TY - JOUR
T1 - The Z' = 12 superstructure of Λ-cobalt(III) sepulchrate trinitrate governed by C-H...O hydrogen bonds
AU - Dey, Somnath
AU - Schönleber, Andreas
AU - Mondal, Swastik
AU - Prathapa, Siriyara Jagannatha
AU - van Smaalen, Sander
AU - Larsen, Finn Krebs
PY - 2016/6/1
Y1 - 2016/6/1
N2 - Λ-Cobalt(III) sepulchrate trinitrate crystallizes in P6
322 with Z = 2 (Z' = 1/6) at room temperature. Slabs perpendicular to the hexagonal axis comprise molecules Co(sepulchrate) alternating with nitrate groups A and B. Coordinated by six sepulchrate molecules, highly disordered nitrate groups C are accommodated between the slabs. Here we report the fully ordered, low-temperature crystal structure of Co(sep)(NO
3)
3. It is found to be a high-Z' structure with Z' = 12 of the 12-fold superstructure with monoclinic symmetry P2
1 (c unique). Correlations between structural parameters are effectively removed by refinements within the superspace approach. Superstructure formation is governed by a densification of the packing in conjunction with ordering of nitrate group C, the latter assuming different orientations for each of the Z' = 12 independent copies in the superstructure. The Co(sep) moiety exhibits small structural variations over its 12 independent copies, while orientations of nitrate groups A and B vary less than the orientations of the nitrate group C do. Molecular packing in the superstructure is found to be determined by short C-H...H-C contacts, with H...H distances of 2.2-2.3 Å, and by short C-H...O contacts, with H...O distances down to 2.2 Å. These contacts presumably represent weak C-H...O hydrogen bonds, but in any case they prevent further densification of the structure and strengthening of weak N-H...O hydrogen bonds with observed H...O distances of 2.4-2.6 Å.The 12-fold superstructure at T = 95 K is described as a commensurately modulated structure in superspace. Crystal packing in the Z' = 12 superstructure is determined by short C-H...O hydrogen bonds.
AB - Λ-Cobalt(III) sepulchrate trinitrate crystallizes in P6
322 with Z = 2 (Z' = 1/6) at room temperature. Slabs perpendicular to the hexagonal axis comprise molecules Co(sepulchrate) alternating with nitrate groups A and B. Coordinated by six sepulchrate molecules, highly disordered nitrate groups C are accommodated between the slabs. Here we report the fully ordered, low-temperature crystal structure of Co(sep)(NO
3)
3. It is found to be a high-Z' structure with Z' = 12 of the 12-fold superstructure with monoclinic symmetry P2
1 (c unique). Correlations between structural parameters are effectively removed by refinements within the superspace approach. Superstructure formation is governed by a densification of the packing in conjunction with ordering of nitrate group C, the latter assuming different orientations for each of the Z' = 12 independent copies in the superstructure. The Co(sep) moiety exhibits small structural variations over its 12 independent copies, while orientations of nitrate groups A and B vary less than the orientations of the nitrate group C do. Molecular packing in the superstructure is found to be determined by short C-H...H-C contacts, with H...H distances of 2.2-2.3 Å, and by short C-H...O contacts, with H...O distances down to 2.2 Å. These contacts presumably represent weak C-H...O hydrogen bonds, but in any case they prevent further densification of the structure and strengthening of weak N-H...O hydrogen bonds with observed H...O distances of 2.4-2.6 Å.The 12-fold superstructure at T = 95 K is described as a commensurately modulated structure in superspace. Crystal packing in the Z' = 12 superstructure is determined by short C-H...O hydrogen bonds.
KW - Z' superstructure
KW - commensurately modulated structure
KW - hydrogen bonding
KW - superspace
UR - http://www.scopus.com/inward/record.url?scp=84971646127&partnerID=8YFLogxK
U2 - 10.1107/S2052520616005503
DO - 10.1107/S2052520616005503
M3 - Journal article
C2 - 27240768
SN - 0108-7681
VL - 72
SP - 372
EP - 380
JO - Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials
JF - Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials
IS - 3
ER -