Heterometal–organic frameworks: Three novel copper(II)–lanthanide(III) 15-metallacrown-5 complexes based on pyrazinohydroxamic acid as new multiple-binding pentagonal platform

Abstract

Abstract Reactions of copper(II) sulfate or copper(II) perchlorate, samarium(III), erbium(III) or neodymium(III) nitrate (5/1 equiv.) with pyrazinohydroxamic acid (H 2 Pyzha) in H 2 O/MeOH led to three new heterobimetallic 15-metallacrown-5 complexes. In a MeOH/H 2 O solution, when adding inorganic salts, the ligands exist as protonated metallacrowns. In the solid state, their structures are more complicated as confirmed by X-ray analysis: metallacrown [Sm (H 2 O) 3 {Cu(pyzha)} 5 (H 2 O) 2 (MeOH) (HSO 4 ) 2 ]·(H 2 O) 2 ·(HSO 4 ) ( 1 ); [Nd(H 2 O) 2 (MeOH) {Cu(pyzha)} 5 (ClO 4 ) 2 (H 2 O) 5 (NO 3 )] ( 2 ); [Eu(H 2 O) 2 (MeOH) {Cu(pyzha)} 5 (ClO 4 ) 2 (H 2 O) 5 (NO 3 )] ( 3 ). The differentiation of atomic and ionic radii between the encapsulated lanthanide(III) could be used to control the bowl-shape distortion of the metallacrowns from the planar geometry. The complex 1 clearly exhibits fluorescence behavior of samarium(III), while 2 and 3 show that of copper(II) and ligand.