Synthesis and Solid-State Structural Characterization of a Series of Aqueous Heterometallic Tridecameric Group 13 Clusters

The synthesis and solid-state characterization
of a complete series of new heterometallic aqueous nanoscale Ga/In
tridecameric clusters is presented. These hydroxo–aquo species
significantly expand the library of discrete, aqueous group 13 clusters.
This report details the synthetic and structural characterization
of these compounds, which are of interest as precursors (inks) for
thin-film oxides with materials applications. Single-crystal X-ray
diffraction (XRD) data show that the hexagonal unit cell lengths of
these clusters fall within the range a, b = 20.134–20.694 Å and c = 18.266–18.490
Å. The unit cell volumes become larger (V =
6494–6774 A3) with increasing indium occupancy.
The compositions of several Ga/In clusters determined by electron
probe microanalysis and elemental analysis are in agreement with single-crystal
XRD results. The transformation of the Ga/In clusters to metal oxides
at high temperature was studied using variable-temperature powder
XRD. With heating, the Ga/In clusters with lower indium occupancies
convert to the β-Ga2O3 structure. For
clusters with higher indium occupancies, phase separation occurs,
and an In2O3 bixbyite-type structure forms.
The stoichiometric control at the molecular level demonstrated herein
is important in designing functional thin films of metal oxides due
to the tunable nature of these heterometallic solution precursors.
In addition, information about the solid-state structure of these
compounds leads to a fundamental understanding of the materials properties
of these clusters for future thin-film and precursor development.