Pseudohalogen atoms

Dimethyltin dichloride has a similar chain structure (375). In diethyltin diiodide (374), dimethyltin diisothiocyanate (376, 377), and di-chloro bis(chloromethyl)stannane (378), however, the distorted, trans-RgSnX geometry of each tin atom is completed by two bridging bonds involving the halogen or pseudohalogen atoms on the same, neighboring molecule. 

When a biomolecular system is separated into QM and MM regions one must usually cut amino acid side chains or the protein backbone at covalent bonds (Fig. 5.2 a). The construction of the covalent boundary between the QM and MM parts is key to accurate results from QM/MM calculations. Because there is no unique way to treat the covalent boundary, several different approaches have been described. In the first applications of coupled QM/MM simulations link atoms were used to create the covalent QM/MM boundary (Fig. 5.2b). Link atoms are atoms added to the QM part to fill the broken valences of the boundary QM atoms. These atoms are placed along the broken QM/MM bond at a distance appropriate for the QM bond added. The link atoms have usually been hydrogen atoms but methyl groups and pseudohalogen atoms have also been used [35]. 

Interhalogen compounds produce diorgano tellurium dihalides with two different halogen/pseudohalogen atoms bonded to tellurium15. 

The imide nitrogen atom was also most reactive to a variety of electrophilic species (hydrogen halides, pseudohalogens, and alkyl halides) in the parent Rimidophosphazenes, R(C—NH)-N=PPh3. With t-butyl hypochlorite the /V-chloro-derivatives, R(C=NCl)-N=PPh3, were obtained. R/ -Vinyl-phenylphosphazenes have been prepared by condensation of aldehydes with active methylene compounds ... 

Analytic derivatives have been reported for both the LSCF and GHO models, making them attractive options for MD simulations (Amara et al. 2000). Their generalization to ab initio levels of theory through the use of core pseudopotentials (along the lines of the pseudohalogen capping atoms described above) ensures that they will see continued development. 

All classical pseudohalogens can be deduced in this way. A base element and paraelement have the same number of valence electrons. This means that covalent electron pairs held in common by base atom and ligand are assigned to the base atom, which becomes electronically isovalent with the reference element. 

These guidelines for distinguishing between normal and iso compounds, developed for compounds in which the pseudo halo gens are bonded to carbon, might not be reliable when the pseudohalogens are bonded to the heavy tellurium atom. Molecular structures are not available for diorgano tellurium dipseudohalides. 

---