research papers
The pseudosymmetries of the title compound resemble a monoclinic unit cell with space group P1121/a. However, the structure of C17H22N2O3 was determined in a triclinic unit cell [a = 10.500 (4), b = 11.617 (3), c = 28.622 (3) Å, α = 83.15 (2), β = 83.41 (4), γ = 68.48 (2)°; V = 3215 (2) Å3, Z = 8: four molecules in the asymmetric unit] by direct methods and refined on F2 values in space group P1 to final R[F2 > 2σ(F2)] = 0.0457 and wR(F2) = 0.114. The conformation of molecule M1 basically agrees with that of M4, whereas molecules M2 and M3 form a second group of conformers. M1–M2 and M4–M3 dimers are related by a pseudoscrew axis along the c axis and complemented by a pseudoglide plane located at z ≃ or , respectively. The analysis of pseudosymmetries in the title crystal was then extended to other structures selected from 66 Cambridge Structural Database entries with P1 and Z = 8. A topological survey of the pseudosymmetries reveals a rich variety of the *21/*c pair. In the unit cells of several crystals one or two coordinates of these types of pseudosymmetries are bound to (2n − 1) values or in their vicinity. Such operators (termed secondary pseudosymmetries) are accompanied by their respective complementary symmetries with translation(s) of ca (2n − 1). Their cooperation with primary pseudosymmetries (possessing standard position and translation) and with themselves seems to shed light on the origin of symmetries in crystals. These observations are also valid for a few monoclinic crystals.
Supporting information
Crystallographic Information File (CIF) | |
Structure factor file (CIF format) |
CCDC reference: 132037