Refinement of the crystal structure of tetrasodium tetrasilicide, Na4Si4

Abstract

Na 4Si4, monoclinic, C12/c1 (no. 15), a = 12.1536(5) Å, b = 6.5452(5) Å, c = 11.1323(6) Å, b = 118.9(1)°, V = 775.3 Å 3 , Z = 4, Rgt(F) = 0.028, wRref(F 2 ) = 0.064, T = 293 K. Source of materialThe Zintl phase Na 4Si4 was prepared from the elements with an excess of alkali metal (Na, ingot, 99.9 %, ChemPur; Si, pieces, 99.999 %, Alfa) in a closed Ta container which was sealed into an evacuated quartz glass ampoule. The reaction mixture was heated up to 750°C within 1 hour, annealed for 3 hours and afterwards cooled down to ambient temperature within 4 days. Well shaped needle-like crystals were obtained by removing the excess of sodium using vacuum distillation at 230°C and 5 × 10 −6 mbar [1,2]. Due to sensitivity of the compound to air and humidity, the investigated single crystal was sealed into a glass capillary under purified argon. Experimental detailsLattice parameters were refined from synchrotron powder diffraction data (l = 0.39987 Å), using 58 reflections between 4°# 2q # 14.5°, and applying LaB 6 as internal standard (NIST, a = 4.15692 Å). DiscussionThe crystal structure of Na 4 Si 4 was first determined by Witte, von Schnering and Klemm from Weißenberg film data on single crystals [1]. Na 4 Si 4 was re-investigated in order to elucidate the chemical bonding by quantum chemical calculations as well as solid state nuclear magnetic resonance measurements. For these investigations, high quality crystallographic data are crucial. The present re-determination confirms structural information obtained in Ref.[1] and provides data of the crystal structure with higher accuracy. Two crystallographic non-equivalent sites for both Si and Na are occupied in the crystal structure. The Si atoms form dis-

Reaction of Sn44− in liquid ammonia: the formation of Rb6[(η2-Sn4)Zn(η3-Sn4)]·5NH3

“…‡ Several of the atoms are located on special position 4i of space group I2/m (four tin atoms, the Zn atom, five Rb cations and three nitrogen atoms). The Rb atom on the general position shows a site occupancy factor of 0.5, so that the electron count is balanced and gives a charge of minus six for the 1a unit, in agreement with the formulation as Sn 4 Fig. 1 shows 1a, and the relevant distances are given in Table 2.…”

NaRb7(Si4–xGex)2 – Soluble Zintl Phases Containing Heteroatomic Tetrahedral ­[Si4–xGex]4– Clusters

“…The Na-E distances [2.963(1) Å for 1a and 2.949(1) Å for 1b] as well as the Rb-E coordination [3.483(2) to 4.024(1) Å for 1a and 3.486(2) to 4.0271(8) Å for 1b] are not influenced by the Si/Ge ratio of the tetrahedra and are in the same range as those in other alkali tetrahedranides. [17,18,21,22,24,26] The Na atoms within the NaRb 7 Ge 8 -type structures are closely coordinated by the tetrahedral clusters (see Figure 1b). [24,26] Consequently, the major Rb + cations exhibit a more open arrangement and, therefore, solvation by solvent molecules might be facilitated in this structure type.…”

Mixed Tetrahedral Zintl Clusters: Single Crystal Structure Determination of [Si4‐xGex]4−, [(MesCu)2(Si4‐xGex)]4−, and the 29Si MAS NMR Spectra of A4Si2Ge2 (A=K, Rb)

“…[10,11] In the heteroatomic compound Na 4 Si 2 Ge 2 the tetrahedral subunits are formed by two independent crystallographic positions of the tetrel elements due to the symmetry in the NaSi-type structure (space group C2/c). [14,18] The Si and Ge occupation at each atom site differs significantly, and thus a superposition of homoatomic [Si 4 ] 4À and [Ge 4 ] 4À clusters in Na 4 Si 2 Ge 2 can be excluded. [18] However, in 1 a and 1 b there is only one independent crystallographic position E per tetrahedral subunit, and the mixed occupancy equally appears at all atom sites E. Therefore, a superposition of a statistical distribution of homoatomic [ Si MAS NMR spectroscopy was applied.…”

“…Data for binary phases and for Na 4 Si 2 Ge 2 are taken from literature. [10,11,14,15,18] Cell volumes of K 2 Rb 2 Si 4 , K 4 Si 2 Ge 2 and Rb 4 Si 2 Ge 2 are calculated from powder X-ray diffraction data (see Figure S1, S2, and S3 in the Supporting Information). The parameter x displays the amount of Ge in the tetrahedral subunit.…”