Nicolet 5700 ftir spectrophotometer

Measurements were performed on a Thermo-Fisher Nicolet 5700 FTIR spectrophotometer equipped with an attenuated total reflectance (ATR) diamond accessory. 20 µL of hydrogel was pipetted onto the crystal surface of the spectrophotometer and the beam path purged with dry CO₂-scrubbed air. Absorbance spectra were obtained using the average of 128 scan with a 4 cm⁻¹ resolution. HPLC grade water background was subtracted from each spectra using the built-in OMNIC software provided with the instrument. All measurements were done in triplicate. The FTIR spectra were smoothed using a Savitzsky-Golay filter with a 9-points window. A baseline was subtracted in the Amide I region (1500–1700 cm⁻¹) from the original spectra using OriginPro v8.5.1 software.

All reagents were of high purity grade quality, obtained from commercial sources, and used without further purification. The preparation and characterization of the POM salts Na_1.5Cs_2.5[Co₄(OH)₃(H₂O)₆(PW₉O₃₄)]·9H₂O (Q-1) and K₅Na₂[Co₇(OH)₆(H₂O)₄(PW₉O₃₄)₂]{Co(H₂O)₂}·20H₂O (Q-2′) have been previously described by us (Duan et al., 2016b (link)). Pure water (ρ > 18 MΩ·cm) was used throughout. It was obtained using an Elix-3/Millipore-Q Academic water purification system. IR spectra were recorded with KBr pellets on a Thermo NICOLET-5700 FT-IR spectrophotometer. Elemental analysis was performed by inductively-coupled-plasma optical-emission-spectroscopy (ICP-OES) on solutions prepared by treating the compounds in a hydrofluoric acid/hydrochloric acid mixture of ratio 1:8 and diluted with water to a known volume. Thermogravimetric analysis was performed on a Mettler Toledo TGA/SDTA851e analyzer. The UV-vis spectra of the relevant POMs (10⁻⁵ M) were recorded on an Agilent 8453 UV-vis spectrophotometer from 190 to 400 nm using 10-mm-optical-path quartz cuvettes in buffer solutions of 0.5 M sodium acetate (pH 4.8).