A Spectroscopic Method for Distinguishing Two Novel Sandwich-Type Tungsten Oxide Cluster Compounds.

This study introduces two novel sandwich-type tungsten-oxygen cluster compounds synthesized by hydrothermal methods, H₄(C₆H₁₂N₂H₂)₃{Na(H₂O)₂[Mn₂(H₂O)(GeW₉O₃₄)]}₂ (Compound 1) and H₂(C₆H₁₂N₂H₂)_3.5{Na₃(H₂O)₄[Co₂(H₂O)(GeW₉O₃₄)]₂}·17H₂O (Compound 2). The two compounds comprise cluster anions [GeW₉O₃₄]^10- coordinated with transition metal atoms, either Mn or Co, and are stabilized by organic ligands. These compounds are crystallized in the hexagonal crystal system and P6₃/m space group. The two compounds were characterized through various techniques. Fourier transform infrared (IR) spectroscopy showed absorption peaks of anionic backbone vibrations of the Keggin cluster at 500-1000 cm^-1, IR spectral peaks of δ(N-H) and ν_as(C-N) of the ligand triethylenediamine at 1000-2000 cm^-1, and IR spectral peaks of the ligand ν_as(N-H) and ν_as(O-H) of water at 3000-3500 cm^-1. Despite similar one-dimensional (1D) IR spectra due to the same cluster anions and similar molecular structures, the two compounds exhibited distinct responses in two-dimensional correlation spectroscopy with IR under magnetic and thermal perturbations. Under magnetic perturbation, Compound 1 showed a strong response peak for ν_as(W-O_b-W), while Compound 2 exhibited a strong response peak for ν_as(W=O_d), possibly linked to differing magnetic particles. Similarly, Compound 1 displayed a strong response peak under thermal perturbation for ν_as(W-O_c-W). In contrast, Compound 2 showed a strong response peak for ν_as(W=O_d); these results may be attributed to the different hydrogen bonding connections between the two compounds, which affect the groups in distinct ways through vibration and transmit these vibrations to the W-O bonds. The research presented in this paper expands the theoretical and experimental data of 2D correlation IR spectroscopy.