Triangular Nickel Complexes Derived from 2‐Pyridylcyanoxime: An Approach to the Magnetic Properties of the [Ni₃(μ₃‐OH){pyC(R)NO}₃]²⁺ Core

Abstract

A series of nickel complexes with nuclearity ranging from Ni(3) to Ni(6) have been obtained by treatment of a variety of nickel salts with the 2-pyridylcyanoxime ligand. The reported compounds have as a common structural feature the triangular arrangement of nickel cations bridged by a central μ(3)-oxo/alkoxo ligand. These compounds are simultaneously the first nickel derivatives of the 2-pyridylcyanoxime ligand and the first examples of isolated, μ(3)-O triangular pyridyloximate nickel complexes. Magnetic measurements reveal antiferromagnetic interactions promoted by the μ(3)-O and oximato superexchange pathways and comparison of the experimental structural and magnetic data with DFT calculations give an in-depth explanation of the factors that determine the magnetic interaction in this kind of system.

NiII‐Pyridyloximato Triangles with a Central μ3‐OH Ligand: Magnetostructural Correlations

“…In good agreement with previous DFT calculations,6b the isosceles response of the magnetic interactions and structural data from Table 4 suggest that the Ni–O–Ni bond angles correlate with the magnitude of the coupling constants whereas there is no evident correlation with the Ni–O–N–Ni torsion angles. This becomes evident in Figure 7, which shows a linear dependence of J with the Ni–O–Ni bond angle, whereas the plot of J as a function of the Ni–O–N–Ni torsion angle shows very different values of J for similar torsion angles and similar J values for any torsion.…”

“…Complexes 1 and 2 are close to magnetically frustrated triangles, whereas complex 3 is an unusual example of an equilateral axial triangle with three‐fold symmetry and the S = 0 ground state. Correlation of the magnetostructural parameters of these three new examples of μ 3 ‐OR/oximato‐Ni 3 isolated triangles and the previously reported6b [Ni 3 (MeOH) 2 (BzO)(OH)(py{CN}NO) 4 ] ( 4 ) and the linked triangles (NEt 3 H){μ 1,5 ‐N(CN) 2 }[Ni 6 (H 2 O)(MeOH)(3‐ClBzO) 2 (OH) 2 (py{CN}NO) 8 ] ( 5 ) has confirmed that the Ni–O–Ni bond angles involving the central RO – bridge are the main factors influencing the magnitude of the superexchange interaction, as was predicted by DFT calculations.…”

“…The key structural parameters and calculated exchange coupling constants for 1 – 3 and the previously reported systems6b [Ni 3 (MeOH) 2 (BzO)(OH)(pyC{CN}NO) 4 ] ( 4 ) and (NEt 3 H){μ 1,5 ‐N(CN) 2 }[Ni 6 (H 2 O)(MeOH)(3‐ClBzO) 2 (OH) 2 (pyC{CN}NO) 8 ] ( 5 ) are listed in Table 4. Complexes 1 , 2 , 4 and 5 have a common isosceles core with one additional syn ‐ syn carboxylato bridge on one side, whereas the sides of 3 are defined exclusively by oximato bridges in an equilateral arrangement.…”

“…The magnetic response of these small molecules is useful for determining univocally the factors that influence the magnetic coupling and, in some cases, for studying phenomenon such as spin frustration. Note, isolated triangles with the {Ni 3 (μ 3 ‐OR)(pyC{R′}NO) 3 } n + core were unprecedented and only very recently have two examples been reported by our group together with DFT calculations to determine the factors that influence the superexchange pathway in the nickel case 6b…”

Jaguar: A high‐performance quantum chemistry software program with strengths in life and materials sciences

“…To compute J, it is therefore very important to be able to tune not only the multiplicity on the different metal centers but also the relative orientation of their net spin (i.e., ferromagnetic or antiferromagnetic coupling). Such a fine tuning is possible in the initial guess algorithm employed in Jaguar, and it is therefore often used in such cases …”