Transition metal geometry optimization

The Zerner s INDO method (ZINDO) is also called spectroscopic INDO (INDO/S). This is a reparameterization of the INDO method specihcally for the purpose of reproducing electronic spectra results. This method has been found to be useful for predicting electronic spectra. ZINDO is also used for modeling transition metal systems since it is one of the few methods parameterized for metals. It predicts UV transitions well, with the exception of metals with unpaired electrons. However, its use is generally limited to the type of results for which it was parameterized. ZINDO often gives poor results when used for geometry optimization. 

Figure 4.7 Optimized geometries of saturated group 6-11 third series transition-metal hydrides MH (see Table 4.4).

Figure 4.14 Optimized geometries of saturated group 6-10 third-series transition-metal alkylidenes H M=CH2 (M = W-Pt).

There are actually very few. Modern optimization techniques practically guarantee location of a minimum energy structure, and only where the initial geometry provided is too symmetric will this not be the outcome. With a few notable exceptions (Hartree-Fock models applied to molecules with transition metals), Hartree-Fock, density functional and MP2 models provide a remarkably good account of equilibrium structure. Semi-empirical quantum chemical models and molecular mechanics models, generally fare well where they have been explicitly parameterized. Only outside the bounds of their parameterization is extra caution warranted. Be on the alert for surprises. While the majority of molecules assume the structures expected of them, some will not. Treat "unexpected" results with skepticism, but be willing to alter preconceived beliefs. 

We use relativistically optimized geometries throughout. (See, e.g., ref. (52) for an example of the optimization procedure that was used for the uranium compounds.) The transition metal complexes M(CO)6 and [MO4]2-, M = Cr, Mo, W, are the only exception experimental geometries have been used in these cases (7). 

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