(4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane)sodium iodide–1,1,2,2,tetrafluoro-1,2-diiodoethane (2/3)

The title complex (CX1), [Na(C18H36N2O6)]I·1.5C2F4I2, is a three-component adduct containing a [2.2.2]-cryptand, sodium iodide and 1,1,2,2-tetrafluoro-1,2-diiodoethane. The diiodoethane works as a bidentate halogen-bonding (XB) donor, the [2.2.2]-cryptand chelates the sodium cation, and the iodide counter-ion acts as a tridentate XB acceptor. A (6,3) network is formed in which iodide anions are the nodes and halocarbons the sides. The network symmetry is C 3i and the I⋯I− XB distance is 3.4492 (5) Å. This network is strongly deformed and wrinkled. It forms a layer 9.6686 (18) Å high and the inter-layer distance is 4.4889 (10) Å. The cations, interacting with each other via weak O⋯H hydrogen bonds, are confined between two anionic layers and also form a (6,3) net. The structure of CX1 is closely related to that of the KI homologue (CX2). The 1,1,2,2,-tetrafluoro-1,2-diiodoethane molecule is rotationally disordered around the I⋯I axis, resulting in an 1:1 disorder of the C2F4 moiety.


Experimental
Crystal data [Na(C 18 (3) Notes: (1) Distance between the nearest iodide anions on the same side of the anionic layer, equal to the cell parameter a; (2) distance between the planes through the iodide anions on the opposite sides of the anionic layer; (3) h = distance between the nearest planes through iodide anions of contiguous layers. (4) V = a 2 h/2, volume of the trigonal prism whose vertices are the three iodide anions on a layer and the same faced on the contiguous one.
In CX2, the cell origin and the atom numbering are different, so that atom labels and symmetry code refer only to CX1; for CX2 the reported values refer to the equivalent atoms and values. Data collection: APEX2 (Bruker, 2008); cell refinement: SAINT (Bruker, 2008); data reduction: SAINT; program(s) used to solve structure: SIR2002 (Burla et al., 2003); program(s) used to refine structure: SHELXL2012 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL2012.
GC, PM, GR and GT acknowledge the Fondazione Cariplo (project  and "5x1000 junior project" for financial support. Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: KJ2225). anions from their alkali and alkali earth salts and to promote the formation of halogen bonding (XB) with diiodoperfluoroalkanes (DIPFA n , where n is the alkyl chain length). Different structures were obtained as a function of the cation and of the haloalkane length. For instance, in the complex with BaI 2 and DIPFA 2 the ratios K2.2.2/BaI 2 /DIPFA 2 are 1:1:1, iodide anions function as monodentate XB acceptors and form the trimer I -···DIPFA 2 ···I - (Fox, et al., 2004). This is probably related to the fact that the iodide anions are hydrogen bonded to a water molecule and the resulting decrease of electron density on the anion may limit the number of XB's it gives rise to. The K2.2.2/BaI 2 /DIPFA 8 adduct presents a quite different stoichiometry and interaction pattern . Here, the ratios among the three component are 1:1:3 and an infinite comb-like supramolecular anion is formed in which iodide anions in the main chain and in the prongs function as tridentate and bidentate XB acceptors, respectively. Here too the cryptand does not saturate the cation coordination sphere and two methanol molecules are bound to barium. In the K2.2.2/KI/DIPFA n adducts (n = 2,6 (Liantonio, et al., 2006) and n=4,8 (Liantonio, et al., 2003) the ratios among the three components is 2:2:3. The cryptand completes the coordination sphere of K + cation and no water or alcohol molecules are present in the crystals.
The iodide anions are free to function as tridentate XB acceptors and unlimited (6,3) anionic networks are formed in all four cases. This net is not planar but strongly wrinkled as the (C-I) 3 ···Igroup is pyramidal. The six iodide nodes are the vertices of a trigonal anti-prism whose dimension can be fully described by the mean distance between two iodide anions on the same side of the layer, and by the distance between the planes through the iodide nodes on the two layer sides. The hole dimension increases with n and for n=6,8 it is so large that the cation cannot fulfill the voids and three different (6,3) nets interpenetrate to give an intriguing borromean system (Liantonio, et al., 2006). In all four structures, two layers are faced vertex to vertex, hole to hole, as two egg trays where the cations are hosted. In the K2.2.2/NaI/DIPFA 2 adducts (CX1) described here, Ianions are tridentate XB acceptors, DIPFA 2 are bidentate XB donors and a (6,3) net is formed which is closely similar to that of the KI analogue (CX2). Figure 1 shows the molecular geometry, with the numbering scheme. The Na + cation is small relative to the cryptand cavity and is therefore not exactly in the middle of the [2.2.2] cryptand cavity, as was the case for K + in CX2. As a consequence, the two independent Na + -N distances are very different. Table 1 reports some geometric details of the supramolecular anion hosting cavity and of the supramolecular cation dimensions in CX1 and CX2. Table 2 shows the halogen and hydrogen bonds of CX1. The 'egg tray′ here is too small to isolate completely the 'eggs′, namely the supramolecular cations, which are linked to each other by a couple of symmetry equivalent weak hydrogen bonds between the methylene hydrogen atom and ether oxygen forming a layer with supplementary materials sup-2 Acta Cryst. (2013). E69, m387-m388 the same topology of the anion network. Both the anion and cation layers are shown in Figure 2 and 3.

Experimental
The complex was prepared in two steps. Equimolar amounts of [2.2.2] cryptand and NaI in ethanol solution were mixed and refluxed for 5 min. After cooling, the solution was added to a chloroform solution of DIPFA 2 (1.5 equivalents). A glass vial containg the resulting mixture was put in a wide mouth flask containing vaseline oil. Vapour exchange at room temperature afforded colourless, thin, hexagonal crystals of good quality after a few days.

Refinement
The tetrafluorodiiodoethane molecule was rotationally disordered. The split model was refined with restraints on geometric parameters and ADPs. The rotation of this molecule around the I···I axis, was so large that SHELXL suggested a second splitting of two F atoms. We considered this suggestion not useful and even dangerous to refinement stability in view of the high correlations between split atoms parameters (already up to 0.87). Hydrogen atoms were positioned geometrically and refined using a riding model, with C-H = 0.95-0.99 Å and with U iso (H) = 1.2 times U eq (C).

Figure 1
The three components of CX1, with numbering scheme of the indepent atoms. The disordered atoms of DIPFA 2 , generated by the twofold axis are omitted for clarity. Probability level at 50%.  A layer of cations and two layers of anions, are shown along the a* axis, only partial overposition is adopted for sake of clarity. One hexagonal ring of supramolecular cations and of supramolecular anions are the topologic units of the layers and are shown in spacefilling style.

Crystal data
[Na (C 18  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 1.64 e Å −3 Δρ min = −0.58 e Å −3 Special details Experimental. OXFORD low temperature device. Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. The tetrafluorodiiodoethane molecule was rotationally disordered. The split model was refined with restraints on geometric parameters and ADPs. The rotation of this molecule around the I···I axis, was so large that SHELXL suggested a second splitting of two F atoms. We considered not useful and even dangerous the suggestion, because the largest correlations between split atoms parameters, already high (<0.87), would be larger.