Nitridogermanate Nitrides Sr₇[GeN₄]N₂ and Ca₇[GeN₄]N₂: Synthesis Employing Sodium Melts, Crystal Structure, and Density-Functional Theory Calculations

Abstract

The alkaline earth nitridogermanate nitrides AE(7)[GeN(4)]N(2) (AE = Ca, Sr) have been synthesized using a Na flux technique in sealed Ta tubes. According to single-crystal X-ray diffraction the isotypic compounds crystallize in space group Pbcn (No. 60) with Z = 4, (Sr(7)[GeN(4)]N(2): a = 1152.6(2), b = 658.66(13), c = 1383.6(3) pm, V = 1050.5(4) x 10(6) pm(3), R1 = 0.049; Ca(7)[GeN(4)]N(2): a = 1082.6(2), b = 619.40(12), c = 1312.1(3) pm, V = 879.8(3) x 10(6) pm(3), R1 = 0.016). Owing to the high N/Ge ratio, the compounds contain discrete N(3-) ions coordinated by six AE(2+) besides discrete [GeN(4)](8-) tetrahedrons. One of the AE(2+) ion is coordinated by only four N(3-) ions, which is rather an unusual low coordination number for Sr(2+). Together with the isolated [GeN(4)](8-) tetrahedrons, these Sr(2+) ions form chains of alternating cation centered edge sharing tetrahedrons. The electronic structure and chemical bonding in Sr(7)[GeN(4)]N(2) has been analyzed employing linear muffin-tin orbital (LMTO) band structure calculations.

Ca4Mg5Ge3N10 and Sr2Mg3GaN4.33: Two Mg‐Containing Nitrides and Their Structural Relation to (Sr,Ba)2Si5N8

“…In Ca 4 Mg 5 Ge 3 N 10 , there are two crystallographic tetrahedral positions. The (Mg/Ge)–N distances vary between 1.954(2) and 2.115(8) Å and are in good agreement with the (Mg/Ge)–N bond lengths found in Ca 2 Mg 5 GeN 6 and Sr[Mg 3 GeN 4 ] [1.99 to 2.11 Å] as well as to averaged Mg–N and Ge–N bond lengths known from other ternary or quaternary nitrides , , . (Mg1/Ge1)N 4 tetrahedra are linked through common corners to adjacent tetrahedra.…”

“…Ga2-N4 2.048 (8) known from other ternary or quaternary nitrides. [18][19][20]27,28,[32][33][34][35] (Mg1/Ge1)N 4 tetrahedra are linked through common corners to adjacent tetrahedra. In contrast, (Mg2/Ge2)N 4 units are connected through common corners and edges, whereby edgesharing can solely be observed between (Mg2/Ge2)N 4 tetrahedra.…”

“…Most syntheses of nitridogermanates and nitridogallates start from the pure elements and employ the Na azide route . Therefore, the starting materials as well as NaN 3 and Na were filled into Ta or Nb ampules, which were hermetically closed by arc welding and fired at around 760 °C.…”

“…[1] Up to now, only a small number of quaternary compounds containing Ge or Ga have been reported, and only a few also contain Mg. [1,[18][19][20][21][22][23][24][25] Most syntheses of nitridogermanates and nitridogallates start from the pure elements and employ the Na azide route. [19][20][21][22][26][27][28][29][30] Therefore, the starting materials as well as NaN 3 and Na were filled into Ta or Nb ampules, which were hermetically closed by arc welding and fired at around 760°C. By thermal dissociation, NaN 3 supplies an increased nitrogen pressure in the ampule.…”

Opposite Modulation of Cell Migration by Distinct Subregions of Urokinase Connecting Peptide

“…Additionally, nitridogermanates are known containing Ge in oxidation state +IV with GeN 4 tetrahedra or trigonal planar GeN 3 units as structural motifs. Whereas compounds containing Ge in different oxidation states are mostly metallic and of black appearance,20–22 compounds containing Ge 4+ are translucent crystals of different color and shape 22–24. The structures of nitridogermanates are typically built up of more or less condensed nitridometallate anions coordinated by alkaline earth atoms as counterions.…”