Agata Trzesowska

New bond-valence parameters for lanthanides.

The bond-valence method, especially the valence-sum rule, is very useful for checking if the structures formed by trivalent lanthanides are correct. In this work bond-valence parameters (Rij), which connect bond valences and bond lengths, have been computed for a large number of bonds taken from the Cambridge Structural Database, Version 5.24 (2002) [Allen (2002). Acta Cryst. B58, 380-388]. The calculated values of bond-valence parameters for metal-organic compounds decrease with an increase in lanthanide atomic number; the Rij values are also smaller than bond-valence parameters calculated for inorganic compounds. A summary of bond-valence sums calculated for Rij given in this work and reported in the literature, and a functional correlation between lanthanide-oxygen distances and coordination number are presented.

New lanthanide-nitrogen bond-valence parameters.

The bond-valence parameters (R(ij)), which connect bond valences and bond lengths, have been computed for lanthanide-nitrogen bonds. It has been found that values of bond-valence parameters decrease with increasing lanthanide atomic number in coordination compounds, and that they are smaller than the R(ij) parameters of inorganic compounds. As expected, the lanthanide-nitrogen bond-valence parameters are larger than lanthanide-oxygen bond-valence parameters. There are no obvious dependencies between the number of N atoms in the coordination sphere and the bond-valence parameter value.

Redetermination of hydrogenhydrazinium dichloride

The crystal structure of the title compound, N2H62+·2Cl−, previously determined by photographic methods [Wyckoff (1923). Am. J. Sci. 5, 15–22; Donohue & Lipscomb (1947). J. Chem. Phys. 15, 115–119], has been redetermined from single-crystal data. The N and Cl atoms are located on threefold rotation axes, whereas the H atom lies in a general position. The [H6N2]2+ cations and the Cl− anions are connected via N—H⋯Cl hydrogen bonds forming a three-dimensional net, whereby R63(14) rings are generated.

3,5,7‐Tri­aza‐1‐azoniatri­cyclo­[3.3.1.13,7]­decane perchlorate

The title compound, C6H13N4+·ClO4−, crystallizes in the space group P21/n. The structure can be solved in the orthorhombic space group Pnma, but analysis of the refinement parameters showed that the choice of the P21/n space group is the correct one. All interatomic distances can be considered as normal. Molecules are assembled by intermolecular N—H⋯O hydrogen bonds into a zigzag chain structure along the b axis. In the structure, weak intermolecular C—H⋯N hydrogen bonds create a two-dimensional net structure in the (011) plane.

New bond-valence parameters for lanthanides. Addendum

Recently, we have been informed that the part of our work [Trzesowska et al. (2004), Acta Cryst. B60, 174–178] concerning the linear correlation between the average bond-valence parameters and atomic number of a lanthanide is in agreement with the results of Chen & Hu (2002).