Interplay of Intra- and Intermolecular Interactions in Solid Iodine at Low Temperatures: Experimental and Theoretic Spectroscopy Study

Iodine-Rich Supramolecular Complexes of Chlorobismuthates(III): Unusual Lone Pair Activity and Features of Halogen Bonding in Crystals

The first chrorobismuthate(III) supramolecular hybrids with halogen-bond-linked I2, (Py(CH2)2Py){[BiCl5](I2)} (1) and (Py(CH2)3Py){[BiCl5](I2)0.5} (2), were synthesized via the reaction between Bi2O3, I2, and salts of the corresponding cations in HCl. The compounds featured one- and two-dimensional (2D) supramolecular motifs built by I···Cl contacts; in the case of 1, Bi(III) is pentacoordinated due to the lone pair activity, which also interacted with I2 pi-orbitals, as confirmed by density functional theory (DFT) calculations. Both complexes exhibited moderate thermal stabilities and relatively narrow optical band gaps.

Studies of Nature of Uncommon Bifurcated I-I···(I-M) Metal-Involving Noncovalent Interaction in Palladium(II) and Platinum(II) Isocyanide Cocrystals

Two isostructural trans-[MI2(CNXyl)2]·I2 (M = Pd or Pt; CNXyl = 2,6-dimethylphenyl isocyanide) metallopolymeric cocrystals containing uncommon bifurcated iodine···(metal-iodide) contact were obtained. In addition to classical halogen bonding, single-crystal X-ray diffraction analysis revealed a rare type of metal-involved stabilizing contact in both cocrystals. The nature of the noncovalent contact was studied computationally (via DFT, electrostatic surface potential, electron localization function, quantum theory of atoms in molecules, and noncovalent interactions plot methods). Studies confirmed that the I···I halogen bond is the strongest noncovalent interaction in the systems, followed by weaker I···M interaction. The electrophilic and nucleophilic nature of atoms participating in I···M interaction was studied with ED/ESP minima analysis. In trans-[PtI2(CNXyl)2]·I2 cocrystal, Pt atoms act as weak nucleophiles in I···Pt interaction. In the case of trans-[PdI2(CNXyl)2]·I2 cocrystal, electrophilic/nucleophilic roles of Pd and I are not clear, and thus the quasimetallophilic nature of the I···Pd interaction was suggested.

Tetrabromoethane as σ-Hole Donor toward Bromide Ligands: Halogen Bonding between C2H2Br4 and Bromide Dialkylcyanamide Platinum(II) Complexes

The complexes trans-[PtBr2(NCNR2)2] (R2 = Me21, (CH2)52) were cocrystallized with 1,1,2,2-tetrabromoethane (tbe) in CH2Cl2 forming solvates 1·tbe and 2·tbe, respectively. In both solvates, tbe involved halogen bonding, viz. the C–Br···Br–Pt interactions, were detected by single-crystal X-ray diffractions experiments. Appropriate density functional theory calculations (M06/def2-TZVP) performed for isolated molecules and complex-tbe clusters, where the existence of the interactions and their noncovalent nature were confirmed by electrostatic potential surfaces (ρ = 0.001 a.u.) for isolated molecules, topology analysis of electron density, electron localization function and HOMO-LUMO overlap projections for clusters.

Atomically Thin Pythagorean Tilings in Two Dimensions

We perform a theoretical study of an atomically thin, two-dimensional layer obtained by positioning atoms at the vertices of the classical Pythagorean tiling. This leads to an unusual geometrical pattern that is only stable for the three halogens Cl, Br, and I. In this Pythagorean structure, halogen atoms are arranged in strongly bound diatomic units that bind together by weaker electrostatic bonds. The energy of these phases is competitive with those of the low-temperature phase of the halogens and the two-dimensional layer obtained by exfoliating it. The Pythagorean layers are semiconducting, with an unusual band structure composed of very mobile holes and extremely heavy electrons. They are also soft, exhibiting small values of the elastic constants and a very low energy flexural mode. Analysis of the allowed Raman transitions reveals breathing-like modes that might be used to fingerprint, experimentally, the Pythagorean structure. Finally, we present a series of substrates that, due to lattice matching and compatible symmetry, can be used to stabilize these peculiar two-dimensional layers.