Structural Evidence for trans-influence

A considerable amount of X-ray data has now been accumulated to support the concept of trans-influence. In a series of ions, PtLCl3 (L = neutral ligand), the Pt—Cl bond trans to the neutral ligand displays much more sensitivity to L than do the c/s-chlorines (Table 3.15) [147], 

Careful comparison of Pt-P bond lengths for the series trany-Pt(Pcy3)2X2 (X = H, Cl, Br, I) with those for p-any-Pt(PR3)2X2 (PR3 = PMe3 or PEt3) shows a more definite increase in Pt-P with anion size for the cyclohexyl-phosphine complexes (Table 3.16) believed to be owing to intermolecular X- H and X- C non-bonded interactions arising from overcrowding [151]. 

A series of phosphine complexes with cw-PtP2Cl2 geometries have been compared (Table 3.17). 

The Pt—P (and Pt—Cl) bond lengths correlate with the electron-donating ability of the phosphine (Tolman s Xi factor) rather than steric factors (the cone angle of the tertiary phosphine) [150b]. 

Study of a series of complexes trans-Pt(PEt3)2HX shows a pronounced dependence of i/(Pt-H) upon the trans-ligand (Table 3.18). 

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