Bond lengths pyridine complexes

The stable silene Me2Si=C(SiMe3(SiMe(r-Bu)2) was first reported as a stable complex with THF,34 and its crystal structure showed the length of the silicon-carbon double bond as 1.747 A. Subsequently, it was possible to remove the THF and isolate the uncomplexed silene, which had a noticeably shorter Si=C bond length of 1.702 A.29 Further investigation showed that stable complexes of this or closely related silenes with trimethyl- or ethyldimethylamine, pyridine, and fluoride ion were also readily formed and moderately stable.31141... 

Complex 10 is prepared by substitution of [TcNBr2(PPh3 )2]. The Tc-N bond length of the tertiary amine N atom coordinated trans to the nitrido ligand is 2.47(1) A and of the pyridine N atoms coordinated cis is 2.141 av. A. The thioether sulfur atom is not coordinated in the solid, but the H NMR spectrum shows that in solution there is an equilibrium between the dibromo form and one in which Br is expelled and the thioether sulfur is coordinated [62]. 

The structure of the corresponding [Co(terpy)2]3 + ion in the complex [Co(terpy)2][Cl]3 is also available.146 In this case too, the C-N bond lengths of the central pyridine (1.86 A) are shorter than those of the peripheral pyridines (1.93 A). 

In these discussions, we have focused attention on details of the physical measurements which confer understanding of structure in pyridine based compounds bond lengths, bond angles, electronic levels in both ground and excited states, and the involvement of solvation, complexation and other environmental features. In the latter, we have, out of necessity, restricted ourselves generally to complexes in which the role of the pyridine structure is of paramount interest, for the whole of the available space could have been filled with lists of complexes incorporating these structures, but where they were of subordinate interest to some other feature, typically the mode of coordination of metallic ions. 

---