Maleamate(–1) and Maleate(–2) Copper(II)–2,2′‐Bipyridine Complexes: Synthesis, Reactivity and Structural and Physical Studies

Abstract

AbstractA systematic investigation of the 1:2:1:2 Cu(NO3)·2.5H2O/H2L/bpy/LiOH·H2O (H2L = maleamic acid) reaction system in MeCN/H2O was carried out. The compounds [Cu2(HL)2(bpy)2(H2O)2](NO3)2 (1), [Cu2(HL)2(bpy)2(H2O)2](NO3)2·2H2O (1·2H2O), [Cu2Li2(L′)2(bpy)2(H2O)6][Cu2(HL)2(bpy)2(H2O)2](NO3)4 (2), [Cu4(L′)2(NO3)2(bpy)4(H2O)2](NO3)2·2H2O (3·2H2O) and [Cu(L′)(bpy)]n·2nH2O (4·2nH2O) were isolated, depending on the crystallization method employed. Complexes 2, 3·2H2O and 4·2nH2O contain the maleate(–2) anion (L′2–), which was formed in situ through metal‐ion‐assisted hydrolysis of the primary amide group of H2L. Efforts to prepare complex 3 from the direct use of maleic acid (H2L′) afforded compounds 4·2nH2O, [Cu4(L′)2(NO3)2(bpy)4(H2O)2](NO3)2·2[Li(NO3)(H2O)3]·4H2O (5·4H2O) and [Cu(NO3)(bpy)(H2O)3](NO3) (6) from the 1:1:1:2 Cu(NO3)·2.5H2O/H2L′/bpy/LiOH·H2O reaction system in MeCN/H2O. The maleamate(–1) ligand presents the less common η1:μ2 coordination mode in the cations of 1, 1·2H2O and 2. The maleate(–2) ligand exhibits the η1:η1:η1:η1:μ3 coordination mode in the [CuII4] cations of 3·2H2O and 5·4H2O and in the [CuII2LiI2] heterometallic cation of 2. The crystal structures of the complexes are stabilized by various H‐bonding patterns. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands. Magnetic susceptibility measurements for 3·2H2O reveal weak ferromagnetic interactions along the periphery of the Cu4 rhombus (J = 3.3 cm–1, –2JijSiSj Hamiltonian formalism), which stabilizes an S = 2 ground state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)