Ternary rare-earth manganese germanides RE3Mn2Ge3 (RE = Ce–Nd) and a possible oxygen-interstitial derivative Nd4Mn2Ge5O0.6

• RE3Mn2Ge3 are the first Mn-containing members of Hf3Ni2Si3-type germanides.
• Crystal structures of Ce3Mn2Ge3 and Nd4Mn2Ge5O0.6 were determined.
• Double-chains of MnGe4 tetrahedra are an important building block.
• RE3Mn2Ge3 exhibits complex antiferromagnetic ordering.

The ternary germanides RE3Mn2Ge3, which have been prepared by arc-melting and annealing at 800 °C, are formed with larger rare-earth components (RE = Ce–Nd), in contrast to other RE3M2Ge3 series. They adopt the orthorhombic Hf3Ni2Si3-type structure (space group Cmcm, Z = 4). Single-crystal X-ray diffraction studies performed for the Ce member (a = 4.3340(3) Å, b = 11.6069(9) Å, c = 14.6717(12) Å) indicate an expanded structure relative to other RE3M2Ge3 series, with essentially nonbonding Ge–Ge contacts between the [Mn2Ge3] layers built up of double-chains of MnGe4 tetrahedra. A minor oxidation product identified in the course of these investigations was proposed to be Nd4Mn2Ge5O0.6, in which a host monoclinic Yb4Mn2Sn5-type structure accommodates interstitial oxygen atoms partially occupying an octahedral void (space group C2/m, Z = 2, a = 16.275(3) Å, b = 4.3779(8) Å, c = 7.3783(14) Å, β = 107.372(2)°). This structure also contains layers with double-chains of MnGe4 tetrahedra which are now connected through Ge2 dimers; isolated Ge atoms in square planar coordination are located between the layers. Magnetic measurements on RE3Mn2Ge3 suggest complex antiferromagnetic ordering phenomena with several field-dependent transitions.

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