Experimental and Computational Insights into the Stabilization of Low-Valent Main Group Elements Using Crown Ethers and Related Ligands

A series of tin­(II) triflate and chloride salts in which
the cations
are complexed by either cyclic or acyclic polyether ligands and which
have well-characterized single-crystal X-ray structures are investigated
using a variety of experimental and computational techniques. Mössbauer
spectroscopy illustrates that the triflate salts tend to have valence
electrons with higher s-character, and solid-state NMR spectroscopy
reveals marked differences between superficially similar triflate
and chloride salts. Cyclic voltammetry investigations of the triflate
salts corroborate the results of the Mössbauer and NMR spectroscopy
and reveal substantial steric and electronic effects for the different
polyether ligands. MP2 and DFT calculations provide insight into
the effects of ligands and substituents on the stability and reactivity
of the low-valent metal atom. Overall, the investigations reveal the
existence of more substantial binding between tin and chlorine in
comparison to the triflate substituent and provide a rationale for
the considerably increased reactivity of the chloride salts.