Tetradentate N2O2 ligand
Diamine-based complexes
X-ray crystallography
Solvent-driven geometry transformation
DFT studies
Nonlinear optical properties
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The design of coordination compounds with solvent-responsive optical properties remains a central challenge in
molecular photonics. Here, we describe the synthesis and full characterisation of a symmetrical tetradentate
diamine ligand, 3,3′-((1,2-phenylenebis(azanediyl))- bis(methanylylidene))bis(pentane-2,4-dione) (H₂L), and its
neutral square-planar complexes [M(L)] (M(II) = Co, Ni, Cu). The Cu(II) complex crystallised as [Cu(L)]⋅0.5
(pyrazine), adopting a nearly square-planar geometry (τ₄ = 0.06) in the solid state, as confirmed by single-crystal
X-ray diffraction. In DMSO solution, UV–Vis spectra revealed reversible axial coordination of two solvent molecules,
driving a transformation to a distorted octahedral geometry. Struc
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