| Summary: | Four new compounds of formulas [Cu(hfac)<sub>2</sub>(L)] (<b>1</b>), [Ni(hfac)<sub>2</sub>(L)] (<b>2</b>), [{Cu(hfac)<sub>2</sub>}<sub>2</sub>(µ-L)]·2CH<sub>3</sub>OH (<b>3</b>) and [{Ni(hfac)<sub>2</sub>}<sub>2</sub>(µ-L)]·2CH<sub>3</sub>CN (<b>4</b>) [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 <b>1</b> and <b>2</b> are isostructural mononuclear complexes where the metal ions [copper(II) (<b>1</b>) and nickel(II) (<b>2</b>)] are six-coordinated in distorted octahedral MN<sub>2</sub>O<sub>4</sub> 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 <b>3</b> and <b>4</b> 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 (<b>3</b>) and 7.82 Å (<b>4</b>). Static (dc) magnetic susceptibility measurements were carried out for polycrystalline samples <b>1</b>–<b>4</b> in the temperature range 1.9–300 K. Curie law behaviors were observed for <b>1</b> and <b>2</b>, the downturn of χ<sub>M</sub><i>T</i> in the low temperature region for <b>2</b> being due to the zero-field splitting of the nickel(II) ion. Very weak [<i>J</i> = −0.247(2) cm<sup>−1</sup>] and relatively weak intramolecular antiferromagnetic interactions [<i>J</i> = −4.86(2) cm<sup>−1</sup>] occurred in <b>3</b> and <b>4</b>, respectively (the spin Hamiltonian being defined as <b><i>H</i></b> = −<i>J<b>S</b></i><sub>1</sub>·<b><i>S</i></b><sub>2</sub>). Simple symmetry considerations about the overlap between the magnetic orbitals across the extended bis-bidentate L bridge in <b>3</b> and <b>4</b> account for their magnetic properties.
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