NOTES
March, 1958
367
'
the above-mentioned unit cell becomes b-centered, and a smaller unit cell can be selected with the symmetry Czh-P21/m or Cz-P21 and $he dimensions a = 6.85, b = 11.51, c = 6.57 A. and 0 = 110.2"; cell content, Ca3(NH4)2(P207)2-6H~0. The smaller translational distances of the subcell, along with the symmetry elements of (% of the larger cell, generate the remaining symmetry elements of C&,, which suggests that C&, is the more probable of the two possible subcell space groups. For this to be true, NH4+ and P20,4- must be in special positions in the subcell. The Ca++ may be in either general or special positions, but in either event there would be a 1-in-4 deficiency of calcium to fulfill space-group requirements. This may account for the diffuse reflections. All the crystals suitable for single-crystal X-ray study had overgrowths of the other calcium ammonium pyrophosphate. A comparison of the relative intensities of the diffuse reflections of two crystals with different amounts of overgrowth indicated only a remote possibility that the overgrowths could have caused the diffuse reflections. Prevalence of the overgrowths suggests that the two pyrophosphates may be structurally related or a t TABLEI X-RAY PATTERNS (Cu KLYRADIATION; CAMERA DIAM. least have similar unit-cell dimensions in two directions. 14.32 CM.;WEDGE-SHAPED SAMPLE) Both crystalline salts have been synthesized also Ca(NH4hPzOr. HzO CadNHdz(PzO7)z. 6H10 from tetrasodium pyrophosphate, calcium chloride d , A. I d,A. I I d,A. I and ammonium salts. 7.23 VS 2.52 M 7.27 VW 2.39 W
drolytic degradation of vitreous calcium polymetaphosphate. Chromatograms of 5% acetic acid solutions of the crystals were identical with pyrophosphate chromatograms. Optical and X-ray properties are reported here. When concentrated NH40H is added t o the viscous, water-immiscible liquid product of the treatment of vitreous calcium polymetaphosphate with water,' a precipitate is formed. Initially amorphous, it crystallizes as spherulites when left in the mother liquor several days. Similar crystals are formed slowly when vitreous calcium polymetaphosphate is treated with concentrated NH40H. Average observed mole ratios CaO :NH3 :Pz06: HzO of 1.13:1.90:1:2.30 in the air-dried product suggest the formula Ca(NH4)2P207.H20. The crystals are thin, colorless monoclinic blades, tabular on (100) or (001). The refractive indexes are a = 1.520, 0 = 1.537, y = 1.540. The crystals are biaxial (-) with 2V = 40" (obsd.) or 46" (calcd.), y = b. Bx, lies in the a-c plane and is inclined to the plate by 68". Interplanar spacings and visually estimated intensities are shown in Table I.
5.51 4.86 4.23 3.86 3.56 3.39 2.98 2.90 2.85 2.75 2.68
WM S WM W VW MS M M VW
2.44 2.39 2.32 2.11 2.06 1.52 1.88 1.72 1.69 1.47 1.45
W VW
VW VW VW W VW W WM VW VW WM WM
6.35 5.73 5.56 4.95 4.20 3 27 3.19 3.11 3.07 2.84 2.74 2.70 2.59
W
S M MS WM M M W S W VW VW VW
2.23 2.18 2.13 2.09 1.88 1.85 1.80 1.73 1.64 1.56 1.50 1.42 1.41
VW VW VW W VW W W VW VW VW VW VW VW
Exposure of Ca3H2(Pz07)~.4H2Oi to concentrated "*OH for several hours yields another product, Average CaO :NH3 :P205 :H2O mole ratios of 1.51: 0.99: 1:3.52 in four preparations indicate the formula Cas(NH4)z(Pz0,)2.6H20. The crystals are monoclinic tablets or plates, tgbglar on (001). Principal forms are (201), (201), (012) and (001)-modifying forms, { 010) and { 1101. The crystals are biaxial (-) with 2V = 60" (obsd.) or 61" (calcd.), OAP = 010. N , A a is 27" in acute p. The refractive indexes are a! = 1.520, 0 = 1.528, y = 1.531. The powder pattern is shown in Table I. Lattice constants, as determined from b- and c-axis rotation and Weissenberg patterns, are a = 7.67, b = 11.51,C' = 11.00 b. and 0 = 92.5'. The systematic extinctions, hQ1 with h I odd and OkO with k odd, indicate the space group Cih-P21/n. With a unit-cell content of 2 [Ca, (NH,) 2 (PZO7) z.6H20], the calculated density is 2.08 g./cc.--exactly the density calculated from refractive indexes. Reflections hkl with h 1 odd are weak or absent and are elongated parallel to c*. When these are ignored,
+
+
(1) E. H. Brown, J. R. Lehr, J. P. Smith, W. E. Brown and A. W. . , Frazier, THIS JOURNAL, 61, 1665 (1957).
VIBRATIONAL SPECTRA OF DIMETHYL ETHER I N THE LOWER FREQUENCY REGION BYYO-ICHIRO MASHIKO AND KENNETH S. PITZER Contribution from the Deparfment of Chemistry, Uniuersify of California Berkeley, Calzfornia Received October 1 7 , 1967
There is some ambiguity in the assignments of the two torsional oscillations of methyl groups about the C-0 axes of the dimethyl ether molecule.'S2 It is the purpose of the present study to 100,
0
I
I
150
zoo
I
1
I
250
300
350
I
400 420
c m:'
Fig. la.
ascertain these frequencies by further measurements of the Raman and infrared spectra. Only Ananthakrishnan3 observed the line a t 160 cm.-l in the Raman effect and there is disagreement (1) K.S. Pitzer, J . Chem. P h y s . , 10, 605 (1942). (2) G . Heriberg, "Molecular Spectra and Molecular Structure. 11. Infrared and Raman Spectra of Polyatomic Molecules," D. Van Nostrand Co., New York, N. Y., 1945, p. 353. (3) R. Ananthakrishnan, Proc. I n d . Acad. Sci., A S , 285 (1937).
NOTES
368
Vol. 62
I
i c m.-'
*
Fig. lb.
a
among several authors in the observations near 300 cm.-l.*--6 The Raman spectrum was taken in the liquid phase without a filter. The far infrared spectrum was studied through the region of 23 to 60 p with a spectrometer described by Bohn, et al.' The usual rock salt region was studied with a Perkin-Elmer model 12C spectrometer. Both regions were measured in the gas phase under appropriate pressures. Results obtained were as follows: Raman: 164(0b), (e); 251(0b), (e); 334(0), (e); 414(lvb), (e&); 489(0b), (e); 530(0), (e$); 918(7), h e , + , f,g,k,i); 1105(lb), (k); 1142(lvb), (k); 1377(0), (k); 1392(0), (k); 1451(4vb), (e,k); 2814(10), (q,p,l,k,i,e,f,g); 2685(7), (k,i,e,) ; 2886(1), (e,k); 2918(5), (q,p,k,i,e) ; 2951(4), (q,p,k,i,e) ; 2985(6), (q,p,k,i,e). Infrared (22-60 p ) : 210-270 (m,b), ca. 410(m). Infrared (2.5-15 p 8 ) : 921(m), 937(m), 1098(s), 1115(s), 1169(s), 1187(s), 1248(w), 1464 (m), 2022(w), 2047(w), 2098(m), 2430(w), 2630(w), 2710(w), 2845(s), 2900(s), 2980(s). Here, frequencies are expressed in cm.-l. (0), (7), etc., are the Raman intensities visually estimated on the plate; b or vb indicates that the line is broad or very broad; e, k, etc., denote the exciting mercury lines Hg-e, Hg-k, etc; w, m, and s denote weak, medium and strong infrared bands, respectively. The weakest Raman lines are on the border of detectability and cannot be taken as absolutely certain. A plot of the infrared absorption spectrum is shown in Fig. 1. In the lower frequency region there are five Raman Lines and an infrared band in addition to 414 cm.-', which is clearly the GO-C bending vibration. These are to be assigned as two modes of torsional vibration together with overtones and combinations. Assuming the point group of the molecule to be Cz,, one of these vibrations has a symmetry class Az (Raman active, infrared inactive) and the other Bz (Raman and infrared active). One can quite definitely assign 265 cm.-l to Bz, since A2 is infrared-inactive and 265 cm.-l is actually observed in the far infrared region. The peculiar infrared contour in the 200-270 cm.-l region is ascribed to a superposition of hot bands at lower frequencies on the 0-1 transition at 265 cm.-l. From a consideration of the vibrational motions, (4) S. C. Sirkar, Ind. J . Phys., 7 , 257 (1932). (5) N. G. Pai, dbid., 9, 121 (1934). (6) A. Hadni, Compl. rend., 289, 348 (1954). (7) C. R. Bohn, N. K. Freeman, W. D. Gwinn, J. L. Hollenberg and K. S. Piteer, J. Chem. Phys.. 21,719 (1953). (8) R. H. Pierson, A. N. Fletcher and E. 8. C. G a n t ~ Anal. . Cham., 28, 1218 (1956), present an infrared spectrum identical to our8 except f3r weak abflorptions near 1600 and 1875 om.-' which we did not find.
~-
Bz should be higher in frequency than An1v9thus leaving 164 cm.-l to be assigned as the latter. The BZ torsional motion is expected to be very anharmonic, hence it is reasonable to take the 0-1 transition at 265 cm.-l and hot bands in the 200-230 cm. -l region. Similarly, 164 cm. -l should be regarded as a lowered value of the true fundamental frequency because of the contributions of the corresponding hot bands t o the intensity of the Raman line. The true frequency was assumed to be 170 em. -I. We propose as the torsional energy level pattern of dimethyl ether the following formula, which is limited in applicability to levels well below the top of the barriers to rotation. E
-hc Eo = 1 7 0 ~ + ~ s2 6 5 ~ ~-2 3(vA,
-
- 21(VB,
I
C'
1)8A,
-
- 35 vA#B* where V A and ~ VB, are the quantum numbers of the 1)&p
two torsional vibrations. Thus, the remaining Raman bands at 334, 489 and 530 cm.-l have the V A ~and V B , values (2,0), (0,2) and (2,1), respectively, in their upper states. The expected (1,l) band a t 400 cm.-' would be buried under the strong 414 cm.-' band. This pattern of levels is a refinement of the assignment of HadniB He has shown that this assignment of torsional vibrational levels yields thermodynamic properties in approximate agreement with those observed We had hoped to discuss the vibrational assignment generally and to refine the thermodynamic calculations, but circumstances make it more feasible t o continue this work separately. Acknowledgment.-We wish to thank Dr. Roger Millikan and Dr. Edward Catalan0 for their aid in the far infrared measurements. (9) K. S. Pitzer, J . Chem. P h y s . , 12, 310 (1944).
(IO) G. B. Kistiakowsky and W. W, Rice, zbzd., 8, 618 (1940). (11) R. 111. Kennedy, M. Sagenkahn and J. G.Aston, J . Am. Chem.
I
; t
I
t I
-t
! I I P "
I
Sac., 63,2267 (1941).
(12) A. Eucken and E. U. Franck, 2.Elektrochsm., 52, 195 (1948).
THE EFFECT OF AROMATIC NITRO COMPOUNDS ON MALONIC ACID BYLOUISWATTSCLARK Departmant of Chemistry, Saint Joeeph CoZleqa, Emmilaburg, Maryland Received October $1, 1967
Studies on the decarboxylation of malonic acid in non-aqueous, basic type solvents* have con(1) L. W. Clark, THISJOURNAL, 62, 79 (1958).
i
