Molecular Minerals™: Lyophillic Colloids for Ceramists

Abstract

This paper will focus on a novel class of inorganic compounds that we term as molecular minerals™ (MMs). MMs are clusters of ceramic fragments encapsulated with organic ligands. These compounds can be crystallized from solution as molecular single crystals and have well‐defined crystal structures that can be described with X‐ray diffraction methods. Most importantly, the ceramic clusters are perfectly monodisperse, and conventional synthetic techniques can be applied to facilitate control of size and composition. The organic encapsulate imparts solubility in organic solvents and polymers. More importantly, the solubility is thermodynamically driven to form a single‐phase system. Thus, unlike nanoparticles, the stability of clusters in solution is spontaneous rather than kinetically derived. A critical tool for creating MMs is a firm understanding of the fundamental issues governing cluster structure and stability. We have demonstrated a unique synthetic approach to these materials, capable of creating materials with oxo, sulfido, selenido, or tellurido ligands, whose ceramic fragment size can currently be varied from about 0.5 to 2 nm. Both homometallic and heterometallic lanthanide (Ln) complexes incorporating the group 12 metals Zn, Cd, and Hg have been prepared. Relative to prior work on metal organic or organometallic Ln complexes, MMs have unprecedented luminescent properties in terms of emission wavelength, emission intensity, and quantum efficiency. These materials match or exceed the luminescent properties of ceramics, glasses, and nanomaterials, while having the additional advantage of polymer solubility. Solubility facilitates the preparation of transparent molecular mineral nanocomposites that can be fabricated as bulk polymers, fibers, and films.