Geometry T-shaped

The interplay between favourable reactivity at a collinear geometry and electrostatic forces favouring a T-shaped geometry leads to a bent geometry at the transition state. 

P NMR spectra indicate the T-shape geometry is retained in solution at -30°C but that the molecule is fluxional at room temperature. Rh(PPh3)3 undergoes a range of addition reactions with Lewis bases (CO, PF3, NH3) to afford various 16- and 18-electron species (Figure 2.14). 

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.

In addition to halogen bonded complexes or ionic salts, it is also possible for sulfur and selenium electron donors to form complexes in which the electron donor atom inserts into the X2 bond, giving a hypervalent donor atom with a T-shaped geometry. It has been recently reported [147] that for dibromine and selenium, this type of complex is favored over halogen bonded complexes. While no purely halogen bonded complex is reported for dibromine, there is one complex (IRABEI) in which one selenium atom of each of several selenanthrene molecules in the asymmetric unit does insert into a Br2 bond, but for one of the molecules, the other selenium atom forms a halogen bond with a Br2 molecule to form a simple adduct (A). 

Figure 4.55 The optimized structure of YH2(C2H5), showing the T-shaped geometry of the agostic Y C—H interaction.

The cation [SeC(NH2)2]3+ adopts T-shaped geometry, as shown in Fig. 16.8.7(c). In this structure, the central Se atom must bear a formal negative charge to have two lone pairs at the equatorial positions of a trigonal bipyramid. 

The unusual systems FHs and F3H, (for which there is no experimental evidence), have been studied by Shillady and Trindle.587 Using a very small basis set, FHa has a T-shaped geometry and is computed to be stable. This type of molecule has been termed hypervalent by Musher.588... 

All these networks contain three connected metal centers that can exist in trigonal or T-shaped geometries. The T-shape geometry can be adopted by M(II) metal atoms when the metal has a coordination number of seven four occupied by the chelation of two nitrates and three occupied by the ligands. The honeycomb or hexagonal networks were shown to form when the metal atom adopts a trigonal... 

The first T-shaped geometry for a three coordinate is d8 system has recently been found (73). 

Another metal geometry or node that is of particular interest because of its potential range of supramolecular isomers is the T-shaped geometry, i.e. a mer-substituted metal moiety with 1 1.5 metal spacer ligand ratio. This node has thus far produced three distinct 2D supramolecular isomers brick wall,46 herringbone,49... 

Whereas there are numerous such examples for Ni°, they are rare for Nin. Examples are the dialkylamides [Ni(NR2)3] and Ni2(/u,-NR2)2(NR2)2, as well as the blue mesityl complex [Ni(mes)3] which has an approximately T-shaped geometry.4... 

---