Tetranuclear complexes composed of dinickel(II) macrocyclic fragments bridged by 5,5′-(1,3-phenylene)bis-1H-tetrazolato and N,N-bis(tetrazol-5-ato)amine coligands: Synthesis, structures and magnetic properties

The dinuclear nickel(II) complex [Ni2LCl]+, where L2− represents a 24-membered macrocyclic hexamine-dithiophenolate ligand, reacts with 5,5′-(1,3-phenylene)bis-1H-tetrazole and N,N-bis(tetrazol-5-yl)amine to give the tetranuclear complexes [(Ni2L)2(N4C–X–CN4)]+, where X = 1,3-C6H4 (1) and NH (2). The new complexes were both isolated as perchlorate or tetraphenylborate salts and characterized by elemental analysis, UV/Vis, IR spectroscopy, and X-ray analysis. The crystal structures of the tetraphenylborate salts show bridging bistetrazolato moieties joining two dinuclear [Ni2L]2+ fragments through their ring N2 and N3 atoms. Temperature-dependent magnetic susceptibility measurements reveal the presence of weak ferromagnetic exchange interactions between the NiII ions in the binuclear [Ni2L]2+ subunits with magnetic exchange coupling constant values of J1 = 16.6 cm−1 for 1[BPh4]2, and J1 = 16.8 cm−1 for 2[BPh4]2 (H = –2JS1S2). The exchange coupling constant J2 across the bistetrazolato bridge in both compounds is less than 0.1 cm−1, which suggests that no significant interdimer coupling occurs across the linking tetrazolato moieties.

The synthesis and characterization of novel tetranuclear nickel(II) complexes by self-assembly of dinuclear Ni2 subunits and bistetrazolato bridges has been achieved. The complexes exist as stable and discrete complexes in solution and in the solid state. In the Ni4 cluster, the magnetic properties are due to the two [Ni2L]2+ units which were found to behave as isolated paramagnetic units with weak ferromagnetic exchange interactions between the spins of the Ni(II) ions.Figure optionsDownload as PowerPoint slide