Gaseous phase ionic formation enthalpy for 3-cyanopyridinecoordination compounds by modified forms of Kapustinskii equation

Abstract In the present work, it is shown that modified forms of Kapustinskii equation can be successfully employed to calculate the gaseous phase ionic formation enthalpy for coordination compounds, considering the reaction: M_(g)²⁺ + 2Br^–_(g) + n3-cyanopy_(g) → [MBr₂(3-cyanopy)_n]_(g); cyanopy = cyanopyridine_. The calculated ionic formation enthalpy (Δ_fIH^θ) values are compared with experimental (calorimetric) values from literature.  The derived equation is as follows: Δ_fIH^θ= [N (Z⁺Z^–) 2ε/d+σ][1-(34.5/d+σ)]k, where ε is the electrostatic charge on the coordinative nitrogen atom and σ is the radius of the coordinative nitrogen atom, as calculated from its exposed area. Both, ε (-0.743) and σ (74.5 pm) values were obtained by molecular modelling calculations (Hartree-Fock, 3-21G, vacuum). The calculated Δ_fIH^θ values agree very well with the experimental ones.

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