Bond lengths anion ligands

However, it was pointed out that two other observations are out of line with the iron(I) formulation and more consistent with an iron(II)-porphyrin radical anion [290] (1) the low-intensity red-shifted Soret band in the UV-VIS spectrum with broad maxima in the a,(3-region compared to, for instance, Fe(TPP) in THF, is typical of a porphyrin radical, and (2) the bond lengths of the porphyrin core indicate population of the (antibonding) LUMO of the ligand (i.e., the presence of an extra electron in the re-system). The presence of porphyrin radical character in the electronic ground state was also inferred from the paramagnetic NMR-shifts of the pyrrole protons at the meso and p-carbon atoms [291]. 

Table 3.31. Trigonal bipyramidal anions, comparing central-atom valency Vm (and percentage ionic character), d-orbital occupancy du, bond lengths Rmx, bond orders />mx (andpercentage ionic character), and ligand atomic charges Qx for oo-bonded (SiH3 , SiFs-, and SiH3F2 ) versus non-w-bonded (CH3F2-)...

With the compound (2-Me2NCH2C6H4)PhSi(H)(03SCF3) 786, it was demonstrated that more than one built-in ligand is needed for the stabilization of trivalent silicon cations as, in this structure, the triflate anion is involved in the coordination to the silicon atoms.810 The related Si-O bond distance of 1.951(1) A is longer than the standard Si-O bond length (approx. 1.6 A) and therefore compound 786 might be best described as contact ion pairs (Figure 5). 

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