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)(2)(L)] (1), [Ni(hfac)(2)(L)] (2), [{Cu(hfac)(2)}(2)(mu-L)]center dot 2CH(3)OH (3) and [{Ni(hfac)(2)}(2)(mu-L)]center dot 2CH(3)CN (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 MN2O4 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 center dot center dot center dot metal separation are 7.97 (3) and 7.82 angstrom (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 chi T-M 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 = -JS(1)center dot 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.

Automated summary

Four new compounds have been synthesized and characterized, including two isostructural mononuclear complexes and two centrosymmetric homodinuclear compounds. Their magnetic properties were studied using static magnetic susceptibility measurements, revealing different behaviors due to the nature of the metal ions and ligands involved.