title: Na6ZnSn2, Na4.24K1.76(1)ZnSn2, and Na20Zn8Sn11: three intermetallic structures containing the linear {Sn-Zn-Sn}6- unit.
abstract: The novel intermetallic compounds Na6ZnSn2 (1), Na4.24K1.76(1)ZnSn2 (2), and Na20Zn8Sn11 (3) were obtained from direct fusion of the pure elements, and their structures were determined by single crystal X-ray diffraction. All three compounds adopt new structure types and contain linear anionic {Sn-Zn-Sn}6- units with rather short Zn-Sn contacts (2.55-2.58 A), separated by alkali metal counterions. Compound 3 comprises layers of interconnected heteroatomic {Zn7Sn5} icosahedra as an additional unique structural motif. The bonding situation in this 16 valence-electron anion is analyzed by quantum chemical methods. The results of NBO, AIM, and ELF calculations (Gaussian03 on HF/3-21G level) reveal covalent bonding between Sn and Zn. The relationship to isovalent CO2 is discussed. Band structure calculations on the density functional theory level (LMTO) show that 1 can be understood as a Zintl phase containing a {Sn-Zn-Sn}6- anion; however, Na-Sn contacts must also be considered. Magnetic susceptibility measurements show a temperature-independent, weak diamagnetism for Na6ZnSn2 (1).
authors.affiliation: Department of Chemistry, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany.
authors.forename: Sung-Jin
authors.initials: SJ
authors.lastname: Kim
authors.forename: Florian
authors.initials: F
authors.lastname: Kraus
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Fässler