Oxalato as polyatomic coordination center and magnetic coupler in copper(II)-polypyrazole inverse polynuclear complexes and coordination polymers

•State-of-the-art on oxalato-centered copper(II)-polypyrazole inverse coordination chemistry.•Oxalato as centroligand and magnetic coupler for copper(II) inverse coordination chemistry.•Oxalato-centered inverse dicopper(II) complexes as ground tests for magnetic coupling phenomenon.•Magneto-structural correlations in oxalato-centered copper(II) inverse coordination polymers.•Vapochromic and magneto-switching in oxalato-centered copper(II) inverse metal–organic frameworks.