Co-crystal sustained by π-type halogen-bonding interactions between 1,4-diiodoperchlorobenzene and naphthalene

The formation of a co-crystal sustained by π-type halogen bonds involving 1,4-diiodoperchlorobenzene and naphthalene is reported.

The formation and crystal structure of a co-crystal based upon 1,4-diiodoperchlorobenzene (C 6 I 2 Cl 4 ) as the halogen-bond donor along with naphthalene (nap) as the acceptor is reported.The co-crystal [systematic name: 1,2,4,5tetrachloro-3,6-diiodobenzene-naphthalene, (C 6 I 2 Cl 4 )•(nap)] generates a chevron-like structure that is held together primarily by �-type halogen bonds (i.e.C-I� � �� contacts) between the components.In addition, C 6 I 2 Cl 4 also interacts with the acceptor via C-Cl� � �� contacts that help stabilize the cocrystal.Within the solid, both aromatic components are found to engage in offset and homogeneous face-to-face �-� stacking interactions.Lastly, the halogen-bond donor C 6 I 2 Cl 4 is found to engage with neighboring donors by both Type I chlorine-chlorine and Type II iodine-chlorine contacts, which generates an extended structure.

Chemical context
Halogen bonding continues to be a highly utilized non-covalent interaction in the formation of multicomponent molecular solids such as co-crystals.Halogen bonding is an attractive interaction between an electrophilic region on a halogen atom and a nucleophilic region on a second atom (Gilday et al., 2015).This electrophilic or positive region, namely the �-hole, is located at the tip of a halogen atom bound to a carbon that interacts with a lone pair on an atom or an electron-rich aromatic surface (Cavallo et al., 2016).In general, iodine generates the largest positive �-hole when combined with neighboring electronegative atoms such as fluorine.The majority of these reported halogen bonds are classified as ntype meaning that the halogen atom is interacting with a lone pair such as on an N or O atom (Walsh et al., 2001).A lesser investigated class of halogen bonds are �-type (i.e.C-I� � �� contacts) where the halogen atom interacts with an electronrich surface such as a polycyclic aromatic hydrocarbon (Vainauskas et al., 2020;d'Agostino et al., 2015;Shen et al., 2012).
A continued goal within our research groups has been in the design and formation of halogen-bonded co-crystals based upon 1,4-diiodoperchlorobenzene (C 6 I 2 Cl 4 ) as the donor.Recently, we reported the formation of photoreactive cocrystals based upon C 6 I 2 Cl 4 along with trans-1,2-bis(pyridine-4-yl)ethylene (Bosch et al., 2019b) and 4-stilbazole (Bosch et al., 2019c) that are held together by primarily C-I� � �N or ntype halogen bonds.With the goal of expanding the type of halogen bonds that C 6 I 2 Cl 4 can form in molecular co-crystals, a study with a polycyclic aromatic was undertaken.Herein, we report the solid-state crystal structure of a co-crystal held together primarily by �-type halogen bonds between C 6 I 2 Cl 4 and naphthalene (nap) resulting in a chevron-like structure.In addition to the �-type halogen bond, the co-crystal (C 6 I 2 Cl 4 )•(nap) is also held together by the combination of C-Cl� � �� contacts, homogeneous face-to-face �-� stacking interactions, Type I chlorine-chlorine contacts, and Type II iodine-chlorine contacts.

Structural commentary
Crystallographic analysis reveals that (C 6 I 2 Cl 4 )•(nap) crystallizes in the centrosymmetric triclinic space group Pı ¯.The asymmetric unit contains half a molecule of both C 6 I 2 Cl 4 and nap where inversion symmetry generates the remainder of each molecule (Fig. 1).The co-crystal is sustained by �-type or C-I� � �� halogen bonds with a distance of 3.373 (1) A ˚along with a nearly perpendicular halogen-bond angle of 90.99 (4) � (Fig. 2).This halogen-bond distance and angle were determined by using the I atom on C 6 I 2 Cl 4 and the calculated plane for the nap molecule.As expected, C 6 I 2 Cl 4 forms two �-type halogen bonds with two different nap molecules, generating a chevron-like pattern (Fig. 2).

Supramolecular features
In addition to �-type halogen bond within (C 6 I 2 Cl 4 )•(nap), the donor C 6 I 2 Cl 4 is found to engage in Type I chlorine-chlorine contacts (Fig. 3).These interactions are found between crystallographically equivalent Cl atoms, namely Cl2� � �Cl2 i [symmetry code: (i) 1 À x, -y, 1 À z], with a distance of 3.499 (1) A ˚and a C-Cl� � �Cl bond angle of � 1 = � 2 = 132.16(6) � (Mukherjee et al., 2014;Desiraju & Parthasarathy, 1989).In addition, neighboring donors also interact via Type II iodine-chlorine contacts.This interaction is found between I1� � �Cl2 i [symmetry code: (i) 1 À x, -y, 1 À z], with a distance of 3.808 (1) A ˚and a C-I� � �Cl bond angle of 111.83 (4) � .Both the aromatic halogen-bond donor and acceptor are found to engage in an offset and homogeneous face-to-face �-� stacking arrangement that stabilizes the co-crystal (Fig. 3).Lastly, C 6 I 2 Cl 4 is interacting with two additional nap molecules via C-Cl� � �� contacts at a distance of 3.391 (2) A measured for Cl1� � �C5.These various non-covalent interactions were also investigated and visualized by utilizing a Hirshfeld surface analysis (Spackman et al., 2021) where d norm is mapped onto the calculated surface (Fig. 4).The darkest red spots on the Hirshfeld surface represents the shortest van der Waals contacts where the �-type halogen bond is located.In addition, the faint red spots indicate separations less than the sum of the van der Waals radii for the C-Cl� � �� contacts.Lastly, dashed lines illustrate the Type I chlorine-chlorine interactions observed within (C 6 I 2 Cl 4 )•(nap).This Hirshfeld The labeled asymmetric unit of (C 6 I 2 Cl 4 )•(nap).Displacement ellipsoids are drawn at the 50% probability level for non-hydrogen atoms while hydrogen atoms are shown as spheres of arbitrary size.

Database survey
A search of the Cambridge Crystallographic Database (Version 2023.2.0 Build 3382240; Groom et al., 2016) using Conquest (Bruno et al., 2002) for structures containing 1,4diiodoperchlorobenzene (C 6 I 2 Cl 4 ) in which the I atom is within the van der Waals radius of an aromatic surface revealed only one structure, refcode HONBIY (Bosch, 2019a).In particular, this multicomponent solid is a monosolvate of benzene where C 6 I 2 Cl 4 forms two �-type halogen bonds, generating a similar chevron-like pattern observed in (C 6 I 2 Cl 4 )•(nap).

Materials and general methods
The solvent toluene along with the halogen-bond acceptor naphthalene (nap) were both purchased from Sigma-Aldrich Chemical (St.Louis, MO, USA) and used without any additional purification.The halogen-bond donor 1,4-diiodoperchlorobenzene (C 6 I 2 Cl 4 ) was synthesized utilizing a previously published method (Reddy et al., 2006).

Synthesis and crystallization
The formation of (C 6 I 2 Cl 4 )•(nap) was achieved by dissolving 50.0 mg of C 6 I 2 Cl 4 in 2.0 mL of toluene and then combined with a 2.0 mL toluene solution containing 13.7 mg of nap (1:1 molar equivalent).Within two days, single crystals suitable for X-ray diffraction were formed upon loss of some of the solvent by slow evaporation.

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.A numerical absorption correction was applied based on a Gaussian integration over a multifaceted crystal and followed by a semi-empirical correction for adsorption applied using SADABS (Bruker, 2016).The program SHELXT (Sheldrick, 2015a) was used for the initial structure solution and SHELXL (Sheldrick, 2015b) was used for the refinement of the structure.Both programs were utilized within the OLEX2 software (Dolomanov et al., 2009). Fractional Figure 1

Figure 2 X
Figure 2X-ray crystal structure of (C 6 I 2 Cl 4 )•(nap) illustrating the chevron-like packing pattern along with �-type halogen bonds.In addition, the Type I chlorine-chlorine and Type II iodine-chlorine interactions between neighboring chevron-based chains are also shown.

Figure 3 X
Figure 3X-ray crystal structure of (C 6 I 2 Cl 4 )•(nap) illustrating the �-type halogen bonds and the offset face-to-face stacking of both the halogen-bond donor and acceptor.

Figure 4
Figure 4Hirshfeld surface of (C 6 I 2 Cl 4 )•(nap) where d norm is mapped onto the surface illustrating the �-type halogen bonds (darkest red spots) and C-Cl� � �� contacts (faint red spots).Lastly, the Type I chlorine-chlorine interactions are shown with green dashed lines.

Table 1
Experimental details.