Crystal structure of Na[N(SO2CF3)2] and coordination environment of alkali metal cation in the M[N(SO2CF3)2] (M+ = Li+, Na+, K+, and Cs+) structures

Crystal structure of Na[TFSA] (TFSA(-) bis(trifluoromethylsulfonyl)amide anion (N(SO2CF3)(2)(-))) has been determined by single-crystal X-ray diffraction. This compound crystallizes in a monoclinic cell (space group: P2(1)/n) with Z = 8 and two ion pairs in the asymmetric unit. Both the crystallographically independent TFSA(-) anions adopt a cis configuration with the C-S center dot center dot center dot S-C torsion angle of -25.2(2)degrees and 25.1(2)degrees The Na+ cations have contacts primarily with five neighboring O atoms (2.344(3)-2.415(3) angstrom for Na1 center dot center dot center dot O and 2337(3)-2.451(3) angstrom for Na2 center dot center dot center dot O) and secondarily with one O atom and one N atom (2.843(3) for Na1 center dot center dot center dot O, 2.929(3) for Na1 center dot center dot center dot N, 2.806(3) for Na2 center dot center dot center dot O and 2.907(3) for Na2 center dot center dot center dot N). Comparison of the present structure with the previously reported M[TFSA] (M+ = Li+, K+, and Cs+) structures revealed that all of them have layered structures composed of the cationic and anionic layers. Coordination environment of M+ in the M[TFSA] structures is discussed based on bond valence sum calculations. (C) 2014 Elsevier B.V. All rights reserved.