Roy, Sukla

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2CRYSTAL STRUCTURE OF THIODIGL^COLLIC ACIDSUKLA ROYIifOXAN A s s o c ia t io n  f o r  t h e  C u l t i v a t i o n  i »  SCIBNCX,Calcutta-32.(ReceimA November 12, 1964)The unit cell and space group of thiodiglycoUic acfi has already been deter­mined (Roy, 1962). The lattice is orthorhombic and |hcre are 4 molecules per unit cell. The systematic absences observed are con8is|ent with the space group Pnam or Pna2i with \a =  5.0.3 ±  .03 A b =  6.66 ±  .03 A c =- 17.76 ±  .03 AAll the intensity data were obtaino<l from Weissenberg photograph about ffl and b axis using multiple film technique (Robertson, 1943). Intensities were estimated visually by comparison with a standard intensity strip. After correc­tion for Lorentz and polarisation factors Fo®(okl), were put on an absolute scale by Wilson’s method. No correction for absorption was made at this stage.The N {Z) statistical test (Howells et al.) was applied to 100 zone reflections for which the projection is centric for Pnam and acentric for Pna2j. It was found that the experimental values of N (Z) agreed very well with the theoretical curve for the centrosymmetric case, thereby implying the space group Pnam.There are 8 general positions for the space group Pnam. Since each unit cell of the crystal contains 4 molecules the sulphur atoms must occupy the following special position,y , i  ; 2. y, 3/4 ; ar, 3/4 ; i+a;, \ —y, 1/4 :Using the okl data a two-dimensional Patterson was computed to facdita1)e the determination of approximate y, z parameters of the sulphnr,atoms...............Approximate coordinates of the sulphur atoms thus obtained were used to calculate the structure factors of the okl reflections.Signs of some of the structure factors thus obtained were then used to compute the (100) electron density projection (Fig. 1) from which an approximate trial structure could be postulated. At this stage the'reliability index was 0 .^ . '' Theoverall temperature factor was taken throughout to be 1.84. ;■ ' ' ' ■' „750 Letter to the Editor'I'hrec <‘.ycIc*H .')f Fourier refinement reduced the R value to But netftirther (change was obwM ved. Two cycles of difference fourier were then earnedout an<l these reduced the E value to 0.2d. Tt was apparent from th(  ^ difference F r^turier that some atoms had a temperature factor higher than 1.34 and the sulphur atom had an anisotropic temperature factor.; Another Patterson projection was computed to dett^rmine the tliird co-ordinate from'the ‘6* axis O-layer data. The E  value for this zone is now 0.30.Further refineintmt is proceeding using difference synthesis and least squares method.Throughout the analysis of the (;rystal the scattering factor value of B^rghus fi  al. were used for carbon and oxygen while saettering factors of sulphur were based on values given by C. H. Stam. . rA C K  N O VS^  I, K D  Gi M K N T^ le  author is thankful to Prof. B. N. Srivastava, D.Sc., P.N.I., for his keen ihierei9t in theproblcun and to Dr. Sankar Kumar Datta for suggesting the problem and guidance throughout the piece tif work. - '" '■ RK F E H K N O E Sc: ,v: Be^hus, J., Haauappeb Y. M., Patters, M., Loopstra, B. ()., Mac Gillary, H., V^nen- ' Sal; A. i r i9 5 6 ,  478. ' '" ' !ftuwels7i&* A*; Phttlfps, lb’. (1. and Rogers, D., 1950, Aota“ Z, ' ’--J ejdT '96/ 49S. .. . . . "' ' " ?.n i . , : '  iRobertson, J. M., 30, ^75. ’ " , . /  -Tomiie, Y. H., and Stam, 0. H., 1958^  Acta CryH., 11, 126.WiWon. A. J. 0„ 1942, Nmwe, 150,

Crystal Structure of Thiodiglycollic Acid

http://arxiv.iacs.res.in:8080/jspui/bitstream/10821/2492/1/Crystal%20Structure%20of%20Thiodiglycoljic%20Acid_Sukla%20Roy.pdf

Crystal Structure of Thiodiglycollic Acid

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