Crystal structure of the co-crystalline adduct 1,3,6,8-tetraazatricyclo[4.4.1.13,8]dodecane (TATD)–4-iodophenol (1/2): supramolecular assembly mediated by halogen and hydrogen bonding

In the crystal of the ternary co-crystalline adduct, the components interact through two intermolecular O—H⋯N hydrogen bonds. The supramolecular adducts are interlinked through of halogen bonds and weak non-conventional hydrogen bonds.


Chemical context
Halogenoorganic compounds are able to play a role in organic supramolecular assemblies as electrophilic species, and have been used as models in the construction of self-assembled architectures. Non-covalent bonds such as hydrogen bonds (HB) and halogen bonds (XB) attract interest in crystal engineering because they have clear directional properties (Umezono & Okuno, 2017). Hydrogen bonds have been used successfully to construct supramolecular architectures as a result of their high directionality, which also results in high selectivity. Halogen bonds exhibit similar directionality and strength to hydrogen bonds and can offer a new approach to the control of supramolecular assemblies (Jin et al., 2014). XB also play important roles in natural systems, and have been effectively applied in various fields including crystal engineering, solid-state molecular recognition, materials with optical properties and supramolecular liquid crystals (Li et al., 2017). The strength of the interactions involving halogens increases on going from chlorine to bromine to iodine. Although hydrogen bonds are likely to be more effective, XB also are also important in crystal packing (Aakerö y et al., 2015;Geboes et al., 2017). In view of the analogies between halogen and hydrogen bonding, we think that the 4-iodophenol molecule offers interesting possibilities for exploring the effect of halogen-bonding interactions on supramolecular assemblies of phenols with polyamines. Following our previous work on acid-base adducts based on macrocyclic aminals and phenols, we report herein the synthesis and crystal structure of the title compound, a supramolecular complex assembled through ISSN 2056-9890 non-covalent HB and XB interactions between 4-iodophenol and 1, 3,6,8-tetraazatricyclo[4.4.1.13,8]dodecane (TATD).
Apart from the C-I/Br bond-length differences and some of the bond angles in the benzene ring, the molecules have similar geometric data (bond lengths and angles). The C14-I1 bond length [2.106 (5) Å ] is in good agreement with the value reported for 4-iodophenol itself [2.104 (5) Å ; Merz, 2006]. The overall molecular conformation of TATD observed here is very close to that of TATD in the related bromophenol adduct (Rivera, Uribe et al., 2015).

Supramolecular features
In the crystal, the three independent molecules are linked via two intermolecular O1-H1Á Á ÁN1 hydrogen bonds (Table 1 and Fig. 1). These supramolecular units are then linked by direction-specific intermolecular interactions, including both non-conventional hydrogen bonds and halogen bonds, C-HÁ Á ÁO and C-HÁ Á ÁI hydrogen bonds, forming slabs lying parallel to the bc plane (Table 1 and Fig. 2). However, considering the donor-acceptor bond lengths of 3.961 (7) Å [C5-H5BÁ Á ÁI1] and 3.455 (6) Å [C13-H13Á Á ÁO1], which exceed the sum of the corresponding van der Waals radii (0.281 and 0.255 Å , respectively), the strength of the these non-conventional hydrogen bonds can be classified as very weak (Steiner, 2003).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were located in a difference electron-density map. The hydroxyl H atom was refined freely, while C-bound H atoms were fixed geometrically (C-H = 0.95 or 0.99 Å ) and refined using a ridingmodel approximation, with U iso (H) set to 1.2U eq of the parent atom   SHELXL2016 (Sheldrick, 2015); molecular graphics: XP in SHELXTL-Plus (Sheldrick, 2008); software used to prepare material for publication: SHELXL2016 (Sheldrick, 2015). Absolute structure: Classical Flack (1983) method preferred over Parsons because s.u. lower Absolute structure parameter: −0.03 (4)

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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )