Low-frequency (500 ~ 100 cm-1) IR of nine substituted arenediazonium tetrafluoroborates and their complexes with 18-crown-6 were reported. The wavenumbers of the complex bonds at ca. 250 cm-1 and the net charge densities on b-N of diazo group calculated with EHMO were correlated with substituent constants (s,+-sm+) and sp+, resp. The observations revealed coordination in these complexes stemed from p-electron transfer from the b-N atom of diazo group to the crown moiety.

Key words: DIAZO COMPOUNDS, INFRARED SPECTROPHOTOMETRY, CROWN ETHER