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(iii) Since the symmetry Oxygenase is non-centrosymmetric, inversion twinning was introduced for all six twin domains. The refinement resulted in insignificant values of the inversion twin volumes. (iv) Second-order harmonic waves were added for displacive modulation of the atoms, but the resulting modulation functions showed ripples indicating fitting of the noise in the data. (v) Isotropic secondary extinction correction resulted in a negative extinction parameter. 3.?Discussion ? 3.1. Variation of molecular conformations for Z�� = 12 ? The crystal structure of the low-temperature phase (phase IV) of Co(sep)(NO3)3 is a high-Z�� structure. Only a few crystal structures feature more independent molecules in the unit cell than the presently observed Z�� = 12 [for example, the amino acid l-tryptophan with Z�� = 16 (G?rbitz et al., 2012 ?); see also the review article by Steed & Steed (2015 ?) and references therein, as well as the high Z�� structure database by Steed (2016 ?)]. High-Z�� structures usually suffer from severe correlations between parameters in structure refinements, and restrictions on Apoptosis inhibitor the parameters beyond symmetry restrictions are necessary. An elegant way of imposing nonsymmetry restrictions is the superspace approach (Sch?nleber, 2011 ?; van Smaalen, 2012 ?; Pinheiro & Abakumov, 2015 ?). Parameters are separated into a relatively small subset of atomic coordinates describing the basic structure [one molecule Co(sep) and three nitrate ions] and parameters describing deviations from the basic structure. For Co(sep)(NO3)3 we have observed satellite reflections in the X-ray diffraction of first order only (Fig. 3 ?), which implies that the superstructure is described by a single harmonic modulation function for each independent parameter of the basic structure; higher harmonics cannot be determined (see the end of ��2.2). Deviations from the basic structure are small indeed, as is easily seen by consideration of a plot of the superstructure, showing the 12 crystallographically independent but nearly indistinguishable copies of the molecule (Figs. 4 ? and 5 ?). Figure 4 Unit cell of the superstructure projected onto (0 0 1). Atoms with ?0.05 click here cf. Fig. 5 ?). H atoms are not shown. Figure 5 (a) The basic structure at T = 95?K (phase IV) projected onto (1 1 0) and (b) the disordered phase at room temperature (phase I; Sch?nleber et al., 2010 ?). H atoms are not shown. The superspace approach reduces the number of independent parameters dramatically compared with the 12-fold supercell. Nevertheless, the monoclinic superspace group of phase IV does not capture the pseudo-trigonal symmetry of the Co(sep) molecule, and further restrictions have turned out to be necessary. We have chosen to use rather narrow restraints on bond lengths and bond angles (��2.2). They are justified in hindsight by the good fit to the diffraction data of the thus refined structure model (Tables 1 ? and 2 ?).