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

A 19F N.M.R. study is reported of the exchange of the fluoro ligands of [BeF4]2-. The exchange rate law is: ����������� rate = kobs4[BeF42-] = k'4[BeF42-]+ k''4[BeF42-][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-.