Pressure-tuning, FT-Raman spectra of m-phthalic acid, m-C6H4(COOH)2, and a gadolinium(III) m-phthalate salt

Pressure-tuning, Stokes FT-Raman spectra of m-phthalic acid, m-C6H4(COOH)2 (H2L), and the gadolinium(III) salt, GdL(HL)(H2O)4·4H2O, have been studied at pressures up to ∼50 kbar using 1064-nm NIR excitation. Sluggish phase transitions were observed for both compounds in the 26–29 and 28–39 kbar regions, respectively. These pressure-induced structural transitions are most likely second-order phase transitions. The pressure sensitivities (dυ/dP) of selected Raman-active modes are reported. The most pressure-sensitive vibrations for m-phthalic acid are those associated with the intermolecular hydrogen bonding modes that occur at low wavenumbers. Some anti-Stokes FT-Raman scattering data are also reported.

► Pressure-induced phase transition region is lower in m-phthalic acid than in the Gd(III) salt.
► Pressure sensitivities of H-bonding modes are extremely high in m-phthalic acid.
► Pressure sensitivities of H-bonding in anti-Stokes Raman scattering are almost the same as in Stokes scattering.