Structural and Spectroscopic Studies of Nickel(II) Complexes with a Library of Bis(oxime)amine-Containing Ligands

A library of tripodal amine ligands with two oxime donor arms and a variable coordinating or noncoordinating third
arm has been synthesized, including two chiral ligands based on l-phenylalanine. Their Ni(II) complexes have
been synthesized and characterized by X-ray crystallography, UV−vis absorption, circular dichroism, and FTIR
spectroscopy, mass spectrometry, and room-temperature magnetic susceptibility. At least one crystal structure is
reported for all but one Ni/ligand combination. All show a six-coordinate pseudo-octahedral coordination geometry
around the nickel center, with the bis(oxime)amine unit coordinating in a facial mode. Three distinct structure types
are observed:  (1) for tetradentate ligands, six-coordinate monomers are formed, with anions and/or solvent filling
out the coordination sphere; (2) for tridentate ligands, six-coordinate monomers are formed with NiII(NO3)2, with
one monodentate and one bidentate nitrate filling the remaining coordination positions; (3) for tridentate ligands,
six-coordinate, bis(μ-Cl) dimers are formed with NiIICl2, with one terminal and two bridging chlorides filling the
coordination sphere. The UV−vis absorption spectra of the complexes show that the value of 10 Dq varies according
to the nature of the third arm of the ligand. The trend based on the third arm follows the order alkyl/aryl < amide
< carboxylate < alcohol < pyridyl < oxime.