Raman Studies of Iodic Acid and Sodium Iodate

Abstract

The Raman spectra of aqueous and crystalline sodium iodate, iodic acid, and deuterioiodic acid have been recorded. The vibrational assignment for the 1 0 3 -ion has been revised, and eight of the nine fundamental vibrations of iodic acid have been assigned. Osmotic and activity coefficients of aqueous solutions of iodic acid and sodium iodate have also been measured, and an ionization constant of 0.18 f 0.01 has been calculated from a combination of these data with the degree of ionization as determined from Raman measurements. This value is somewhat higher than those which have been reported from conductance measurements.The Raman spectra of aqueous solutions of iodic acid and alkali metal iodates have been investigated by numerous workers.2 The measurements of the depolarization values of the Raman lines of the chlorate, bromate, and iodate ions were made by Shen, Yao, and W U .~ In their study, they used the sodium salts for the chlorate and bromate ions while a 6.1 N solution of iodic acid was used to study the Raman spectrum of the iodate ion. The strong line a t 806 cm.-' in the BrOa solution was quite symmetrical and assigned to v1 and the v3 fundamental was not observed. However, in the iodic acid solution the 779-cm.-' line was asymmetrical with a strong shoulder at 826 cm.-l. The shoulder was assigned as the vg fundamental of the pyramidal IO3ion. Although this assignment for the 1 0 3 -ion has been accepted by recent research w0rkers,~!5 there is a strong indication that this shoulder arises from a vibration of the undissociated HI03 molecule rather than from the IO3-ion.6 Therefore, a reinvestigation of the Raman spectra of aqueous solutions of both sodium iodate and iodic acid was undertaken.The Raman spectrum of crystalline Na1032* has been studied and four frequencies of approximately the same intensities in the range 737 to 808 cm.-l were reported. The Raman spectrum of crystalline iodic acid has also been studied2*v7,8 but the earlier work is incomplete and no vibrational analysis has been carried out. A comparison of the strong Raman lines of the crystalline iodic acid in the 1-0 stretching region with those reported as fundamentals in a recent infrared study4 shows a discrepancy between the frequencies chosen as fundamentals in the infrared and the strong Raman lines we observed. Thus, the Raman spectra of crystalline KaIo3, HO'IOz and DO'IO2 were investigated for the purpose of removing this discrepancy and giving a more complete vibrational assignment.Many values have been reported for the ionization constant of iodic acid and these are summarized in Table I.9-15 Most of them have resulted from meas-(1) Tennessee Eastman Fellow, 1964Fellow, -1965 (2) For a review of the early spectrographic literature, see (a) J. H.

The solid-state 19F NMR spectrum of [N(CH3)4][IO2F2], a vibrational study of [N(CH3)4][IO3] and [N(CH3)4][IO3]·2H2O, and the X-ray crystal structures of [N(CH3)4][IO2F2] and [N(CH3)4][IO3]

“…The stretching modes of the IO 3 À anion in the N(CH 3 ) 4 + salt are in excellent agreement with those previously observed by infrared spectroscopy [10] and with the vibrational spectra of alkali metal iodates, such as NaIO 3 [19,20]. The symmetric IO 3 stretch in the anhydrous iodate was assigned to the Raman band at 755 cm À1 , which overlaps with the n 3 (A 1 ) band of the N(CH 3 ) 4 + cation, and to the infrared band at 759 cm À1 .…”

“…intermolecular contacts in the crystal lattice when compared with the alkali metal iodates (see Section 2.2). This is in accord with the bending modes in the Raman spectrum of aqueous KIO 3 [20], which have significantly lower frequencies (320 and 358 cm À1 ) when compared with those of crystalline NaIO 3 [19,20] 3 ]. This is a consequence of hydrogen bonding between the anion and the water of crystallization, which results in hydrogen-bonded IO 3 À layers separated by cation layers in the crystal structure [11].…”

“…The assignments for n 1 (A 1 ) and n 3 (E) are reversed in these references. Surprisingly, the correct assignments for IO 3 À had been reported in two earlier vibrational studies of NaIO 3 [19,20] and they are now confirmed by theoretical calculations.…”

Rubidium Cerium (IV) Iodates with High UV‐Light‐Driven Photocatalytic Efficiency

“…The Raman spectra of RbCeI 5 O 15 ⋅H 2 O is shown in Figure , three bands at 838, 823 and 813 cm −1 correspond to asymmetric stretching v 3 of [IO 3 ]; six bands at 781, 758, 730, 715, 698 and 678 cm −1 belong to the symmetric stretching v 1 of [IO 3 ], while the band at 776 cm −1 is assigned to the doubly degenerate [IO 3 ] antisymmetric stretching; three bands at 420, 403 and 393 cm −1 come from the symmetric bending v 2 of [IO 3 ]; four bands at 361, 326, 315 and 250 cm −1 derive from the asymmetric bending v 4 of [IO 3 ]; other bands at 190, 172, 152, 125, and 115 cm −1 belong to the lattice modes …”

“…The two compounds share common features as shown in [31][32][33][34] The infrared spectrum of RbCeI 5 O 15 ⋅H 2 O discloses the rotation and vibration of its structure components. As documented in Figure 3, evident IÀ O vibration was observed between 400 and 900 cm À 1 .…”