Infrared Spectra and Characteristic Frequencies of Inorganic Ions Their Use in Qualitative Analysis FOIL A. MILLER AND CHARLES H. WILKINS Department of Research in Chemical Physics, Mellon Institute, Pittsburgh 13, Pa. Polyatomic ions exhibit characteristic infrared spectra. Although such spectra are potentially useful, there is very little reference to them in the recent literature. In particular, the literature contains no extensive collection of infrared spectra of pure inorganic salts obtained with a modern spectrometer. In order to investigate the possible utility of such data, the infrared spectra of 159 pure inorganic compounds (principally salts of polyatomic ions) have been obtained and are presented here in both graphical and tabular form. A table of characteristic frequencies for 33 polyatomic ions is given. These characteristic frequencies are shown to be useful in the qualitative analysis of inorganic unknowns. Still more fruitful is a combination of emission analysis, infrared examination, and x-ray diffraction, in that order. Several actual examples are given. It is evident that a number of problems involving inorganic salts containing polyatomic ions will benefit by infrared study. The chief limitation at present is the practical necessity of working with powders, which makes it difficult to put the spectra on a quantitative basis.
A
LTHOUGH there has been a vast amount of work on the Raman spectra of inorganic salts ( 2 , 4 ) , the study of them in the infrared has been relatively neglected. Schaefer and Matossi (10) have reviewed work done up to 1930, most of which deals with reflection spectra. The most extensive surveys of infrared absorption spectra have been made by Lecomte and his coiTorkers (6, 7 ) , but unfortunately many of their data are somewhat out of date and are not always presented in the most useful form. References to studies on a few ions are given in the books by Wu (12) and by Herzberg ( 3 ) . There has recently been renewed interest in the detailed study of the infrared spectra of selected salts, as exemplified by the papers of Halford ( 8 ) , Hornig ( I I ) , and their coworkers. The well known Colthup chart ( 1 ) contains characteristic frequencies for nitrate, sulfate, carbonate, phosphate, and ammonium ions. An excellent recent paper by Hunt, Kisherd, and Bonham ( 5 ) contains the spectra of 64 naturally occurring minerals and related inorganic compounds. Aside from sixteen spectra in this latter paper, there is in the literature no compilation of infrared spectra of inorganic salts obtained with a modern spectrometer. I t therefore seemed worth while to make a fairly extensive survey to seek answers to the following questions: Is it generally possible to obtain good spectra? Do the ions possess frequencies which are sufficiently characteristic to be useful for analytical purposes? What is the effect on the vibrational frequencies of varying the positive ion? Is infrared spectroscopy useful in the analysis of salts? This paper presents the spectra from 2 to 16 microns of 159 pure inorganic compounds, most of which are salts containing polyatomic ions. A chart of characteristic frequencies for 33 such ions is given. The use of these data for the qualitative analysis of inorganic mixtures is demonstrated. Finally, a number of interesting or puzzling features of the spectra are described.
A brief classification of the various types of vibrations in crystals may be appropriate. Ionic solids are considered fiist. In a crystal composed solely of monatomic ions, such as sodium chloride, potassium bromide, and calcium fluoride, the only vibrations are “lattice” vibrations, in which the individual ions undergo translatory oscillations. The resulting spectral bands are broad and are responsible for the long wave-length cutoff in transmission. I n a crystal containing polyatomic ions, such as calcium carbonate or ammonium chloride, the lattice vibrations also include rotatory oscillations. Of greater interest in this case, however, is the existence of “internal” vibrations. These are essentially the distortions of molecules whose centers of mass and principal axes of rotation are a t rest. The internal vibrations are characteristic of each particular kind of ion. I n molecular solids, such as benzene, phosphorus, and ice, the units are uncharged molecules held in the lattice by weak forces of the van der Waals type, andoften also by hydrogen bonds. The same classification into internal and lattice modes can be made. A few examples of such solids are represented in this paper (boric acid, and possibly the oxides of arsenic and antimony). Finally there are the covalent solids, such as diamond and quartz, in which the entire lattice is held together by covalent bonds. Here the distinction between lattice and internal vibrations disappears. One might a t first expect an ill-defined and featureless spectrum, but such is not the case. Actually there are bands that are very Characteristic. The situation is in some ways analogous to that in a polymer, which in spite of its size and complexity possesses a remarkably discrete spectrum. Silica gel is the only representative of this type included here. EXPERIMENTAL
Origin and Preparation of Samples. Practically all the samples were commercial products of C.P. or analytical reagent grade. The samples were gound to a fine powder to minimize the scattering of light, and were examined as Sujol mulls. When there were spectral features that were obscured by the Sujol bands, the samples were either run as a dry powder or mulled in fluorolube (a mixture of completely fluorinated hydrocarbons. Fluorolube is a product of the Hooker Electrochemical Co., perfluoro lube oil of E. I. du Pont de Semours & Co.). Some compounds, such as ferric nitrate nonahydrate (No. 49) and calcium permanganate tetrahydrate ( S o . l50),seemed to mull up in their own water of hydration. When the fine powder x a s rubbed between salt plates, it acquired the appearance and feel of a typical mull, but no appreciable fogging of the salt plates resulted. For other compounds, such as potassium carbonate, breathing on the sample achieved the same result. This is not recommended, however, for it varies the water content unnecessarily, and with potassium carbonate some of the bands are shifted. Although these techniques are satisfactory for qualitative examination, it may be of interest t o list some other methods which have been mentioned in the literature for handling inorganic solids. Lecomte, who introduced most of them, has pointed out that a finely ground dry powder scatters very little radiation of wave length greater than 6 microns and consequently it may be used directly in that region (6, 7 ) . He also suggests coating 1253
ANALYTICAL CHEMISTRY
1254 Table I.
Index to Infrared Curves and Tables of Data
Formula Boron hletaborate
No. 1 2 3
Tetraborate
Type Sulfur (Contd.) Sulfate
Formula
No.
4
5 6
Perborate
7
Misc.
8 9
Carbon Carbonate
PbCOa SHiHCOa NaHCOa KHCOa
10 11 12 13 14 15 16 17 18 19 20
Cyanide
NaCN KCY
21 22
Cyanate
KOCX AgOCN
23 24
Thiocyanate
NHISCN NaSCN KSCN Ba(SCN)z. 2Hz0 Hg(SCS)z Pb(SCN)z
L1&03
NazCOz KzCOa 3hfgCOs hlg(OH)n.3HzO CaCOa BaCOa
coco3
Bicarbonate
Silicon Metasilicate Silicofluoride Silica gel Sitrogen Nitrite
31 32 NazSiFs SiOr , XHZO
33 34
Nah-02 KNO? AgNOz Ba(SOz!z Hz0
36 36 37 38
Nitrate
Subnitrate
39 40 41 42 43 44 45 46 47 48 49 BiOSOz.Hz0
Phosphorus Phosphate, tribasic
Phosphate, dibasic
Thiosulfate
Metabisulfite
60 61 62 63 64 65
Selenium Selenite
104
105 106 NazSeOa CuSeOa, 2H20
107 108
Selenate
(NHhSeOi NazSeOi. lOHzO KzSeOh CuSeOl. 5HzO
109 110 111 112
Chlorate
NaC108 KClOa Ba(Cl0s)z.Hz0
113 114 115
Perchlorate
NHiClOi SaClOa, H20 KClOa Mg(CIO*)z
116 117 118 119
NaBrOa KBr03 AgBrOa
120 121 122
Bromine Bromate Iodine Iodate
Periodate
123 124 125 KIOi
Vanadium Metavanadate Chromium Chromate
Dichromate
Molybdenum Molybdate Heptamolybdate Tungsten Tungstate Manganese Permanganate
66 67 68
103
Persulfate
50
51 52 53 54 55 56 67 58 59 (NHdzHPOi hazHPOi.12HzO KiHPOi MgHPOi. 3Hz0 CaHPOa. 2H20 BaHPOi
Bisulfate
Complex ions Ferrocyanide
126 127 128
(NHl)zCrOa NazCrOi KzCrOa MgCrO4.7HzO BaCrOb ZnCrOa, 7HzO PbCrOa Alr(CrOd8
129 130 131 132 133 134 135 136
(NH4)zCrzOi NazCrtO~.2H20 KzCrrOr CaCrzOl.3HzO CuCrzOr ,2Hz0
137 138 139 140 141
NazMoOi, 2HzO Kd~foOi.5HnO
142 143
(~Hdahfo7O24.4HzO
144
NanWOi.2HzO KzWOI CaWOi
145 146 147
NaMn04.3HzO KMnOi Ca(MnOi)*.lHzO Ba(Mn0h
148 149 150 151 152 153 154 155
71
Ferricyanide
NarFe(CN)a. 10HzO KdFe(CN)o.3Hn0 c a ~ F e ( C N ) a12Hz0 . KaFe(CN)s
Orthoarsenate, tribasic Orthoarsenate, dibasic
Car(.4sOi)z NazHAsO4.7HzO PbnHAsOi
72 73 74
Cobaltinitrite
NasCo(N0r)o
156
Hexanitratocerate
(NHdzCe(N0ah
157
Orthoarsenate, monobasic
KHz.4~04
75
Oxide
AszO:
76
NHhCl BaCln. 2Hz0
158 159
Nujol, fluorolube
160
SbzOa Sbzos
77 78
(NHI)ZSOSHzO NazSOa KzSOa 2Hz0 CaSOa 2Hz0 BaSOa ZnSOs 2H20
79 80 81 82 83 84
69 70
Antimony Oxide Sulfur Sulfite
Chlorine Chloride Mulling agents
V O L U M E 24, NO. 8, A U G U S T 1 9 5 2 Table 11. v w = very weak
w
=
weak
C m . - 1 Microns I 1. Sodium metaborate NaBOz 862 11 60 w 925 10 80 vs, b 8 50 ni 1175 1310 7 64 rs 1655 6 05 m 3470 2 85 YS, vb 2.
M a nesium metaborate
M%Bo~)~.~H~o
808 838 892 952 1005 1085 1130 1220 1370 1420 1640 3360 3500
12.4 11.95 11.2 10.5 9.95 9.2 8.8 8.2 7 3 7 05 6 1 2 98 2 86
3.
960 1340 1380 3280 4.
~~
5.
w s s
w s s
Lead metaborate Pb(B0z)n. HzO 1 0 . 3 s, vb 7.45 m 7.2 Nujol? 3.05 m
Sodium perborate NaBOs.4HzO vw 13 0 w 12 0 11 75 w vw 11 4 TS 10 7 9 8 8 9 3 m 8 5 s 8 05 s 6 05 w vs 3 0 Boric acid &BO3 12.4 m vw 11 3 8.37 s,sp 6.9 vs 3.15 s
8.
807 885 1195 1450 3270
s
Manganese tetraborate MnBiOi.8HzO 10.1 9 . 4 1 s , vb 8.7 7.3 s 6.9 m 6.1 w 2.95 8
7. 770 833 852 877 934 1020 1075 1175 1240 1655 3330
m
Potassium tetraborate K2BiOi. 5Hn0 14.2 vw 12.8 vw 12.0 s 10.9 s 10.0 s 9.45 vw 9.2 s 8.85 v w 8.65 w 8.05 m 7 . 6 2 sh 7.45 s 6.95 s 6.05 w 4 03 vw 3.03 s 2.95 s 2.81 s
705 782 833 918 1000 1060 1085 1130 1155 1240 1315 1340 1440 1655 2480 3330 3390 3560
990 1065 1150 1370 1450 1640 3390
w s
Sodium tetraborate NazBiOi. lOHzO 14.05 w 12.9 w 12.1 s 10.6 s 10.0 s w 9.3 8.85 m 7.95 m 7.85 m 7.35 vs 7.05 vs 6.85 Nujol? 6.05 m 3.0 vs
712 775 828 843 . 1000 1075 1130 1260 1275 1360 1420 1460 1650 3330
6.
s m vw
1255
Positions and Intensities of Infrared Absorption Bands s = strong
m = medium
verystrong s h = shoulder b = broad = KBr region (15-25~) eyamined
vs =
*
Microns I 9. Boron nitride BN 810 12.35 w 1390 7.2 s
Cm. -1
Lithium carbonate LipCOp 1 1 . 5 8 in 6.92 s 6.7 s
10.
864 1445 1490 11. 700 705 855 878 1440 1755 2500 2620 -3000
Sodium carbonate NapCOa 14.3 in 14.2 m 11.7 v w 11.4 s 6 . 9 5 vs 5.7 m, sp 4.0 m 3 . 8 2 vw 3.3 m, vb
-
12. Potassium carbonate KzCOa 865 11.55 m 1 1 . 1 vw 900 6.9 vs 1450 -3220 3.1 m, vb
-
13. M a nesium carbonate basic 3 M g e O ~Mg(OH)n.3H;O . 1 2 . 5 vw 800 11.7 vw 855 vw 885 11.3 7 . 0 vs 1430 vs 1490 6.7 2.9 111, vb 3450 14.
Calcium carbonate CaCOa 14.0 w 11.4 s , s p 7 . 0 vs 5.6 vw 3.95 vw
715 877 1430 1785 2530
15. Barium carbonate BaCOa 697 1 4 . 3 5 vi 858 11.65 s , s p 6 . 9 5 vs 1440 16. 747 865 1450 -3330
Cobaltous carbonate COCOS 1 3 . 4 vw 11.55 m 6.9 vs 3 . 0 w , vb
17.
685 840 1410 18.
703 832 993 1030 1045 1325 1400 1620 1655 1890 2550 3060 3160 19. 662 698 838 1000 1035 1050 1295 1410 1460 1630 1660 1900 2040 2320 2500 2940
Lead carbonate PbCOa 14.6 w 1 1 . 9 vw 7.1 YS
Ammonium bicarbonate NHiHCOi 14.25 12.02 10.08 9.7 9.58 7.55 7.15 6.17 6.05 5.3 3.92 3.27 3.17
s s, sp
s
w, SP w , SP vs, b vs, s p
s s
w m VS,SP
20. 705 833 990 1010 1370 1410 1630 2380 2600 2950
E} 5.27 m 5
vw w (COZ?) s. b
hficrons I Potassium bicarbonate KHCOa 14.2 s 12.0 s , s p 10.1 s 9.9 9 m, sh 7.3 vs 7.1 6 . 1 5 vs 4.2 w 3 . 8 5 s , vb 3.37 m
s p = sharp
22. Potassium cyanide KCN (KHCOa, K ~ C O Simpurities) 1 2 . 0 m , imp. 833 882 11.35 vw, imp. 1440 6 . 9 5 s , imp. 1635 6.12 8 2070 4.83 s 23. Potassium cyanate KOCN (KHCOa impurity) 706 833 980 1010 1210 1310 1410 1640 2130 2630
1210 1310 1345 2170 3450 25. 1420 1650 2050 2860 3060 3149 26. 758 950 1620 2020 3330 27. 746 945 1630 2020 3400 28. 1630 2060 3500 29. 835 1105 1150 1370 1615 2090 3450
14.17 12.0 10.2 9.9 8 25 7.65 7.1 6.1 4.7 3.8
s. imp. s,rmp. m, !mp. m , imp. m , sp. n', s,p. v s , !mp. vs, imp. s , yb s , imp.
24. Silver cyanate AgOCN 8 . 2 5 vw 7.65 w 7 . 4 3 vw vs 4.6 2.9 vw Ammonium thiocyanate NHiSCN 7.05 s 6 05 m 4 88 s 3.5 m 3.27 s 3.18 s Sodium thiocyanate NaSCN w 13 2 vw, b 10 5 6 18 m 8 4 9 ni 3 0 Potassium thiocyanate KSCN 13.4 m 10.6 vw, vb 6.13 m s 4.9 2.95 m Barium thiocyanate Ba(SCN)z. 2HzO 6.15 m 4 . 8 5 vs, s p 2 . 8 5 vs Mercuric thiocyanate Hg(SCN)z 1 2 . 0 vw 9 . 0 5 vw vw 8.7 s 7.3 w 6.2 4.78 8 2.9 w
30. Lead thiocyanate Pb(SCN)E 2030 4.93 8. sp w 2080 4.8
imp. = impurity
Cm. -1 Microns I 31. Sodium metasilicate NarSiOa. 5Hz0 715 14.0 s 775 12.9 s 832 12.03 s 980 10.2 YS 8.9 m 1125 8.58 m 1165 5.9 m 1695 2330 4.3 m 3280 3 . 0 5 vs, vb 32.
21. Sodium cyanide NaCN (NasCOa impurity) 11.55 m , imp. 865 1310 7 . 6 5 vw 1460 6 . 8 5 vs,imp. 6.1 m 1640 2080 4.8 s 4.5 w, vb 2220 3.0 m , vb 3330
vs, sp
Sodium bicarbonate NaHCOs 1 5 . 1 5 w (COZ?) 14.35 R 11.95 10.0 9.65 9.55 7.73 7.1 6.85
4.9 4.3 4.0 3.4
Cm. -1
vb = verybroad
Potassium metasilicate KtSiOa 13.0 vw 1 0 . 1 vs, vb 6.15 vw 3.0 m
770 990 1625 3330 33.
Sodium silicofluoride Na2SiFa 13.73 v s m,sh 12.7 9.05 vw
728 790 1105
34. Silica gel SiOz. xHzO 12.5 10.55 9,l5 8.4 6.1 3.0
800 948 1090 1190 1640 3330 35.
s,sh vw
m
Sodium nitrite NaNOz
831 1250 1335
12.03 8.0 7.5
36.
w w vs
m, s p vs
m,sh
Potassium nitrite KNOz
830 1235 1335 1380 2560 3450
12.05 s , s p 8.1 vs 7 . 5 m, sp 7.25 m 3.9 vw 2.9 vw 37.
833 848 1250 1380
Silver nitrite AgNOz 12.0 w 11.8 v w vs 8.0 7.25 vs
38. Barium nitrite Ba(N0n)z. H20 820 1235 1330 1640 3360 3510
12.2 8.1 7.53 6.1 2.98 2.85
39.
m , SP
;:i5} 6.13 w 5.75 w w
3410
2.93
40. 836 1358 1790 2428 41. 824 1380 1767 42.
803 835 1348
m m m ,sp
Ammonium nitrate NHiNOa 12.05 w
830 1340 1390 1630 1740
733
w vs
Sodium nitrate* NaNOa 11.96 m , s p 7.36 vs 5.59 v w 4.12 vw Potassium nitrate KNOI 12.14 m, s p 7 . 2 5 vs 5 . 6 6 vw Silver nitrate AgNOa 13.64 vw 12.45 11.98 w vw 7.42 YB
ANALYTICAL CHEMISTRY
1256 Table 11. vw = very weak
w = weak
Cm. - 1
RZicrons I 43. Calcium nitrate Ca(N0a)z 820 12.20 w 9.58 vw 1044 s 1350 7 4 1430 7.0 s 6.1 m 1640 s 3450 2.9 44.
13.72 6 , SP 12.24 S , S P 7 . 4 0 vs 7.05 m,sp 5 64 w, SP 4.15 b UT,
46. Cupric nitrate Cu(N0a)z. 3Hz0 11.96 w 7.26 vs 6.30 6, SP 5 58 v w 4 . 1 1 vw 3 15 w 2.98 s, b
47. 807 836 1372 1640 3230 3410
726 807 836 1373
Lead nitrate Pb(N0a)z 13.77 u' 12.39 v w 11.96 w, sp 7.28 w
835 1361 1613 1785 2440 3230
49. Ferric nitrate Fe(NOa)a,9HzO 11.98 w 7 . 3 6 vs 6.19 m 5.6 vw 4.1 vu. 3 . 1 s , vb
50. 816 1325 1380 1640 3390
*
1
55.
Manganese phosphate, tribasic Mns(P0a)z. 7Hz0 935 10.7 vw, sh 980 10.2 w 1020 9.8 s 1040 9.6 ?sh 1070 9.35 s 1145 8.75 w 1250 8.00 w 1300 7.7 w 2470 4.05 vw 3170 3,l5'! 3330 3450
i:: I
56.
Nickel(ous) phosphate, tribasic Nia(P0a)~. 7Hz0 735 13.6 w. vb 877 11.4 w Rh 943 io 6. w., .~. 100.5 9.95 s 1060 9 . 4 5 w, sh -1440 ?) 6 . 9 5 w (Sujol 1595 6.27 w -3030 3.3 s 3450 2.9 m,sp
-
57.
+
Lead phosphate, tribasic Pbs(P0a)z
59.
Chromic phosphate, tribasic CrPOa. H?O 1030 9.7 vs, vb 1625 6.15 w 3230 3 . 1 E, b
60.
Ammonium phosphate, dibasic (NHa)zHPOc
Potassium phosphate, tribasic KaPOi 10.0 vs, vh 1000 6 . 3 w , vb 1590 3180 3.15 vs, b
53. Magnesium phosphate, tribasic Mga(POajz.4HzO 768 13.05 w, b 887 1 1 . 3 vw, b 1% 1040
1135 1155 1230 1640 3260 3460
%E5]
8.83 8.65 8.13 6.1 3.07 2.9
," m
w,sh w
m s m, s h
vb = very broad
sp = sharp
m
::::}
-
71. 64.
Calcium phosphate, dibasic CaHPOa. 2H20 880 11.35, m 990 10.1 1050 9.5 1 s, r b 1125 8.9 J 1350 7.4 ? 1650 6.07 m -2270 4.4 m, vb -3000 3.3 m 3610 2.85 v w , sh
65.
Sodium metaarsenite NaAsO, 14.36 vs, b 13.35 m 12.9 w,ah 12.0 s, sp 11.8 s , s p 7.06 v w 6.85 m, sp 2.90 w , b
697 748 775 833 848 1420 1460 3450
--
72.
Calcium orthoarsenate, tribasic Ca,(AsO4)2
Barium phosphate, dibasic BaHPOa
73. 2440 2700
66. 900 1080 1275 1420 1440 -1610 -2270 2900 3050
67.
4.1 3.7
w
w
Ammonium phosphate monobasic NHaHzPOa 11.1 w , vb 9.25 m, b 7.85 m 7.05 w, sh 6 . 9 5 rn 6.2 w, vb 4.4 w, vb 3 . 4 5 w, sh 3.28 m
--
Sodium phosphate, monobasic NaH2POa. HzO
1640 2850 2820
Sodium orthoarsenate, dibasic NazHAsOa.7HzO 712 836 1175 1280 1640 2175 2380 -3130
-
74.
Lead orthoarsenate, dibasic PbzHAsOc 743 13.45 m , b 800 12.5 vs
75.
Potassium orthoarsenate, monobasic KHzAsOa
750 850 1020 1266 1585 -2275 -2740
--
6.1
m , vb
4 . 2 5 s, b 3.55 s , b
803 840 1040 77.
61.
Sodium phosphate, dibasic NanHPOa. 12HzO 11,55 9 865 1 0 . 4 5 w, sh 958 10.15 S 985 1070 9 . 3 5 17s 1125 8.9 u-,sh 1145 8 . 7 5 vw, sh 1185 8 45 w 126.5 7.9 W 1630 6.13 m -2220 4 . 5 w , vb 3280 3 . 0 5 vs, vb
-
62.
imp. = impurity
Cm.-' hlirrons I 70. Calcium phosphate monobasic, Ca(H2POa)z. ~ 2 0 670 14.9 m, vh 855 w, r b 885 915 10 9 ' v w , sh 950 10 5 s. h 1085 9 2 s,b 1160 8 6 w 1235 8 1 s,b 1640 6.1 m 2320 4.3 m, vb -2980 3.35 s , v b
76.
51.
52.
35
Copper(icj phosphate, tribasic C~a(POa)2.3Hz0 645 15.5 m 855 11.7 m 925 10.8 s 960 10.4 s 1010 9.9 s 1070 9.35 s 1100 9.1 m , sh 8.75 m 1140 7.75 m 1290 3390 2.95 m 58.
b = broad
Cm. -1 Microns I 63. Magnesium phosphate, dibasic MgHP04.3H20 882 11.35 m 1020 9.8 s 1055 9.5 s 1160 8 6 8
N
Bismuth subnitrate BiONOa. H20 12 27 vw 7.55 s 7.25 vs 6.1 vw 2.95 m, b
Sodium phosphate, tribasic NaaPOa. 12H20 694 1 4 . 4 real? 1000 1 0 . 0 vs 6.9 vw 1450 6.03 m 1660 3200 3.13 vs, b
ah = shoulder
= I
v. vb 3.13 2.981 s 2.9 )
102.
Barium thiosulfate BaSzOs.U2O
m s m vw m
820 848 877 1005 1065 1160 1280 1325 1640 2600 2900
Potassium bisulfate KHSOa 12.2 w , s h 11 8 s 11.4 s 9.95 5 9.37 S , SP
8.6
vs,b
7.78 s 7.55 w, s h 6.1 w m. vb 3.85 v w 3.45 s , v b
2:: j>
98. Ammonium thiosulfate (NHdzSzOa 953 10.5 s 1065 8.4 s 1390 t.18 s 1650 6.05 w 2960 3.4 s , vb 99. Sodium thiosulfate Na&03.5H20 677 14.8 s 757 13.2 v w , sh 1000 10.0 vs 1125 8.9 8.6 1165 1630 G,l5 w 1660 6.03 m
) '"
2080 3390
2.95 vs
100. Potassium thiosulfate KzSzOs. H20 658 15.2 676 14.8 10 03 s 995 1120 8 95 v s 1625 6 15 v w 3300 3 03 w
Cm. -1
Potassium selenate KsSeOa 12.35 v w . s h 12.13 s , sp
11.67 11.42 11.15 9.22 9.0 8.75 7.28 5.73 4.18
89?
Sodium metabisulfite* Na&Os
4.56
m
21.91 14..58
.: I2 a31
m
18.81 m 1.5. 171
660 fifi7 973
1,j.n /
in.25 0.4.5 8..5 7.9
lofin
11x0
1265
112.
vs
v w , sh
Potassium metabisulfite KZSZO5 RR2 1,5.l rn 475 1 0 . 2 5 cs iofin 4.ii 10x0 9 . 2 i ni
104.
1105
9 0.5 R. i
105. fi?7
702 865
lOR0 1085
-1190 1280 14211 3260
ni 7's
8.0 r w , ~ h Ammonium persulfate (NHi)zSzOq 15.7 vw 14.23 s 12.5- w 11 ..?.a 7-w
-
4.45 4.23 8.4 7.8 7.0.5
s,sp
3.07
E
m,
s , 3p
I060
9 1?
1270
7 88
1100
7 7
3300
3 02 w
107. 720 788
112.5 1450 3330
r
Sodium selenite NazSeOa 18.7 vs 12.7 s 8.4 w , h 6.9 Nuiol ? 3.0 w, b
+
-
109.
@ 860 1235 1420 1640 2320 -3140
Ammonium selenate (NH4)zSeOa 13.0 \
i:;i31
vs,vb
11.63,' 8.1 w 7.03 s 6.1 m 1.3 ni 3.18 v s
-
938 962
1610 3S40 3570 116.
vs
108. Copper selenite CuSe08.2Hz0 714 14.0 v s 768 17.0 m.sh 807 12.4 r w , s h 918 10.9 m 1570 6.35 m 1650 6.05 w 4.4 vw, v b 2270 -3120 3.2 1 3450 2.9 1
770
114.
vs w, sp w,8p
Copper selenate CuSeOa. 5Hz0
13.0 m, b 11.65 s 10.85 m 6.25 m , s p 3.1 \ 2.951
113.
935 965 990
vw vw
Sodium chlorate NaClOa 10.7 s , s p 10.35: 10.1 ( vs Potassium chlorate KClOa 10.65 w
10.4
YS
t:;:5]
KzS201
14.1
770 858 922 1600 3220 3390
vw m vw
115. Barium chlorate Ba(ClOa)n.H z O
SD
w,sh
v'
106. Potassium persulfate
710
1080 1110 1140 1375 1745 2390
vs 1's
I
Microns
875 857 103.
imp. = impurity
110. Sodium selenate Na~Se04.10H~O 735 13.6 vw, sh 793 12.6 vs 838 11.95 vs 573 11.45 vs I105 9 05 m 1125 8.9 m, s p 8.6 w 1165 1240 8.07 m 1390 7.2 s 1640 6.1 m 2350 4.25 s 3220 3.1 m 3500 2.85 s , s p
810 824
793 97.
sp = sharp
111.
117.5 1250 8.0 8.1 6.02 3.85 2.88
I
Rlicrons
-
vb = very broad
1060 1136 1420 3330
vs. v b 6.2 m,s p 2.83 s , s p 2.80 s , s p
Ammonium perchlorate NHaClOa 9.45 v s 8.8 s , s h 7.05 s 3.0 s, sp
117. Sodium perchlorate 1100 1630 2030 3570
NaCIOI. HzO 0.1 vs, b 6.14 s , s p 4.93 vw 2.80 s , sp
118. Potassium perchlorate KClOc w 637 15.7 940 10.65 v w 1075 93 s 1140 8 . 7 5 s . SI1 1990 5,02 cw
119. Magnesium perchlorate MgClOi 652 15.35 rn 10.58 w 943 10.4 w 962 9.45 vs 1060 8 . 85 \I 1130 6.13 s , sp 1625 4.8 P , vb 2100 2.83 s 3540
ANALYTICAL CHEMISTRY
1258
Table 11. Positions and Intensities of Infrared Absorption Bands (ConcEuded) vw
=
very weak
K
= weak
m = medium
C m - 1 Microns I 120. Sodium bromate NaBrOz 807 1 2 . 4 vs 121.
Potassium bromate KBrOa 12.65 vs
790
122. 765 797 1280
Silver bromate AgBrOs 13.08 s 12.55 vs 7 . 2 5 Nujol ?
+
123.
Sodium iodate NaIOs
;;; i;:?}
vs
800
m
12.5
124. 738 755 800
Potassium iodate KIO? 13.55 vs 13.25 s 12.5 w
125. Calcium iodate Ca(I0s)z. 6HzO 13.35 m 748 13.15 m 760 775 12.9 s 817 12.25 8 827 1 2 . 1 vw, sh 838 11.93 v w , s h 1610 6.20 w , s p 3350 3450
i::8}
126. 848
Potassium periodate KIOa 1 1 . 8 vs
127. Ammonium metavanadate NHdVOa 690 14.5 s, vb 843 11.85 s 888 11.25 s 935 10.7 s 1415 7.08 s , sp 3200 3.12 8 , sp 128. 693 828 910 935 957 3450 129. 74 5 843 865 935 1410 1650 2860 2990 3120 130.
680 820 855 890 915 1665 2125 3170 131. 858 935
Sodium metavanadate NaVOa . 4 & 0 1 4 . 4 s, b 12.08 s 1 1 . 0 vw 10.7 10.45} 2.9 w, b Ammonium chromate (NHd)zCrO4 13.4 m 11.85 m, ah 11.55 vs, b 1 0 . 7 m. sh 7.1 8 6.05 m 3.5 m.sh 3.35 s 3.2 m,sh
s = strong
1
10.90 6.0 4.7 3.15
*
= very = KBr
strong s h = shoulder b = broad region (15-25p) examined
Cm.-1 Microns Z 132. M a nesium chromate MgErO4.7HzO 695 14.4 w, v b 765 1 3 . 1 w, b 855 11.7 m , s h 877 1 1 . 4 vs 1620 1650 ::I%} 2270 4.4 m, b 3260 3 . 0 7 vs, b
133.
Barium chromate BaCrOa
i i g ii:z5} vs b 930 3450
142.
1
135. Lead chromate PbCrO4 825 855 vw. vb 885 11.3
::::1
vs.b
Potassium chromate KzCrOh 11.65 w, sh 11.45 vs 10.7 s
=
very broad
820 855 900 1680 3280 143.
Copper dichromate CuCrz01.2HzO 1 3 . 3 s , vb 10.65 s 6.15 m 2.9 s Sodium molybdate NazMoO,. 2 H ~ 0 12.2 vs 11.7 m 11.1 m , s p 5.95 w 3.05 s Potassium molybdate KzMoOa.5HzO 1 2 . 1 va 11.1 m 3.02 m
825 900 3310 144.
Ammonium heptamolybdate (NHa)nMoiOzi.4HzO 663 1 5 . 1 vs 836 11.95 m 877 11.4 vs 913 10.95 w , s h 1420 7.05 s 1640 6.1 w 3080 3.25 s, b
sp = sharp
136. 745 950 1010 1300 1625 3460 3520
Aluminum chromate Alr(CrO4)s 13.4 s , v b 10.5 s , b 9.9 s 7 . 7 vw 6.15 m
;:ii}
137. Ammonium dichromate (NH4zCrzOi 730 1 3 . 7 vs 877 11.4 m 900 11.1 m 925 10.8 s , s h 950 10.55 s 1410 7.1 s,sp 2850 3.5 m, sh 3060 3170
::%}
145. 810 822 8.50
925 1670 3310
Sodium tungstate NazW04.2 H z 0 12.35 w , s h 12.15) 11,751 vss 10.8 w 6.0 w 3.02 s
146. Potassium tungstate KsWOc 750 13.3 vw 823 1 2 . 1 5 vs, b 925 10.8 w 1680 5.95 w 3170 3.15 m 3320 3.01 w,sh 147.
794 1640 3390
Calcium tungstate Caw04 1 2 . 6 vs, vh 6.1 w 2.95 m
152. Sodium ferroc anide NaaFe(CN)s. lOd0 1625 6.15 s , s p 2000 5.0 vs 2020 4.95 m, sh
153. 930 995 1630 1650 2015 3410 3510
Sodium dichromate NalCrzOr .2Hz0 13.55 vs 12.8 m 11.25 8. sp 11.0 m , s p 9 . 0 7 vs 7.2 Nujol 1 8 , SP 2.85 8
;:A;}
+
139. 568 760 795 885 905 920 940 1305
Potassium dichromate* KnCrzOi 17.61 w 13.15 vs 12.55 m 11.3 m, SP 11.05 m , s p 10.85 w , ~ h 10.65 vs, b 7 . 6 5 vw
148.
Sodium permanganate NaMn04.3Hz0 840 1 1 . 9 vw, sh 896 11.15 vs 1625 6.15 s,sp w,b 3510 2.85 s
$::: ::e} 149.
Potassium permanganate KMnOd 845 11.85 w 900 11.1 vs 1725 5.8 w 150.
840 905 1625 3470
Calcium permanganate Ca(Mn03z.4HzO 11.9 m 11.05 vs, b 6.15 8 , s p 2 . 8 8 vs
Potassium ferrocyanide &Fe (CN)8.3H20 10.75 vw 10.05 vw 6.13 8 , sp 6.07 m 4 . 9 6 vs
;:%}
154.
Calcium ferrocyanide CazFe(CN)n. 12Hz0 1615 6 18 m 2015 4 . 9 6 vs, sp 3390 2 . 9 5 vs, b
155. Potassium ferricyanide KsFe(CN)e 2100 4.77 s
847 1333 1430 1575 1645 2665 2780 3450
Sodium cobaltinitrite NaaCo(N0l)s 11.8 s , s p 7.5 vs 7.0 vs 6.35 m 6.07 w 3 . 7 5 vw,s p 3.6 vw, sp 2.9 m
157.
Ammonium hexanitratocerate (NHdzCe(N0dn 745 13 42 8 , sp 803 12 45 m, sh 807 12.4 8 , sp 815 12 25 vw 1030 9 7 s, s p 1050 9 5 vw 1260 7 95 vs 1325 7 55 w 1420 7 05 s 1530 6 6 vs, b 3210 3 11 s, b 158.
138.
imp. = impurity
Cm.-1 Microns I 151. Barium permanganate Ba(Mn0a)t 840 11.9 m , s p 877 11.4 s 913 10.95 s 935 10.7 m
156.
vs, b m,sh s,sp m, b
750 940 1625 3450
10.75 s , s h 2.9 w
134. Zinc chromate ZnCr04.7HzO 720 13.9 m 795 12.55 s 875 11.4 940 10.65 1050 9.5 1090 9,l5 s,b 1183 8.45 m 1620 6 . 1 5 vw 1820 5.5 vw, b 2700 3.7 w, b 3450 2.9 s,b
vb
Cm.-1 Microns I 140. Calcium dichromate CaCrzO7.3HzO 725 1 3 . 8 vu. 830 12.05 m 900 11.1 m 940 10.65 s 1625 6.15 m 3450 2.9 s 141.
Sodium chromate NaKrOd 14.7 m
i?:: 11.2
vs
1410 1780 2000 2860 3070 3150
Ammonium chloride* NHiCl 7.1 8 , sp 5.75 w,b 5.0 vw 3.5 m
::?!}
159. Barium chloride BaClz.2HzO 700 1 4 . 3 vs, vb 1615 6.18 8 , sp 1645 6.07 8,sp 3370 2 . 9 7 vs
2918 2861 1458 1378 720
160. Nujol 3.427 s 3.495 a 6.859 m 7.257 m 13.89 w
V O L U M E 2 4 , NO. 8, A U G U S T 1 9 5 2
1259
one of the salt plates with a very thin layer of solid paraffin to The purities of the samples are indicated in the legends for the hold the particles in place (6, 7 ) . The fine powder may be precurves. pared by grinding, by evaporation of a suitable solvent (6, 7 ) , or Some idiosyncrasies of the curves warrant mention. Many of by sedimentation ( 5 ) . Vacuum evaporation which has been them show weak remnants of the carbon dioxide bands near 4.3 used for preparing films of ammonium halides ( I I ) , may be useful and 14.8 microns. The latter always appears as a sharp upward for other relatively volatile inorganic materials. pip. Many of the curves exhibit a drop in transmission near Spectroscopic Procedures. 8 1 1 samples were examined from 15 microns and then a small increase beginning at 15.5 microns. 2 to 16 microns with a Baird XIodel A infrared spectrophotometer. The initial decrease is due to the absorption by the sodium chloride Wave lengths are accurate to about zt0.03 micron, although for plates, which was not compensated in the reference beam. The broad bands the error of judging the center may exceed this. It reason for the later increase is not known, but it is not real. It was sometimes found that duplicate spectra for the same comhas the effect of suggesting an incorrect position for bands near pound differed by more than this amount. Some oossible reasons are mentioned below. Table 111. Infrared Bands of Various Nitrates (Cm.Representative ex a m p 1 es of Intensity m, s p a w m, sp w VS S S VS vw several ions were examined in .. , . 836 .. 1358 .. .. 1790 2428 the potassium bromide region 824 1767 .. 1380 , . .. 733 803 835 1318 .. with a Perkin-Elmer 12B spec, . .. 820 1044 (1359) ( 1430) (lii0, 737 .. 815 .. 1387 1795 1441 .. 2iio trometer. Likewise, a series of 729 .. 817 .. 1352 1418 1774 (2410) ten nitrates was examined in the (1785) .. 835 .. 1361 , . . . (1640) i6ij .. (807) 836 ., 1372 .. rock salt region with this same 836 .. 1378 .... 1587 1790 2431 726 807 836 .. 1373 , . .. instrument in order to fix the Bands >3000 cm.-L are omitted. wave lengths of absorption more ( ) Baird values, less accurate. accurately. a w, ni, s = weak, medium, strong. g p = sharp. v = very. No attempt was made to put the spectra on a quantitative basis. RESULTS 16 microns. For example, in ferrous sulfate heptahydrate The spectra are presented a t the end of this paper. Table I ( S o . 91) the curve indicates a band a t 650 cm.-l (15.5 microns), lists the compounds examined and gives the numbers of the corbut actually it is a t 611 ern.-' (16.5 microns). responding spectral curves. Table I1 summarizes the positions DISCUSSION OF RESULTS of the bands in wave numbers and in microns, and gives estimated peak intensities. If more precise wave numbers have been The spectra range in quality from surprisingly good ones, with determined with the Perkin Elmer spectrometer, they are used. sharp, intense bands (see curves for barium thiocyanate dihyAsterisks indicate those compounds examined in the potassium drate, No. 28; strontium nitrate, No. 44; and ammonium bromide region. hexanitratocerate, No. 157,) to very poorly defined ones such as The spectra themselves are shown in graphical form. Nujol those for potassium silicate, S o . 32; monobasic magnesium bands are marked with asterisks; portions of curves run in fluorophosphate, No. 69; and monobasic potassium orthoarsenate, lube are indicated by an F. The spectra of Nujol and fluorolube KO.75. I t seems to be characteristic of the phosphates, and are included for comparison (No. 160). I n a few cases the ponder especially of their monobasic and dibasic modifications, to have was used without a mulling agent; these are indicated by P. ill-defined spectra. The reason for this is not clear, but it may be due to lack of a single, well-ordered crystal c rn-1 structure. Effect of Varying Positive Ion. One of the purposes of this study was to ascertain whether the various ions have useful characteristic frequencies. It was therefore of interest to know the effect of altering the positive ion. The spectra of ten SUIfates are shown in Figure 1 in the form of a line graph. I t is seen that two characteristic frequencies occur, one a t 610 to 680 em.-' ( m ) and the other a t 1080 to 1130 cm.-l (s). There is enough variation between the individual sulfates so that it is often possible to distinguish between them from the exact positions of the bands. Table I11 presents similar data for ten nitrates. Again there are characteristic frequencies, a t 815 t o 840 cm.-' (m) and 1350 to 1380 (vs). The authors I have been unable to find any orderly relation between the positions of these nitrate bands and a MnSO4.2W property of the positive ion, such as its charge or I I mass. This is not surprising, for there are a t least ZrSO4.4W three reasons why a frequency may shift slightly as I I1 . I C r S 04' K2S 04 the kind of positive ion is changed. 24 W
Figure 1.
Comparison of Infrared Spectra of Ten Sulfates W. Water vh. Very broad s h . Shoulder
The different charges and radii of the various positive ions produce different electrical fields in the various salts. These doubtless affect the vibrational frequencies of the negative ions. (Continued on page 1298)
ANALYTICAL CHEMISTRY
1260 IW
/4n I
I
I
10
A~
Z;\ $U:
z
i
40
f~
20
,
~
~
1
J
~I
2
500)
4
8
7
low
Urn
2SW
5 6 I WAVE LENGlH IN MICRONS
WAVE NUMBER5 IN CM' ,5WI,W ?OW
I200
IIW
~
\
~
Sodium metaborste, NaBOz
;I
C.P.
~
I
0
I
,
F
= bo
W
I
10
liW
Iwo
I1
12
I
I1
1s
I4
' 0
WAVE NUMBERS IN CMI 9w
aw
b2S
700
Magnesium metaborate, Mg(BOz)z.SH:O C.P.
2
1
4
5 b 7 WAVE LENGTH IN MICRONS WAVE NUMBERS IN CM
5wo
100)
Urn
2100
lwa
Ism
,104
I
I1W
9
I100
IO
IIW
Iwo
12 I1 WAVE LENGTH IN MICRONS
11
9w
I4
WAVE NUMBERS IN CM' I00
IS
7w
I6
b2S 100
lM
Lead metaborate, Pb(BOdn.Hz0
IO
IO
560
bO
C.P
3
z
g*
40
z
20
20
0
I
2
4
5 6 7 WAVE LENGTH IH MICRONS
8
IO
P
I,
I1 I1 WAVE LENGTH IN MICRONS
I4
IS
I6
0
Sodium tetraborate, Na2BO. 10Hz0 C.P.
WAVE LENGTH IN MICRONS
WAVE LENGTH IN MICRONS
WAVE NUMIRS IN C H 500)
(ooo
100)
2Mo
low
,5Wl,W
1100
IIW
llW
Iwa
9W
WAVE NUMBERS IN CM1
ud
IM
7w
625
Potassium tetraborate KgBdO?.5HzO
IO
c
iz * z
e
1"
:
20
0 WAVE LENGTH IH MICRONS
WAVE LENGlH
IH
MlCRMlS
P.
V O L U M E 2 4 , NO. 8, A U G U S T 1 9 5 2
1261
IW
80
1
I
.
E
i ZbQ
I
z
I!
r
"
10
1
1
,
C.P. M)
*
Y
~
v
20
0'
I
IW.
4
5
8
7
b
\l/*la/ !1
s
I
11
IO
0
1
10
II
0
11
I1
I4
I.
I5
IO
V "
l
*
j
I V
ilo
1
'1'"Sodium perborate,
60/
r
I
?;aBOa.lHdI Y
E'O
'
I
'I
10
s5
Manganese tptraborate, MuB4&.8HzO
6'*
j
II
L'
f, '0.
1
I I
\AIL
I
I
I
~
~
I
1
6
7
1 I
V
(0
*
I
~
:L/;
I
C.P.
lh/--,
I
~
10
I I I
I
l
l
I1
I I1
I1
10
0 I5
I4
Ib
Boric acid, HiBO 02.
SVX 100.
Y
IO
1VX
4oW
.
odium molybdate.
SaAfo0~2HzO .4 R
Iopdurn
-2
lwo
ludm
Iffl
AT
M
P
I
$@
M
I
*
I
/
Z"
\
!~
:
Y
20
C.P.
i
~
I
2
P
molybdate, I 43:Im Potassium KzMoo4.mo
1
i
\J
I
I
P
f
10
I
'10
~
O
1
I
4
'
-" . I
S b WAE W T H M UCRONS
l o
8
9
0
,I
1 I1 WAVE LENOlH IN W C U S
I,
IS
b
,4z .4 m nion u ni I
\
/
W
/
s
F
53 -,pf, J M
I"
he1)tamolybdate ~NH~)s~Io;Ou.4HiO
-
x
U
I
.1R 4
10
10
0
0
1
1
4
5 b 7 WAVE LENOM IN MICRONS
8
V
IO
!
1
1
I.
I5
I6
WAVE LENOW IN WCRONS
WAVE NUMBfRS IN C M '
5
lm
Sodium tungstatr, S~~WOL~IIIO
(0
c P. M
10
1
I
I
5 b 7 WAVE LEN6M IN MICRONS
D
.
0 ,I
WAVE I 1LEN6TH 111 11 MKRONI
I.
I5
Ib
1289
Potassium tungstate KzWO4 C.P
Calcium tungstate
Caw04 Pure
WAVE NUMIIERS IN C M ' 15% I100
I1W
IM
IIW
em
Iwp
..
WAY€ WMERS IN CMI 800
'15
7m
I
I '
-,i
\
,~
',
I48
~,-.--
I4
?
~
Sodium permanganate. NaMnOc3HzO C.P
bo
'
1
"i,:
I * f
-
i
I
10
;,
W
1
0
3
1
4
I
5 6 7 WAVE LENGTH IN MICRONS
9
IO
WA-
WAVE NUMlElS vi C M ' yxxl
Mm
UD)
IW
1m
2mo
lxx)
lux)
llm
,100
IIW
Imo
.m
I3
I2
I
0
I4
15
W l H IN Y C I C U S
b
W A M NWlERS IN W-l
7m
8rn
b25
im
10
I4
E 5
AR
= 60
M
4
-
5
Potassium permanganate, KhlnOi
40
10
P
10
20
0
1
4
5 b WAVf LEN6TH IN MICRMIS
7
8
1,
11 11 W A M LWOTH IN MICRONS
I.
0 I5
Ib
Calcium permanganate, Ca(MnOa)z.4Hn0 C P
ANALYTICAL CHEMISTRY
1290
Bariuui permanganate Ra(3lnOi)z C.P.
Sodium ferroeyanide, SaiFe(CN)s.lOH.O C.P
Potas.ium ferrocyanide, KqFe(CX"i).3I1~0 hK
sbx rom '
rn
2rm
15m
-
Im
10
\
f
n
Ef M
I
E
II
\,
4
110
Pure
i~
60
10
I
,I
*
IO
IIO
I I
l
I
0
I
4
Ca!cium ferrocyanide, CarFe(CN)s.l2H>O
I54
I
I
J I
I
I J
5*
I
I
I 5
b
7
I
O 9
0
I
I1
,I
I,
I5
Ib
Potassium ferricyanide, KsFe(CN)s
AR
V O L U M E 24, NO. 8, A U G U S T 1 9 5 2 5WO
IMo
1wP
2x4
WAVE NUMBERS IN C M 1 1x4 I r n 1wP
I1W
1291 IIW
IIW
WAVE NUMBERS IN C M '
lca
aw
VW
615
7W
Sodiuiii coliultiriitritr NarCo iSO.!*
f-
~
I 1
I
1
LO
1 -
% . K
I
I
I
I
i
1
I I
157Iw
r-\ I
I
'e
I ~
10
AR
Barium chluride, BaC12.2H10
.i R
ANALYTICAL CHEMISTRY
1292
Table IV. 1.0 1
Eniiwion Sa
I.; Ca
To explore this possibility, u series of eight synthetic mixtures wa? prepared and analyzed independently by the three techniques. ( A photographic x-ra!. procedure was used.) This iriformation was then pooled, thr data were re-esamined, and ii combined analysis was obtained. The test was not completel!fair because it, was known that infrared spectra have been ohtained for nearly all the inorganic salts in the laboratory, and that t'hese same salts would he used in making up the mixtures. I n addition, t,he components n-ere mixed in roughly equ:il amounts by bulk. The results are shoa-n in Table IT'. The analysis of misture 3 is discussed in greater detail below. I t is apparent that no one of the techniques by itself is powerful enough to give a complete analysis of even these idealized unknoums. This is partl)- because there was no prior information about the caontent of the samples, and therefore every possibility had to be considered. -1s xith any other anal) much more detailed and reliahlr
Use of Infrared Spectra in Qualitative Anal>-sis
Independrnt d n a l y - e . Infrared SaHCOi
Final Cornbined rinalysis
X-ray
Actual Composition WaHCOi
CaCOr KSOi
NH4NO.I SO,--Silica eel
4T14SOI Very poor pattern
B
Silica gel
.II
Ph
x
Yellon
4
I'ellon-
Na ICKr20; K N a S C S or N H i K S Cr Ifp(cloi)? Sulfide odor Ph Y Cd SiL?HlOi Bi
B
Sa
AI K*CI.yOi NaSCN AIg(ClO,)?" Pb 1
Sothing Very poor p a t t e r n
KilCrzOi S-aSCX
RSCS CaS0. L H j O
NazBIO; 10H?O CdS SaBiOx '!
SatBaO; IOtLO CdS
')
c ?P
.\IO
Ca I.; S a '?
Sr 11
K*S?O6 CaCOa PhCrO4 KazSOr Y Caar PO, I 2
Sh Si P
ca C
P?
Ba Na
I.
.11 ? SI.? 7
KaI.03 Ba(K0s A nitrate; prohahly BaPhSOI '? isos)?.possibly SaSOz Other component(s) Possibilities: Another nitrate, SaBrOl. Sa?WO, or K?\VOi. S a l l o O , or K l l o O ~
Changing the positive ion may produce a different crystallin? arrangement, resulting in a different symmetry or iiitensity of the electrical field around a negative ion. A difference in t,he type or extent of hydration probably alters some of the frequencies.
Cm-1 700
600 8 BO; 840:
3
c coj
a
nco;
3
SILICATES N NOi NO:
900
1100
!OW
1200
Z
4
s
Y
soq
¶
*A L l
1
-
II
L
nso;
3 5
ClOi Br Br 0;
I lo;
v voj c, c,o; GE .o= !
* s
i
- k l i
I
-1-
1 3 4
I
3 3 2 8
,
5
A
4
600
Figure 2.
700
800
900
1000
1100
IPW
1300
1400
Characteristic Frequencies of Polyatomic Inorganic Ions
m, w. Strong, medium, weak sp. Sharp s.
-
L *LP
No h b o i 2 w wo; 3
Mn MnOZ
-
A
s20j 2 szoi 2 se sao; 2
s*o; c uo;
A
,
1
IO
s20g
-
+
NH;
17 P Po: 9 HPOq 6 H PO' 5 2. 4 5 SO; 6
1400
1300
-21
SCN'
the other hand Hunt, J\-isherd, and Bonham ( 5 ) found that for anhydrous carbonates there is an approximately linear relationship between the wave length of the 11- to 12-micron band and the logarithm of the mass of the positive ion(s). Hunt has kindly pointed out that, the authors' data tit his curve, with the exception of lit,hium carbonate. Characteristic Frequencies of Inorganic Ions. Just as with sulfates and nitrates, most other polyatomic ions exhibit characteristic frequencies. These are summarized in Figure 2 . It is evident that they are distinctive and that they do not have a great spread in wave numbers. Qualitative Analysis. The usefulness of these charactei,istic frequencies in qualitative analysis is obvious. It appeared that the infrared spectrum might give, rapidly and easily, some information about the polyatomic ionE that are present in an unknoivn inorganic mixture. If only one or two compounds are involved, it might, even be possible to narrow the possibilities to a fex- specific salts. It also seemed that a combination of infrared, emission, and x-ray analysis might be very effective. Presumably emission analysis would determine the metals, infrared would say something about the polyatomic ions, and x-ray analysis might, give their combinat,ion into specific salts. 011
800
3
* In most, but not all, examples ** Literature value
V O L U M E 2 4 , NO. 8, A U G U S T 1 9 5 2
1293
results can be obtained if there is some advance information ahout the nature of the unknowns. However, Table I\- also shoTvL: that the three techniques are nicely complementary, and th:it together they are capable of providing a considerable amount of information even when such prior knowledge is lacking. Although thrre are two or three surprising errors in the combined :inaI?ws, the over-all rwults are verj- encouraging. It is espec-iall:. noteworth>-that the actual chemical compounds are giveir iri miny ca.vs. WAVE N U M B S IN CM.1 15W1400
1100
1100
IIW
1000
tain possibilities for the x-ray analysis which greatly simplify its interpretation. The advantages of this physical analysis include small sampk requirement, reasonable time, and the ability t o determine the actual compounds in man>- cases. I t is evident, too, t'hat any or all of these three techniques are valuable preliminaries to a ishemica1 analyis on an unknown material, especially a quantitative one. Variability of Spectra. It is not uncommon to find that the spectra of t,wo samples of the same compound are somewhat different. There are several possible reasons for thin.
In the spectra of sodium IMP~RITIES. cyanide, potassium cyanide, and potassium cyanate (Xos. 21, 22, 23) bands have been marked that are plainly due to 60 the corresponding carbonates and bicar2= bonates. CRYSTALORIESTATIOX. It is well knonm that the spectra of anisotropic y crystals depend on the orientation of 8 the sample. Consequently it is desirable io t o have completely random orientation of the crystallites to avoid such effects. This is an additional rewon for grinding L p d 0 the sample very finely. I5 Ib 8 9 IO 11 12 I3 I4 WAVE LENOTH IN MICRONS PoLnioRPmsai. Different crystalline forms of the same compound are often Figure 3. Portion of Infrared Spectrum of Lead S i t r a t e raDable of eshibitine slightly ., . different infrared spectra ( 2 1 1.. WAVE NUMBERS IN C M ' \ . A R Y I S G DXGREES O F HYDRATIOX. 1200 1100 1000 900 800 ~
t>
8
I
-4
0
IO
II
WAVE LENGTH,
Figitre 1 . I n vier\
caw
12
I
2 5 y
,
I3
1.1
Znonialous H a n d in Unknown 3 (:a301 .hould be w r i t t e n C a S 0 ~ . 2 A ? 0
Isi)i\-ii)i..ii, Ti:i.iisrui I.>. S-I,:~?. :in;ilysis of a conipletely o i r i i ~ \vhi~11 ~ thrr(J art' nlow than two unknowi sani~)IeI ~ ~ ~ i ~tiiffii.ult coniponc~ntr. It is not :i1)plii,:iI)lv t o noncrystallinc material.. ( r f . unknown 2 ) and runs into troul)lc \\-ith substances that gaiii 01' lose water of hydi,ation readily. I n both c5ase.q infmred i i often a rcliable tool. Suhstanc~eslike metal osides, hytirosides, and sulfides gener:illy h:ivcl no sharply defined infrared absorption from 2 t o 10 i d e from possible water and 0-H bands. On the ot1rc.r y are often good samples for x-ray analysis (vf. cadmium sulfide in unknown 4). The principal fault with emission analysis is its great sensitivity : it is frequently difficult t o distinguish between major components :ind impurities. This fact arcounts for t,he surprising oversight 01 cdcium in unknoivn 2 , and tungsten in 8. Infrared examination has advantages over wet chemistry for detecting the more unusual ions, such as BOz-, B407--, SzOs--, and S?Os--, since these are not included in the usual schemes of
The proper sequence in using these techniques is the order cniission, infrared, and then s-ray. The first two present rer-
Several esamples of variable spectra have been otiserved, lor Lvhirh the muse is not definitely knonn. Tn-o different samples of potassium metabisulfite, KzS206,were esaniincd, and proved to have different, patterns of band intensities in one region (see curve 104). I n potassium carbonate there is a hand a t 880 c m - ' or a t 865 em.-', and in one spectrogram out of a total of ten hoth hands appear. There is no cleai correlation b e t w e n position and water content. Figure3 shows that the mode of preparation is important. It rompares the spectra of two lead nitrate samples, one prepared nornially with Sujol and one with very little Sujol. Differmces near 1300 rm.-l and 880 t o TOO cm-I are striking. This may be an orientation effect. X more baffling case of unexpected variation was ol)serveil with unknon-n S o . 3. In analyzing this by infrared, calcium sulfate dihydrate was missed completely and magnesium percahlorate \\-as reported in its place. The reason is brought out in Figure 4. Pure calcium sulfate dihydrate has a single broad lmnd centered near 1140 cm.-' (8.8 microns), whereas in inisture 3 a strong doublet was observed a t 1080 and 1140 cni.-l Thtx origin of the doublet was puzzling berause no other ($omponcnt of 3 but calcium sulfate has a band near here. Calcium sulfate dihydrate had been run as a Nujol mull and mixture 3 as a dry powder. Reversing each did not change their spectra. Then calcium sulfate dihydrate was mised with each of the other components in turn in the dry state, and the mixtures \wre es:mined as Nujol mulls. It \vas found that the misture with ium thiocyanate gave a doublet. \Tith sodium thiorj-anate there was also a doublet, but it TI-as much less pronounced. It seems unlikely t,hat a chemical reaction between calcium sulfate dihydrate and potassium thiocyanate could account for these peculiar results, bemuse the materials are in the solid state. Two other possible causes are changes in crystal structure, presumably caused by changing the hydrate, and an orientation effect. The following observat,ions seem to rule out variable water content as a cause, and suggest the orientation effect.
A calcium sulfate dihydratepotavsium thiocyanat'e mixture heated a t 170' C. for 3 days gave the two bands near 1100 em.-' Only one band was found after the salt plates were separated and t h e mull e ~ p o s e dt o air for an hour.
A N A L Y T I C A L CHEMISTRY
1294 Another portion of the same heated mixture was esposetl to air under more humid conditions for an hour and then mulled in Nujol: two bands again resulted. This mull was opened to the air for an additional half hour, and only one band was found. \\-hen calcium sulfate dihydrate alone was heated overnight a t 170" C., three bands were found. The sulfate vibration absorbing near 1100 cni.-l is triply degenerate (12), and this may be a case of splitting of the degeneracy as a result of altering the crystal symmet'ry. Finally, potassium sulfate has exhibited a similar variability in this same band, .
~
_-_
Table V. Characteristic Frequencies i n Complex Ions Complex I o n
Fe(CN)s--Fe(CKjc---Fe(CS)sNO--
cm.- 1 2100 -2010 2140 1923
847
Ce(S0ds- -
1336 1430 745
SO?
1080
1260 1420 1530
Simple Ion
csC?i cs -
XO (gac)
SOP SO,-
cm.-1 2070-80
2070-80 2070-80 1878 820-33 1235-80 1328-80 i26-40 815-35
...
13.40-80
I t is much safer to base arguments on the identity of spectra than on their nonidentity. >lore empirical experience with the spectra of salts from many different' sources should improve t,his situation. Miscellaneous Observations. AXOMALOUS DISPERSION ANU CHRISTIAXSEN FILTER EFFECTS.These have been adequately described in the literature ( 5 , 9). Examples will be seen in the steep-sided band of magnesium carbonate a t 3 microns (No. 13), of sodium thiocyanate near 5 microns (No. 26), and of potassium ferricyanide near 5 microns ( S o . 155). WATERAXD HYDROXYL BAXDS. The sharpness of the \\-ater bands near 3 and 6 microns in sodium and magnesium perchlorate (Nos. 117, l l S ) , and the high value of their 0-H stretching frequency ( >3500 cm.-I), are striking. Apparently t'here is very little hydrogen bonding in these salts. It, is interesting t o note that animoniuni perchlorate (KO. 116), \vhicah forins no hydrate, has a high K-H stretching frequency. Other compounds with sharp water bands are barium chlorate (KO.115) and 1)ai~iuni chloride (No. 159). I n bicarbonate there is a band a t 2500 to 2600 cni.-', in Iiisulfate at 2300 to 2600 cm.-' (very broad), and in HPOI--, H2P04-, HAs04--, and HP;IsO4-at about 2300 em.-' (very broad). Their
is evidence that these are 0-H stretching frequencies of the hydroxyl groups attachrd to the rentral atom. B.%RInf CHLORIDE.Several chlorides of the purely ionic type were examined to observe how the hands due to watcr of hydrat,ion varied. Among these was barium chloride dihydrate ( S o . 159). Surprisingly it has a strong band a t 700 cm.-', which )\-as totally unexpected but was c,onfirnied on a second sample. I t is not attributable to carbonate or bicmhonate, hut may tie due to a torsional motion of the w:itcr molecules in tlic lattice. COMPLEXIoss. The rliaracteristic. frequcncic:; carry over moderately wcll into roinplex ions-for exainple, pot ricyanitie has a band a t 2100 c m - l , and each of the rhree ferrocyanides has one near 2010 cni-'. This is obviously thc stretching frequency of the C S - gi'oupj which in simplr ryanides is 2070 to 2080 c i n - ' Other examples are shon.n in Tnl)le V. CoIiPoazrns WITH So ABSORPTIOS.Sickel hydroxide, fci~ic* oside, cadmium sulfide, and mercuric sulfide have no absorption in the rock salt rcgion aside from watcr mid hydroryl hands. ACLYO&LEl)(;\I
EX1
The authors are inciel)ted to two colleagues, D. T. P i t i i i x i i and E. S. Hodge, for carrying out t h r x-ray and emission analyses, respectively. Helen Golob prepared many of the curvrs. The Chemistry Departments of the University of Pittsburgh and Carnegie Institute of Technolog!- graciou3ly provided many of t,he samples. LITERATURE CITED
Colthup, N. E . , ,I. Optical S o c 40 397 (lCJ50'. Glockler, G., Rec. M u d e r n I'hys., 15, 111 (1913). Hersberg. G., "Infrared and Raman Spectra of Polyatomic Molecules." Sew I-ork. D. Van Noatrand Co., 1945. (4) Hihhen, J. H., "The Ranian Effect and Its Chemical -ippIications." S e w York. Reinhold Puhlishinrr Coru.. 1939. ( 5 ) Hunt, J . M.,Wisherd. 11.P., and Ronhani, L. k., .is\r.,C H i c v . , 22, 1478 (1950).
Lecomte. J., AM^. Chim. d c t n . 2, 727 (1948). (7) Lecomte, J.. C'ahiers p h y s . . 17, I (1943!, and referelives cited therein. (8) Sewman, It.. and €Idford, R. S.. .I. C'Aem. Phys.. 18, 1 2 i 6 , 1 9 1 (6)
(1950'.
(9) Price, TT. C.. and Tetlow, K. S . , I b i d . , 16, 1157 (194q). (10) Schaefer, C.. and Xlatossi, F.. "Das ultrarote Spektrum," Herlin, Julius Springer., 18:30; repi.inted by Edwards Bi,os., Inc., Ann Arbor, l f i c h . (11) \Vagner, E. L., and I-Ioi,nig, D. F.,J . Chem. P h y s . . 18, 296, 305 (1950). (12) Wu, Ta-You, "Vibrational Spectra and Structure of Polyatomic Molecules," 2nd ed., .%nn .%I hor, Mich., J. W.ICcIwat ds. 1946. RECEITED for review July 3 , 1931
.ici.epted J u n e 7 , 19z2
