Infrared Spectra, Magnetic Susceptibility and Electronic Spectra as Aids in the Study of Structure and Bonding of the Hexamethyl phosphoramide Adducts of Some Dioxouranium (VI) Salts

Department of Chemistry, Jadavpur University, Calcutta 700032 Manuscript received 17 April 1974; revised 14 December 1974; accepted 7 March 1975 The complexes of the types [UO2X2(HMPA)2] (X = Cl, Br, NO3 and NCS and HMPA = hexa­methyl phosphoramide) and [UO2(NCS)2(HMPA)3] have been thoroughly characterized by the i.r. spectra, magnetic susceptibility and electronic spectra. If has been found that the asymme­tric stretching frequency (v3) and \(\chi m\) (the molar magnetic susceptibility) of the dioxouranium (VI) ion depend in a more or less similar extent on the donor ability of the anionic ligands towards the uranyl (VI) ion—a typical hard acid. The electronic spectra in the visible region of all the complexes which are originated due to oxygen-). uranium charge transfer and are essentially the T←S transition are found to be very much sensitive to the equatorial (secondary) ligands. It has also been found that the complexes where equatorial coordination numbers are greater than four, do not absorb below 20,000 cm-1. The π→π* band of hexamethyl phosphoramide undergoes unusual blue shift in going from a nonpolar to a polar solvent and a probable reasoning is incorporated. The effect of coordination on this π→π** band of the pure phosphoramide has also been discussed