A ¹⁹F nuclear magnetic resonance study of the exchange of the fluoro ligands of the tetrafluoroberyllium(II) ion

Abstract

A ¹⁹F N.M.R. study is reported of the exchange of the fluoro ligands of [BeF4]^2-. The exchange rate law is:

            rate = k_obs4[BeF₄^2-] = k'4[BeF₄^2-]+ k''4[BeF₄^2-][BeF₃H₂O-]

where k'(298 K) = 69±3 s^-1, ΔH^‡ = 30±3 kJ mol^-1, ΔS^‡ = -110±10 J mol^-1 K^-1 and k''(298 K) = (1.6±0.5)×10³ dm³ mol^-1 s^-1, ΔH^‡ = 26±3 kJ mol^-1, ΔS^‡ = - 96±9 J mol^-1 K^-1. The k' exchange process appears to be predominantly dissociative in nature, and the k'' exchange process apparently proceeds through a fluoro bridged species [Be₂F₇]^2-.