Ti-Cl bond distances

TiCU Geometry Optimization. The optimized Ti-Cl bond lengths (see Table I) for TiCU with a variety of basis sets are all longer than the experimental value and differ from that by 0.016 to 0.051 A. Splitting the Cl(533-53) basis set, which allows the orbitals freedom to expand or contract, only decreased the Ti-Cl bond length an average 0.005 A. However, when we add d-type polarization functions to the chlorine basis set the Ti-Cl bond distance decreases an average 0.026 A. 

As we improve the TiCU wavefunction by adding f-type polarization functions to the titanium basis set the Ti-Cl bond distance shortens further. When a chlorine basis set without d-functions is used, the addition of an f-function on titanium shortens the Ti-Cl bond 0.017 A. However, when a chlorine basis set with d-functions is used, the Ti-Cl bond only shortens 0.(X)6 A to 2.181 A. Although this Ti-Cl distance is the shortest of all the optimized geometry calculations, it is still 0.011 A longer than the experiment... 

As the wavefunction approaches the Hartree-Fock limit one would expect the Ti-Cl bond distance to be shorter than the experiment because of the lack of bond-pair correlation. The bond-pair correlation added by the GVB wavefunction lengthened the Ti-Cl bond 0.021 A, because the GVB wavefunction adds only limited left-right correlation and none of the dynamical correlation. For most A-B bonds, the calculated bond lengths at the SCF level are too short, and the correlation added by a GVB calculation accounts for a major portion of the non-dynamical correlation error in the SCF wavefunction. But for Ti-Cl bonds, both the SCF and GVB calculations predict too long a bond distance because they do not include necessary dynamical atomic correlation of the Cl atoms. 

We improved the calculation further by using a CASSCF wavefunction with an active space of 8 electrons in 8 orbitals (8/8). The results of the geometry optimization (see Table IV) give a Ti-C bond length of 2.119 A and a Ti-C-H angle of 105.4° (the Ti-Cl bond distance and Cl-Ti-C angle were frozen at the ED values). In... 

Optimization of the geometry of TiCU at the SCF level results in a Ti-Cl bond length which is longer than the experiment, even when d- and f-type polarization functions are added to the basis set. For covalently bonded systems one expects a wavefunction at the Hartree-Fock limit to give bond lengths shorter than the experiment if they are not sterically crowded. Because the Hartree-Fock wavefunction overestimates the Cl -Cl repulsions, the Ti-Cl bond distances remain long, even in large basis sets. 

Chlorine bridges are also found in diethylaminotitanium trichloride. In the TiNClj co-ordination sphere, four of the chlorine atoms are bridging, with Ti-Cl distances in the range 2.46—2.71 A, and the terminal Ti-Cl bond length is 2.25 A. The Ti-N distance of 1.85 A is shorter than expected for a single bond and may indicate N->Ti 7r-bonding. 

TbfnCl2(2,6-Me2C6H30) (XVI) is well soluble in dichloromethane and THF, is of low solubility in toluene, and is completely insoluble in aliphatic solvents. It could be isolated in 21% yield as red crystals with four molecules per unit cell in the monoclinic crystal system P2i/c. As listed in Table 6.3, the Ti-Ct distance measures 2.0701 A, and the Ti-Cl bond lengths amount to an average of 2.270 A (Fig. 6.12). Like in compound XV also in XVI it is to assume that face-to-face n-stacking interactions take place between the benzofused ring C12-C17 and the phenoxide ring C30-C35 as the distance between its respective centroids measures 3.62 A. 

In CP2MXY complexes (M Ti, Zr, Hf), the ligands X and Y together donate a total of four electrons to the neutral fragment CP2M. When Y is a non-ff-donor, as CH3 in complex III, all ir bonding is provided by X(0R) this leads to maximum contraction of the Zr-0 distance. It was noted previously (3.) that the Ti-Cl distance in... 

To test the basis set effects, we have performed a series of calculations with the 6-311+G(2df) basis. The differences in the geometries are very small (forTiH3+, the TiH bonds are 1.63 A instead of 1.61 A the H-Ti-H angle is 58° instead of 60°). The difference is much larger when the HF is compared with the DFT for the same basis set (the H-Ti-H angle becomes 88 4). ForTiC14, the Ti-Cl distance calculated with our basis set, 2.18 A, is closer to the experimental value, 2.17 A [24], than that obtained with the allelectron calculation, 2.12 A. May be artificially, our optimised basis set is more realistic than larger ones. 

Bond Distance Ti-Cl = 2.185 A Bond Angle Cl-Ti-Cl = 109.4712 Product of the Moments of Inertia ... 

---