Synthesis, structure, magnetism, and electrochemical properties of a linear pentanuclear Ni5 compound derived from an oligo--pyridylamino ligand: Ni5(-dmpdda)4(NCS)2

Abstract

The synthesis, crystal structures, electrochemical, and magnetic properties of a linear pentanuclear Ni5 compound derived from an oligo--pyridylamino ligand, [Ni5(-dmpdda)4(NCS)2] [dmpdda-H2 = N,N'-di(4-methylpyridin-2-yl)pyridine-2,6-diamine], are reported. Ni5(-dmpdda)4(NCS)2 involve a Ni5 linear chain unit with all of the Ni-Ni-Ni angles being nearly 180 degrees, terminated by two axial ligands. The pentanuclear linear metal chain is helically wrapped by four syn-syn-syn-syn type dmpdda2- ligands. There are two types of Ni-Ni distances in this complex. Terminal Ni-Ni distances bonded with the axial ligand are longer (2.377 angstrom); the inner Ni-Ni distances are short at 2.2968 angstrom. Terminal Ni(II) ions bonded with the axial ligands are square-pyramidal (NiN4NCS) with long Ni-N bonds (2.092 angstrom), consistent with a high-spin Ni(II) configuration. The inner three Ni(II) ions have short Ni-N (1.901-1.925 angstrom) bond distances, consistent with a square planar (NiN4), diamagnetic arrangement of a low-spin Ni(II) configuration. This compound exhibits magnetic behavior similar to [Ni5(-tpda)4(NCS)2], indicating an antiferromagnetic interaction of two terminal high-spin Ni(II) ions.