New insights into the application of the valence rules in Zintl phases—Crystal and electronic structures of Ba7Ga4P9, Ba7Ga4As9, Ba7Al4Sb9, Ba6CaAl4Sb9, and Ba6CaGa4Sb9

Abstract

a b s t r a c tCrystals of three new ternary pnictides-Ba 7 Al 4 Sb 9 , Ba 7 Ga 4 P 9 , and Ba 7 Ga 4 As 9 have been prepared by reactions of the respective elements in molten Al or Pb fluxes. Single-crystal X-ray diffraction studies reveal that the three phases are isotypic, crystallizing in the orthorhombic Ba 7 Ga 4 Sb 9 -type structure (space group Pmmn, Pearson symbol oP40, Z¼2), for which only the prototype is known. The structure is based on TrPn 4 tetrahedra (Tr¼ Al, Ga; Pn¼ P, As, Sb), connected in an intricate scheme into 1D-ribbons. Long interchain Pn-Pn bonds (d P-P 43.0 Å; d As-As 43.1 Å; d Sb-Sb 43.3 Å) account for the realization of 2D-layers, separated by Ba 2 þ cations. Applying the classic valance rules to rationalize the bonding apparently fails, and Ba 7 Ga 4 Sb 9 has long been known as a metallic Zintl phase. Earlier theoretical calculations, both empirical and ab-initio, suggest that the possible metallic properties originate from filled anti-bonding Pn-Pn states, and the special roles of the "cations" in this crystal structure. To experimentally probe this hypothesis, we sought to synthesize the ordered quaternary phases Ba 6 CaTr 4 Sb 9 (Tr¼ Al, Ga). Single-crystal X-ray diffraction work confirms Ba 6.145(3) Ca 0.855 Al 4 Sb 9 and Ba 6.235(3) Ca 0.765 Ga 4 Sb 9 , with Ca atoms preferably substituting Ba on one of the three available sites. The nuances of the five crystal structures are discussed, and the chemical bonding in Ba 7 Ga 4 As 9 is interrogated by tight-binding linear muffin-tin orbital calculations.

Clathrate BaNi2P4: An Interplay of Heat and Charge Transport Due to Strong Host–Guest Interactions

“…Ba1 is located in the center of a P8 square prism with Ba1- BaNi2Ge (Ba-Ni = 3.096 Å). [28][29][30] Such short distances in BaNi2P4 may indicate weak bonding interactions similar to the recently detected host-guest Ba-Au interactions in the Ba8Au5.3Ge40.7…”

Crystal and Electronic Structure and Optical Properties of AE2SiP4 (AE = Sr, Eu, Ba) and Ba4Si3P8

“…The shortest Ba–P interactions are in the range of 3.04–3.27 Å. Such short distances are uncommon, but are seen in Ba 4 P 3 (3.088 Å), Ba 5 P 5 I 3 (3.04 Å), and Ba 7 Ga 4 P 9 (2.96 Å) …”

Synthesis, Crystal and Electronic Structures of the Pnictides AE3TrPn3 (AE = Sr, Ba; Tr = Al, Ga; Pn = P, As)

“…Since other groups had also explored the same ternary systems and had used the traditional solid-state synthesis methods [6][7][8][9][10][11][12], we focused our exploratory work aimed at new compounds and structures on the metal flux method [13,14]. After OPEN ACCESS all, the triel elements Ga and In are particularly well-suited for such endeavors, and we have applied this technique to grow crystals of many new phases [1][2][3][4][5][15][16][17][18][19][20].…”

“…Published examples from our prior work on the subject include BaGa2Pn2 (Pn = P, As) [16], CaGa2Pn2 (Pn = pnictogen, i.e., P, As) and SrGa2As2 [17], AE3Ga2Pn4 and AE3Al2Pn4 (AE = Ca, Sr, Ba, Eu and Yb; Pn = P, As) [18], Ba3Al3Pn5 (Pn = P, As, Sb) and Ba3Ga3P5 [19], Ba7Ga4Pn9 (Pn = P, As, Sb) [20], among others.…”