Structural Variety of Isopropyl-bis(2-picolyl)amine Complexes with Zinc(II) and Copper(II)

Abstract

A variety of structurally different complexes of the isopropyl-bis(2-picolyl)amine (iPr-bpa) ligand were prepared with ZnA2 and CuA2 salts (A = Br–, Br–/PF6–, BF4–/F–, ClO4–). The choice of different counterion affected the stoichiometry, coordination number, geometry, and formation of geometrical isomers. Crystal structures of four Zn(II) complexes, namely, two monomers (mer-[Zn(iPr-bpa)Br2] and fac-[Zn(iPr-bpa)Br2]), one F–-bridged dimer ([Zn2(μ-F)2(iPr-bpa)2](BF4)2), and one ML2 complex ([Zn(iPr-bpa)2](ClO4)2) were determined, and their solution structures were studied by NMR spectroscopy. For the ML2 complex, relative stabilities of geometrical isomers were determined using density functional theory calculations. For Cu(II) complexes, five crystal structures were determined, namely, two monomers ([Cu(iPr-bpa)Br2] and [Cu(iPr-bpa)(ClO4)2(H2O)]), a Br–-bridged dimer ([Cu2(μ-Br)(Br)2(iPr-bpa)2](PF6)), a F–-bridged coordination polymer ([Cu(μ-F)(iPr-bpa)]n(BF4)n × nCH3OH), and a cyclic, CO32–-bridged trimer ([Cu3(tri-μ-CO3)(ClO4)3(iPr-bpa)3](ClO4)). The different crystallographic structures of Cu(II) complexes are reflected in their different magnetic properties investigated by electron spin resonance spectroscopy and magnetic susceptibility measurements.