The chelating 2-pyridone ligand (E)-6-(1-((2-(methylthio)phenyl)imino)ethyl)pyridin-2(1H)-one (1) has been used to synthesize five
nickel(II) complexes that have been characterized by single-crystal
X-ray diffraction, UV/vis and IR spectroscopies, and benchtop magnetometry.
Reaction of NiX2 (X = BF4, Cl) with 1 yielded the C
2-symmetric halide-bridged
Ni dimers [(μ-F)Ni2(κN,N,O-1
–
)2(κN,N-1)2](BF4) (2) and [(μ-Cl)Ni2(κN,N,O-1
–
)2(κN,N-1
–
)(κN,N-1)] (3), where 2 is formed via a rare example
of fluoride abstraction from BF4
– by
a transition metal. Remarkably, the reaction of Ni(OAc)2 with 1 followed by different methods of crystallization
yielded three different products: the dimer [(μ-OH2)Ni2(κN,N,O-1
–
)(κN,N-1
–
)(κN,N-1)(OAc)2] (4), as well as the monomers [Ni(κN,N-1
–
)2(MeOH)2] (5) and [Ni(κN,N-1
–
)(κN,N-1)(OAc)(OH2)] (6). This observation is emblematic of the soft energy
landscape of coordination motifs and nuclearity that pyridone ligands
provide with late 3d transition metals. To better understand the solution
versus solid-state speciation, solid-state UV/vis reflectance and
solution-state UV/vis absorbance spectra were obtained. Surprisingly,
the solution-state UV/vis spectra of 4 and 6 each provided nearly identical absorption spectra (λmax ≈ 360 nm), which matched neither of the solid-state reflectance
spectra of 4 or 6 (λ ≈ 590,
790, 970 nm; 3A2g → 3T1g, 3A2g
→1E2g, and 3A2g → 3T2g, respectively). Rather, the solution spectra are consistent only
with the spectroscopic features (MLCT) of a conventional square-planar
Ni(II) species.
