorescence spectra of (1) and (2) show that the fluorescence quenching of the tptz fluorophore proceeds via an energy transfer process. Magnetic susceptibility data derived from paramagnetic NMR revealed effective magnetic moments of 2.75 l B for (1), and 2.91 l B for (2) at room temperature. Cyclic voltammetry of (1) shows that the Ni(III/II) reduction couple is quasi-reversible whereas in complex (2), the Ni(II/I) couple indicates an electrochemical (EC) mechanism.

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The reaction between 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) and sulfuric acid in the presence of NH 4 PF 6 yielded crystals of [TPTZH 2 ](PF 6 ) 2 ÁH 2 O, characterized by spectroscopic methods and single-crystal X-ray diffraction. The structural data indicate that the diprotonated form, [TPTZH 2 ] 2? , is more planar than the neutral TPTZ molecule. Due to the presence of PF 6 anions located between neighboring dications, the triazine and/or pyridyl rings in each dication cannot interact in a p-p fashion. The proton affinity of TPTZ was computed using density function theory (B3LYP hybrid functional). Calculated thermochemical results and proton affinities indicate that for the first protonation, the favorable N atoms are different from those obtained from calculations based on Merz-Kollman atomic charges. For the second protonation, the proton affinities show a clear preference of the protonation on two N atoms, this time not contradicted by Merz-Kollman atomic charges, and in agreement with the experimental data. In the UV-Vis spectrum, two visible absorption bands of [TPTZH 2 ](PF 6 ) 2 ÁH 2 O are most likely arising from an outer-sphere charge-transfer. The photoluminescence properties of TPTZ and [TPTZH 2 ](PF 6 ) 2 were studied at room temperature in CH 3 CN solution.