Functional metal-organic molecules and materials derived from rigid and flexible P-N scaffolds

GRAPHICAL ABSTRACT

Abstract

Employing phosphoramide ligands of formula, (RNH)₃PO in reaction with Pd(OAc)₂, a facile route to access the highly basic trianions, [(RN)₃PO]³⁻ ((X)³⁻) analogous to PO₄³⁻ ion were developed. The (X)³⁻ ligand, containing a central binding group, acts as a rigid cis-blocking ligand and stabilizes trimeric or prismatic Pd(II) clusters of formula {Pd₃X(OAc)₃}_{1 or 2}. Further, the trinuclear (Pd₃X)³⁺ motifs were utilized as supramolecular synthons for obtaining neutral cluster cages for Pd(II) ions in tetrahedral and cubic topologies via a bridging ligand substitution strategy. In contrast, phosphoramides containing peripheral metal binding groups provide a flexible ligand platform and yield multi-metallic assemblies in various dynamic architectures. By using pyridyl functionalized flexible dipodal phosphoramide ligand (L) we were able to generate interesting examples of centrosymmetric and noncentrosymmetric {Cu^IIL₂}_n frameworks. Investigation of the electric field-dependent polarization (P-E loop) of the noncentrosymmetric {Cu^IIL₂}_n frameworks leads to the observation of a potentially ferroelectric behavior in them that are governed by the counter anions and topology of the framework.

Keywords:

• Self-assembly
• metal-organic polyhedra
• metal-organic frameworks
• guest-encapsulation
• ferroelectric behavior
• dielectric constant

Funding

This work was supported by DST (SR/S1/IC-50/2012), India and IISER, Pune.