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

Abstract

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