A model chemistry for the evaluation of intermolecular interaction between aromatic molecules (AIMI Model) has been developed. The CCSD(T) interaction energy at the basis set limit has been estimated from the MP2 interaction energy near the basis set limit and the CCSD(T) correction term obtained by using a medium size basis set. The calculated interaction energies of the parallel, T-shaped,and slipped-parallel benzene dimers are -1.48, -2.46, and -2.48 kcal/mol, respectively. The substantial attractive interaction in benzene dimer, even where the molecules are well separated, shows that the major source of attraction is not short-range interactions such as charge-transfer but long-range interactions such as electrostatic and dispersion. The inclusion of electron correlation increases attraction significantly. The dispersion interaction is found to be the major source of attraction in the benzene dimer. The orientation dependence of the dimer interaction is mainly controlled by long-range interactions. Although electrostatic interaction is considerably weaker than dispersion interaction, it is highly orientation dependent. Dispersion and electrostatic interactions are both important for the directionality of the benzene dimer interaction.

Origin of Attraction and Directionality of the π/π Interaction: Model Chemistry Calculations of Benzene Dimer Interaction

Crystal engineering. From molecules to materials

We report the supramolecular chemistry of several metal complexes of N-(4-pyridyl)benzamide (NPBA) with the general formula [Ma(NPBA)2AbSc], where M = Co2+, Ni2+, Zn2+, Mn2+, Cu2+, Ag+; A = NO3-, OAc-; S = MeOH, H2O; a = 0, 1, 2; b = 0, 1, 2, 4; and c = 0, 2 NPBA contains structural features that can engage in three modes of intermolecular interactions:  (1) metal−ligand coordination, (2) hydrogen bonding, and (3) π−π stacking NPBA forms one-dimensional (1-D) chains governed by hydrogen bonding, but when reacted with metal ions, it generates a wide variety of supramolecular scaffolds that control the arrangement of periodic nanostructures and form 1- (2−4), 2- (5), or 3-D (6−10) solid-state networks of hydrogen bonding and π−π stacking interactions in the crystal Isostructural 7−9 exhibit a 2-D hydrogen bonding network that promotes topotaxial growth of single crystals of their isostructural family and generates crystal composites with two (11) and three (12) different components Furthermore, 7−9 can 

Engineering the structure and magnetic properties of crystalline solids via the metal-directed self-assembly of a versatile molecular building unit.

Two-photon absorption (TPA) cross sections of four representative series of octupolar molecules are theoretically investigated. The general structure−TPA-property relationship is described by using the effective four-state valence-bond three-charge-transfer model. As the charge-transfer character of the ground electronic state increases due to the strong donors or acceptors, (i) the transition dipole matrix elements between the ground and 2-fold degenerate excited states increase, (ii) the energy gap decreases, and consequently (iii) the TPA transition amplitude monotonically increases. Thus, the design strategy to maximize the TPA cross section of the octupolar molecule is established. On the basis of the four-state model, the first hyperpolarizability of the octupolar molecule is found to be linearly proportional to the TPA cross section. This theoretical relationship is confirmed by using the ab initio calculation results. The Hammett correlation analysis of the TPA cross section and first hyperpolariz...

Two-photon absorption and nonlinear optical properties of octupolar molecules.

The polarity of a semiconducting molecule affects its intrinsic photophysical properties, which can be tuned by varying the molecular geometry. Herein, we developed a D3h -symmetric tricyanomesitylene as a new monomer which could be reticulated into a vinylene-linked covalent organic framework (g-C54 N6 -COF) via Knoevenagel condensation with another D3h -symmetric monomer 2,4,6-tris(4'-formyl-biphenyl-4-yl)-1,3,5-triazine. Replacing tricyanomesitylene with a C2v -symmetric 3,5-dicyano-2,4,6-trimethylpyridine gave a less-symmetric vinylene-linked COF (g-C52 N6 -COF). The octupolar conjugated characters of g-C54 N6 -COF were reflected in its scarce solvatochromic effects either in ground or excited states, and endowed it with more promising semiconducting behavior as compared with g-C52 N6 -COF, such as enhanced light-harvesting and excellent photo-induced charge generation and separation. Along with the matched energy level, g-C54 N6 -COF enabled the two-half reactions of photocatalytic water splitting with an average O2 evolution rate of 51.0 μmol h-1  g-1 and H2 evolution rate of 2518.9 μmol h-1  g-1 . Such values are among the highest of state-of-the-art COF photocatalysts.

Vinylene-Linked Covalent Organic Frameworks (COFs) with Symmetry-Tuned Polarity and Photocatalytic Activity.

The principles of crystal engineering have been used to design a family of structures with potential as octupolar nonlinear optical (NLO) materials. The major aim in such an exercise, a carry-over of molecular symmetry into the crystal, is possible with a retrosynthetic approach. An appropriate choice of precursor trigonal molecules leads from the concept of the dimeric Piedfort unit. The crystal structures and NLO properties of a series of 2,4,6-triaryloxy-1,3,5-triazines, 1−6, are reported. These compounds consistently form quasi-trigonal or trigonal networks that are two-dimensionally noncentrosymmetric. Substitutional variations on the phenyl moieties that were expected to maintain or to perturb this trigonal network have been explored. Molecular nonlinearities have been measured by Harmonic Light Scattering (HLS) experiments. Among the compounds studied, 2,4,6-triphenoxy-1,3,5-triazine, 1 adopts a noncentrosymmetric crystal structure with a measurable SHG powder signal. All these crystal structures a...

Crystal Engineering of Some 2,4,6-Triaryloxy-1,3,5-triazines: Octupolar Nonlinear Materials

The invention relates to a new form of acetyl salicylic acid designated as Form AB as well as processes for their preparation and formulation comprising it Also, the invention relates to solid state forms of acetyl salicylic acid Form AB, in particular Form AB-A, as well as processes for their preparation and formulation comprising them

Solid state forms ab of acetyl salicylic acid

Most of the highly strained molecules are either sensitive to heat or liquid under ambient conditions or both. This makes it difficult to get exact structural data, usually obtained by single crystal X—ray structure determination.

Roland Boese

Papers

Crystal Engineering of Some 2,4,6-Triaryloxy-1,3,5-triazines: Octupolar Nonlinear Materials

Solid state forms ab of acetyl salicylic acid

How to Get Structures of Strained Compounds: Low Temperature Structures and X-X Electron Deformation Densities