metal-organic compounds
(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)
aNFMLab, Department of Chemistry, Materials and Chemical Engineering, "Giulio Natta", Politecnico di Milano, Via Mancinelli, 7, I-20131 Milano, Italy
*Correspondence e-mail: giancarlo.terraneo@polimi.it
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 C3i 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.
Related literature
For other K2.2.2./salt/haloperfluorocarbon complexes, see: Fox et al. (2004); Metrangolo et al. (2004); Liantonio et al. (2003, 2006).
Experimental
Crystal data
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Data collection: APEX2 (Bruker, 2008); cell 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.
Supporting information
https://doi.org/10.1107/S1600536813016085/kj2225sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536813016085/kj2225Isup2.hkl
The complex was prepared in two steps. Equimolar amounts of [2.2.2]
and NaI in ethanol solution were mixed and refluxed for 5 min. After cooling, the solution was added to a chloroform solution of DIPFA2 (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.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
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 Uiso(H) = 1.2 times Ueq(C).(4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo(8.8.8)hexacosane (K2.2.2) is one of the most popular cryptands in supramolecular chemistry and crystal engineering. Our group has used this [2.2.2]
to generate naked halide anions from their alkali and alkali earth salts and to promote the formation of halogen bonding (XB) with diiodoperfluoroalkanes (DIPFAn, 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 BaI2 and DIPFA2 the ratios K2.2.2/BaI2/DIPFA2 are 1:1:1, iodide anions function as monodentate XB acceptors and form the trimer I-···DIPFA2···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/BaI2/DIPFA8 adduct presents a quite different stoichiometry and interaction pattern (Metrangolo, et al., 2004). 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 does not saturate the cation coordination sphere and two methanol molecules are bound to barium. In the K2.2.2/KI/DIPFAn 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 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···I- group 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/DIPFA2 adducts (CX1) described here, I- anions are tridentate XB acceptors, DIPFA2 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 cavity and is therefore not exactly in the middle of the [2.2.2] 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 the same topology of the anion network. Both the anion and cation layers are shown in Figure 2 and 3.For other K2.2.2./salt/haloperfluorocarbon complexes, see: Fox et al. (2004); Metrangolo et al. (2004); Liantonio et al. (2003, 2006).
Data collection: APEX2 (Bruker, 2008); cell
SAINT (Bruker, 2008); data reduction: SAINT (Bruker, 2008); 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 (Sheldrick, 2008).Fig. 1. The three components of CX1, with numbering scheme of the indepent atoms. The disordered atoms of DIPFA2, generated by the twofold axis are omitted for clarity. Probability level at 50%. | |
Fig. 2. 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. | |
Fig. 3. The same molecular assembly as shown in Figure 2, projected down the c axis |
[Na(C18H36N2O6)]I−·1.5C2F4I2 | Dx = 2.116 Mg m−3 |
Mr = 1057.11 | Mo Kα radiation, λ = 0.71073 Å |
Trigonal, R3c | Cell parameters from 20222 reflections |
a = 11.634 (2) Å | θ = 2.2–29.8° |
c = 84.945 (15) Å | µ = 3.84 mm−1 |
V = 9957 (4) Å3 | T = 93 K |
Z = 12 | Hexagonal table, colourless |
F(000) = 6012 | 0.28 × 0.25 × 0.03 mm |
Bruker APEXII CCD diffractometer | 2604 reflections with I > 2σ(I) |
Radiation source: sealed tube | Rint = 0.035 |
φ and ω scans | θmax = 30.0°, θmin = 1.4° |
Absorption correction: multi-scan (SADABS; Bruker, 2008) | h = −15→15 |
Tmin = 0.676, Tmax = 1.000 | k = −15→15 |
47282 measured reflections | l = −114→114 |
2994 independent reflections |
Refinement on F2 | Primary atom site location: structure-invariant direct methods |
Least-squares matrix: full | Secondary atom site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.032 | Hydrogen site location: inferred from neighbouring sites |
wR(F2) = 0.076 | H-atom parameters constrained |
S = 1.07 | w = 1/[σ2(Fo2) + (0.040P)2] where P = (Fo2 + 2Fc2)/3 |
2994 reflections | (Δ/σ)max = 0.001 |
148 parameters | Δρmax = 1.64 e Å−3 |
44 restraints | Δρmin = −0.58 e Å−3 |
[Na(C18H36N2O6)]I−·1.5C2F4I2 | Z = 12 |
Mr = 1057.11 | Mo Kα radiation |
Trigonal, R3c | µ = 3.84 mm−1 |
a = 11.634 (2) Å | T = 93 K |
c = 84.945 (15) Å | 0.28 × 0.25 × 0.03 mm |
V = 9957 (4) Å3 |
Bruker APEXII CCD diffractometer | 2994 independent reflections |
Absorption correction: multi-scan (SADABS; Bruker, 2008) | 2604 reflections with I > 2σ(I) |
Tmin = 0.676, Tmax = 1.000 | Rint = 0.035 |
47282 measured reflections |
R[F2 > 2σ(F2)] = 0.032 | 44 restraints |
wR(F2) = 0.076 | H-atom parameters constrained |
S = 1.07 | Δρmax = 1.64 e Å−3 |
2994 reflections | Δρmin = −0.58 e Å−3 |
148 parameters |
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. |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
I2 | 0.0000 | 0.0000 | 0.47358 (2) | 0.01498 (10) | |
I1 | 0.22447 (2) | 0.05878 (2) | 0.44381 (2) | 0.02001 (9) | |
C7 | 0.3618 (9) | 0.1058 (7) | 0.42456 (12) | 0.029 (2) | 0.5 |
F1 | 0.4634 (7) | 0.2274 (9) | 0.42658 (10) | 0.065 (3) | 0.5 |
F2 | 0.4115 (9) | 0.0252 (9) | 0.42395 (11) | 0.080 (3) | 0.5 |
C8 | 0.3016 (8) | 0.1016 (6) | 0.40861 (12) | 0.028 (2) | 0.5 |
F3 | 0.2439 (9) | 0.1750 (10) | 0.40947 (12) | 0.074 (3) | 0.5 |
F4 | 0.2054 (7) | −0.0222 (8) | 0.40618 (10) | 0.083 (4) | 0.5 |
Na | 0.3333 | 0.6667 | 0.48841 (2) | 0.0176 (4) | |
N1 | 0.3333 | 0.6667 | 0.52071 (5) | 0.0147 (9) | |
C1 | 0.2462 (3) | 0.5297 (3) | 0.52603 (3) | 0.0167 (6) | |
H1A | 0.1525 | 0.5071 | 0.5248 | 0.020* | |
H1B | 0.2622 | 0.5232 | 0.5374 | 0.020* | |
C2 | 0.2684 (3) | 0.4311 (3) | 0.51696 (4) | 0.0174 (6) | |
H2A | 0.3585 | 0.4461 | 0.5191 | 0.021* | |
H2B | 0.2029 | 0.3397 | 0.5202 | 0.021* | |
O1 | 0.2542 (2) | 0.44777 (19) | 0.50055 (2) | 0.0159 (4) | |
C3 | 0.2593 (3) | 0.3468 (3) | 0.49158 (3) | 0.0186 (6) | |
H3A | 0.1802 | 0.2595 | 0.4938 | 0.022* | |
H3B | 0.3394 | 0.3422 | 0.4944 | 0.022* | |
C4 | 0.2632 (3) | 0.3789 (3) | 0.47452 (4) | 0.0186 (6) | |
H4A | 0.2602 | 0.3067 | 0.4680 | 0.022* | |
H4B | 0.1857 | 0.3884 | 0.4718 | 0.022* | |
O2 | 0.3838 (2) | 0.5009 (2) | 0.47155 (3) | 0.0180 (5) | |
C5 | 0.4235 (3) | 0.5180 (3) | 0.45540 (4) | 0.0198 (6) | |
H5A | 0.4210 | 0.4363 | 0.4516 | 0.024* | |
H5B | 0.5162 | 0.5918 | 0.4546 | 0.024* | |
C6 | 0.3357 (3) | 0.5475 (3) | 0.44487 (3) | 0.0191 (6) | |
H6A | 0.3687 | 0.5597 | 0.4339 | 0.023* | |
H6B | 0.2442 | 0.4708 | 0.4450 | 0.023* | |
N2 | 0.3333 | 0.6667 | 0.44990 (5) | 0.0173 (9) |
U11 | U22 | U33 | U12 | U13 | U23 | |
I2 | 0.01522 (13) | 0.01522 (13) | 0.01451 (17) | 0.00761 (6) | 0.000 | 0.000 |
I1 | 0.01636 (13) | 0.02578 (14) | 0.01665 (12) | 0.00961 (9) | 0.00183 (7) | 0.00086 (8) |
C7 | 0.028 (5) | 0.051 (6) | 0.021 (5) | 0.030 (5) | 0.005 (4) | 0.002 (4) |
F1 | 0.025 (3) | 0.080 (6) | 0.025 (3) | −0.022 (4) | 0.007 (2) | −0.019 (5) |
F2 | 0.114 (8) | 0.145 (7) | 0.058 (6) | 0.122 (7) | 0.058 (5) | 0.066 (5) |
C8 | 0.017 (5) | 0.048 (6) | 0.020 (5) | 0.017 (4) | 0.004 (4) | 0.003 (4) |
F3 | 0.086 (7) | 0.137 (7) | 0.060 (6) | 0.101 (6) | 0.046 (5) | 0.063 (6) |
F4 | 0.033 (4) | 0.089 (7) | 0.028 (3) | −0.043 (4) | 0.009 (3) | −0.022 (5) |
Na | 0.0162 (7) | 0.0162 (7) | 0.0204 (10) | 0.0081 (3) | 0.000 | 0.000 |
N1 | 0.0115 (13) | 0.0115 (13) | 0.021 (2) | 0.0057 (6) | 0.000 | 0.000 |
C1 | 0.0148 (14) | 0.0158 (15) | 0.0172 (14) | 0.0058 (13) | 0.0007 (11) | 0.0012 (11) |
C2 | 0.0184 (16) | 0.0147 (15) | 0.0184 (15) | 0.0078 (13) | −0.0009 (12) | 0.0023 (11) |
O1 | 0.0194 (11) | 0.0140 (11) | 0.0163 (10) | 0.0099 (9) | 0.0001 (8) | 0.0004 (8) |
C3 | 0.0219 (16) | 0.0120 (15) | 0.0211 (15) | 0.0079 (13) | 0.0002 (12) | −0.0011 (11) |
C4 | 0.0167 (15) | 0.0135 (15) | 0.0221 (15) | 0.0049 (13) | 0.0016 (12) | −0.0015 (12) |
O2 | 0.0182 (11) | 0.0143 (11) | 0.0185 (11) | 0.0058 (9) | 0.0000 (8) | −0.0003 (8) |
C5 | 0.0192 (16) | 0.0188 (16) | 0.0207 (15) | 0.0091 (13) | 0.0038 (13) | 0.0002 (12) |
C6 | 0.0197 (16) | 0.0195 (16) | 0.0168 (14) | 0.0089 (13) | 0.0001 (12) | −0.0016 (12) |
N2 | 0.0167 (14) | 0.0167 (14) | 0.018 (2) | 0.0084 (7) | 0.000 | 0.000 |
I1—C8i | 2.153 (11) | O1—C3 | 1.427 (4) |
I1—C7 | 2.156 (11) | C3—C4 | 1.492 (4) |
C7—F1 | 1.325 (5) | C3—H3A | 0.9900 |
C7—F2 | 1.327 (5) | C3—H3B | 0.9900 |
C7—C8 | 1.514 (7) | C4—O2 | 1.434 (4) |
C8—F4 | 1.325 (5) | C4—H4A | 0.9900 |
C8—F3 | 1.327 (5) | C4—H4B | 0.9900 |
N1—C1ii | 1.468 (3) | O2—C5 | 1.430 (4) |
N1—C1 | 1.468 (3) | C5—C6 | 1.520 (4) |
N1—C1iii | 1.468 (3) | C5—H5A | 0.9900 |
C1—C2 | 1.508 (4) | C5—H5B | 0.9900 |
C1—H1A | 0.9900 | C6—N2 | 1.464 (3) |
C1—H1B | 0.9900 | C6—H6A | 0.9900 |
C2—O1 | 1.428 (4) | C6—H6B | 0.9900 |
C2—H2A | 0.9900 | N2—C6iii | 1.464 (3) |
C2—H2B | 0.9900 | N2—C6ii | 1.464 (4) |
F1—C7—F2 | 106.7 (7) | O1—C3—C4 | 108.7 (2) |
F1—C7—C8 | 107.6 (5) | O1—C3—H3A | 109.9 |
F2—C7—C8 | 107.4 (5) | C4—C3—H3A | 109.9 |
F1—C7—I1 | 109.0 (5) | O1—C3—H3B | 109.9 |
F2—C7—I1 | 112.3 (6) | C4—C3—H3B | 109.9 |
C8—C7—I1 | 113.5 (4) | H3A—C3—H3B | 108.3 |
F4—C8—F3 | 106.5 (7) | O2—C4—C3 | 108.1 (2) |
F4—C8—C7 | 107.5 (5) | O2—C4—H4A | 110.1 |
F3—C8—C7 | 107.7 (5) | C3—C4—H4A | 110.1 |
F1i—C8—I1i | 118.8 (9) | O2—C4—H4B | 110.1 |
F4—C8—I1i | 110.4 (6) | C3—C4—H4B | 110.1 |
F3—C8—I1i | 110.5 (6) | H4A—C4—H4B | 108.4 |
C7—C8—I1i | 114.0 (4) | C5—O2—C4 | 113.2 (2) |
C1ii—N1—C1 | 110.97 (18) | O2—C5—C6 | 112.9 (3) |
C1ii—N1—C1iii | 110.97 (18) | O2—C5—H5A | 109.0 |
C1—N1—C1iii | 110.97 (18) | C6—C5—H5A | 109.0 |
N1—C1—C2 | 112.3 (2) | O2—C5—H5B | 109.0 |
N1—C1—H1A | 109.1 | C6—C5—H5B | 109.0 |
C2—C1—H1A | 109.1 | H5A—C5—H5B | 107.8 |
N1—C1—H1B | 109.1 | N2—C6—C5 | 112.0 (3) |
C2—C1—H1B | 109.1 | N2—C6—H6A | 109.2 |
H1A—C1—H1B | 107.9 | C5—C6—H6A | 109.2 |
O1—C2—C1 | 108.6 (2) | N2—C6—H6B | 109.2 |
O1—C2—H2A | 110.0 | C5—C6—H6B | 109.2 |
C1—C2—H2A | 110.0 | H6A—C6—H6B | 107.9 |
O1—C2—H2B | 110.0 | C6iii—N2—C6ii | 111.84 (19) |
C1—C2—H2B | 110.0 | C6iii—N2—C6 | 111.84 (19) |
H2A—C2—H2B | 108.3 | C6ii—N2—C6 | 111.84 (18) |
C3—O1—C2 | 110.8 (2) | ||
F1—C7—C8—F4 | 176.1 (9) | C1iii—N1—C1—C2 | 162.6 (3) |
F2—C7—C8—F4 | 61.5 (8) | N1—C1—C2—O1 | −54.8 (3) |
I1—C7—C8—F4 | −63.3 (8) | C1—C2—O1—C3 | −173.3 (2) |
F1—C7—C8—F3 | −69.6 (8) | C2—O1—C3—C4 | −172.2 (2) |
F2—C7—C8—F3 | 175.9 (7) | O1—C3—C4—O2 | 63.8 (3) |
I1—C7—C8—F3 | 51.1 (7) | C3—C4—O2—C5 | 158.4 (2) |
F1—C7—C8—I1i | 53.4 (8) | C4—O2—C5—C6 | 71.9 (3) |
F2—C7—C8—I1i | −61.2 (7) | O2—C5—C6—N2 | 58.0 (3) |
I1—C7—C8—I1i | 174.0 (2) | C5—C6—N2—C6iii | −154.9 (3) |
C1ii—N1—C1—C2 | −73.6 (4) | C5—C6—N2—C6ii | 78.7 (4) |
Symmetry codes: (i) −x+2/3, −x+y+1/3, −z+5/6; (ii) −y+1, x−y+1, z; (iii) −x+y, −x+1, z. |
Experimental details
Crystal data | |
Chemical formula | [Na(C18H36N2O6)]I−·1.5C2F4I2 |
Mr | 1057.11 |
Crystal system, space group | Trigonal, R3c |
Temperature (K) | 93 |
a, c (Å) | 11.634 (2), 84.945 (15) |
V (Å3) | 9957 (4) |
Z | 12 |
Radiation type | Mo Kα |
µ (mm−1) | 3.84 |
Crystal size (mm) | 0.28 × 0.25 × 0.03 |
Data collection | |
Diffractometer | Bruker APEXII CCD |
Absorption correction | Multi-scan (SADABS; Bruker, 2008) |
Tmin, Tmax | 0.676, 1.000 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 47282, 2994, 2604 |
Rint | 0.035 |
(sin θ/λ)max (Å−1) | 0.702 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.032, 0.076, 1.07 |
No. of reflections | 2994 |
No. of parameters | 148 |
No. of restraints | 44 |
H-atom treatment | H-atom parameters constrained |
Δρmax, Δρmin (e Å−3) | 1.64, −0.58 |
Computer programs: APEX2 (Bruker, 2008), SAINT (Bruker, 2008), SIR2002 (Burla et al., 2003), SHELXL2012 (Sheldrick, 2008), ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2006).
CX1 | CX2 | |
Hole side1 | 11.634 (2) | 11.7478 (15) |
Layer height2 | 9.6686 (18) | 9.6380 (13) |
h3 | 4.4889 (10) | 4.5343 (7) |
V3 | 303.79 (7) | 312.89 (6) |
M+—O1 | 2.460 (2) | 2.6650 (12) |
M+—O2 | 2.692 (2) | 2.7737 (13) |
M+—N1 | 2.744 (5) | 2.941 (2) |
M+—N2 | 3.271 (5) | 2.985 (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 = a2h/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. |
X···Y—C | CX1 X···Y | CX1 C—X···Y | CX2 X···Y | CX2 C—X···Y |
I2···I1—C7 | 3.4492 (5) | 175.99 (17) | 3.4492 (5) | 176.30 (16) |
I2···I1—C8i | 3.4492 (5) | 168.30 (16) | 3.4492 (5) | 166.40 (16) |
O1···(H3B—C3)ii | 2.63 | 147.9 | 2.60 | 147.6 |
Symmetry codes: (i) 2/3-x, 1/3-x+y, 5/6-z; (ii) x-y,x, 1-z. |
Acknowledgements
GC, PM, GR and GT acknowledge the Fondazione Cariplo (project 2010–1351) and "5x1000 junior project" for financial support.
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(4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo(8.8.8)hexacosane (K2.2.2) is one of the most popular cryptands in supramolecular chemistry and crystal engineering. Our group has used this [2.2.2] cryptand to generate naked halide anions from their alkali and alkali earth salts and to promote the formation of halogen bonding (XB) with diiodoperfluoroalkanes (DIPFAn, 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 BaI2 and DIPFA2 the ratios K2.2.2/BaI2/DIPFA2 are 1:1:1, iodide anions function as monodentate XB acceptors and form the trimer I-···DIPFA2···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/BaI2/DIPFA8 adduct presents a quite different stoichiometry and interaction pattern (Metrangolo, et al., 2004). 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/DIPFAn 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···I- group 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/DIPFA2 adducts (CX1) described here, I- anions are tridentate XB acceptors, DIPFA2 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 the same topology of the anion network. Both the anion and cation layers are shown in Figure 2 and 3.