The interaction of hydrazine with kaolinite was studied using a combination of infrared (IR) spectroscopy, inelastic neutron scattering (INS), and X-ray powder diffraction. Under ambient temperature and pressure conditions, anhydrous hydrazine is readily intercalated into the interlamellar region of kaolinite resulting in a kaolinite-hydrazine (KH) intercalation complex with a 001 J-spacing of 1.03 nm. Under reduced pressure, the surface loading of hydrazine is reduced to 0.5 hydrazine molecules/unit cell, and the 001 «/-spacing of the KH complex undergoes a partial collapse to a highly ordered KH complex with a 001 «/-spacing of 0.95 nm. This transition from 1.03 to 0.95 nm is accompanied by strong perturbations in the IR and INS spectra for vibrational modes of both the kaolinite and the intercalated hydrazine species. The transition from the 1.03 complex to the 0.95-nm KH complex is made possible by the keying of one of the hydrazine amine groups into the siloxane ditrigonal cavity of the kaolinite surface as evidenced by changes of the IR active stretching and bending modes of the inner OH group. The IR and INS spectra reveal strong hydrogen bonds between the intercalated hydrazine molecules and the kaolinite surface itself. The strongest hydrogen bonds are intermolecular hydrogen bonds formed between intercalated hydrazine molecules for the 1.03-nm KH complex and are manifested by a strong, broad band at 2975 cm"1 in the IR spectrum. This band is absent in the IR spectrum of the 0.95-nm KH complex and is replaced by a band at 3270 cm"1, indicating a net increase in the distance between intercalated hydrazine molecules. Additionally, strong intercalation-induced perturbations occurred for the twist, scissor, asymmetric and symmetric wag modes, and torsional modes of hydrazine for both the 1.03- and 0.95-nm KH complexes.