From the Nonexistent Polar Intermetallic PtPr via PtPr 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 PtPr (1) crystallizes in a new structure type ( mP56, P2/ 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 GaGd structure type, PtPr (2, tI80, I4/ mcm, a = 11.931(9) Å, c = 14.45(1) Å, Z = 16), that is practically overlapping with the rhombohedral PtPr 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, PtSnPr (3), and PtSnPr (4), as well as PtSnPr (5). 3 is a representative of the PtGeCe 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 T E R family ( T = transition metal, E = main group (semi)metal, R = rare-earth metal; PtSnPr: oP52, Pnma, a = 27.623(1) Å, b = 4.5958(2) Å, c = 9.3499(5) Å). PtSnPr (5) crystallizes as a variant of the NiSnGd 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 Pr 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.