Organo-Functionalized Polyoxometalates

Abstract

Polyoxometalates (POM) or transition metal oxide clusters are a sub-class of metal oxide-based materials of contemporary interest. POMs are molecular systems which contain highly symmetrical structures and are characteristics of group 5 and 6 metals, especially V, Mo, and W. Typical POM clusters have nuclearities ranging from 6 to 18 metal centers and are purely inorganic in their compositions. POMs can act as multielectron redox systems, while retaining their robust oxometallic framework structure. POMs have been receiving increasing attention, in part due to their potential as redox active materials for applications in various areas and their suitability as attractive molecular building units for making new functional materials of desirable properties and functions. In recent years, there has been a growing interest in the functionalization of polyoxometalates with organic moieties to synthesize organo-functionalized POMs. During the course of the work described in this thesis, we explored the synthesis of organo-functionalized polyoxometalates with special interest in polyoxovanadates incorporating heterometal center(s) in addition to vanadium in the structure. The focus of the work was on low nuclearity POMs. The thesis describes the synthesis and full characterization of a new organo-functionalized polyoxovanadate cluster - [(n-C4H9)4N]2[V6O13{(OCH2)3C (CH2CH3)}2]. The cluster compound has been characterized by a series of analytical techniques- FT-IR, Thermo Gravimetric Analysis, Bond Valence Sum calculations and complete single X-ray diffraction structure analysis. The hexavanadate cluster features {V6O19} oxometallate core composed of six edge sharing {VO6} octahedra defined by five bridging oxygen atoms and a terminal {V=Ot} oxo group. The {V6O19} oxometallic core of the cluster adopts the Lindqvist structure incorporating two 1,1,1-tris(hydroxymethyl)propane organic ligands. Six of the oxygens in the {V6O19} core come from the three alkoxy groups from two organic ligands. To the best of our knowledge, this organo-functionalized POM cluster has not been reported in the literature previously.