Control of magnetic spin states by various mixed anionic ligands in trinickel complexes: synthesis, crystal structures and physical properties

Abstract

This study provides an opportunity to control the magnetic spin of nickel atoms using various mixed anionic ligands. A series of linear trinickel complexes supported by two kinds of ligands, oligo-α-pyridylamido and sulfonyl amido/amido, were synthesized and their structures were determined by X-ray diffraction. The three nickel atoms of [Ni₃(Lpts)₂(dpa)₂] (1) (dpa⁻ = dipyridylamido, Lpts²⁻ = N,N′-bis(p-toluenesulfonyl)pyridyldiamido) display short Ni–N (∼1.90 Å) bond distances, which are consistent with a low spin state of Ni(II) ions, and exhibit spin states of (0, 0, 0) for the three Ni(II) ions. One of the terminal Ni(II) ions of [Ni₃(Lms)₂(dpa)₂(H₂O)] (2) (Lms²⁻ = N,N′-bis(4-methylsulfonyl)-pyridyldiamido) and [Ni₃(Lpts)₂(pepteaH₂)] (4) (pepteaH₂²⁻ = pentapyridyldiamidodiamine) bonded with an axial ligand exhibits a square pyramidal (NiN₄X) geometry with long Ni–N bond distances (∼2.10 Å) which are consistent with a high spin Ni(II) configuration. The spin states of these trinickel complexes are (1, 0, 0). Complex 2 and 6 can be interchanged by the removal or addition of an axial water molecule. The structural features of 6 are comparable with those of 1. Both the terminal Ni(II) ions in [Ni₃(LAc)₂(dpa)₂] (3) (Lac²⁻ = N,N′-biacetyl-pyridyldiamido) are in square pyramidal geometry and exhibit high spin. The spin states of the nickel ions in 3 are (1, 0, 1), and the two terminal nickel ions exhibit antiferromagnetic interactions. The molecular structure of [Ni₃(Lpts)₂(dpa)₂](BF₄) (5), which was obtained by the one-electron oxidation of 1, is similar to those of the neutral analogue 1, except for the presence of a counter anion to compensate for the positive charge on the Ni₃ core. All of the Ni–Ni bond lengths of 5 are slightly shorter (ca. 0.05 Å) than those in the neutral analogues. This is attributed to the formation of partial Ni–Ni bonding.