Infrared Spectra-Structure Correlation Study of Vanadium-Oxygen Compounds LEO D. FREDERICKSON, Jr. Spectran laboratories, Inc., Denver, Colo. DONALD M. HAUSEN Union Carbide Nuclear Co., Grand lunction, Colo. Plnfrared absorption bands characteristic of vanadium-oxygen vibrational modes in various compound classes-e.g, deca-, hexa-, meta-, pyro-, and orthovanadates, vanadyl salts and oxides-have been assembled in the form of a spectrastructure correlation chart. Hexavanadates, decavanadates, and vanadyl compounds show good correlation between spectra and structure of their classes. The metavanadate classification appears identifiable on the basis of the presence of more strong bands, and each pattern is suitably distinctive to permit qualitative identification. Ortho- and pyrovanadates appear to b e identifiable as a class or group, b y virtue of lower frequency absorption band groups. Spectral data and interpretations are summarized in the paper.
oxytribromide, are liquids under normal conditions. The economic importance of vanadium in our technology and the complex conventional chemistlry of the element have prompted this investigation of the infrared absorption spectra of a variety of vanadium-oxygen compounds, for the purposes of establishing the feasibility of qualitative analysis for pure compounds, commercial products, and minerals, and determination of spectrastructure correlations for the vanadiunioxygen vibrational frequencies. EXPERIMENTAL
The infrared spectra reported in this study were recorded on two PerkinElmer Model 21 spectrophotometers, both equipped with sodium chloride optics. Samples were examined in the solid state both as potassium bromide pellets and as mulls in mineral oil; in the liquid state, in conventional sandSALOGUUS TO phosphorus in its wich-type demountable cells. Solids higher valence states, vanadium were mortar-ground for preliminary forms covalent linkages with oxygen, particle-size reduction, followed by and this, together with its relatively further grinding to suitable infrared light atomic weight, provides for the particle size in a mechanical vibratorappearance, and therefore study, of the mixer. Mulls were prepared in the vanadium-oxygen fundamental vibrausual manner, with final grinding and mulling done between infrared windows tions in the rock-salt region of the in the mull medium. Concentration of infrared spectrum. samples in matrix potassium bromide for Compounds containing vanadium and pellets was 1% by weight or less. KBr oxygen in combination comprise a used was Harshaw Chemical Co. invariety of chemical classifications, prifrared-quality powder. marily as a result of the conditions of Vanadium compounds examined were acidity during their formation. Orthoobtained from various commercial and vanadates (XaV04)are formed a t relaprivate sources and were of the highest tively high pH, pyrovanadate salts purities obtainable; usually C.P. salts (X4Vz07) a t intermediate alkalinity, were examined. No special purification of materials was attempted, although mctavanadates (xVo3) at or near neuevery effort was made to select the tral p H values, while complex polypurest ones, and to establish the idenvanadates (X2V6016, XfiV10028) are the tity of compounds through careful check result under acidic conditions. Of the of physical descriptions and properties four known oxides of vanadium, V Z O ~ as given in the literature, as well as and Vz04 contain covalent oxygens in examination of infrared spectra with their structures; other oxides, V203 respect to detection of obvious impuriand VO, display poorly defined spectra ties, etc. Certain of the compounds t h a t may not indicate V-0 covalency. were prepared for examination in the laboratories of the investigators when Other classes include vanadyl comthey could not be readily obtained from pounds with a single, covalent oxygen other sources. Identity of vanadate linked to vanadium, and the vanadium compounds was necessarily confirmed in ores including the minerals vanadinite, most instances by comparison with x-ray hummerite, metahewettite, pascoite, diffraction pattern data. corvusite, carnotite, and tyuyamunite. Spectra were recorded in the range While the majority of vanadium com5000 to 650 cm.-1, at medium to low pound;; exist as crystalline solids, somc resolution for the instruments used. of the analogs of phosphorus, notably Some of the spectral presentations do not include all of this range, as no invanadium oxytrichloride and vanadium
A
818
0
ANALYTICAL CHEMISTRY
formation of importance in the work was to be found therein. FUNDAMENTAL VANADIUM-OXYGEN VIBRATIONS
I n an attempt to correlate observed infrared absorption spectra with chemical structure, a vanadium-oxygen compound (or compounds) was sought, possessing simple structure and free from extraneous potential interactions and distortions which might be expected to be present in the more elaborate structures to be included in the study. Such a compound was available in the phosphorus analog, vanadium oxytrichloride, a tetrahedral structure with Csv symmetry. This compound is a liquid, thus providing the desired freedom from crystal lattice forces and interactions, to permit more nearly normal location of fundamental vanadium-oxygen vibrational frequencies to appear in its spectrum. Examination of the spectrum of this molecule, as shown in Spectrum 1, shows the presence of a single strong absorption band located at 1035 cm.-*, assigned as the V I fundamental by Miller and Cousins (6), and identified as arising from the V-0 stretching motion in the molecule. Another simple compound, although solid, was found in vanadium pentoxide, shown in Spectrum 2. Here, the V-0 stretching mode is observed as a strong band located a t 1020 cm.-’, or very nearly the same location for this V-0 mode in VOCl,. These two spectra tend to locate the “normal” position for this stretching vibration between oxygen and vanadium. Another broad band is present in the spectrum of vanadium pentoxide, cen~ tering a t 825 cm.-I The V Z O structure has been described ( 2 ) as a double chain of distorted, trigonal bipyramids, joined a t the corners to form layers, the latter held together by lattice or residual forces. The V205structure consists of VO bondings of variable bond lengths, some of which vibrate at lower frequencies than others. The 1020 cm.-l band has been assigned to a VO bond which is considerably shorter than other bonds in the structure; the 825 cm.-* band very probably arises from the stretching modes of the longer VO bonds. Further support for these assignments
from Siebert's work ( 7 ) on the tctr:thedral ion in aqueous solution whose assignmeni,s are as follows:
C(JII1CS
y1
Y2
0
v4
Si0
345
825
480
nhere v1 arid v3 ale the syinrnetric and assymmetric stretching modes, respectively, for a lower frequency bond. .I slight long wavelmgth shift of both Y-0 bands is apparent, in spectrum 3 for potassium fluorov:madate. VANADIUM COMPOUNDS AND INFRARED SPECTF!A
Metavanadates. A nuinLcr of metavanadates were obtained from several sources for exunination during t h e course of this invwtigation. Studies by Evans et (11. (9,4 ) have denioristrated t h a t the crystal structure of both the hydrated and anhydrous potassium inetavanadate is of the chain type, of composition (VOa).-)L, cross-linked on trigonal pyramid edges with other chains, and vanadium esisting in fivefold coordination wii h oxygen in the crystal lattice. Examination of eight infrared spectra for meta-salts, (Spectra 4-10), shows wide variation in individual patterns for changes in the substituted cation. In these eptxtra, several absorptions appear which are apparently t,he result, of V-0 st'retching modes for c m l i of several, different osygen atoms according to the part'icular location or arrangement within tlhe lattice. A t lower frequency, a broad and general absorption occurs wliich is similar to the V20h pattern. ?'his is apparently caused by lower frequency VO bondings.
Cation Exchange in KBr-Pellet Spectra. Observation of t h e spectra in 4 t o 7 shows t h e meta-salts t o be recorded both as K B r pellet spectra a n d as mulls, with considerable differences between them. These differences were first noted as a probable interaction or cation exchange between t h e meta-salts a n d t h e matrix potassium bromide, incurred during t h e process of grinding, mixing, and pressing of t h e pellet for infrared examination. To prove this theory, several individual salts were examined by x-ray diffraction technique before and after pelleting in KBr. The x-ray evidence thus obtained indicated that the crystallinity was destroyed under conditions imposed by pelleting, for vanadate salts showing large spectral differences between pellet and mull techniques. Further, i t was observed that pota,'si u in nietavanadate, when subjected to identical pelleting condit'ions, produced infrared spectra identical to those produced by mulling in mineral oil; x-ray diff ractinn examination after pelleting also showed this salt unchanged as a result of the conditions of pelleting. I n summary, sodiurn and ammonium metavanadates appear to have been partially metathesized after prlletizing, resulting in amorplwus, solid solutions of t h e vanadates in the KDr. Discrepancies in infrared spect,ra of certain metavanadate salts in KBr media are attributed to cation exchange, involving the K + ions of the potassium bromide, and the cation of the metasalt involved. Minor matrix effects '
FREQUENCY.
1100 I
1050
950 I
lo00 I
I
900
have also been obseived in spectra for vanadates of multivalent elements, such as calcium and magnesium in KBr pellet form. K B r pellet spectra are, in most instances, reproducible even though they do not correspond to mull spectra, and also may be suitably distinctive for ube in qualitative identification. The extent to which variation in concentration of meta-salt in matrix KBr mill affect the resulting pattern in infrared spectra has not been explored to any extent, since most epectra require minimum concentrations of sample. Hexavanadates. T h e spectra in Nos. 11 t o 17 illustrate t h e absorption patterns for six compounds in t h e simple polyvanadate rlass. Absorptions in the V-0 stretching frequency region are relatively strong in intensity, and occur a t two rather constant locations, one near 1000 cm.-l, and the other near 960 em.-'. Structural studies of Block ( 1 ) and of Wadsley (8) on hexavanadates show that, for these substances, vanadium may coordinate n i t h either five or six oxygens, existing in the form of zig-zag chains of VO6 octahedra, joined at corners to form roriugated sheets or layered structures. Vanadium exists in the final, assumed structure in the form of V308anions, interleaved with cations. Observation of these spectra for various substituted cations shows this structure to be little affected by atomic mass or cationic radii differences. These spectra show the presence of a strong VO band of loner frequency, located near i50 cm.-', although there is minor variation in its location from
CM-l
8(IO
850
750
METAVANADATES (SEVERAL
('4-0
700
STRETCHING)
STRONG BANDS)
ORTHWVANADATES ( V - 0 STRETCHING) ( S E V E R A L STRONG BANDS)
P Y R O V A N A D A T E S (V-0 STRETCHING) ( S E V E R A L S T R O N G BANDS)
S -
vs -
vs
4
S
H E X A V A N A D A T E S ( V - 0 STRETCHINO) ( T W O
DECAVANADATES
(V-0
VANADYL
(V-0
SALTS
11 WAVrLEN5TU.
Figure 1 .
S T R E T C H I N G ) ( O N E S T R O N O BAND)
S T R C T C U I N O ) (ONE STRON5 B A N D )
I
I
10
STRONG B A N D S )
12
1
14
13
MICRONS
Infrared absorption-structure correlation chart, V - 0 vibrations VOL. 35, NO.
7,JUNE 1 9 6 3
819
1,
Vanadium oxytrichloride, VOCI,
2.
Vanadium pentoxide, Vz06
3.
Potassium fiuorcvanadate
4.
Sodium metavanadate, N a V 0 3 (In Nuiol)
5.
Sodium metavanadate, N a V O a (In KBrl
40
PO
0
7
820
e
ANALYTICAL CHEMISTRY
10 It 12 WAVLLLNOTH ( M I C R O W S )
13
14
15
1400
FREQUENCY (CM') 1 0 0 0 950 900 8XJ 800
1200
700
750
650
80
60
6. Ammonium metavanadate, NHdV03 (In Nuiol) 40
P
I
!
!
P
!
I
!
!
!
,
.
!
!
!
!
!
!
:
1
80
60
7. Ammonium metavanadate, NH4V03 (In KBr) 40
20
8. Potassium metavanadate, KVOa
9. Calcium metavanadate, Ca(VOa)n
10.
Mercury metavanadate, Hg(VO&
VOL. 35, NO. 7, JUNE 1963
821
1403
1200
FREOUENCY (CM ) 1000 950 900 8x1
750
800
650
700
1 1. Sodium hexavanadate, Na2V6O17*3H20
12. Potassium hexavanadate, K2VeOI7.3H20
1 3. Ammonium hexavanadate, (NH4),VS017.-
3 HzO
14.
Barium hexavanadate, BaV6o17.3HzO
15. Calcium hexavanadate, CaV,jO17.3H20
7
10
I1
w&vE:LENarn
822
ANALYTICAL CHEMISTRY
12 (MICRONE)
13
14
15
16.
Magnesium hexavanadate, MgV6017*3Hz0
17. Metahewettite, CaV6017.3HzO
18.
19.
Pascoite, C a ~ V I U O 1~5. H z 0
Hummerite, KzMgzVloOa. 16HzO
20.
Amine decavanadate
VOL. 35, NO.
7,JUNE 1963
823
FREQUENCI (CM') 960 300 em
looa
.oo
too
750
.eo
2 1.
Sodium ammonium decavanadate, Nar(NH&VIoOn. 1 6Hz0
22.
Sodium pyrovanadate, Na4V207qnH20
23.
Calcium pyrovanadate, CaZVz01.2HzO
24. Strontium pyrovanadate, SrZV20i .nHzO
2 5 . Zinc pyrovanadate, Zn2VZOi.nH20
8
IO
9
I1
LE
WAVILLLNOTCI CMICROW.)
824
ANALYTICAL CHEMISTRY
1.
14
26. Sodium orthovanadate, NaaV04
2 7. Magnesium orthovanadate,
2 9 . Vanadinite, PbS(VO&CI
30. Vanadium tetroxide, VzOI
7
8
9
IO
I1
WAVELENOTH
I2
13
14
ia
VOL. 35, NO.
7,JUNE 1963
825
1400
FREQUENCY C M ) 1000 950 900 850
1200
700
7-
Iyx)
.eo
100
60
3 1. Vanadium trioxide, V20, 40
20
0
100
K,
W
32. Vanadyl chloride, VOCll 40
20
0
100
!-
0
Y " 0
z
f
33, Vanadyl sulfate, VOSO4
40
i z
4 ao L
k
0 100
mo
.o
34. Ammonium vanadyl tartrate 40
20
0
lo0
35. Vanadyl oxalate 40
so
0 7
826
0
.
s
IO
I1
I2
WAVE L KNOT U tM I C R O W )
ANALYTICAL CHEMISTRY
1s
14
compound t o compound. Part of this absorption is probably (due to the presence of water. Wadsley’s work (8) also indicates that there is one short T‘O bond at each vanadium atom with the remaining VO bonds being appreciably longer and more variable. The 1-0 stretching modes in the hexavanadate spectra are therefore observed to o x u r in two distinct regions, 950 to 1000 cm.-l and 720 to 760 em.-‘ Decavanadates. T h e spectra of several representatives of this classification are presented in Spectra 18-21. Previous a t t e m p t s t o elucidate t h e structure of these compounds b y x-ray diffraction technique83 have been largely unsuccessful; however, t h e presence of strong infrared bands in the 975 em.-’ region, attributable to V-0 stretching motions, indkates some similarity to hexavanadate spectra-structure correlations and suggeats a sheet- or layer-type configuration for these salts. Generally, only one strong band predominates in this region for decavanadates, in contrast to two such bands associated with the previously described hexa-salts. This significant difference \)errnits the differentiation between the two classes by means of infrared spectra. Other absorptions of lower frequency in the spectra of the decavanadates appear to correlate with structure, but their assignment is not as obvious as is the apparent V-0 stretzhing mode near 960 em.-’ It is apparent that the spectra of individual members of this class are not suitably distinctive for use in qualitative analysis, b u t may only be identified as members 01’ the class. Ortho- and Pyrovanrtdates. A limited number of representatives of these classes were available for study, a n d their spectra are presented i n Spectra 22-29. Included are vanadinite, a supposed lead-orthovartadate salt, a n d volborthite, a syntheti,: copper-orthovanadate. Generally, the spectra show absorptions occurring a t frequencies lower than is the case for other classes studied, and while qual.itative identification of individuals appears a possibility, no unique correlation or classifying information appears for the spectra as a group. The VO bonds in these compounds are of the longer type, compared to the other classes which contain both long and short type VO bonds. Oxides. I n addition to the primary stable oxide VzOs, the tetravalent vanadium occurring i n VzC4 is shown to possess an infrared srlectrum, as in Spectrum 30. The barisis appearing in this spectrum are not a s intense as in the primary oxide, althcugh location of the principal absorptior s indicates the likely covalent nature of the bonding. A poor infrared spectrum has been observed for the oxide V203, showing a broad, weak absorption between 1000
and 900 cin.-l I t s spectrum has been included in Spectrum No. 31, although it shows no definite structure or evidence of covalence between vanadium and oxygen in this form. Vanadyl Salts. A number of compounds were studied which contain vanadium in t h e vanadyl configuration (VO-X) wherein a single oxygen atom exists in covalence with vanadium. These spectra are shown in Spectra Nos. 32-35. An extremely strong absorption band is noted in these spectra, located near 1000 em.-’, and arising from the V-0 stretching motion. Such structures contain no polymeric arrangement or multiplicity of vanadium atoms that might distort fundamental frequencies, and these compounds show nearly “normal” location for the V-0 stretching fundamental. The strength and characteristic location of this absorption in these compounds nearly assures the ‘dentification of this form of vanadium-oxygen bond. Vanadium Minerals. Among the naturally occurring sources of vanadium, the minerals hummerite (K&i.g2Vlo0%. 16H20), metahewettite (CaV80n.3HzO), and pascoite (CasV10028. 15Hz0) have been established as containing vanadium in the polyvanadate class of structures (9). This has been confirmed by the infrared spectra, which exhibit the strong V-0 stretching bands in the 950-cm.-l region, analogous to the polyvanadate spectra shown in Spectra Nos. 11-21. The classification of hummerite as a decavanadate is shown to be correct, with exact correspondence of spectral features of this class near 960, 845, 800, and 750 cm.-l However, pascoite, whose structure has been indicated (6) to be of the hexa-class, possesses spectral features indicating that i t should be classified with the decavanadates. Metahewettite, assumed to possess the hexavanadate structure, shows confirming evidence of this in its spectral pattern, with absorption bands located near 1000, 960, and 740 cm.-’ SPECTRA-STRUCTURE CORRELATIONS
Infrared absorption bands characteristic of V-0 vibrational modes in the various compound classes studied have been assembled in the form of a spectrastructure correlation chart in Figure l . Hexavanadates, decavanadates, and vanadyl compounds show very good correlation between spectra and structure of their classes. The metavanadate classification appears to be identifiable on the basis of the presence of more strong bands, and each pattern is suitably distinctive to permit qualitative identifications. Ortho- and pyrovanadates appear to be identifiable as a class or group, b y virtue of lower frequency absorption band groups, with individual mcmbers identifiable also. Other mis-
cellaneous compounds have been included in the correlation. DISCUSSION
Other minerals containing vanadium, such as corvusite, carnotite, and tyuyamunite were examined by infrared; however, their spectra are not included in this paper since there was reason to doubt the purity of the samples available for study. Other minerals accompany these substances in nature, and the samples examined showed evidence for such contamination, with accompanying distortion in their infrared spectra. Matrix effects produced in the infrared spectra of certain of the compounds when examined in potassium bromide pellet medium have been observed by a number of workers, with many types of compounds, and are believed to be generally recognized by spectroscopists as a potential hazard, particularly in structural analysis work. It is the authors’ conclusion that mineralogical examination b y infrared spectrometry might be performed most reliably using mull technique in the light of the experiences with KBr pellets during this work. ACKNOWLEDGMENTS
The authors are indebted to the following: William P. Schoder, UCNC, Grand Junction, Colo., for synthesis of many pure vanadium compounds; John Lane, UCNC, Grand Junction, Colo., for background information on vanadium chemistry and assistance in preparation of samples for examination; Tom Nillensifer, T h e Shattuck Chemical Co., Denver, Colo., H. R. Grady, Vanadium Corp. of America, Cambridge, Ohio, and Richard P. Fischer, U.S.G.S., Denver, Colo., for their kindness in supplying samples; and to William Riggle, UCNC, Grand Junction, Colo., for drafting of figures. LITERATURE CITED
(1) Block, S., Ph.D. thesis, Johns Hopkins
University, Baltimore, RId., 1954.
(2) Bystrom, A., Wilhelmi, K. A,, Rrct-
zen, D., Acta Chem. Scand.
4,
1119
(1950).
(3) Christ, C. L., Clark, J. R., Evans, H. T., Jr., Acta Cryst. 7, 801 (1954). (4) Evans, H. T., Jr., Block, S., Bid!. Geol. SOC.Am. 64, 1419 (1953). ( 5 ) Miller, F. -4.) Cousins, L R., J . Chetn. Phys. 26, 329 (1957). (6) Palache, C., Berman, H., Frondel, C., “Dana’s System of Mineralogy,” 7th ed.. 3. 10.55 (1951). ( 7 ) Siebert, Hans,‘ Z. Anorg. Allgem. Chem. 274, 24-33 (1953). (8) Wadsley, A. D., Acta Cryst. 8 , 695 (1955). (9) Weeks, A. U., Thompson, M. E., U.S. Geol. Surv. Bull. 1009-D (1934). RECEIVED for review September 13, 1962. A4cceptedApril 4, 1963. Presented in part at the XVIIIth Intl. Congress of Pure and Applied Chemistry, Montreal, Canada. August 1961, and a t the Fourth Annual Rocky Mountain Spectroscopy Conference, August 1961. VOL. 35, NO. 7, JUNE 1963
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