Distribution of fluorine in hydroxyapatite studied by infrared spectroscopy

Abstract

In pure hydroxyapatite the O–H stretching and librational modes give rise to i.r. bands at 3 573 and 631 cm^–1. On introduction of F, the band at 631 cm^–1 shifts to higher wavenumbers, ultimately to 641 and 647 cm^–1, and decreases in intensity. This shift can be correlated with the number n of OH groups in the chain sections between F which have the generalised form ⋯ F HO (HO)_n HO:OH (OH)_n OH F ⋯. The ‘tail-to-tail’ configuration, ⋯ HO:OH ⋯, gives rise to bands at 680 (bending) and 3 643 cm^–1(stretching). The OH bonded to one F gives rise to bands at 720 and 3 546 cm^–1. If OH is dispersed in a chain composed mainly of F, the configuration ⋯ F OH F ⋯, the O–H stretching and bending bands lie at 3 540 and 747 cm^–1 respectively.