University:
Purdue University
Course:
CHM 69600 | Special Topics In Chemistry
Academic year:

2019
Views:

412

Pages:

2
Author:

Carolyn Charles

X-ray Crystallography 12650 - CHM 69600-006 Homework Assignment 3: Space Groups and Symmetry Questions are 5, 10 or 15 points, as indicated. Due date: One week after assignment. 1) To which point groups do the following space groups belong? P1, P21/c, P212121, Pmmm, Cmca, I4, P3121, R3m, P63/mmc, Pa3. Give both the Herman-Maugin as well as the Schoenfliess symbols for the point groups. 10 pts 2) List some of the important differences between space groups P21/m, P21 and Pm; and between space groups Pm3 and P3m1 5pts 3) A space group has a three-fold axis, another a four-fold screw axis as one of its symmetry elements. What Crystal Systems can each belong to? 5 pts 4) Which of the following space groups contain translational symmetry of one kind or another within their unit cells? P1, P2, P21/c, P212121, Cmca, I4, P3, R3m, P63/mmc, Pa3 For each, name the type of symmetry elements that contains the translational component (leave out symmetry elements not given in the shortened Hermann-Maugin symbol used above). 5 pts 5) Can systematic absences distinguish between the following space groups: P1 and P1; P2 and C2; P2 and Pm; P2 and Pc; P2/c and Pc; I4 and I4/m; I41 and Ia; R3/m and P3 Explain your answers. 10 pts 6) Imagine an organometallic compound with three fold molecular symmetry. Would you be worried if unit cell determination on the diffractometer proposed a C-centered monoclinic space group? 10 pts 7) What information can be extracted from the positions of a sufficiently large number of diffraction spots? No information is available about the intensity other than if a reflection is observed or not. Explain your thoughts. 5 pts

Space groups. Homework 3

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