Four isostructural lanthanide(III) coordination compounds based on a new N-oxydic pyridyl naphthalenediimide ligand: synthesis and characterization

Naphthalenediimides, an attractive class of electron-deficient organic dyes with rich redox and photoredox properties, have been investigated extensively as building blocks for coordination networks or metal–organic frameworks in recent decades. However, most of the available work has focused on d-block metal cations rather than f-block lanthanide ions, whose complexes exhibit a large variability in coordination numbers. In this article, four coordination polymers composed of naphthalenediimides and lanthanide cations, namely catena-poly[[[tris(nitrato-κ2 O,O′)lanthanide]-bis{μ-N,N′-bis[(1-oxidopyridin-1-ium-3-yl)methyl]-1,8:4,5-naphthalenetetracarboxdiimide-κ2 O:O′}-[tris(nitrato-κ2 O,O′)lanthanide]-μ-N,N′-bis[(1-oxidopyridin-1-ium-3-yl)methyl]-1,8:4,5-naphthalenetetracarboxdiimide-κ2 O:O′] methanol disolvate], {[Ln(C26H16N4O4)1.5(NO3)3]·CH3OH} n , with Ln = Eu, 1, Gd, 2, Dy, 3, and Er, 4, have been successfully synthesized under hydrothermal conditions. Single-crystal X-ray diffraction analyses revealed that the four compounds are isomorphic and that each asymmetric unit contains one nine-coordinated Ln centre, one and a half diimide ligands, three nitrate anions and one uncoordinated methanol molecule. In addition, each metal centre is surrounded by nine O atoms in a distorted tricapped trigonal–prismatic geometry. Two centres are bridged by two cis ligands to form a ring, which is further bridged by trans ligands to generate one-dimensional chains. Neighbouring chains are stacked via π–π interactions between pyridine rings to give a two-dimensional structure, which is stabilized by π–π interactions between naphthalene rings, forming the final three-dimensional supermolecular network. Solid-state optical diffuse-reflectance spectral studies indicate that compound 4 is a potential wide band gap semiconductor.