Supermolecules

The nonrelativistic 1,2 A conical intersection seam in the H2 + OH supermolecule has been well studied [28-30] because of its role in the non-adiabatic quenching reaction... 

On one hand, there are the dielectric properties, which are especially important for polai solvents like water. Bulk properties can, on the other hand, only be modeled by using a supermolecule approach with explicitly defined solvent molecules. 

The charge transfer term arises from the transfer of charge (i.e. electrons) from occupied molecular orbitals on one molecule to unoccupied orbitals on the other molecule. This contribution is calculated as the difference between the energy of the supermolecule XY when this charge transfer is specifically allowed to occur, and an analogous calculation in which it is not. 

According to these basic concepts, molecular recognition implies complementary lock-and-key type fit between molecules. The lock is the molecular receptor and the key is the substrate that is recognised and selected to give a defined receptor—substrate complex, a coordination compound or a supermolecule. Hence molecular recognition is one of the three main pillars, fixation, coordination, and recognition, that lay foundation of what is now called supramolecular chemistry (8—11). 

Fig. 32. Hexameric self-assembled supermolecule involving self-recognition (198).

We showed the possible existence of various forms of helically coiled and toroidal structures based on energetic and thermodynamic stability considerations. Though the formation process of these structures is not the subject of this work, the variety of patterns in the outer and inner surface of the structures indicates that there exist many different forms of stable cage carbon structures[10-19]. The molecules in a onedimensional chain, or a two-dimensional plane, or a three-dimensional supermolecule are possible extended structures of tori with rich applications. 

In the second group come molecular dynamics and Monte Carlo simulations, especially those where the solvent is modelled without being explicitly included. Their fourth class is the related supermolecule class, where we actually include solvent molecules in the simulation, and treat the entire array of molecules according to the rules of quantum mechanics or whatever. 

Resonance energies and tautomerism of substituted aromatic heterocycles and their benzo derivatives Reaction-field-supermolecule approach to calculation of solvent effects... 

The simplest discrete approach is the solvaton method 65) which calculates above all the electrostatic interaction between the molecule and the solvent. The solvent is represented by a Active molecule built up from so-called solvatones. The most sophisticated discrete model is the supermolecule approach 661 in which the solvent molecules are included in the quantum chemical calculation as individual molecules. Here, information about the structure of the solvent cage and about the specific interactions between solvent and solute can be obtained. But this approach is connected with a great effort, because a lot of optimizations of geometry with ab initio calculations should be completed 67). A very simple supermolecule (CH3+ + 2 solvent molecules) was calculated with a semiempirical method in Ref.15). 

The continuum models represent a real alternative to the supermolecule approach. In this cases the solvation energy Esolv is assumed to be a sum of individual terms which can be calculated separately (see Eq. (6)). 

In Eq. (6) Ecav represents the energy necessary to create a cavity in the solvent continuum. Eel and Eydw depict the electrostatic and van-der-Waals interactions between solute and the solvent after the solute is brought into the cavity, respectively. The van-der-Waals interactions divide themselves into dispersion and repulsion interactions (Ed sp, Erep). Specific interactions between solute and solvent such as H-bridges and association can only be considered by additional assumptions because the solvent is characterized as a structureless and polarizable medium by macroscopic constants such as dielectric constant, surface tension and volume extension coefficient. The use of macroscopic physical constants in microscopic processes in progress is an approximation. Additional approximations are inherent to the continuum models since the choice of shape and size of the cavity is arbitrary. Entropic effects are considered neither in the continuum models nor in the supermolecule approximation. Despite these numerous approximations, continuum models were developed which produce suitabel estimations of solvation energies and effects (see Refs. 10-30 in 68)). 

In Ref.125) the calculation of an activation barrier for reaction (21) in the gas phase is considered to be an error of the MINDO/3 method and the process is assumed to be activationless. But in respect to the medium effect a barrier of 54 k J mol-1 is obtain-ed which agrees again with the results from Huron-Claverie calculations. Bertran et al. calculated the influence of the solvation on the electrophilic attack of a proton 133) or a methyl cation 134,135) on ethene using a MINDO/3 supermolecule model. Smaller reaction enthalpies also result in solution than in the gas phase in addition to the appearance (H+ + ethene) or the increase (CH 4 + ethene) of an activation barrier1361. 

An additional method for investigating the interactions in the system consisting of cation, counterion and monomer could have been the calculation of a supermolecule... 

Table 23 contains the formation enthalpies for individual points of the potential energy hypersurface of the C4H9BF4 supermolecule, that is, a molecule which can be considered to be made up of the following components C2H, C2H4 and BF4. The same table provides further possibilities to divide the supermolecule C4HgBF4 into logical constituents. 

J. Almlof and M. Feyereisen, SUPERMOLECULE, a program for ab initio electronic structure calculations M. Feyereisen, J. Nichols, J. Oddershede, and J. Simons, J. Chem. Phys. 96, 2978 (1992). 

Polymers and supermolecules modified using electron push-pull chro-mophores are also of particular interest for nonlinear optics (NLO) [10-15]. NLO material has attracted much interest over the past 20 years and has been widely applied in various field (telecommunications, optical data storage, information processing, microfabrication, etc.). Chemists have developed ways to introduce NLO chromophores into many type of polymers, such as Hnear polymers, cross-linked polymers, and branched polymers, and have demonstrated their performance in NLO appHcations. 

Tzeng, B.-C., Yeh, H.-T., Huang, Y.-C., Chao, H.-Y., Lee, G.-H. and Peng, S.-M. (2003) A Luminescent Supermolecule with Gold(l) Quinoline-8-thiolate Crystal Structure, Spectroscopic and Photophysical Properties. Inorganic Chemistry, 42, 6008-6014. 

Coco, S., Cordovdla, C., Donnio, B., Espinet, P., Garda-Casas, M.J. and Gudlon, D. (2008) Self-Organization of Dendritic Supermolecules, Based on Isocyanide-Gold(I), -Copper(l), -Palladium(II), and -Platinum(ll) Complexes, into Micellar Cubic Mesophases. Chemistry - A European Journal, 14, 3544-3552. 

At infinite separation, one arrives at two boron atoms each having a donut-like cylindrical density as indicated in Figure 5-3. However, such a density cannot be obtained from real atomic p-orbitals. In other words, the density that results from the supermolecule is simply inaccessible from calculations on the isolated atoms. Whatever we do, we will never generate the correct charge density (and therefore energy) of the dissociated B2 molecule by calculations of the isolated boron atoms and the requirement of size-consistency is violated. Only if one switches to complex orbitals such as lpx rpyl, are cylindrical atomic densities possible. But even then, we are still in trouble and face a different problem. Just as... 

Paraphrasing Corey s historic definition of synthon [203], Desiraju defined a supramolecular synthon as a structural unit within a supermolecule that can be formed or assembled by known or conceivable synthetic operations involving intermolecular interactions [204], The robustness of the XB has allowed several supramolecular synthons based on this interaction to be identified and some examples have been presented in this chapter. 

The AB supermolecule is described by a single determinant wave function formulated in terms of doubly occupied molecular orbitals with no orthonormality constraints. For a system with 2N = 2Na +2Nb electrons the SCF-MI wave function expressed in terms of the antisymmetrizer operator A is... 

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