Tetraethylammonium tetrakis(1,1,1,5,5,5-hexafluoroacetylacetonato)terbate(III)

The title compound, (C8H20N)[Tb(C5HF6O2)4], is a tetrakis β-diketonate complex of hexafluoroacetylacetone with terbium(III), and tetraethylammonium as the counter-ion. This compound shows typical green terbium(III) luminescence upon excitation at about 335 nm. The coordination geometry around the TbIII atom is a slightly distorted square antiprism. One hexafluoroacetylacetone ligand has a disordered CF3 group [occupancies of 0.575 (4) and 0.425 (4)]. A three-dimensional network is built up by linkage of TbIII complexes via C—H⋯F interactions.

For instance, rare-earth β-diketonates have been investigated as extractants in solvent-solvent extraction processes, as NMR shift reagents, as active materials in liquid lasers and novel types of organic light-emitting diodes (OLEDs), as active compounds in electroluminescent devices (e.g. flat-panel displays), as luminescent probes in bioassays, as precursors for chemical vapor deposition and as catalysts in organic reactions. These rare-earth β-diketonate complexes can be grouped into three main types: tris complexes, Lewis base adducts of the tris complexes (or ternary rare-earth β-diketonates) and tetrakis complexes.
An overiew of the different types of rare-earth β-diketonate complexes, their crystal structures and applications, is given by Binnemans, 2005.
Here, we describe the crystal structure of a tetrakis complex of hexafluoroacetylacetone (hfac) with the terbium cation, Tb(III), and tetraethylammonium (Et 4 N) as the counter ion, which shows typical green Tb(III) luminescence upon excitation at about 335 nm.
The title compound crystallizes in the monoclinic space group P2 1 /n, with four formula units in the unit cell. The asymmetric unit consists of one Tb(III) cation, four hfac anions and one Et 4 N cation, which in total equals one formula unit.
Each Tb(III) ion is eight-coordinated by oxygen atoms from four chelating hfac ligands. The coordination polyhedron around Tb(III) can be best described as a slightly distorted square antiprism ( Figure 1). There are no solvent molecules coordinating to the Tb(III) ion. One of the CF 3 groups of one of the hfac ligands is found disordered.  (Danford et al., 1970). However, no coordinates are available for the latter structure (reference code QQQBZM, CSD (Version 5.32) (Allen, 2002)).

Experimental
General synthetic procedues for the synthesis of rare-earth β-diketonate complexes are given in Melby et al., 1964. The title compound was synthesized by mixing 3.6 ml of a 1 N sodium hydroxide solution with 9 ml of an ethanol (95%(v/v)) solution of hexafluoroacetylacetone (0.505 ml, 3.6 mmol) in a 50 ml Erlenmeyer flask at 60 °C. Subsequently, under stirring, 9 ml of aqueous Tb(NO 3 ) 3 .5H 2 O solution (0.3906 g, 0.9 mmol) was added dropwise and finally 1.8 ml of aqueous tetraethylammonium chloride solution (0.0705 g, 0.426 mmol) was added dropwise. The mixture was concentrated by heating until the onset of crystallization. Finally, the solution was filtered and kept overnight to stand at room temperature, to allow the formation of single crystals.

Refinement
All hydrogen atoms were placed at calculated positions and further refined with isotropic temperature factors fixed at 1.2 times U eq of the parent atoms (1.5 times for methyl groups). 1,2 and 1,3 distance restraints to target values, together with restrained U ij components (for the fluorine atoms) had to be added to model the disorder of the CF 3 group on one of the hfa ligands [refined occupancy factors were 0.575 (4) and 0.425 (4)]. Fig. 1. Coordination geometry of the title compound, showing 50% probability displacement ellipsoids. The disorder of one of the CF 3 groups is not shown.  Tetraethylammonium tetrakis(1,1,1,5,5,5-hexafluoroacetylacetonato)terbate(III)