Reversible Switching of Electronic Ground State in a Pentacoordinated Cu(II) 1D Cationic Polymer and Structural Diversity

Two copper­(II) polymeric complexes
{[Cu­(HPymat)­(MeOH)]­(NO3)}n (1) and {[Cu4(Pymab)4­(H2O)4]­(NO3)4} (2) were synthesized with the carboxylate-containing Schiff-base ligands
HPymat– and Pymab– [H2Pymat = (E)-2-(1-(pyridin-2-yl)­methyleneamino)­terephthalic
acid, HPymab = (E)-2-((pyridine-2-yl)­methyleneamino)­benzoic
acid]. Complex 1 is a one-dimensional Cu­(II) cationic
polymeric complex containing free protonated carboxylic groups and
nitrate anions as counterions. Complex 2 is a zero-dimensional
tetranuclear cationic Cu­(II) complex containing nitrate anions as
counterions. Complex 1 shows rhombic electron paramagnetic
resonance (EPR) spectra in the solid state at room temperature (RT)
and 77 K and tetragonal EPR spectra in dimethyl sulfoxide (DMSO) and
dimethylformamide (DMF) and “inverse” EPR spectrum in
CH3CN. Complex 2 shows rhombic EPR spectra
in the solid state at RT and 77 K. But complex 2 shows
tetragonal spectra in DMSO, DMF, and CH3CN. Thermogravimetric
analysis was also performed for both complexes 1 and 2. Mean-square displacement amplitude analysis was carried
out to detect librational disorder along the metal–ligand bonds
in crystal structures.