(μ-1,4,7,10-Tetraoxacyclododecane)bis[(1,4,7,10-tetraoxacyclododecane)lithium] bis(perchlorate)

12-Crown-4 ether (12C4) and LiClO4 combine to form the ionic title compound, [Li2(C8H16O4)3](ClO4)2, which is composed of discrete Li/12C4 cations and perchlorate anions. In the [Li2(12C4)3]2+ cation there are two peripheral 12C4 ligands, which each form four Li—O bonds with only one Li+ atom. Additionally there is a central 12C4 in which diagonal O atoms form one Li—O bond each with both Li+ atoms. Therefore each Li+ atom is pentacoordinated in a distorted square-pyramidal geometry, forming four longer bonds to the O atoms on the peripheral 12C4 and one shorter bond to an O atom of the central 12C4. The cation occupies a crystallographic inversion centre located at the center of the ring of the central 12C4 ligand. The Li+ atom lies above the cavity of the peripheral 12C4 by 0.815 (2) Å because it is too large to fit in the cavity.

12-Crown-4 ether (12C4) and LiClO 4 combine to form the ionic title compound, [Li 2 (C 8 H 16 O 4 ) 3 ](ClO 4 ) 2 , which is composed of discrete Li/12C4 cations and perchlorate anions. In the [Li 2 (12C4) 3 ] 2+ cation there are two peripheral 12C4 ligands, which each form four Li-O bonds with only one Li + atom. Additionally there is a central 12C4 in which diagonal O atoms form one Li-O bond each with both Li + atoms. Therefore each Li + atom is pentacoordinated in a distorted square-pyramidal geometry, forming four longer bonds to the O atoms on the peripheral 12C4 and one shorter bond to an O atom of the central 12C4. The cation occupies a crystallographic inversion centre located at the center of the ring of the central 12C4 ligand. The Li + atom lies above the cavity of the peripheral 12C4 by 0.815 (2) Å because it is too large to fit in the cavity.

Comment
Crown ethers complex with metal ions through the oxygen atoms with remarkable selectivity. They have high conformational flexibility, act as host molecules for various guests (Jagannadh et al., 1999), and have a broad range of applications. Their importance has been studied in numerous fields such as molecular design (Lehn, 1973), supramolecular chemistry (Lehn, 1995), analytical chemistry (Doyle & McCord, 1998;Hayashita et al., 1992) and medicine (Fruhauf & Zeller, 1991). In this study, the goal was to understand the nature of crown ether/Li + complexes, and to extend its application to facilitate the characterization of host-guest type drug delivery systems. Thus, we are developing a systematic methodology based on experimental X-ray crystallography. As a result several novel complexes including the title compound (I) were synthesized.
12-crown-4 ether (12C4) and LiClO 4 combine to form an ionic compound composed of discrete cations and anions. The cation is formed by two Li + metals and three 12C4 ligands interacting to form a complex while the anion is uncomplexed perchlorate. In the cation, two of the 12C4 ligands are peripheral, each interacting with only one Li + . The third 12C4 lies between the two Li + atoms and two opposite oxygen atoms each interact with one of the Li + atoms. The cation occupies an inversion center located at the center of the ring of the central 12C4. Each Li + is pentacoordinate with a distorted square pyramidal geometry forming four bonds to the oxygen atoms of a peripheral 12C4 and one bond to an oxygen atom belonging to the center 12C4. The Li-O bond to the central 12C4 is significantly shorter (1.936 (3) Å) than those to the oxygen atoms on the peripheral 12C4 (av. 2.077 (14) Å). The peripheral 12C4 has approximate C4 symmetry and is in the common [3333] conformation (Raithby et al., 1997;Jones et al., 1997) with the oxygen atoms being coplanar within of 0.013 Å .
The central 12C4 is in the [66] conformation (Raithby et al., 1997). The Li + atom resides above the cavity of the peripheral 12C4 by 0.815 (2) Å. The average diagonal length measured between atom pairs O1/O3 and O2/O4 of the peripheral 12C4 is 3.8211 (15) Å resulting in an adjusted diameter of the cavity of 1.0211 Å (Shoham et al., 1983;Dalley, 1978) . The Li + has an ionic diameter between 1.18 Å and 1.52 Å; thus it is to large to fit in the cavity (Shannon, 1976).
The Li + cation complexes form sheets in the ac plane which stack along the b axis. The anions are positioned between adjacent sheets of cations.
These two solutions were then mixed together according to a 1:1 molar ratio of 12C4/LiClO 4 .The final solution was kept in a desiccator and the solvent was allowed to evaporate gradually in order to produce a supersaturated solution. The supersaturated solution was stored at -20 °C refrigerator, until crystals formed after 48 hours. Two types of colorless crystals suitable for X-ray diffraction were obtained and separated from the solution, one of which was compound (I) the other being 1,4,7,10-tetraoxacyclododecane-trideuteroacetonitrile-lithium perchlorate (Guzei et al., 2010).

Refinement
All H atoms were placed in idealized locations and refined as riding, with C-H=0.99 Å and U iso (H) = 1.2U eq (C).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.  (7) 0.0226 (7) 0.0045 (6) 0.0020 (6) 0.0022 (6)  C10 0.0167 (7) 0.0260 (7) 0.0207 (7