New polynuclear compounds based on N-methyliminodipropionic acid: Solution studies, synthesis and X-ray crystal structures

Abstract

Six new polynuclear coordination compounds based on 3d transition metal ions (Cu(II), Ni(II)) and Zn(II) with the flexible dicarboxylate compound N-methyliminodipropionic acid (H2midp) were prepared and characterized by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction. Four of these compounds are 1D coordination polymers, namely [Cu(midp)(H2O)] (1), [Cu3(midp)2(H2O)4](NO3)2·6H2O (2) [Cu3(midp)2(H2O)4](CF3SO3)2·4H2O (3) and [NaZn(Hmidp)2](CF3SO3) (6). The structural analysis revealed that the chain structure of 1 is composed of [Cu(midp)(H2O)] units connected by the free carboxylato oxygen atom of neighbor units, in an alternate fashion. In 2 and 3, on the other hand, there are two [Cu(midp)H2O] units, connected by a central Cu(II) ion coordinating again to the free oxygen atom of the carboxylato groups. The Zn(II) compound is heteronuclear and the complex adopts a 1D cationic polymeric structure with zinc and sodium ions connected by two Hmidp– anions. The two other compounds are dinuclear, [Cu2(Hmidp)2(μ-H2O)2(H2O)2](CF3SO3)2·6H2O (4) and ([Ni2(midp)2(H2O)4] (5). Additionally, a Co(II) and a Cu(II) coordination compound were obtained with the same ligand and characterized by IR spectroscopy, thermal analysis and elemental analysis including metal quantification. For the copper compound the formula [Cu(Hmidp)](ClO4)·3H2O (7) is proposed while for the Co(II) compound (8) the proposed formula is [Co(midp)(H2O)2]. Solution studies of the ligand–M(II) systems (M(II) = Mn, Fe, Co, Ni, Cu, Zn, Cd and Pb) were also carried out in order to help the selection of the best synthetic conditions and also to complement the structural knowledge in the exploration of the potential formation of coordination polymers in these systems.