Photochromism in oxalatoniobates.

Addition of 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen) or 2-aminopyridine (2-NH2-py) to aqueous solutions of (NH4)[NbO(C2O4)2(H2O)2]·3H2O (Nb-Ox) yields tris-oxalate complexes (bpyH2)(bpyH)[NbO(C2O4)3]·2H2O (1), (phenH)3[NbO(C2O4)3]·3H2O (2), and (2-NH2-pyH)3[NbO(C2O4)3]·2H2O (3), which were characterised by XRD, IR and EA. Bipyridinium salt 1 demonstrates remarkable photoactivity even under irradiation by daylight. The nature of the photoactivity was studied by diffuse reflectance (DR) spectroscopy, ESR and quantum-chemical calculations.