From the Nonexistent Polar Intermetallic Pt3Pr4 via Pt2- xPr3 to Pt/Sn/Pr Ternaries.

Although the Pt-Pr phase diagram has been explored well, recent work on rare-earth metal cluster halides with endohedral transition metal atoms has provided a new binary intermetallic that is nonexistent in the known phase diagram: The binary Pt3Pr4 (1) crystallizes in a new structure type ( mP56, P21/ c, a = 12.353(2) Å, b = 7.4837(9) Å, c = 17.279(2) Å, β = 118.003(7)°, Z = 8) with six crystallographically independent Pt as well as eight Pr positions. The subsequent detailed investigation has led to another previously unreported, binary phase with the Ga2Gd3 structure type, Pt2- xPr3 (2, tI80, I4/ mcm, a = 11.931(9) Å, c = 14.45(1) Å, Z = 16), that is practically overlapping with the rhombohedral Pt2Pr3 existing in the phase diagram. Application of different tin containing fluxes to reproduce the newly detected phases brought about two almost iso-compositional ternary compounds with Sn, Pt4Sn6Pr2.91 (3), and Pt4Sn6Pr3 (4), as well as Pt12Sn24Pr4.84 (5). 3 is a representative of the Pt4Ge6Ce3 type ( oP52, Pnma, a = 7.2863(3) Å, b = 4.4909(2) Å, c = 35.114(2) Å), while 4 represents a new variant of the prolific T4 E6 R3 family ( T = transition metal, E = main group (semi)metal, R = rare-earth metal; Pt4Sn6Pr3: oP52, Pnma, a = 27.623(1) Å, b = 4.5958(2) Å, c = 9.3499(5) Å). Pt12Sn24Pr5- x (5) crystallizes as a variant of the Ni8Sn16Gd3 type ( cI82, Im3̅, a = 12.274(1) Å, Z = 2). Electronic structure calculations provide hints on the origin of the structural changes ( pseudo-polymorphism) for Pt xPr3 with x = 1.97 and 2.00, respectively, and reveal that heteroatomic Pt-Pr bonding strongly dominates in both binaries while the addition of the reactive metal tin leads to dominating Pt-Sn bonding interactions in the ternaries; Pt-Pt bonding interactions are strong but represent a minority in the binaries and are not present at all in the ternaries.