Mono- and Binuclear Copper(II) and Nickel(II) Complexes with the 3,6-Bis(picolylamino)-1,2,4,5-Tetrazine Ligand.

Four new compounds of formulas [Cu(hfac)(L)] (), [Ni(hfac)(L)] (), [{Cu(hfac)}(µ-L)]·2CHOH () and [{Ni(hfac)}(µ-L)]·2CHCN () [Hhfac = hexafluoroacetylacetone and L = 3,6-bis(picolylamino)-1,2,4,5-tetrazine] have been prepared and their structures determined by X-ray diffraction on single crystals. Compounds and are isostructural mononuclear complexes where the metal ions [copper(II) () and nickel(II) ()] are six-coordinated in distorted octahedral MNO surroundings which are built by two bidentate hfac ligands plus another bidentate L molecule. This last ligand coordinates to the metal ions through the nitrogen atoms of the picolylamine fragment. Compounds and are centrosymmetric homodinuclear compounds where two bidentate hfac units are the bidentate capping ligands at each metal center and a bis-bidentate L molecule acts as a bridge. The values of the intramolecular metal···metal separation are 7.97 () and 7.82 Å (). Static (dc) magnetic susceptibility measurements were carried out for polycrystalline samples - in the temperature range 1.9-300 K. Curie law behaviors were observed for and , the downturn of χ in the low temperature region for being due to the zero-field splitting of the nickel(II) ion. Very weak [ = -0.247(2) cm] and relatively weak intramolecular antiferromagnetic interactions [ = -4.86(2) cm] occurred in and , respectively (the spin Hamiltonian being defined as = -·). Simple symmetry considerations about the overlap between the magnetic orbitals across the extended bis-bidentate L bridge in and account for their magnetic properties.