Pr₆₂Fe₂₁M₁₆C₃₂ Versus Pr₂₁Fe₈M₇^′C₁₂ (M = Si, P; M′ = Si, Ge, Sn): Competing Intermetallic Carbides Grown from a Pr/Ni Flux

Abstract

Reactions of silicon, carbon, and iron in a low-melting flux mixture of praseodymium and nickel produced two competing intermetallic compounds. Pr62Fe21Si16C32 has a new structure type in tetragonal space group P4/mmm (a = 15.584(2) Å, c = 11.330(1) Å, Z = 1) that features trigonal planar FeC3 units that share corners to form a framework of cylindrical channels encompassing a network of silicon-centered praseodymium clusters. Slight variation of reactant ratio and heating profile produced Pr21Fe8Si7C12 instead; this compound has the previously reported cubic La21Fe8Sn7C12 structure type. Identical Pr/Si clusters and FeC3 subunit motifs are found in both structure types. In addition to reactant ratio and heating profile, size effects play a role in determining which structure forms. Replacing silicon with smaller phosphorus atoms produces only the tetragonal structure; replacement with larger elements (M = Ge, Sn) yields only cubic Pr21Fe8M7C12. Magnetic susceptibility measurements on single crystals of Pr62Fe21Si16C32 indicate antiferromagnetic ordering of the Pr moments below 17 K and no magnetic moment on iron atoms. The behavior of Pr21Fe8Si7C12 is more complex, revealing magnetic contributions from both Pr and Fe atoms and possible spin frustration.

Structural Disorder in Intermetallic Boride Pr21M16Te6B30 (M = Mn, Fe): A Transition Metal Cluster and Its Evil Twin

“…The magnetic behavior of iron in these RE/Fe/M/M′ compounds correlates with the extent of Fe–Fe bonding. No moment is seen on iron in compounds with little or no Fe–Fe interactions (for instance, Pr 61 Fe 21 Si 16 C 32 ) . Compounds with Fe n clusters where n ≥ 4 do exhibit a magnetic moment on iron, often leading to complex magnetic behavior such as spin glass formation in La 21 Fe 8 Sn 7 C 12 , ferromagnetism in Ce 33 Fe 13 B 18 C 34 , and the ferrimagnetism observed in this work for Pr 21 Fe 16 Te 6 B 30 .…”

Flux Synthesis of a Metal Carbide Hydride Using Anthracene As a Reactant

“…Synthesis and crystal growth of rare earth transition-metal carbides has been carried out in metal fluxes with great success. Eutectics formed from early rare earth metals (La, Ce, Pr, Nd) and late transition metals (Co, Ni, Cu) are excellent solvents for carbon; we have used such eutectics as growth media for carbides including La 21 Fe 8 Sn 7 C 12 , Ce 33 Fe 13 B 18 C 34 , Pr 62 Fe 21 Si 16 C 32 , and Nd 2 Co 2 SiC. − , All these reactions used amorphous carbon (acetylene carbon black) as a precursor. We are now investigating the use of organics as a source of carbon, and possibly of hydrogen.…”

“…Slow cooling of the solution allows products to be isolated as crystals . Our group has explored synthesis in a variety of rare earth/transition metal (R/T) eutectic flux mixtures; these fluxes are excellent solvents for carbon and have yielded metal carbides such as La 21 Fe 8 Sn 7 C 12 , Ce 33 Fe 13 B 18 C 34 , and Pr 62 Fe 21 Si 16 C 32 . − Complex metal hydrides can be readily synthesized in fluxes containing alkaline earth metals, as indicated by the formation of LiCa 7 Ge 3 H 3 and Ca 54 In 13 H 27 from reactions of CaH 2 with other elements in Ca/Li melts. , Alkaline-earth-based fluxes have also yielded metal carbide hydrides, including LiCa 2 C 3 H from Ca/Li and Ba 12 InC 18 H 4 from Ba/Li melts. , …”