ABSTRACT
The [Zn1-xNix(HF2)(pyz)2]SbF6 (x = 0.2; pyz = pyrazine) solid solution exhibits a zero-field splitting (D) that is 22% larger [D = 16.2(2) K (11.3(2) cm-1)] than that observed in the x = 1 material [D = 13.3(1) K (9.2(1) cm-1)]. The substantial change in D is accomplished by an anisotropic lattice expansion in the MN4 (M = Zn or Ni) plane, wherein the increased concentration of isotropic Zn(II) ions induces a nonlinear variation in M-F and M-N bond lengths. In this, we exploit the relative donor atom hardness, where M-F and M-N form strong ionic and weak coordinate covalent bonds, respectively, the latter being more sensitive to substitution of Ni by the slightly larger Zn(II) ion. In this way, we are able to tune the single-ion anisotropy of a magnetic lattice site by Zn-substitution on nearby sites. This effect has possible applications in the field of single-ion magnets and the design of other molecule-based magnetic systems.
ABSTRACT
Starting generally with a 4:6:3 molar ratio of Pt, Sn, and R (where R = La-Sm), with or without the application of a NaCl flux, seven ternary compounds were obtained as single crystals. The platinides Pt4Sn6R3 (R = La-Nd) crystallize with the Pt4Ge6Pr3 type of structure (oP52, Pnma, a = 27.6-27.8 Å, b = 4.59-4.64 Å, c = 9.33-9.40 Å). With R = Pr, Pt4Sn6Pr3-x (oP52, Pnma, a = 7.2863(3) Å, b = 4.4909(2) Å, c = 35.114(1) Å) is also obtained, which might be considered a high-temperature polymorph with disorder on the Sn- and Pr-sites. For R = Nd and Sm, a structurally related isostructural series with a slightly different composition Pt3Sn5R2-x (oP52, Cmc21, a = 4.50-4.51 Å, b = 26.14-26.30 Å, c ≈ 7.29 Å) has been observed, together with Pt7Sn9Sm5 (oS42, Amm2, a = 4.3289(5) Å, b = 28.798(4) Å, c = 7.2534(9) Å) under the same conditions. The latter exhibits the rare Zr5Pd9P7-type structure, linking polar intermetallics to metal phosphides, in accord with P7Pd9Zr5≡Pt7Sn9Sm5. All structures may be described in terms of either negative Pt/Sn networks encapsulating positive R atoms, or {PtSnx} clusters (x = 5, 6, or rarely 7) sharing vertices and edges with R in the second coordination sphere and with considerable heterometallic Pt-R bonding contributions.
ABSTRACT
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, ß = 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, Im3Ì , 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.
