Crystal Structures of (Pyrene)₁₀(I₃^-)₄(I₂)₁₀ and [1,3,6,8-Tetrakis(methylthio)pyrene]₃(I₃^-)₃(I₂)₇:  Structural Trends in Fused Aromatic Polyiodides

Abstract

We report here the synthesis, crystal structures, and electronic band structures of (pyrene)10(I3 -)4(I2)10, 1, and of [1,3,6,8-tetrakis(methylthio)pyrene]3(I3)3 -(I2)7, 2. In both systems, the organic molecules form face-to-face cationic stacks that are separated from one another by a polyiodide network. Band calculations at the extended Hückel (eH) level suggest that the stacks of pyrene molecules in 1 have undergone a Peierls distortion. This Peierls distortion is abetted by rotation of the pyrene molecules within the face-to-face stacks. Within the chains, the pyrene HOMO bands are 3/4-filled. Band calculations on 2, at both the LDA-DFT and eH levels, suggest that 2 is a Mott insulator. The various intermolecular interactions in these crystals are assessed. Strongest are the I···I contacts. These contacts are rationalized as being Lewis acid−Lewis base (charge-transfer) interactions between HOMO and LUMO orbitals. HOMO interactions also are responsible for the stacking sequence observed in 1. In 1, the strength of intermolecular interactions follows the order inorganic−inorganic (i.e., I···I) > organic−organic (i.e., π − π) > organic−inorganic (i.e., C−H···I). Thus, 1 belongs to the family of two-component systems (here, organic and inorganic) where the interface of the two components has a relatively high free energy. An analogy is made to other two-component systems, such as block copolymers. The topology of the interface is analyzed, and a relationship between the dimensionality of the organic network and the ratio of the inorganic volume to the total volume is presented.

Triiodide Organic Salts: Photoelectrochemistry at the Border between Insulators and Semiconductors

“…The electronic interactions between the triiodide anions and the aromatic moieties within cations are excluded on the basis of calculated density of states for the lowest energy transitions. The I 3 − − I 3 − interactions in these structures are therefore stronger than organic – organic or I 3 − − organic interactions which were reported previously . There is a large energy separation between iodide‐centered orbitals and carbon centered ones, despite of some weak hydrogen bonds and close contacts of the C−H⋅⋅⋅I type.…”

A Novel Halogen Bond Acceptor: 1-(4-Pyridyl)-4-Thiopyridine (PTP) Zwitterion

“…the PTP is a neutral zwitterionic molecule, it is possible to avoid introducing any undesirable cations into the system. I2 is the simplest bidentate XB donor, which can be used to link organic molecules together via XB [35][36][37][38][39][40]. However, I2 is not always the most ideal linker due to its redox properties, which easily lead to unwanted side reactions.…”

Organoiodine complexes: Structural and functional variety

“…A correla tion between the length of the intermolecular CH...I con tact and the bond angle has been plotted using data from the Cambridge Structural Database (CSD). 49 The angle for a strong hydrogen bond is near 180°, while weaker hydrogen bonds are characterized by much smaller angles (140°-160° for a bond length of 3.0 Å and 100°-130° for a bond length of 3.6 Å). A CSD based distribution of the iodine-iodine bonds in organic polyiodides over the bond length is shown in Fig.…”

“…49 In both systems, the organic molecules form cationic stacks separated by a polyiodide network. Different intermolecular interactions in the crys tal structure 1 have been arranged in the order of decreas ing Gibbs energy: halogen-halogen (I...I), hydrophobic, π-π stacking, and hydrogen bonds (C-H...I).…”

“…3. 49 The distribution peaks appear at 2.88 (valence bonds in the molecule I 2 and the anion I 3 -) and 3.96 Å (intermolecular contacts in polyiodides and complex polyiodide networks). Intermolecular inter actions in the crystal structures of organic polyiodides have been subjected to topological analysis; it has been emphasized that a certain (≤15%) proportion between the inorganic and total volumes of the atoms in a molecule should be observed for a compound to have supercon ducting properties.…”