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-κO,O')lanthanide]-bis{μ-N,N'-bis[(1-oxidopyridin-1-ium-3-yl)methyl]-1,8:4,5-naphthalenetetracarboxdiimide-κO:O'}-[tris(nitrato-κO,O')lanthanide]-μ-N,N'-bis[(1-oxidopyridin-1-ium-3-yl)methyl]-1,8:4,5-naphthalenetetracarboxdiimide-κO:O'] methanol disolvate], {[Ln(CHNO)(NO)]·CHOH}, 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.