Synthesis and Structural Characterization of ... - Jacobs University

Chapter 2
Experimental
2.2 Instrumentation
2.2.1 Fourier transform infrared spectroscopy
Infrared spectra with 4 cm -1
resolution were recorded on a Nicolet Avatar 370 FT-IR
spectrophotometer as KBr pellet samples. The following abbreviations were used to assign the
peak intensities: w = weak; m = medium; s = strong; vs = very strong; b = broad; sh =
shoulder.
2.2.2 Single crystal X‐ray diffraction
The crystals were mounted in Hampton cryoloops using light oil for data collection at 173 K.
Indexing and data collection were performed using a Bruker X8 APEX II CCD diffractometer
with kappa geometry and MoK α radiation (λ = 0.71073 Å). Data integration and routine
processing were performed using the SAINT software suite. Direct Methods (SHELXS97)
solutions successfully located the W atoms, and successive Fourier syntheses (SHELXL97)
revealed the remaining atoms. 1-2 Refinements were done with full-matrix least-squares
methods against F 2 using all data. Further data processing, including multi-scan absorption
corrections, was performed using SADABS. 3 Some water molecules of hydration were modeled
with varying degrees of occupancy, a common situation for polytungstate structures. In the
final refinements, all non-disordered heavy atoms were refined anisotropically, while the O
and disordered countercations were refined with fractional occupancies. No H or Li atoms
were included in the models. The degree of refinement is commonly expressed by the R factor,
which is a measure of the degree of deviation of the predicted model (calculated) from the
scattering amplitudes (observed):
R = Σ║F(obs)│- │F(calc) ║/ Σ │F(obs) │
42