Crystal Structure and Band Gap Engineering in Polyoxometalate-Based Inorganic–Organic Hybrids

We have demonstrated engineering
of the electronic band gap of the hybrid materials based on POMs (polyoxometalates),
by controlling its structural complexity through variation in the
conditions of synthesis. The pH- and temperature-dependent studies
give a clear insight into how these experimental factors affect the
overall hybrid structure and its properties. Our structural manipulations
have been successful in effectively tuning the optical band gap and
electronic band structure of this kind of hybrids, which can find
many applications in the field of photovoltaic and semiconducting
devices. We have also addressed a common crystallographic disorder
observed in Keggin-ion (one type of heteropolyoxometalate [POMs])-based
hybrid materials. Through a combination of crystallographic, spectroscopic,
and theoretical analysis of four new POM-based hybrids synthesized
with tactically varied reaction conditions, we trace the origin and
nature of the disorder associated with it and the subtle local structural
coordination involved in its core picture. While the crystallography
yields a centrosymmetric structure with planar coordination of Si,
our analysis with XPS, IR, and Raman spectroscopy reveals a tetrahedral
coordination with broken inversion symmetry, corroborated by first-principles
calculations.