FT-IR and Raman spectroscopic study of hydrated borates

FT-IR and Raman spectroscopic study of hydrated borates

Spectrochimica Acta, Vol. 51A, No. 4, pp. 519-532, 1995 Pergamon 0584-8539(94)00183-9 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain...

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Spectrochimica Acta, Vol. 51A, No. 4, pp. 519-532, 1995

Pergamon 0584-8539(94)00183-9

Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0584-8539/95 $9.50 + 0.00

FT-IR and Raman spectroscopic study of hydrated borates Li JuN,t XIA SHUPING and GAO SHIYANG Institute of Salt Lakes, Academia Sinica, Xining, People's Republic of China (Receioed 22 April 1994; in final form 23 July 1994;accepted 26 July 1994)

Abstraet--FT-IR and Raman spectra of 27 hydrated borates are recorded and reexamined. On the basis of the spectra by Janda and Heller with boron isotope substitution and by Zha at different temperatures, the probable assignment of vibration spectra of monoborates, diborates, triborates, tetraboratcs, pentaborates, and hexaborates are given. The bands of symmetricpulse vibration of the correspondingpolyborate anions are also indicated.

INTRODUCTION VIBRATIONAL spectroscopy is usually a traditional method for the characterization and identification of new compounds. Although the structural chemistry of hydrated borates is understood, the comprehensive and critical assignments of vibrational modes for polyborate anions have not been available until now. Vibrational spectra of hydrated borates are always very complicated for the following reasons: the ability of the boron atom to coordinate to three and four oxygen atoms enables a wide range of theoretical structural entities to be formulated. The borates can exist as not only the monomer but also polymer. Polymerization by elimination of a water molecule between two hydrated units results in chain formation, furthermore, it gives sheets or networks [1-3]. Secondly, the bands of O - H deformation modes in hydrated polyborate anions always overlap with the bands of stretching and bending modes of B - O . It is difficult to distinguish these vibration modes. Thirdly, normal coordinate analysis of the spectra of hydrated borates is often impossible as no information is available about the point group of isolated molecules, the site group of hydrated borates, as well as the vibrational units being large molecules with low symmetry. Three comprehensive collections of IR spectra of hydrated borates are given by MOENKE [4, 5], WEIR [6], and VEASOVA and VAEYASHKO [7, 8]. Those spectra show many discrepancies between the spectra of individual borates measured by different workers. For this reason, Weir concluded that it was not possible to identify borates from their IR spectra, and quoted the divergent data reported for the colemanite by various workers as an illustration of his argument, however, this conclusion is pessimistic. Many workers have researched Raman spectra of hydrated borates. MAYA [9], MAEDA [10], and JANDA and HEELER [11] have recorded Raman spectra of polyborate anions in solid and in solution, by comparison of the spectra of solution with that of solid, the structure of which was known, they gave evidence that polyborate anions exist in solution. JANDA and HEELER [12] have studied the IR and Raman spectra of tetraborates and pentaborates with boron isotope substitution. They assigned the bands of the symmetric pulse vibration of the polyborate anion ring for the first time. DEVARAJAN et al. [13] have carried out tentatively normal coordinate analysis for the pentaborate anion. ZRA [14] has studied FT-IR spectra of some hydrated borates at different temperatures in order to find the modes of B - O - H bending. DEGEN and NEWMAN [15] have recorded Raman spectra of several hydrated borates. In this work, F-q'-IR and Raman spectra of 27 hydrated borates were recorded and reexamined, and tentative assignments were also given.

t Author to whom correspondence should be addressed. 519

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Table 1. Description of samples Borate

Structural formula

Origion of samples

Monoborates

H3BO3 NaBO2.4H20 LiBO2.8H20 CaB204" 4 H z O CaB204" 6H20

B(OH)3 Na[B(OH)4] •2H20 Li[B(OH)4] •6H20 Ca[B(OH)4]2 Ca[B(OH)4]2.2H20

MgB204"3H20

Mg[B20(OH)6]

Inderite Kurnakovite Mg2B6Oti • 17H20 Ca2B60. •5H20 Ca2B6OH •9H20

Mg[B303(OH)5 ] •5H20 Mg[B303(OH)5] .5H20 Mg[B303(OH)5]•6H20 Ca[B304(OH)3]• HzO Ca[B303(OH)5]•2H:O

Borax Kernite K2B4OT"4H20 Li2B407"3H20 MgB407"9H20

Na2[B4Os(OH)4]" 8H20 Na2[B406(OH)2]" 3H20 Kz[B4Os(OH)4]"2H20 Li~[B4Os(OH)4] •H20 Mg[B4Os(OH)4]•7H20

NaB5Os- 5H20 LiB5Os"5H20 KB508"4H20 NH4B508"4H20 Ulexite

Na[BsO6(OH)4]•3H20 Li[BsO6(OH)4] • 3H20 K[B506(OH)4] •2H20 NH4[BsO6(OH)4]•2H20 NaCa[B506(OH)6] •5H20

MgB6010"6H20 MgB6Ol0"7H20 MgB60 io"7.5H20 CaB6Ol0"4H20 CaB6OI0.5H20

Mg[B6OT(OH)6] •3H20 Mg[B607(OH)6]•4H20 Mg[B6OT(OH)6]•4.5H20 Ca[B6Og(OH)2]•3H20 Ca[BsOa(OH)B(OH)3].3H20

Reagent grade (G.R./> 99.8% ) Reagent grade (A.R./> 99%) Synthetic Synthetic Synthetic

Diborates

Synthetic Triborates

Synthetic Natural mineral Synthetic Natural mineral Synthetic

Tetraborates

Reagent grade (G.R./>99.9%) Natural mineral Synthetic Synthetic Synthetic

Pentaborates

Synthetic Synthetic Synthetic Synthetic Natural mineral

Hexaborates

Synthetic Synthetic Synthetic Synthetic Synthetic

Miscellaneous

Synthetic

2MgO- 2B203 •MgCI2• 14H20

EXPERIMENTAL

Most of the hydrated borates studied here are in synthetic form in order to obtain pure samples. The descriptions of samples are given in Table 1. The synthetic methods used are taken from the literature. Table 2 lists reagents and temperature for synthesizing, chemical analysis, and references. All of the samples were characterized by X-ray powder diffraction. FT-IR spectra were recorded on a NICOLET 170SX FT-IR spectrometer with samples prepared as KBr pellets. Raman spectra were recorded on a SPEX 1403 spectrometer using the beam of 5145 nm at 300 nW of an argon ion laser, the samples were held in a pyrex tube.

RESULTS AND DISCUSSION

F T - I R spectra were recorded in the range of 4000-220 c m - ~, but the bands in the far infrared region are difficult to assign, they m a y arise from lattice vibration, the librational and translational vibrations o f water molecules, as well as the M - O stretching vibration [30, 31]. R a m a n spectra were r e c o r d e d in the range of 1800-300 c m - t .

521

FI'-IR and Raman spectroscopic study of hydrated borates Table 2. Syntheses and chemical analyses (wt.%) of hydrated borates Chemical analysis Borate CaB204 •4H20 CaB~O4.6H20 LiBO2- 8H20 MgB204-3H20 Inderite Mg2B6Ojl • 17H20 Ca2R6Oi1.9HzO Li2B407-3H20 K2B407"4H20 MgB4OT"9H20 LiB5Os'5H20 NaBsOs'5H20 KB5Os.4H20 NHaB5Os" 4H20 MgB6010.6H20 MgB6010.7H20 MgB6Oi0.7.5HzO CaB6Om0"4HzO CaB6Om0"5H20 2MgO-2BzO3. MgCI2.14H20

Synthesis

ixO

B203

H20

Ref.

NaBO2.4H20, CaCI2, 50°C NaBO2.4H20, CaCI2, 20°C H3BO3, LiOH. H20, 40°C H3BO3, MgB407.9H20, 100°C Borax, MgSO4.7H20, 40°C Borax, NaBO2-4H20 MgSO4.7H20, 25°C Natural mineral ulexite, 40°C H3BO3, LiOH.H20, 40°C H3BO3, KOH, 30°C H3BO3, MgO, 25°C H3BO3, L i O H ' H 2 0 , 60°C H3BO3, Borax, 25°C H3BO3, KOH, 25°C H3BO3, Ammonia water, 20°C H3BO3, MgO, MgCI2-6H20, 100°C H3BO3, MgO, 25°C H3BO3, MgO, 25°C H3BO3, CaO, 70°C H3BO3, Ca(CH3COO)2- H20, 20°C H3BO3, MgO, MgCI2.6H20, 40°C

28.10 23.82 7.90 24.33 14.37 13.59

35.56 29.76 18.48 42.25 37.28 35.01

36.34 46.41 73.62 33.42 48.35 51.40

16 16 17 18 19 20

43.04 62.78 45.55 40.46 62.51 59.05 59.13 64.08 58.58 55.54 54.17 61.93 58.91 24.60 16.61)

33.80 23.92 23.86 47.63 32.19 30.44 24.81 26.29 30.14 33.75 35.33 21.57 25.36 44.68

21 17 22 23 17 24 22 25 26 26 26 27 28 29

23.16 13.30 30.59 11.91 5.30 10.51 16.06 9.63 11.28 10.71 10.50 16.40 15.73 14.11 (MgCI2

At first, we studied the vibrational spectra of monoborates including H3BO3 (three coordinated boron) and metaborates (four coordinated boron), because all polyborate anions can be regarded as consisting of various BO3 planar triangles and BO4 tetrahedrons. From the obtained Raman spectra of hydrated borates except for H3BO3, the most prominent feature is that we observed the strong Raman line near 855 cm -~, but former workers did not. In the following sections, tentative assignments have been made. Monoborates

IR and Raman spectra of H 3 B O 3 a r e shown in Fig. 1 (deposited) and have been studied by many workers [32]. The four normal modes of vibration of isolated planar Table 3. Observed frequencies of FT-IR and raman spectra of H3BO 3 FT-IR 3202 b 2515 m 2362 m 2262 s 2030 vw 1423 bs 1193 vs 883 m 811 m 644 s 546 vs

Raman

Assignment

v(O-H)

1171 w 882 vs

501 s

va~(Bo)-O) vas(Bo)-O ) v,(B(3~-O) y(Bo~-O) Y(B(3)-O) 8(Bo)-O) vs(B(3)-O )

b = broad, m = middle, s = strong, v=very, w=weak, s h = shoulder, B(3)-O means three coordinate boron, B(4)-O means four coordinate boron. SA(A) 51:4-C

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4000 3580 3160 27 23201900 1480 1 0 640 220 Wave numbers (cm-l) Fig. 2. FT-IR spectra of mc'taborates: 1, CaB204.6H20; 2, CaB204.4H20; 3, LiBO2-8H20; 4, NaBO2.4H20.

2

300 450 600 750 900 10501200 13501500 1650 1800 Raman shift (cm "l) Fig. 3. Raman spectra of metaborates: 1, CaB204"6H20; 2, CaB204"4H20, 3, LiBO2"8H20; 4, NaBO2.4H20.

FT-IR and R a m a n spectroscopic study of hydrated borates

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Table 4. Observed frequencies of F T-IR and R a m a n spectra of me t a bora t e s

LiBO2"8H20

NaBO2- 4 H 2 0 FT-IR

Raman

3073 b 2618 w 2470 w

463 s

FT -IR

CaB204.6H20

Raman

F T-IR

3557w 3503w 3401 w

Raman

A s s i gnme nt

3545 w 3448w v(O-H)

2471 b 1621 vw

1669 w 1455 m 1345 w 1266 s

708 m 605 w 524 vw

Raman

3503 s 3425 s 3302 w 3262 w

3359b

1131 s 1079 w 1001 vs 944 vs 825 vs

FT-IR

CaB204"4 H 2 0

2405 w 2196w 1693w

6(H-O-H)

1257vw

6(B-O-H)

1335 w 1282w

1340s 1256m 1211m 1069 vs

1184 m

1198 m

1108 w

1090 m

911 m

967 m

v.,(B(,)-O) 952 w 857 vs 768 m 579 vs

467 m 391 vw

952 m 900 w 762 m 695 m 598 m 552 m 494 m 443 vw 389 w

852 vs 746 s

390 w

744 m 673 w 581 m 535 m 501 m 420 s 377 w

854 vw 758 vs

749 w 680 vw 584 vw 555 m 525 m 427 m 384 vw

547 w

390 vw

859 vs 755 s

389 vw

T a b l e 5 . Observed frequencies of FT-IR and R a m a n spectra MgB204- 3I-I20 and 2 M g O . 2B203. MgC12.14H20 MgB2Oa'3H20

VI'-IR

Raman

3571 vs

1297 vs 1221 m 1163 vs 1042 vs 953 vs 873vw 802 vs 589 vs 509 vw 490 w 453 m 407 w

2MgO'2B203"MgC12"14H20

VI'-IR

Raman

3586m 3536w 3475 w

3419 vs 3179 vs 2531m 1301 w 1156m 900 m 860s 745 vs 629 w 508 w 479 w 390 m

of

2926m 1671m 1297m 1236m 1127s 1036m 955m 799 s 619 w 508 m

v(O-H)

6(H-O-H)

v.(B~4~-O) cS(B-O-H)

941 w 855 vs 752 m 624 w 465 w

405 vw

Assignment

389 m

v~(B~4~-O) vs(Bt4~-O)

6(Bt4)-O)

v3(B(4)--O) v3(B(4)---O)

} r(a~,ro)

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4000 3580 31 0 2740 2320 1 1480 1060 640 220 Wave numbers (cm "l) Fig. 4. FT-IR spectra of diborates: 1, 2MgO .2B20 3. MgCl 2 • 14H20; 2, MgB204.3H20.

molecules are given [30]. The most probable interpretations are given in Table 3. Infrared bands in the 2362 cm- ~region may arise from the stretching mode of O-H of the strong hydrogen bond, which was not assigned by former workers. Figures 2 and 3 are FT-IR and Raman spectra of hydrated metaborates. Infrared spectra of hydrated metaborates have been fully studied by KESSLER [33]. The four normal modes of vibration of the tetrahedral molecule are given by NAKAMOTO[30]. All of the normal modes are Raman active, only v3 and v4 are IR active for an isolated molecule, however the vibrational spectra of a crystal are quite different from that of an isolated molecule because of the site symmetry effects, there are two symmetric stretching bands of Bt4)-O in the Raman spectra, which also appeared in the FT-IR spectra. One of them is located at 855 cm -~ which was not observed by former

l

V 2

300 450 600 750 900 1050 1200 1350 1500 1650 1800 Raman shift (cm "l) Fig. 5. Raman spectra of diborates: 1, 2MgO-2B20 3. MgCl 2.14H20; 2, MgB204 .3H20.

FT-IR and Raman spectroscopic study of hydrated borates

525

300 450 600 750 900 1050 1200 1350 1500 1650 1800 Raman shift (em "1) Fig. 7. Raman spectra of triborates: 1, Ca2B6011.9H20; 2, Mg2B6Oll.17H20; 3, inderite; 4, Kurnakovite.

researchers, it is noted that our IR spectra differ from that by former workers, primarily, the position and the number of bands of B - O stretching and bending in the IR spectra are different. Diborates

The only vibrational spectra of hydrated borates studied here are those of MgB204" 3H20 (pinnoite). Its polyborate anion consists of two BO4 tetrahedrons with an oxygen bridge. By comparison of vibrational spectra of 2MgO.2B203.MgCI2.14H20 with that of pinnoite, we found that the bands of two borates were similar, and therefore, the anion group of this borate may be [B20(OH)6] 2-, the structural formula may be written as 2Mg[B20(OH)6]. MgCI2.8H20. The probable vibration modes for these two borates are listed in Table 5. Triborates

The polyborate anion of triborates studied here is [B303(OH)5] 2- which consists of one BO3 planar triangle and two BO4 tetrahedrons. The structure of Ca:B6Oll" 5H20 is a one-dimensional chain as a result of polymerization. Because of fluorescence, we did not record the Raman spectrum of colemanite. FT-IR spectra of hydrated triborates are given in Fig. 6 (deposited) and Raman spectra in Fig. 7. Table 6 lists the vibrational frequencies of triborates. The spectra of C a 2 B 6 O l l - 1 3 H 2 0 (inyoite) were measured by ZHA [14]. On the basis of the results of JANDA and HELLER [11], the Raman frequency of 613 cm -1 may be assigned to the symmetric pulse vibration of [B303(OH)4]- because the depolarization factor is zero. Similarly, we thought the strong Raman frequency near 630 cm- l would be the symmetric pulse vibration of [B303(OH)5] 2- . Moreover, the very strong Raman line near 855 cm -1 is assigned to the symmetric stretching modes of

526

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.-,

t~

O

O

FT-IR and Raman spectroscopic study of hydrated borates

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300 450 600 750 900 1050 12001350 1500 1650 1800 Rarnan shift (cm "t) Fig. 9. Raman spectra of tetraborates: 1, MgB4OT"9H20; 2, Li2B4OT"3H20; 3, K2B407. 4H20; 4, Na2B4OT'4H20; 5, Na2B4OT"10H20.

tetra-coordinated boron, which was observed in the Raman spectra of hydrated metaborates. From the results of ZHA [14], the bands near 1200 cm -~ are B - O - H bending modes. The probable assignments are given in Table 6. Tetraborates

Figure 8 (deposited) shows FT-IR spectra of hydrated tetraborates and Fig. 9 Raman spectra. The polyborate anion [B4Os(OH)4]2- consists of two BO3 planar triangles and two BO4 tetrahedrons. By elimination of one water molecule, it will change into a one-dimensional chain [B406(OH)2]2- which was found in Na2B4OT"41-120 (kernite). The symmetric pulse vibration frequency of the tetraborate anion is near 560 cm -~, and the bending modes of B - O - H are near 1130 cm -1. The assignments for hydrated tetraborates are given in Table 7. Pentaborates

Figure 10 (deposited) shows FT-IR spectra of hydrated pentaborates and Fig. 11 Raman spectra. [BsO6(OH)4]- is composed of two six-membered rings which consist of two BOa planar triangles and one BO4 tetrahedron, but [BsO6(OH)6] 3- found in ulexite is different, its six-membered ring consists of one BOa planar triangle and two BO4 tetrahedrons. The band near 530 cm-1 in IR and Raman spectra is the symmetric pulse

528

Ll JuN et al. Table 7. Observed frequencies of FF-IR and R a m a n spectra of tetraborates

Na2B4OT.10H20

Na2B4OT.4H20

K2B4OT'4H20

FF-IR

FF-IR

FT-IR

R a m a n FT-IR

3555 m

3559 m

3487 w 3449 w

3428 w 3323 b 3006 w

3376 m 3276 m 3014 b 2631 w 2479 w 1687 w

3583w 3507w 3452w 3337w 3196w

1686w 1648w 1419 m 1357w

Raman

1708 w

Raman

1460 m 1347 s 1243 m 1154 w ll60vw 1071 w 1136 vw 1035 vw 1036 w 1015m 1034vw 1096m 997 vw 974 vw 1001 vs 948 m 948 m 874 w 933 w 921 s 833 m 852 w 828m 856vs 834vs 766 vw 756 vw 765vw 742w 713m 690 s 673 w 654 vw 651 m 623 m 617 w 613 m 535 m 576 vs 5 5 2 m 565m 496 w 500 m 494 m 448w 461 m 457 w 463 w 457 w 385 w 391vw 388w 393m

Li2B407.3H20

MgB4OT.9H20

R a m a n FT-IR R a m a n 3606 w 3508 w 3401 b 3158 b

3217 m 2991 b 2469 w 1672 w

2325 b 1690 m 1424 s

1359s

571vs 456 w 397w

f

v(o--n)

)

6 (H-O-H) "~ v~(Bo)-O) ) ) 6(B-O-H)

1383 w 1245 s

1352 w

ll16m 1030s

1097w 1028s 1056m 1045 w~vas(Bt4)-O ) 1001 w J 896 w 954 m 949 m vs(B(3)-O ) 845w 817 m 855 m vs(B(4)-O) 772s 764 vw 787 m vs(Bt4)-O )

979 w 864vs 767w

Assignment

905 s 822m 780w 706 m 658 m 565vs 506 m 452 s 385vw

1276 m 1202 m

659 543vs 493 w 446 vs 391m

m

}y(B(3)-O )

583 vs Vp(tetraborate anion) 507 vw / 473 m 450 w 6(B(4)-O) 397 w 408 w )

4

300 450 600 750 900 1050120013501500 16501800 Raman shift (era q) Fig. 11. R a m a n spectra of pentaborates: 1, Ulexite; 2, NH4BsOs.4H20; 3, K B s O s . 4 H 2 0 ; 4, NaBsOs. 5H20; 5, LiBsOx • 5H20.

FF-IR and Raman spectroscopic study of hydrated borates

529

Table 8. Observed frequencies of FF-IR and Raman spectra of pentaborates

LiBsOs'5H20 NaBsOs-5H20 KBsOs"4H20 NI-I4BsOs'4H20 FT-IR

Raman FT-IR Raman FT-IR Raman FF-IR Raman FT-IR Raman

3237 b

3455 vw 3389 vw 3236 b

3452 vw 3384 vw

3438 b 3263 w

2367 w 2246 w 1699 vw

2381 vw 2211 vw 1680 w

3065 m 2485 w 2352 vw 1653 w

3102 w 2458 w 2175 w 1647 vw

1402 w 1330 w

1414 m 1330 m

1431 vw 1351 w

1434 w 1348 w

1178 s 1105 m

1205 w 1165 s 1084 m 1022 w 924m 934m

1248 m ll00s

1236 m

1044 m 930s

796 w 775w 779m 722 w 692 m 612vw 576 vw 532 vw 474s 402m 385s

Ulexite

785s 696 s 642vw 593 vw 560 vw

530 vs 492w 474m 464w 393w 358s

1025 m 922m 923vs 856 vs 773m

782vs 693 s 590 w

529 vs 493m 507m 464w 454m 386w 370m

1089 m 1021 m 919m 923s 856 m 788 w 768w 779s 746 vw 691 m 640w 594 w 558 vs 509w 459w 372w

543 w 505m 459s 371m

3598 m 3523 m 3422 w 3306 vw 3217 vw 3130 w 2510 m

Assignment

] v(O--H)

1666 vw 6(H-O-H) 1631 w 1416m } 1356 w vas(Bt3~-O) 1321 w 1211 m }d(B-O-H) 1101 vw 1059 vw ~ / vas(B(4)-O) 1000m 916m 922 w v~(Bo)-O) 857 m 860 s 862 vs vs(Bt4)-O) 788 m 767m 745 w 748 m vs(Bt4}-O) 642715mm

t 7(B~3}-O) 595 m }d(Bo)_O)/d(B~4)_O)

555 vs 537 m 510m 460w 444 m 369w 377 w

531 w vp(pentaborate anion) 485 w ] 440 w ~6(Bt4FO ) 392 vw)

vibration o f the p e n t a b o r a t e anion. F o r NH4B5 O 8 - 4 H 2 0 , the vibrational m o d e s of N H 4 c a n n o t be assigned. T h e p r o b a b l e assignments are given in Table 8.

Hexaborates Figure 12 (deposited) shows F T - I R spectra of h y d r a t e d hexaborates and Fig. 13 R a m a n spectra. I R spectra of h y d r a t e d hexaborates have b e e n studied by LEHMANN and KESSLER [34]. [B607(OH)6] 2- f o u n d in m a g n e s i u m hexaborates consists o f three sixm e m b e r e d rings which consists o f o n e BO3 planar triangle and two BO4 tetrahedrons. T h e f r a m e o f [B609(OH)2] 2- is the same as that o f [B607(OH)6] 2-, but only has one water molecule. While the f r a m e of C a B 6 O l 0 - 5 H 2 0 is [B5Os(OH)] 2- which consists of two s i x - m e m b e r e d rings, B ( O H ) 3 attaches to the side chain o f [B5Oa(OH)] 2-. T h e p r o b a b l e assignments are given in Table 9. It is noted that the pulse vibrations of triborates and of h e x a b o r a t e s are close to 635 cm -~, they p r o b a b l y are m a d e of the same s i x - m e m b e r e d ring. In s u m m a r y , the p r o b a b l e vibrational bands of h y d r a t e d p o l y b o r a t e anions are listed in Table 10. T h e R a m a n f r e q u e n c y near 855 cm -~ is the symmetric stretching m o d e o f B(4)-O. U p to the present time, there are no sufficiently reliable m e t h o d s to distinguish obviously bending m o d e s o f B(3)-O and B(4)-O, m o d e s o f B - O stretching and of B - O - H bending. R a m a n bands in the 650-610, 590-540, 560-530 c m - i regions m a y be used as evidence to identify the entity o f the triborate anion and h e x a b o r a t e anion, tetraborate anion, and p e n t a b o r a t e anion. It is n o t e d that I R spectra of h y d r a t e d borates c a n n o t give full characterization o f h y d r a t e d borates, R a m a n spectra o f h y d r a t e d borates are simpler to interpret than the c o r r e s p o n d i n g I R spectra.

530

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al.

o

C ¢

q e~

e

~z e~

0 e~

©

©

0

FT-IR and Raman spectroscopic study of hydrated borates

300 450 600 750 900 1050 1200 1350 1500 1650 1800 Raman shift (cmq) Fig. 13. Raman spectra of hexaborates: 1, CaB6Olo.5H20; 2, CaB6010"4H20; 3, MgB6Ol0. 7.5H20; 4, MgB6010-7H20; 5, MgB6010.6H20.

Table 10. Vibrational bands of hydrated polyborate anions Bands (cm l) 3600-3000(IR, Raman) 2900-2200 (IR) 1700-1600 (IR) 1450-1300 (IR) 1300-1150 (IR) 1150-1000 (IR, Raman) 960-890 (IR, Raman) 890-740 (IR, Raman) 750-620 (IR) 650-610 (IR, Raman) 590-540 (IR, Raman) 560-530 (IR, Raman) 590-510 (IR) 500-380 (IR, Raman)

Assignment O-H stretching O-H stretching because of hydrogen bond H-O-H bending (lattice water) Asymmetric stretching of Bts~-O In-plane bending of B-O-H Asymmetric stretching of BI41-O Symmetric stretching of Bt3~-O Symmetric stretching of Bt4~-O Out-of-plane bending of B(3~-O Symmetric pulse vibration of triborate anion and hexaborate anion Symmetric pulse vibration of tetraborate anion Symmetric pulse vibration of pentaborate anion Bending of Bt3~-O and Bt4)-O Bending of Bt4~-O

IR and Raman mean IR active and Raman active, respectively.

531

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Ll JuN et al.

T h e British L i b r a r y D o c u m e n t S u p p l y C e n t r e S u p p l e m e n t a r y P u b l i c a t i o n N o . Sup 13093 c o n t a i n s 6 p a g e s o f S p e c t r a . R e t r i e v a l i n f o r m a t i o n is given in t h e N o t e s for C o n t r i b u t o r s at t h e b a c k o f e a c h issue o f Spectrochimica A c t a Part A . Acknowledgements--The authors thank Mr Liu Peiqi and Ms Sheng Fenling of Lanzhou University for the operation of the Raman and FT-IR spectrometer, and Mr Yang Bo for X-ray powder diffraction analysis. We also thank U.S. Borax Corp. for the donation of ulexite, kernite, and colemanite.

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