Crystallographic Insight into the Mg2+ Coordination Mode and N(SO2CF3)2– Anion Conformation in Mg[N(SO2CF3)2]2 and Its Adducts

Abstract

Magnesium bis(trifluoromethylsulfonyl)amide (Mg[TFSA]2) and its adducts ([Mg(L)n][TFSA]2) with common ligands (L) such as ethanol, ethyl acetate, and water, namely [Mg(C2H5OH)4][TFSA]2, [Mg(C2H5OH)6][TFSA]2, [Mg(C2H5OOCCH3)2][TFSA]2, [Mg(H2O)2][TFSA]2, and [Mg(H2O)6][TFSA]2(H2O)2, have been prepared and characterized by single-crystal X-ray diffraction and Raman spectroscopy. In every case, Mg2+ is octahedrally coordinated by six O atoms of TFSA– and/or the ligand. The crystal structure of Mg[TFSA]2 indicates the presence of disordered cis (12 %) and trans (82 %) ligand anion conformers. [Mg(C2H5OH)4][TFSA]2 appears to be a new example of a coordination compound in which the TFSA– anions adopt a trans conformation while bonded to the metal core. The crystallographic data has allowed us to propose a scheme of stepwise σ-donor ligand coordination to the Mg2+ core in Mg[TFSA]2 and [Mg(L)n][TFSA]2 salts. This scheme is consistent with the literature data and indicates that the conformation of TFSA– anions in [Mg(L)n][TFSA]2 depends on the number of ligands coordinated to the Mg2+ core, regardless of the ligand.