CD OU158335> OSMANIA UNIVERSITY LIBRARY f W**7 * AccessioaNo. '" / CallNo.S/f, ; / /// Author \*jC#t/* f /&& f Title '" ^/ti>f,,f4frjr/ ^Jf' C-M$ $ fj j Tlljs book should be returned on or before the date last marked below. THE STRUCTURE OF CRYSTALS Supplement for 1030-1034 to the SECOND EDITION BY RALPH W. G. WYClvOFF American Chemical Society Monograph Series BOOK DEPARTMENT REINHOLD PUBLISHING CORPORATION Successor to THE CHEMICAL CATALOG COMPANY, INC. 330 WEST FORTY-SECOND STREET, NEW YORK, U. S. A. 1935 COPYRIGHT, 1935, BY REINHOLD PUBLISHING CORPORATION AH rights reserved THE HADDON CRAFTSMEN, INC CAMDEN, N. J. Preface This supplement is a summary of new X-ray structure determina- tions published during the past four years. As such it follows strictly the form used in Part II of the second edition of "The Structure of Crystals" and aims to include all new studies that lead at least to cell dimensions. In order to facilitate comparison, the figure numbers and paragraph desig- nations are continuations of those in the book. As before, reference num- bers, with the year in bold-face, apply to the appended bibliography. The grouping of compounds is identical with that previously used except that in the chapter covering the type RX3 a separate table has been created of . for crystals the composition Rx (MX2) y The writer is indebted to R. B. Corey and K. Pestrecov for much help in making the illustrations and to A. A. Murtland for assistance in pre- paring the bibliography. Rockefeller Institute for Medical Research New York, N. Y. February, 1935 Table of Contents The chapters in this supplement are all lettered A and correspond in content to the similarly numbered chapters in Part II of the book second edition. CHAPTER XA. STRUCTURES OF THE ELEMENTS 7 CHAPTER XIA. STRUCTURES OF THE TYPE RX 15 CHAPTER XIIA. STRUCTURES OF THE TYPE RX2 23 CHAPTER XIIIA. STRUCTURES OF THE TYPE R2X3 .... 34 CHAPTER XIVA. STRUCTURES OF THE TYPE RX3 , OF HIGHER COM- POUNDS OF RmXn, AND NEW COMPOUNDS OF THE TYPE Rx (MX2) y 37 CHAPTER XVA. STRUCTURES OF THE TYPE Rx (MX3) y ... 52 CHAPTER XVIA. STRUCTURES OF THE TYPE Rx (MX4) y ... 63 CHAPTER XVIIA. STRUCTURES OF THE TYPE Rx (MX6) y ... 77 CHAPTER XVIIIA. STRUCTURES OF HYDRATES AND AMMONIATES AND OF MISCELLANEOUS INORGANIC COMPOUNDS .... 81 CHAPTER XIXA. STRUCTURES OF THE SILICATES 106 CHAPTER XXA. STRUCTURES OF ORGANIC COMPOUNDS . 130 APPENDIX. A BIBLIOGRAPHY OF CRYSTAL STRUCTURE DATA . 165 Chapter XA. Structures of the Elements Most of the new data of Table I arc accurate determinations of the cell dimensions of the metallic elements. For some metals which can easily be prepared in a state of great chemical purity the edge lengths of the units are now known with an accuracy of 0.0002 to 0.0003 A. The error for most elements is, however, about ten times greater. Spacings to the fourth decimal place have real significance only if the purity is precisely known, if the sample is sufficiently outgassed and otherwise pre- pared for measurement and if the temperature is determined. It is not always possible to be sure from the published data that all these condi- tions have been properly met; the accuracy limits stated in Table I are therefore for the most part those set by the investigators themselves. New information about the atomic arrangements in elements are re- corded in the paragraphs that follow. (v) In place of the previously described tetragonal structure for gallium there has recently been given an orthorhombic (pseudo-tetragonal) ar- rangement based on Vjf and having its eight atoms in the special positions: (f) iuv; J, u, i-v; J, u+, v; J, u+i J-v; Juv; i u, v+; i i-u, v; J, J-u, v+J with" u=0.159, v=0.080. As is evident from Figure 275 (drawn for comparison with Figure 168) this arrangement is very different from the earlier one. FIG. 275ff (left) The unit cell of the new ortho- rhombic arrangement found for metallic gal- lium as projected on its b-face. FIG. 2756. (right) A packing drawing of the gallium atoms shown in a. 8 THE STRUCTURE OF CRYSTALS (w) The rhombohedral structure of mercury has recently been confirmed by single crystal measurements at -50 C. At the same time it is shown that the diffraction data upon which a false hexagonal arrangement was based (1922, 1) apparently were a mixture of the lines of mercury and of solid CO2 . (x) Three recent determinations agree with the original in giving indium a face-centered tetragonal arrangement with atoms at 000; ^0; JOJ; OJ. (y) The X-ray patterns from the /3-form of nitrogen are thought to in- dicate that it is a close-packed assemblage of spherical (rotating) N2 molecules. The parameter chosen for the center of gravity of these mol- ecules is 0.22. (z) Hexagonal nickel prepared by a glow discharge in N2 has the dimen- sions stated in the table; prepared in H2 its unit is larger: a =2.66 A, c =4.29 A. It reverts to cubic nickel if heated to 300 C. (aa) This modification of tungsten, said to be obtained by electrolyses under various conditions, is thought to have 8 atoms in its unit. The atoms have been placed at (2a) and (6g) (of 1930, 352) though no in- tensity data are given in support of this assignment. (ab) The recorded unit cube of a-rhodium is considered to contain 48 atoms. This modification is produced by the reduction of rhodium salts, mixed with the usual form it is also said to result from electrolytic reduction ; (ac) Plastic sulfur is rubber-like in that it crystallizes on stretching. The monoclinic unit recorded in the table contains 112 atoms; its space group is given as C^. As monoclinic sulfur (either stretched or not) ages, the diffraction lines of the orthorhombic form gradually appear. (ac?) The monoclinic cell of a-Se contains 32 atoms; its space group is reported to be C^. Crystals of a solid solution of selenium and sulfur (55.2 wt. % Se), which presumably are isomorphous with a second modi- fication of monoclinic Se, have been assigned a unit different from that of the /?-Se reported in the table. The unit of this mixed crystal has a = 8.48 A, b = 13.34 A, c =8.33 A, /3=6730'. (ae) The two uranium atoms in the centered unit having the dimen- sions of the table are said to be at 000; 0||. Another determination has made uranium body-centered cubic with a =3.43 A (1930, 424). (of) A second form of beryllium is reported to be present to the extent of about 10% in samples which have been heated for some time in vacuo at 600-~800 C. It is described as hexagonal with a -7.1 A, c =10.8 A and with ca 60 atoms in this unit cell (1933, 224). (ag) Electrodeposition at high pH yields 0-cobalt, at low pH a mixture of and a forms (1932, 262). The /3-cobalt becomes cubic above 450 C without change in crystal boundaries; it reverts only on cold rolling or through high temperature annealing (1932, 463). STRUCTURES OF THE ELEMENTS TABLE I. THE CRYSTAL STRUCTURES OF THE ELEMENTS Graphite 0-Ca (>450 C) Hexagonal (ah} 3.98 6.52 1933, 121, 156; 1934, Calcium 93. Cb Cubic B.C. (c) 3.294 1931, 323, 324; 1932, Columbium 0.001 371; 1934, 43. 5.6058 1931, 238; 1932, 428a. 0.0005 7 1932, 372. 1932, 262. 1931, 367a; 1932, 369; 1934, 125. 1932, 348; 1933, 328, 342; 1934, 357. 1930, 439; 1931, 16; 1932, 62, 336, 369; 1933, 128, 342; 1934, 124, 137. 1 At 600 C, a =4.1276 A (1934, 199). 2 There is no allotropic change up to 600 C (1931, 8; 1933, 420). At475C, a =4.1010A. 4 The thermal expansion from room temperature to the melting point has been carefully measured by X-ray means (1931, 127; 1932, 163; 1934, 120, 121a). 6 Photographs of incandescent electrodes show that expansion is all normal to the basal plane. 6 of of From a very ductile preparation Cb made by thermal decomposition CbCl fi in vacuo. Other a 's are ca 0.01 A larger. 7 The other precision measurement (1931, 238) gives lower values: a =2.9724, Co =5.6042. 8 At 475 C, a =3.6514 A. Measurements have been made up to 1100 C (1930, 439; 1933, 128; 1934, 137). 10 THE STRUCTURE OF CRYSTALS Element Crystal Type of a c or a References system structure 1 There is no X-ray evidence for a structural transition. * This form appears as a surface layer on the a-material after vacuum annealing at 350 for several days. Another determination, on 99.88% Ni, gives a -3.6143 A. STRUCTURES OF THE ELEMENTS 11 Element Crystal Type of a c or a References system structure Pr Hexagonal C.p. (6) 3.657 6.924 1932, 93, 390. Praseodymium i Pt Cubic F.c. (a) 3.9161 1933, 342, 343; 1934, Platinum 0.0003 199. Re Hexagonal C.p. (6) 2.7553 4.4493 1931, 3, 4, 305; 1932, Rhenium 0.0004 0.0003 428a. -Rh Cubic (afc) 9.211 1931, 225, 226. Rhodium 0-Rh Cubic B.C. (c) 3.7955g 1931, 225; 1932, 348; Rhodium 1933, 342, 343. S Monoclinic (oc) 26.4 12.32 1930, 119a; 1931, 448; Sulfur (Plastic form stretched) bo-9.26, 0-7915' 1932, 447; 1934, 175.