Slow evaporation of water from hydrated salen transition metal complexes in the gas phase reveals details of metal ligand interactions

Water clusters of salen [N,N'-ethylenebis(salicylideneaminato)] transition metal complexes [(salen)M, M = Cr3+, Mn3+, Co3+] formed by electrospray sou rce have been investigated using a Fourier transform ion cyclotron resonanc e (FT-ICR) mass spectrometer. Kinetics of water evaporation from the cluste r ions is observed to be highly dependent on the central metal ion. For exa mple, the evaporation rate of water from solvated salen chromium ion ([SCr + nH(2)O](+)) is significantly slower than that from solvated salen mangane se ([SMn + nH(2)O](+)) and solvated salen cobalt ([SCo + nH(2)O](+)) ions. Furthermore, the clusters of salen chromium ions with two waters attached e xhibit special stability, indicated by their prominence in the overall clus ter distribution. In contrast, no specific solvation is observed for the ma nganese and cobalt complexes. The lability observed for the hydrated salen cobalt complex suggests that the high-spin state is likely to be involved i n the evaporation process. These results are in accordance with observation s in solution-phase chemistry and can be explained by ligand field theory.