Ba₃Pt₄Al₄—Structure, Properties, and Theoretical and NMR Spectroscopic Investigations of a Complex Platinide Featuring Heterocubane [Pt₄Al₄] Units

Abstract

Ba3Pt4Al4 was prepared from the elements in niobium ampules and crystallizes in an orthorhombic structure, space group Cmcm (oP44, a = 1073.07(3), b = 812.30(3), c = 1182.69(3) pm) isopointal to the Zintl phase A2Zn5As4 (A = K, Rb). The structure features strands of distorted [Pt4Al4] heterocubane-like units connected by condensation over Pt/Al edges. These are arranged in a hexagonal rod packing by further condensation over Pt and Al atoms with the barium atoms located inside cavities of the [Pt4Al4](δ-) framework. Structural relaxation confirmed the electronic stability of the new phase, while band structure calculations indicate metallic behavior. Crystal orbital Hamilton bonding analysis coupled with Bader effective charge analysis suggest a polar intermetallic phase in which strong Al-Pt covalent bonds are present, while a significant electron transfer from Ba to the [Pt4Al4](δ-) network is found. By X-ray photoelectron spectroscopy measurements the Pt 4f5/2 and 4f7/2 energies for Ba3Pt4Al4 were found in the range of those of elemental Pt due to the electron transfer of Ba, while PtAl and PtAl2 show a pronounced shift toward a more cationic platinum state. (27)Al magic-angle spinning NMR investigations verified the two independent crystallographic Al sites with differently distorted tetrahedrally coordinated [AlPt4] units. Peak assignments could be made based on both geometrical considerations and in relation to electric field gradient calculations.

Crystal Structure, Spectroscopic Investigations, and Physical Properties of the Ternary Intermetallic REPt2Al3 (RE = Y, Dy–Tm) and RE2Pt3Al4 Representatives (RE = Tm, Lu)

“…Figure 14 depicts an exemplary fitted spectrum of YPt 2 Al 3 . As observed for Ba 3 Pt 4 Al 4 (E b (Pt 4f 7/2 ) = 70.9 eV) [46], the binding energies of …”

From 3D to 2D: Structural, Spectroscopic and Theoretical Investigations of the Dimensionality Reduction in the [PtAl2]δ− Polyanions of the Isotypic MPtAl2 Series (M=Ca–Ba, Eu)

“…Thus, a negative polarization can be attributed, in line with the calculated Bader charges (see below). PtAl and PtAl 2 , in contrast, exhibit larger binding energies due to a transfer of electron density from the Pt atoms into covalent Pt−Al bonds, attributing a formal positive charge on the Pt atoms . Therefore, one can conclude, that the less electronegative alkaline earth elements are responsible for the charge transfer.…”

Sr2Pd4Al5: Synthesis, Crystal and Electronic Structures, and Chemical Bonding of a Polar Intermetallic Compound

“…The shortest distances between two Al atoms are found between Al2 and Al3 with d(Al2-Al3) = 270 pm. This is somehow surprising because other alkaline-earth compounds that feature a 1:1 ratio of the transition metal and the aluminum (e.g., CaPdAl [4a] and CaPtAl, [5b] of TiNiSi type; Ba 3 Pt 4 Al 4 [9] of its own structure type, or SrPt 2 Al 2 [8] of incommensurate modulated CaBe 2 Ge 2 type) exhibit no homoatomic bonding with distances smaller than 280 pm. The topology of the polyanionic framework does not feature clear building blocks as seen in other compounds.…”

“…In addition to equiatomic CaPdAl [4] and CaPtAl, [5] CaPd 3 Al 5 [6] and the recently published Ca 2 Pd 2 Al and Ca 2 Pt 2 Al [7] have also been reported. For the analogue Sr-Pd/Pt-Al and Ba-Pd/Pt-Al systems we have recently reported the intermetallic compounds SrPt 2 Al 2 , [8] which exhibits an orthorhombic (3+2)D incommensurately modulated structure, and Ba 3 Pt 4 Al 4 , [9] which forms a new structure type. CaPdAl, CaPtAl, SrPt 2 Al 2 , and Ba 3 Pt 4 Al 4 have intermetallic phase with a polyanionic [Pd 4 Al 5 ]…”