900", making refractive index determinations im-
possible. Acknowledgment.-The author is glad to acknowledge the enthusiastic counsel of Dr. Harold C. Hodge throughout the course of the work. Summary 1. The mean refractive indices of powdered enamel and dentine samples, with differing and known density limits, were determined by the Becke line procedure. 2 . T h e refractive indices of dried enamel lie
1 C O V l RIBIJTION FROM THE
GATESAND
between 1.612 and 1.630 and are proportional to the density 3. The refractive indices of dried dentine lie between 1.555 and 1.580 and are roughly proportional to the density when the fractions are dried under the same conditions for both determinations. Vacuum drying brought about a marked lowering of refractive index. 4. Secondary cementum exhibited a refractive index of 1.560-1.570 which was little affected by vacuum drying. RECEIVEDSEPTEMBER 9,1938
CRELLKN 1,ABORATORIES OF CHEXISTRY, CALIFORNIA IX5TrTUTE OF
TECHXOLOGY,
So. 0681
The Crystal Structure of Ammonium Cadmium Chloride, NH,CdCl, BY HENRIBRASSEUR~ AND LINLJS PAULING In crystalline cadmium chloride, CdC12, there are octahedral groups CdCh condensed into layers, each chlorine atom being adjacent to three cadmium atoms2 Tetrahedral coordination is shown by cadmium3 with cyanide groups in K2Cd(CN)4, and with sulfur, selenium and tellurium atoms in the sphalerite and wurtzite type crystals CdS, CdSe and CdTe, and might well occur with chlorine also. There are accordingly two types of reasonable structures for complexes with the composition (CdCG),, the first involving octahedra with shared corners, as for example in the cubic crystal KMgF3, and the second involving rings or chains of tetrahedra, as in the metasilicates. We have determined completely the structure of the orthorhombic crystal NH4CdC13,and have found it to be based on octahedral coordination about the cadmium atoms, the CdC1, octahedra being polymerized into infinite double rutile strings which extend parallel to the c-axis of the crystal.
Experimental Methods and Results The crystals of NH4CdC13 used in this investigation were obtained by evaporation of an aqueous solution containing equimolar amounts of NH4Cl and GdCh. The transparent white needles used for the x-ray photographs were about 0.1 sq. mm. in cross section and 3 to 10 mm. in length. In addition to single crystals many twins were ob(1) Fellow of the Belgian-American Educational Foundation. (2) I,. Pauling, Pmc. Nail. Acad S G I, 16, 709 (1929), L Panlink and J. L. Hoard, Z. Krist., 74, 546 (1930) 13) R. G Dickinson 1 1 ~ TOURVAT, s 44, 774 (1922)
tained; the nature of the twinning was not studied. Crystallographic study4 has shown the crystals to be orthorhombic, with axial ratios 0.6059:l: 0.7992 and density 2.93. X-ray photographs prepared with 15' oscillation about the directions [loo], [OlO], and [OOl], with use of CuKa radiation filtered through nickel, gave the folfowing dimensions for the unit cell a(, = 8 96 * 0.02 A. ho = 11.87 * 0.03 8. co = 3 97 * 0.01
A.
These lead to the axial ratios 0.603: I : 0.267, in good agreement with the crystallographic values, after dividing the crystallographic c-axis by three. All indices used in this paper refer to the X-ray axes ao,bo, cg given above. The observed reflections show the lattice to be simple. The absence of prism reflections (hOZ1 with h odd and (OkZI with k 1 odd provides strong evidence that the space group is DijP n n m or its subgroup C,",-P n a. In the absence of any observed deviation from holohedral habit of the crystals, we have assumed the space group to be D$,;this assumption is given later justification by the derivation of a satisfactory atomic arrangement based 011 the holohedral space group. The Atomic Arrangement The sets of equivalent positions provided by D::-Pnam are
+
( 4 ) H. Traube, 2. Kuisl., 29, 602 (1898). A Johnsen, N. Jahrb. k'inernl, 2, 116 (1903).
Dec. , 1938
CRYSTAL STRUCTURE OF AMMONIUM CADMIUM CHLORIDE
4a: 000, 0+0, to+. ++$ 4b: 005, OQQ, +00, ++0 I C : xy 114, 4 x 4 y 1/4, - x t y3/4, q 3 / 4 Xd: X Y Z , x Q - y Z, xQ y Z, Q Z, ATZ, -x yz, $ x, Q - y + - 2 , x y Q
+
+ -
+
++
+
+-
+
+
+ ++
odd, in order to obtain the factors with which the
+
-z
The unit cell contains 4 NHhCdCb, the number of molecules calculated from the cell dimensions and density being 3.99. The possibility that 8 Cl occupy the positions 8d is ruled out by the small value 3.97 A. of co, since the distance c0/2 = 1.99 A. between non-bonded chlorine atoms is very much less than that found in any crystal. It was noted, moreover, that the intensities of the X-ray reflections indicate strongly that all of the atoms are in planes c0/2 apart. An arrangement of this type leads to the same structure factor for all the reflections (hkO), (hk2), (Rk4), etc., and also for all the reflections ( h k l ) , (hk3), etc.; and it was observed that on oscillation photographs the intensities of the reflections with I = 2 and I = 4 reproduce those with I = 0, but somewhat diminished because of the larger scattering angles, and that similarly the intensities of the reflections with I = 3 reproduce those with I = 1. This observation requires that all of the atoms occupy the positions 4c, forming layers a t z = l/* and L; = 3/4. (Layers a t z = 0 andz = l / ~are ruled out by the fact that positions 4a and 4b could accommodate only two of the five atoms in the molecule.) There are ten parameters to be evaluated in the determination of the atomic arrangement : x N H 4 , YNH4, XCdi Y C d i XI, YI, X I I ~3'11, XIII and 3'111 (the subscripts I, I1 and I11 referring to the three nonequivalent sets of chlorine atoms). As the first step in this process sections of the three-dimensional Patterson-Fourier diagram5 were made for the levels z = 0 and z = l/2, as recommended by Harker16with use of the general equation P(X,y,Z) = z h ZlC 21 1 FiLil / * cos %(hx + k y -t l z ) (1) The calculations could be based on the observed values of intensities of planes (hkO) and ( h k l ) alone, because of the intensity regularities, mentioned above, which result from the special values 1/4 and a/4 for the z coordinates of all the atoms. The function f 2 / Z z cf being the atomic scattering power and Z the atomic number) in its dependence on sin O/h has nearly the same values for the atoms Cd, C1, and N. An averaged function for these atoms was plotted, and summed over I for series of reflections (hkl), with I either even or ( 5 ) A. L. Patterson, Z Kuirt., SO, 517 (1935). (6) D. Harker, J. Chem. Phys., 4, 381 (1936).
2887
intensities for reflections (hkO) and (hkl) were multiplied to give the sums over I in Equation 1. The remaining double summations for z = 0 and z = '/z were then carried out with the aid of the Beevers-Lipson strips,' all of the data of Table I being used. The values of F given in the table were obtained from visually estimated intensity values by correction for the Lorentz and polarization factors, the temperature factor being ignored. Contour diagrams representing the results of the calculations are shown as Figs. 1 and 2.
1 1
Origin
b0/2
ad2
Fig. 1.-Patterson-Harker diagram for the section = 0. The peaks represent the following principal interatomic distances: A, Cd-Cd; B, Cd-ClI, CdC ~ I I I ; C, Cd-CIII (occurring twice); D, Cd-Chi, Cd-Clr; E, Cd-Clr; F,Cd-Chr.
z
Origin
bo/2
I
no/2
Fig. 2:-Pattersoti-Harker diagram for the section The peaks represent the following principal interatomic distances: A, Cd-Cd; B, Cd-Cd; C, Cd-CII; Cd-Cln; E, Cd-CIIII; F, Cd-ClI; G, Cd-Clrr : Cd-Ch.
z =
Peaks in the Patterson-Fourier diagrams represent interatomic distance vectors between pairs of atoms extending from the origin, weighted by the (7) C. A . Beevers and H.Lipson, Phil. Mag., 17, 855 (1034): Proc. Phys. SOC. (London), 48, 772 (1938).
HENRIBRASSEUR AND LINUSPAULING
2888
Vol. 60
TABLE I Reflections kkO, h + k even.
hkO
-
1
k
Foe~cd.
10 0 0 110 130 150 170
36.9 18.8 -11.6 -21.8 4.2 -11.8 9.6 11.6 38.2 -28.4 9.8 37.4 -15.3 -13.4 23.1 i.l -27.7 -17.7
120 140 160 180 1.10.0 1.12.0 1.14.0 1.16 0 1.18 0 210 230 250 270 290
24 8 i2.y 23 6 16.0 3G.4 33 4 1.5 . - 3.E 6 . 8 -24.9 24.8 -22.9 33.8 -i3.8 3.7 2.8 -10.6 9.8 6.5 29.9 19.7 28.5 17.9 28 8 18.5 5.0
020 040 060 080
0 10.0 0.12 0 0.14 0 0.16.0 0 18.0 200 400 600 800
hkl 111 131 151 171 191 1.11.1 1.13.1 1.15.1 1.17.1 201 22 1 241 261 281
011 031 051 Oil 091 0.11 1 0.13.1 0.15.1 0.17.1 121 141
161 181 1 10 1 1.12.1
-
--
27.1 3.9 3.2 -38.9 -23.2 -28.3 -10.9 0.6 9.1 38.3 44.9 12.0 9.8 -11.8
-
-
24.4
15.1 14.8 22.1
....
8.0 8.2 14.8 46.5 14.0
5.1 31.8 12.2 10.5 10.0 3.5
L7.3 X3.c
-
ilk@
190 11.1.0 11.3.0 11.5.0
11.7.0 11.9.0 220 240 260 280 2.10 0 2,12.@ 2.14.0 2.16 0
::to 3 G 3.50
2.11.0
2 . 13 . 0 '2 . 15 .0 2.17.0 320 340 360 380 3.10.0 3.12.0 3,14.0 3.16.0 410 4.30
1
Fdcd.
-11.0 -10.8 -10.5 6.3 8.7 15.0 -10.2 -27.2 0.2 11.8 13.2
-
11.6
-.is.; 5.7 -12.4 -19.2 13..i
-
-
i b
18. 1 7.4 , . . ....
.... 9.1 8.8 16.8
....
9.4 Y.4 13.1 21.1 10.5 12.5 10.4 14.8
370 390 3.11 0 3.13.0 3.15.0 3.17.0 420 440 460 480 4.10.0 4.12.0 4.14.0 4.16 0 510 ,530 5.j0
Reflections hkO, h i - k odd. -15.7 16.8 450 -16.5 ?0.(J a;@ -20.0 li.(j 490 1.6 . 4.11.0 5.1 17.7 4 . 1 3 . 0 S.2 7.4 4.15.0 6.8 2.0 320 10.2 6.3 540 -11.4 .. 330 2.1 580 - 2 . 8 . . 5.10.0 1.1 . 5.12.0 5'14.0 11.1 3.2 -37.9 45.5 5.16.0
-
..
Reflections h k l . k+k even. hk 1 -15.0 13.3 441 - 3.9 . , . 461 3.8 6.1 481 19.2 20.0 4.10.1 1.4 4.12.3 4.9 0.1 .... 4.14.1 - 8.9 7.4 4.10.1 5 ii 5 11 -- 4.9 . . . 531 9.0 12.2 531 4.G .. . ,271 - 4.2 ..., 5!ll 21.0 5.11.1 -27.9 29.3 5.13.1 -32.5
. ... 37.7 24.6 21.1 13.1 8.2 4.0 22.5 23.3 4.3 10,o
-
10.5. 1.14.1 1.38.1 211 231 251 071 291 2.11.1 2.13.1 2.15.1 2.17.1 321 341 361 381
Reflections -17.6 7.2 -27.4 -16.8 -18.0 --- 4.8 8.5 4.4 9.1 4.6 15.5 31.2 -37.4 17.3 - 9.3
-
-
1
4
(4
Fenled.
*ye
hkO
-24.3 46.9 32.4 13.0 8.5 -16.3 -21.6 -10.5 5.4 11.7 18.6 -[).2 - 4.9 -20.0 14.0 -- 6.9 -17.6
30.4 46.1 39.6 21.8 7.4 21.8 19.5 12.2
570 590 5.11.0 5.13'0 5.15.0 620 040 660 680 6.10.0 6.12.0 8.14.0 710 730 750 770 790
-
-
Structure -26.8 -10.3 - 5.2 10.8 8.8 19.7 23.6 29.6 -13.2 - 7.3 9.0 10.7 20.5 23.4
,
..
14.5 13.8 .
e,
-
3
llkO
j -Id
3
1
-_
-.
16.2 5.4
13.4 5.4 13.3 7 9 45.6 44.9 28.0 29.6 7.6 7.1 8.2 -36.9 41.0 7 . 0 15.7 6.3 2.8 4.0 8.5 5.4 20.8 15.2 16.9 18.6 9 . 2 16.8 -17.1 23.1
k -
Structure factor: 4 Z, f; cos kxi cos kyi
,
. ... 21.8 11.1
. .. .
26.4
-
8.4 -18.7 - 2.9 -12.1 4.1 35.6 9.2 - 9.2 -11.1 -12.6 - 3.9 4.0 15.3 5.4 0.5 -23.2 5.4
-
-
factor: 4 & f s hiu h r i sin kyi 32.5 610 - 9.8 6.8 630 1.5 .. 650 5.0 15.7 670 6.5 690 5.8 11.9 18.2 6.11.0 9.3 25.7 6.13.0 2.9 4.9 6.15.0 32.5 12.2 720 6.5 . ... 740 16.0 10.i 760 22.8 .... 780 15.7 16.6 7.10.0 8.6 7.12.0 -23.2 29.3
-
-
-
2
*. 7-
1
;i F o e ~ o d .
5.1 18.6 2.6
. .. .
6.5 33.3 5.0 15.6 14.2 16.5
.... .... 12.2
. ... ,
(..
25.6 7.9
7.1
.... .,.
.
8.0 8.0 8.0 10.5
. ... 7.8 20.2 19.7 18.9
7.7
h kO
31 Fcalcd.
7.11.0 7.13.0 820
-14.5 6.9 -10.1
840
8.1
-
860 880 8.10.0 8.12.0 910 930 950 970 990 9.11.0 10.2.0 10.4.0 10.6.0
2.0 7.7 7.6 2.9 -15.1 -0.7 4.0 29.9 23.6 31.6 -16.9 3.7 1.9
7.14.0 810 830 850 870 890 8.11.0 8.13.0 920 940 960 980 9.10.0
-24.5 9.8 5.8 27.1 22.1 4.6 9.2 -32.5 6.0 2.7 4.6 10.0 1.4
hkl 7.11.1 801 821 841 861 881 8.10.1 8.12.1 911 931 951 971 991
-12.6 45.4 17.9 1.2 -10.4 -12.5 4.1 -10.0 6.6 1.4 -10.6 0.6 3.7
-
-
-
i
7.4
,... 4.0 7.7
.... 7.7 10.5
....
18.2
....
....
25.8 30.9 41.7 17.9
....
....
31.5 5.4 2.8 35.6 23.8
,...
6.3 40.2 I
.
.
.
. . I .
8.3 6.6 5.4
23.7
Structure factor: 4 Zi fi sin hri cos K Y I
hkl -11.1 - 5.0 17.7 21.4 6.2 7.4 -29.7 8.8 -12.5 12.2 17.6 36.3 27.1 13.5
-
11.1)
.... 16.9 16.8
.. . . . ..
24.6 6.5 15.4 14.5 22.9 37.6 36.8
..
.
h k l , k + k odd. Structure factor: 4 16.9 3.10.1 14.1 16.8 , . ,. 3.124 11.4 7.4 23.2 21.8 23.9 3.14.1 17.5 3.16.1 27.5 31.2 11.8 411 - 3.8 , . . . -27.9 27.9 5.7 431 13.9 14.5 8.3 431 .. 471 - 3.2 . . . . 1.4 . .. . 5.1 491 5.6 10.2 6.8 4.11.1 0.5 .... 11.7 4-13.1 14.9 29.3 4.15.1 12.6 31.8 321 - 2.8 4.0 16.8 14.2 541 16.9 5.3 3.4 2.0 36i
-
products of the scattering powers of the atoms. The principal peaks expected are those for Cd-Cd
5.15.1 601 621 641 661 681 6.10.1 6.12.1 6.14.1 711 73 1 751 771 791
-
7.3 3.4 8.3 -10.5 -3.1 5.5 3.2 7.2 -11.2 16.8 6.8 -24.4 -23.0 -27.6
Z i f i cos hiri sin k.vi 551 l5,3 5.10.1 9.7 5.12.1 13.4 -14.8 5.14.1 611 5.9 631 20.2 651 23.7 671 24.4 691 4.8 6.11.1 -17.1 6.13.1 -20.7 7.2 721 741 7.1 761 20.2
-
11.6
..., 6.0 3.4
..._ 7.4
.... . ... 7.4 20.7
. .. .
21.9 26.0 22.0
11.6
. ..
.
21.3 6.5 7.1 26.4 32.4 26.0
....
24.0 24.8 7.1 7.4 19.4
781 7.10.1 7.12.1 811 831 851 871 891 8.11.1 921 941 961 981 9.10.1
-
-
-
1.2 3.8
-19.5
-
6.6 -11.4 -12.5 3.9 1.2 2.7 -18.9 -16.2 -25.7 - 0.9 2.8
-
,... 46.9 23.5 1.7 3.7 12.3
,... 4.8
.... 7.1 9.1
.... .... .. . .,. 19.4
. .. 15.1 8.3 11.1
.... 11.6 17.8 10.5 31.6
.. .
....
and Cd-Cl. At z = 0 the Cd-Cd peak should occur for the two atoms a t ZCd, >'Cd '/4 and ' / z
+
CRYSTAL STRUCTURE OF AMMONIUM CADMIUM CHLORIDE
Dec., 1938
-
that is, at the point 2ycd. The most pronounced peak in Fig. 1 is in fact at I/*, 0.385, corresponding to YCd = 0.0575. The most pronounced peak of Fig. 2, a t 0.1667, l/2, similarly corresponds to - 2XCd and leads to the value XCd = 0.1667. Another Cd-Cd peak, a t 2XCd2YCd, also appears on this diagram in the position required by these parameter values. These values of XCd and y c d can be combined with the coordinates of the remaining peaks to obtain values for the coordinates for chlorine atoms. Thus for the level z = 0 Cd-CI or Cd-N peaks are expected a t XCd - X,YCd - y ; XCd - x, '/z - YCd - y ; etc. The parameter values obtained in this way are XI = 0.305 YI = 0.219 XCd
'/z
YCd '/4;
+
XII XIII
= .164 = .025
YII
= .505 .893
YIII =
In addition the ammonium ions can be assigned = 0.43, YNH* = 0.82, the parameter values x", inasmuch as these positions are the only ones compatible with a minimum NH4-Cl distance of about 3.1 8. These parameter values lead to a structure which is stereochemically satisfactory, as described below. In order to obtain more accurate values of the parameters a section at z = '/4 of a three-dimensional Bragg-Fourier calculation was carried out, with use as the signs of the F s of those given by the approximate parameter values. The summation over 1 for the series o(x,y,z) = BA 2.k & Fhkl cos 2 T ( h ky h) (2) was made in a way similar to that for the Patterson diagrams, namely, by summing the quantity . f/Z for series of reflections (hkl) with 1 even or odd to obtain factors for Fhkoand Fhkl. The Bragg-Fourier diagram at z = l/4, shown as Fig. 3, has a very high peak for the cadmium atom, three peaks for the three chlorine atoms, and a small peak for the ammonium ion, in positions corresponding to the following parameter values, which differ by only small amounts from the initial values:
ing factors8were used in the calculation of the F values.
= 0.165
XI
= .284 YI
XII XIII
X
N
0.054 .215 .167 YII = .496 = .026 YIII = 2398 .43 YNH, = .82 = ~ YCd
a
The agreement between observed and calculated amplitudes of reflection is seen from Table I to be satisfactory. Screening-constant atomic scatter-
bo
Origin
ad2 Fig. a.-Bragg-Fourier diagram for the section z = I/,. The four peaks in the upper part of the diagram represent, from left to right, the atoms Cd, C ~ I ,C111, and Clm, and the two peaks below represent C~III(in part) and "4.
Description of the Structure The structure found for NH4CdCb is shown in Fig. 4. Each cadmium atom is surrounded by six chlorine atoms, which form a nearly regular octahedron. The Cd-Cl distances have the values 2.60 ( 2 ) , 2.62, 2.64, and 2.72 (2) A., the average of these, 2.65 B.,being almost identical with the Cd-C1 distance in CdCl2, 2.66 A. The variation about the average is probably not real, but the result of small errors in the parameter values. The Cl-C1 distances along octahedral edges have the values 3.53 (2), 3.68 (2), 3.69 (2), 3.73 (2), 3.80 ( 2 ) , and 3.97 (2) A. Each octahedron shares two opposed edges with other octahedra to form octahedral strings parallel to the c-axis, as in the rutile structure. These rutile TABLE I1
+ +
XCd
2889
INTERATOMIC DISTANCES rn N&CdCl# Atom
Neighbors
Distance A. Atom Neighbors
Cd
2Cl11 1 C11 1C~III 2 Clr11
2.60 2.62 2.64 2.72
NH4
4c11 1 ClIII 2 Clrr 1 ClII 1C~III
3.27 3.34 3.40 3.47 3.82
CII
1 Cd 4NH4 2 Clrr 2 C~III 2 Clm 2ClI 1C~II 2 Clr 1 Clrr
2.62 3.27 3.73 3.76 3.80 3.97 4.30 4.59 4.64
Distance b.
Clrr
2Cd 2NH4 1NHa 1 ClIII 2 Cl11 2Clr 2 C~III 2 ClII 1 Clr 1 C1I
2.60 3.40 3.47 3.53 3.62 3.76 3.80 3.97 4.30 4.64
Clrrr
1 Cd 2 Cd INH,
2.64 2.72 3.34 3.82 3.53 3.68 3.69 3.76 3.80 3.97
1NHt 1 ClII 2 C~III 2 Cl11 2 Clr 2 Clr 2 ClIII
(8) L. Pauling and J. Sherman, 2. K r i s f . , 81, 1 (1932).
HENRIRRASSEUR AND LINUSPAULING
2890
strings are further condensed in pairs, each octahedron sharing two edges with octahedra of the adjacent string. The four shared edges are, as usual for partially ionic crystals, somewhat shorter than the unshared edges.
Vol. GO
The chlorine atoms form bonds to the following numbers: Cli: 1 with Cd, 4 with NH4 C l r ~ : 2 with Cd, 3 with NHI Clcil: 3 with Cd, 2 with NHI
These have the total strengths 7/9, 1, and 11/9, respectively; there is, P accordingly, some discrepancy with 0 the electrostatic valence rule.g It is interesting that the substance C crystallizes with this structure rather than a structure such as that of KMgF3, in which the halogen 0 atoms are equivalent, each being common to two octahedra. The arrangement of the chlorine atoms is compact; as shown in P I Table 11, each chlorine atom has eleven or twelve chlorine atoms as , neighbors, a t distances between 3.53 and 4.64 1 2 . The authors are indebted to the Belgian-American Foundation for Fig. $.--The structure of NHdCdC16, projected on the plane (001) and heavy circles those a t 2 = 3/,. the grant Of a Fellowship to One Light circles represent atoms at a = Cadmium and chlorine atoms are shown as small and large circles, and am- of them, permitting this investigamonium ions as circles of intermediate size. tion to be carried out.
P
'162
Each ammonium ion is in contact with iiiiie chlorine atoms, at about 3.27 ( Z ) , 3.27 ( Z ) , 3.34, 3.40 ( Z ) , 3.47, and 3.82A. The average of these distances, excluding the largest, is 3.31 A., which is nearly the same as in NH4C1 (NH4-C1 = 3.27 A. for the high temperature form, with the sodium chloride structure, and 3.34 A. for the low temperature form, with the cesium chloride structure). The nine chlorine atoms are arranged in the most compact configuration possible for coordination number nine-a triangle of three in the equator, and smaller triangles above and below rotated through G O O . The Cl-Cl distances along the edges of this polyhedron have the values 3.62 ( Z ) , 3.69 ( 2 ) , 3.73 (2), 3.76 (4), 3.80 ( 2 ) , 4.30 ( 2 ) , 4.59 (21, and 4.64 (2) A. Cleavage along planes of the zone [OOI] might be expected for the crystal; no cleavage has been reported, however, nor did we observe any in esperiments with our small crystals.
Summary
A complete structure determination has been made of the orthorhombic crystal NH4CdCls. The unit of structure has the dimensions a. = 8.96 * 0.02 A., bo = 14.87 * 0.03 A., CO = 3.97 * 0.01 A., and contains 4 NHkCdCb. The atomic positions are xy 1/4, $ 4- x 4 - y 1/4, 3 - x 4 y 3/4, Xy 3/4 of the space group Dil - P n a m, with the following parameter values x , y : Cd, 0.163, 0.054; (211, 0.254, 0.215; ClII, 0.167, 0.496; ClIIr, 0.028, 0.898; NH4,0.43, 0.82. The CdC& complexes occur in the crystal as infinite polymers, in the form of double rutile strings of CdCle octahedra parallel to the caxis. These complexes are held together by ammonium ions, each of which has nine chlorine atoms coordinated about it. Interatomic distances in the crystal (Table 11)are closely related to those in CdClz and NH4Cl.
+
PASSDEXA, CALIF. (9) L Pauling,
T H I S JOLIRVAI..
RECEIVED SEPTEMBER 6 , 1938 61, 1010 (1929).
