Helical Homometallic Trinickel String Complexes with Mixed Hard Nitrogen and Sulfur Donors: Structural and Magnetic Studies

Abstract

Abstract A new tridentate and rigid ligand containing S,N-hetero donor, the 1H-1,8-naphthyridine-2-thione (Hnpt), is designed and developed to build up the first homonuclear nickel string supported by the mixed-donor ligands. Three asymmetric nickel strings possessing the structural feature of the (4,0) configuration are synthesized, namely the (4,0)-Ni3(npt)4(NCS) (1), (4,0)-[Ni3(npt)4(NCS)](PF6) (2) and (4,0)-Ni3(npt)4(NCS)2 (3). Due to the nature of the naphthyridyl group and sulfur donor, complex 1 is composed of one stabilized mixed-valent unit [Ni2]3+ and one low spin nickel thiolate. 1 and 2 are the quasi-1D coordination polymers in the solid-state, in which the molecules are linked by the weak intermolecular Ni⋯SCN interactions. 2 and 3 possess the same Ni36+ oxidized state with the different donation of axial ligands. The weaker donor in 2 yields the low spin state in the middle Ni(II). The stronger axial donor and the rigidity of ligand in 3 lead to the change of torsion angle, creating the unprecedented high spin Ni(II) inside the nickel string. This high spin Ni(II) with the square planar geometry is an unusual structure and magnetism among nickel strings. Detailed magnetic studies allow us to establish the spin state of each nickel in these three complexes. Besides, three different torsion angles with the same ligand and metal provide us with an opportunity to examine the factors governing the helicity of rigid ligands.