T-shape complexes

Figure 1. Schematic of the radial cuts of the ground- and excited-state potential energy surfaces at the linear and T-shaped orientations. Transitions of the ground-state, T-shaped complexes access the lowest lying, bound intermolecular level in the excited-state potential also with a rigid T-shaped geometry. Transitions of the linear conformer were previously believed to access the purely repulsive region of the excited-state potential and would thus give rise to a continuum signal. The results reviewed here indicate that transitions of the linear conformer can access bound excited-state levels with intermolecular vibrational excitation.

The probability distribution for the n = 2 intermolecular level. Fig. 12c, indicates that this state resembles a bending level of the T-shaped complex with two nodes in the angular coordinate and maximum probability near the linear He I—Cl and He Cl—I ends of the molecule [40]. The measured I C1(B, v = 2f) rotational product state distribution observed following preparation of the He I C1(B, v = 3, m = 2, / = 1) state is plotted in Fig. 12d. The distribution is distinctly bimodal and extends out to the rotational state, / = 21,... 

For bromide and iodide, the nature of the countercation influences the structure of the anionic complex. In fact, when the [(18-C-6)-K]Br and [(18-G-6)-K]I salts are used, the anionic complexes ([ 163—X]—, X = Br, I) remain mononuclear and adopt a T-shaped structure (Figure 11). In both cases, the Hg-X bonds are shorter than those observed in the corresponding dinuclear complexes in agreement with the terminal location of the anion. The reaction of bis(pentafluoro)phenylmercury 164 with [(18-C-6)-K]Br and [(18-C-6)-K]I also afford T-shaped complexes [164-Br] and [164-1]. The Hg-Br (2.93 A) and Hg-I (3.12 A) bonds found in these complexes are longer than those observed in [163-Br] and [ 163—1] indicating that 164 is a weaker Lewis acid than 163.206... 

The effect of variation of metal and ligand on the energies of the orbitals of the T-shaped complex is shown in Figure 13.8 in which a number of principles are illustrated. 

An MO study of CO insertion into the Me—Ptn bond has considered a number of pathways, and the factors involved have been weighed. Trans influence arguments and the facility of the supporting ligands to migrate between different structures are considered. The relative stabilities of isomers and the potential barrier for isomerizations are investigated the Y-shaped complex is unstable and isomerizes to a T-shape with no barrier. The relative stability of T-shaped complexes is explained by the trans influence effect.603... 

The important parameter is the coupling coefficient between the ionic and the covalent curves. Since the observed spectrum lies in the vicinity of the covalent curve, this implies that the coupling term is small (=0.1 eV), which has been interpreted as the effect of the ground state—a small coupling being expected for the T-shaped complex (Jouvet et al. 1987). 

In Ref. [34], this attachment is discussed in detail along an optimized path obtained for reaction in aqueous solution here, instead, a comparison with the reaction in gas phase will be presented. It is useful to recall that the ring structure has a maximum weight at a geometry close to that of the transition state, while Er3 4 increase monotonically, starting from zero at the T-shaped complex and arriving at a maximum when the chloronium ion intermediate is formed. The wavefunction of the intermediate is very well represented by the resonance of structures I 2, 3 and F4 with the... 

One would expeet the sort of bonding described above to lead to a T-shaped complex, as indieated in Fig. 6.5a. It is also conceivable that this same attraction of the H atom to the n cloud could be represented by a sort of eyelic structure in Fig. 6.5b wherein there are two sueh interaetions possible. This arrangement, a kind of staggered parallel geometry, has also been referred to as S-shaped. There has been some controversy in the literature as to which is actually observed in the gas phase, or whether both coexist " . 

The measurement of interaction dipoles by beam deflection gives an indk ation of the structure of the Van der Waals molecule. A recent example is given by Howard and coworkers , who experimentally established that the interaction dipole of ( 2)2 is less than 10 D. Since it has sometimes been suggested that the dimer is a T-shaped complex (a favourable configuration for quadrupole-quadrupole interaction, see above), they estimated the induction contribution to the dipole moment for this conformation (at R = 4.1 A) and found 0.18 D for this value. So they conclude that the dimer has most likely a staggered parallel configuration, which is in accordance with recent ab initio calculations . ... 

Dichloro(ri-2- 2,2 -bipyhmidyl )platinum(II) (VIII-11) was among the most effective catalysts. The authors proposed that the process is electrophilic in character and occurs with the cationic, highly electrophilic, coordinatively unsaturated, 14-electron, T-shaped complex (VIII-12), as shown in Scheme VIII. 9. 

The geometry has been fixed at the Cio symmetry of the T-shape complex and the PES has been analyzed in terms of two variables the Cl-Cl distance and the distance between the C-C bond-midpoint and the nearest chlorine atom. All the remaining geometric parameters have been optimized for the free molecule at HE -i- MP2 level for any couple of values of the previously defined PES variables. The basis set used for the calculation is a standard 6-31G basis augmented for chlorine, only for the dispersion contribution, with the same d and / Gaussian shells of the previous two examples. 

This CAS(6,5) falls into two limiting CAS(4,4) descriptions in the regions of the reactants and of the intermediate the p orbital on the approaching Cl for the T-shape complex and the p orbital on the detached Cl when the chloronium ion is formed are doubly occupied in these two limits. 

For the T-shape complex alone in the gas phase, there is a vast literature from theoretical calculations the intermolecular distance y is found to lie in the interval 2.8-... 

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