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

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 {CuIIL2}n frameworks. Investigation of the electric field-dependent polarization (P-E loop) of the noncentrosymmetric {CuIIL2}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.