Setting ambiguity inC2/cwith dibromidotetrakis(1H-pyrazole-κN²)manganese(II) as an example

Abstract

trans-Dibromidotetrakis(1H-pyrazole-kappaN(3))manganese(II), [MnBr2(C3H4N2)4], crystallizes in the C2/c space group with the Mn atom located on a centre of inversion. As a result, there is just one half-molecule in the asymmetric unit. Geometric parameters are in the usual ranges. The Mn centre is octahedrally coordinated by four pyrazole residues in the equatorial plane and by two bromide ligands in the axial positions. The molecular conformation is stabilized by N-H...Br hydrogen bonds. The structure of the title compound had already been described [Lumme & Lindell (1987). J. Coord. Chem. 15, 383-392] in a different setting, with the Mn atoms located on inversion centres on Wyckoff position d (1/4, 1/4, 1/2; 3/4, 1/4, 0; 3/4, 3/4, 1/2; 1/4, 3/4, 0). In the conventional setting, however, the Mn atoms are situated on Wyckoff position a (0, 0, 0; 0, 0, 1/2; 1/2, 1/2, 0; 1/2, 1/2, 1/2). In this special case, if the c axis has the same length as the short diagonal of the ac plane, the transformation from one setting into the other yields almost indistinguishable cell parameters, and the possibility of confusion arises. This setting ambiguity could be the reason why two structures in different settings might be taken as polymorphs even though they can easily be transformed. As a result of this, care should always be taken to use the conventional setting.

Synthesis, Characterization and Assessment of the Antioxidant Activity of Cu(II), Zn(II) and Cd(II) Complexes Derived from Scorpionate Ligands

“…The presence of neutral pyrazole in this complex was denounced by the missing band characteristic of the stretching vibration of B−H bond, and by the appearance, instead, of a broad band at 3148 cm −1 due to the vibration of the pyrazolyl N−H bond. This relatively rare behavior was already observed with other scorpionate ligands in the presence of transition metal(II) or metal(III) ions [36][37][38][39][40][41][42][43], and it is due not only to the different acidity of the metal centers, but also by the degree of steric crowding around the boron center in the corresponding scorpionate ligands [44].…”

The role of lattice matching techniques in the characterization of polymorphic forms

“…For example, the structure of the tetrapyrazole manganese NCS complex published by Lumme et al (1983) [22] is similar to the structure of Takahashi [6]. On the other hand, the lattice of the tetrapyrazole Mn Br complex published by Ruth et al [23] is similar to the complex of Yan [5]. …”

Setting ambiguity inC2/cwith dibromidotetrakis(1H-pyrazole-κN2)manganese(II) as an example. Addendum

“…We wish to withdraw from our paper (Ruth et al, 2007) our remarks concerning the results of Bolotina et al (2003). Their results do not need to be revised because the same setting has been used for all structure determinations.…”