Monoclinic superstructure of Pr3Rh4Ge4.

Pr₃Rh₄Ge₄ was synthesized by melting of the elements in an arc-melting furnace followed by annealing in a sealed tantalum ampoule in a muffle furnace. Structure refinement was based on temperature dependent single-crystal X-ray diffractometer data. At ambient temperature Pr₃Rh₄Ge₄ adopts the U₃Ni₄Si₄ type structure with strongly enhanced anisotropic displacement parameters for Rh1. Below 230 K additional reflections start to appear and at 110 K the structure could be described with the (3+1)D superspace group I2/ m(α0γ)00; α=1/2, γ=1/2; ( Z=2). This commensurately modulated structure could be refined with 1448 F² values, 39 variables and residuals of wR=0.0417 for the main reflections and wR=0.1520 for the satellites of 1^st order, [ a=408.36(2), b=421.12(3) and c=2504.4(2) pm]. The commensurate description could be transformed to a 3D supercell with space group A2/ m and Z=4: a=816.72(2), b=421.12(3), c=2537.5(1) pm, β=99.26(1)°, 1448 F² values, 69 variables and wR=0.0499. The relation of the U₃Ni₄Si₄ type structure, the (3+1)D modulated and the 3D supercell is discussed on the basis of a group-subgroup scheme. Temperature dependent magnetic susceptibility data reveal Curie-Weiss paramagnetism with an experimental moment of 3.72(2) μ_B/Pr atom and a Weiss constant of -12.6(5) K. No magnetic ordering is evident down to 3 K. [ABSTRACT FROM AUTHOR]