A new Cu(II) [12]metallocrown-4 pentanuclear complex based on a Cu(II)-malonomonohydroxamic acid unit

The first example of a CuII) [12]-MC-4 hydroxamic metallacrown compound containing a carboxyl group as a supporting donor function is described. The solution equilibria of malonomonohydroxamic acid (MACZ, H2L) with Cu(n) are investigated in aqueous solution using a combination of potentiometry, UV-vis absorption spectrophotometry, EPR spectroscopy and ESI mass spectrometry. Among the four complexes fitting the best speciation model ([CuL], [CU5L4H-4]2-, [CuL2]2- and [CuL2H_ 113-), a pentameric metallacrown molecule of composition Cu : L = 5 : 4 predominates in solution over the pH 4 to I I range, and the corresponding complex was isolated in the solid state. The crystallization of the complex [CU5L4H-4]2- in the presence of [Cu(en)2(H20)2]2+ cations resulted in the isolation of [Cu(en)(2)(H2O)(2)]n[Cu(en)(2)(H2O)(mu-H20){CU5(L4H-4)(H2O)(3)}(2)]n center dot 2on H2O (1), whose crystal structure has been determined by X-ray analysis. The structure of 1 consists of centrosymmetric complex cations [Cu(en)2(H20)2]21, infinite complex anionic chains [Cu(en)2(H20)( t-1-120)ICUAL4H-4)(1120)312 b2- and solvate water molecules. Within the complex anionic chains, the decanuclear double-decked bis([12]-MC-4) complex anions JCU5(L4H-4)(H20)3J2 4- are united by the [Cu(en)2(H20)2]2+ complex cations due to the bridging function of the axial water molecule 0(5). The magnetic behaviour of 1, studied in the temperature range 1.8-300 K, suggests the presence of both antiferromagnetic and ferromagnetic contributions to the observed magnetic susceptibility, resulting in a ground state of S = 2 per formula unit.