Poly[[tetraaquatris(μ3-hexane-1,6-dicarboxylato)diterbium(III)] 0.25-hydrate]

In the title terbium coordination polymer, {[Tb2(C6H8O4)3(H2O)4]·0.25H2O}n, the TbIII atom is nine-coordinated, forming a TbO9 polyhedra. Furthermore, two symmetric TbO9 polyhedra share their edges, forming Tb2O16 dimers, which are linked by adipate bridges into a layered structure. Intermolecular O—H⋯O hydrogen bonds link these layers into a three-dimensional network. One of the C atoms of the adipate ligand is disordered over two positions with site-occupancy factors of 0.622 (9) and 0.378 (9). The structure also contains a disordered molecule of water of hydration, lying close to a special position, with partial occupancy.

In the title terbium coordination polymer, {[Tb 2 (C 6 H 8 O 4 ) 3 -(H 2 O) 4 ]Á0.25H 2 O} n , the Tb III atom is nine-coordinated, forming a TbO 9 polyhedra. Furthermore, two symmetric TbO 9 polyhedra share their edges, forming Tb 2 O 16 dimers, which are linked by adipate bridges into a layered structure. Intermolecular O-HÁ Á ÁO hydrogen bonds link these layers into a three-dimensional network. One of the C atoms of the adipate ligand is disordered over two positions with siteoccupancy factors of 0.622 (9) and 0.378 (9). The structure also contains a disordered molecule of water of hydration, lying close to a special position, with partial occupancy.

Comment
In recent years, a great interest has been focused on the crystal engineering of novel coordination polymers, not only due to their intriguing topological structures but also potential application as functional materials in areas such as ion exchange, catalysis, optics, gas separation/storage and sensing (Moulton & Zaworotko, 2001;Wood & Thompson, 2007). The REadipate (RE = rare earth metal) system has been examined extensively owing to the rich structural diversity of this family of materials. A great many of compounds have been reported which exhibit structure types ranging from 1-D chain to 2-D layer and 3-D framework topologies (Dimos et al., 2002;Duan et al., 2004;Kim et al., 2004;Kiritsis et al., 1998). Arguably much of this diversity is related to the flexibility of the aliphatic dicarboxylic backbone. In this paper, we report the hydrothermal synthesis and single-crystal X-ray diffraction analysis of a novel Tb-adipate compound, which is isotypic with La(III) (Kim et al., 2004) and Dy(III) (Lill et al., 2005) analogous complexes.
The crystal structure of the title complex consists of nine oxygen atoms coordinated to Tb(III) (Fig. 1) of which seven oxygen atoms are from four adipate ligands and two from two independent coordinated water molecules. Two symmetric TbO 9 polyhedra share their edges to form a Tb 2 O 16 dimeric unit about an inversion centet. These dimers are further linked through adipate anions to form a two-dimensional layer perpendicular to (010) (Fig. 2).
C9-atom of the adipate ligand was disordered over two sites with site occupancy factors 0.622 (9) and 0.378 (9). The structure also contains a disordered molecule of water of hydration lying close to a special position with partial occupancy.

Experimental
Colorless prismatic single crystals of the title complex were obtained using hydrothermal methods in a sealed 20 ml Teflonlined Parr bomb. TbCl 3 . 6H 2 O (0.2 g), adipic acid (0.1 g) and H 2 O (10 ml) were placed in the bomb and sealed. The bomb was then heated under autogenous pressure for 7 d at 433 K and finally cooled to room temperature. Upon opening the bomb, a few single crystals was obtained for X-ray single-crystal diffraction analysis.

Refinement
The H-atoms bonded to C-atoms were placed in calculated positions using a riding model, with C-H = 0.93-0.97 Å and U iso = 1.2U eq . The H-atom of water molecules were located from the difference maps and fixed at those locations with supplementary materials sup-2 Figures Fig. 1. A view of part of the title structure. Ellipsoids are drwan at the 50% probability level. Symmetry code: