Synthesis and structure of mono- and binuclear copper(II) complexes with polyfunctional nitroxide 4-(1′carboxy-2′-oxopropylidene)-2,2,5,5-tetramethyl-3-imidazolidine-1-oxyl, [Cu(LH)2(H2O)2] and [Cu2L2(H2O)5]. Caterpillar-like reaction