Metal String Complexes: Synthesis, Crystal Structures and Magnetic Properties of Heptanuclear Nickel(II) Complexes, [Ni₇(μ₇‐teptra)₄X₂] (teptra = tetrapyridyltriamido, X = Cl⁻, NCS⁻)

Abstract

Abstract The synthesis, crystal structures and magnetic properties of linear heptanuclear nickel(II) complexes [Ni 7 (μ 7 ‐teptra) 4 X 2 ], (teptra = tetrapyridyltriamido), with the axial ligand X = Cl − ( 1 ), NCS − ( 2 ), are reported. The hepta‐nuclear metal chain is helically wrapped by four syn‐syn‐syn‐syn‐syn‐syn teptra 3− ligands. Both of the [Ni 7 (μ 7 ‐teptra) 4 ] 2+ moiety are isostructural involving a Ni 7 linear chain unit with all of the ∠Ni‐Ni‐Ni being 180°, terminated by two axial ligands. Three types of NiNi distances are found in these complexes. The longest ones bonded with the axial ligands are 2.383(1), 2.374(2) and 2.375(2), 2.354(2), and the intermediate ones are 2.310(1), 2.304(1) and 2.300(2), 2.303(2) Å for ( 1 ) and ( 2 ), respectively. The innermost NiNi distances are the shortest ones with the distances of 2.226(2), 2.214(2) and 2.194(2), 2.206(2) Å for ( 1 ) and ( 2 ), respectively. Two terminal Ni(II) ions bonded with the axial ligands are in a square‐pyramidal (NiN 4 X) environment and exhibit long NiN bonds (−2.10 Å) which are consistent with a high‐spin Ni(II) configuration. The inner five Ni(II) ions displayed short NiN (∼1.90 Å) bond distances which are consistent with a square‐planar (NiN 4 ), diamagnetic arrangement of a low‐spin Ni(II) configuration. The magnetic measurement of ( 1 ) shows an antiferromagnetic interaction of two terminal high‐spin Ni(II) ions with the coupling constant J = −3.8 cm −1 . The NiNi, NiN distances and magnetic behavior among tri‐, penta‐, and hepta‐nickel(II) complexes are compared and discussed.