Pyridine bond lengths

Tire calculated Ca-N" bond lengths, Table III, of these pyridinium cations [as well as the bond orders, BO, and the reaction energies, zIT/r, for a hypothetical dissociation to give the corresponding carbenium ion 44 and pyridine (Scheme 13)] indicate that these bonds are significantly weakened... 

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]. 

We have recently investigated X-ray structure of 3-methoxycarbonyl-[l,4,2] diazaphospholo[4,5-a]pyridine as first example of molecular structure determination for [l,4,2]diazaphosphole ring [84], The ester substituent lies strictly in the molecular plane with carbonyl group in the trans orientation with the formal C=P bond. Endocyclic P-N and P-C bonds are averaged between respective single and double bond lengths. 

However, the replacement of two bpym molecules by weaker ligands such as pyridine (py) and particularly NCS affords the compound [Fe(bpym) (py)2(NCS)2]l/4py (Fig. 2). The average Fe-N bond length, 2.186(8) A, at room temperature, is consistent with an iron(II) ion in the HS state. The thermal dependence of XmT (XM=molar magnetic susceptibility, T=tempera-... 

Stmctures of a wide number of hcxahydro-oxazolo[3,2- pyndincs have been determined using X-ray analysis. In most cases, the objective was stmctural confirmation and results usually were unexceptional. It should just be mentioned here that the crystal structure of trans-(3R,2aS)-(—)-3-phenyl-2,3,5,6,7,8-hexahydro-oxazolo[3,2-tf]pyridine-5-thione revealed a significant participation of the tautomeric thio-enolic form as reflected by the short N-C(=S) bond length of 1.328 A <2003AXEo519>. 

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). 

Figure 96 X-Ray structure of [ConL4]8 + in [Co4L4][SbF6]8 (R = Me). Average bond lengths Co-N(pyridine)= 2.10 A Co-N(pyrimidine) = 2.23 A.

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