January 2015 Model Answer Written Assignment_Group B
GROUP B
MODEL ANSWER
Yoshida et al., Flexibility of Hydrogen Bond and Lowering of Symmetry in Proton Conductor, Symmetry 2012, 4, 507-516.
DO NOT PLAGIARISE THIS MODEL ANSWER
PLAGIARISM FROM ANY SOURCE AUTOMATICALLY LEADS TO A ZERO SCORE
Paragraph 1
M3H(XO4)2 compounds are used for electrolytic fuel cells (where M=K, Rb ,Cs; X=S, Se). At different temperatures, the compound exhibits different degrees of symmetry. There are 3 distinct phases observed. Below 369K, the phase 3 structure belongs to a monoclinic system with the space group C2/m, with lattice parameters a3=10.903(3)Å, b3=6.3904(8)Å, c3=8.452(2)Å, β3 = 112.46(1)°, Z=2 at room temperature. Above 369K, the phase 2 structure displays monoclinic-A2/a symmetry. The lattice parameters are a2 = 11.037(1) Å, b2 = 6.415(1) Å, C2 = 16.042(4) Å, β2 = 102.69(1)° and Z = 4 at 400 K. Above 456K, the phase 1 structure changes to a trigonal system with the lattice parameters of a1 = 6.4260(6) Å, c1 = 23.447(2) Å, Z = 3 at 470 K. Each of these 3 systems possesses their own symmetric elements. The structure in phase 3 is aligned parallel to the “a” plane, giving it a high degree of reflective symmetry, as well as rotational symmetry or at least order 2. This alignment is due to the presence of hydrogen bonds in the structure, which align the individual SeO4 tetrahedrons nicely. As seen in figure 2(a), the structure possesses rotational symmetry around the center of order 2, and it is also symmetric horizontally and vertically, with 2 unique mirrors. It also forms a nice tessellation, indicating plane symmetry. In phase 2, the alignment is approximately along the [3 -1 0] and [3 1 0] directions. This reduces the symmetry by removing the reflection across the horizontal, as well as rotational symmetry. It however, retains the vertical reflective symmetry and plane symmetry. In phase 1, structure changes, and only plane symmetry is present. This change in symmetry is due to how the hydrogen bonding changes at
MODEL ANSWER
Yoshida et al., Flexibility of Hydrogen Bond and Lowering of Symmetry in Proton Conductor, Symmetry 2012, 4, 507-516.
DO NOT PLAGIARISE THIS MODEL ANSWER
PLAGIARISM FROM ANY SOURCE AUTOMATICALLY LEADS TO A ZERO SCORE
Paragraph 1
M3H(XO4)2 compounds are used for electrolytic fuel cells (where M=K, Rb ,Cs; X=S, Se). At different temperatures, the compound exhibits different degrees of symmetry. There are 3 distinct phases observed. Below 369K, the phase 3 structure belongs to a monoclinic system with the space group C2/m, with lattice parameters a3=10.903(3)Å, b3=6.3904(8)Å, c3=8.452(2)Å, β3 = 112.46(1)°, Z=2 at room temperature. Above 369K, the phase 2 structure displays monoclinic-A2/a symmetry. The lattice parameters are a2 = 11.037(1) Å, b2 = 6.415(1) Å, C2 = 16.042(4) Å, β2 = 102.69(1)° and Z = 4 at 400 K. Above 456K, the phase 1 structure changes to a trigonal system with the lattice parameters of a1 = 6.4260(6) Å, c1 = 23.447(2) Å, Z = 3 at 470 K. Each of these 3 systems possesses their own symmetric elements. The structure in phase 3 is aligned parallel to the “a” plane, giving it a high degree of reflective symmetry, as well as rotational symmetry or at least order 2. This alignment is due to the presence of hydrogen bonds in the structure, which align the individual SeO4 tetrahedrons nicely. As seen in figure 2(a), the structure possesses rotational symmetry around the center of order 2, and it is also symmetric horizontally and vertically, with 2 unique mirrors. It also forms a nice tessellation, indicating plane symmetry. In phase 2, the alignment is approximately along the [3 -1 0] and [3 1 0] directions. This reduces the symmetry by removing the reflection across the horizontal, as well as rotational symmetry. It however, retains the vertical reflective symmetry and plane symmetry. In phase 1, structure changes, and only plane symmetry is present. This change in symmetry is due to how the hydrogen bonding changes at