A new family of single-pocket metal complexes bearing
O,N,O-tridentate
and O,N-bidentate chelating members {Cu, 1b (P21/n); Ni, 1c (C2/c); Mn, 1d (I2/a); Cu, 2b; and Ni, 2c (both P21/c)}, starting
from synthesized and fully characterized Zn(II) (1a; I2/a) and Cu(II) (2a; C
2) precursors, were conveniently prepared via
cation-induced solvent-assisted and ligand-induced solvent-assisted
transformations. Herein, we show multistep solvent-assisted transformations
from cis-1a → trans-1b → cis-1c → cis-1d, as well as all-trans
2a → 2b → 2c. All processes are one-way irreversible, as substantiated by thermodynamic
aspects (enthalpies based on Gibbs free energies) derived from density
functional theory calculations. On the other hand, complex 2a′ (C2/c; a polymorphic form of 2a) was obtained through a routine synthetic procedure. The
compounds have been established by various spectroscopic techniques
(infrared, UV–vis, ESI-MS, 1H, and 13C NMR), elemental analysis, and X-ray crystallography. Single-crystal
X-ray studies reveal that complexes 1a–d exhibit a pseudo-octahedral geometry around each metal center, with 2a displaying a four-coordinate seesaw geometry Cu(II) sphere
(Addison parameter; τ = 0.42), while 2a′ (τ = 0.00), 2b (τ = 0.00), and 2c (τ = 0.00) possess a perfect square-planar configuration around
each metal center. Furthermore, distortion is stabilized by the presence
of peripheral O-donor atoms from the bulky −OMe group, and
by virtue of its size, increased bond lengths and angles are accommodated.
Ligand substitution induced coordination geometry transformation from
quasi-square-planar 2a to perfect square-planar 2b. Assessment of the metric parameter shows that the distances
between the two Cu–Omethoxy are all largely positive
due to Jahn–Teller distortion, indicating an unprecedented
tetragonal bipyramidal geometry in 1b.
