Pseudobinary phases (SnSe) BiSe exhibit a very diverse structural chemistry characterized by different building blocks, all of which are cutouts of the NaCl type. For SnSe contents between x = 5 and x = 0.5, several new phases were discovered. Next to, for example, SnBiSe ( x = 4) in the NaCl structure type and SnBiSe ( x = 0.5) in the layered defect GeSbTe structure type, there are at least four compounds (0.8 ≤ x ≤ 3) with lillianite-like structures built up from distorted NaCl-type slabs (L4,4-type SnBiSe, L4,5-type SnBiSe, L4,7-type SnBiSe, and L7,7-type SnBiSe). For two of them (L4,7 and L7,7), the cation distributions were determined by resonant X-ray scattering, which also confirmed the presence of significant amounts of cation vacancies. Thermoelectric figures of merit ZT range from 0.04 for SnBiSe to 0.2 for layered SnBiSe; this is similar to that of the related compounds SnBiTe or PbBiTe. Compounds of the lillianite series exhibit rather low thermal conductivities (∼0.75 W/mK for maximal ZT). More than other "sulfosalts", compounds in the pseudobinary system SnSe-BiSe adapt to changes in the cation-anion ratio by copying structure types of compounds containing lighter or heavier homologues of Sn, Bi, or Se and can incorporate significant amounts of vacancies. Thus, (SnSe) BiSe is a multipurpose model system with vast possibilities for substitutional and structural modification aiming at the optimization of thermoelectric or other properties.

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LnTt (Ln = La, Nd; Tt = Si, Ge, Sn) compounds crystallize in the CrB‐ or the FeB‐structure type with 1∞[Tt2–]‐polyanionic zigzag chains and can be rationalized as Ln3+Tt2–e–. They take up hydrogen at gas pressures from 10 to 160 bar and temperatures up to 750 K. The hydrides LnTtH1–x (0.04 ≤ x ≤ 0.39) crystallize either in a hydrogen filled CrB‐structure type (ZrNiH type, C‐phase, Cmcm: LaSiD0.92(1), LaGeD0.88(1), NdSiD, NdGeD0.95(1), LaSnHx) or in a hydrogen filled FeB‐structure type (LaGeH type, P‐phase, Pnma: LaSiD0.61(3), LaGeD0.96(4), NdSiD0.88(6)). In both cases, hydrogen atoms partially fill tetrahedral Ln4 voids as proven by neutron powder diffraction. While CrB‐structure type LnTt reacts to C‐phase only, FeB‐structure type LnTt hydrogenates to mixtures of C‐ (major phase) and P‐type hydrides. Electronic structure calculations reveal the depopulation of Ln‐d states, which cause the metallic conductivity in LnTt to be the main electronic effect upon hydrogenation. They further suggest Zintl phase hydrides LnTtH to be still poor metallic conductors with a pseudo bandgap at the Fermi level. The hydrogenation reaction from LnTt to LnTtH may thus be regarded as an incomplete metal to semiconductor transition.

Many Zintl phases take up hydrogen and form hydrides. Hydrogen atoms occupy interstitial sites formed by alkali or alkaline earth metals and / or bind covalently to the polyanions. The latter is the case for polyanionic hydrides like SrTr2H2 (Tr = Al, Ga) with slightly puckered honeycomb-like polyanions decorated with hydrogen atoms. This study addresses the hydrogenation behavior of LnTr2, where the lanthanide metals Ln introduce one additional valence electron. Hydrogenation reactions were performed in autoclaves and followed by thermal analysis up to 5.0 MPa hydrogen gas pressure. Products were analyzed by powder X-ray and neutron diffraction, transmission electron microscopy, and NMR spectroscopy. Phases LnAl2 (Ln = La, Eu, Yb) decompose into binary hydrides and aluminium-rich intermetallics upon hydrogenation, while LaGa2 forms a ternary hydride LaGa2H0.71(2). Hydrogen atoms are statistically distributed over two kinds of trigonal-bipyramidal La3Ga2 interstitials with 67% and 4% occupancy, respectively. Ga-H distances (2.4992(2) Å) are considerably longer than in polyanionic hydrides and not indicative of covalent bonding. 2H solid-state NMR spectroscopy and theoretical calculations on Density Functional Theory (DFT) level confirm that LaGa2H0.7 is a typical interstitial metallic hydride.

The hydrogenation properties of Laves phases LnMg (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Er, Tm, Yb) were investigated by thermal analysis, X-ray, synchrotron, and neutron powder diffraction. At 14.0 MPa hydrogen gas pressure and 393 K, PrMg and NdMg take up hydrogen and form the colorless, ternary hydrides PrMgH (P422, a = 632.386(6) pm, c = 945.722(11) pm) and NdMgH (P422, a = 630.354(9) pm, c = 943.018(16) pm). The crystal structures were refined by the Rietveld method from neutron powder diffraction data on the deuterides (PrMgD, P422, a = 630.56(2) pm, c = 943.27(3) pm; NdMgD, P422, a = 628.15(2) pm, c = 940.32(3) pm) and shown to be isotypic to LaMgD. The LaMgD type of hydrides decompose at 695 K (La), 684 K (Ce), 684 K (Pr), 672 K (Nd), and 639 K (Sm) to lanthanide hydrides and magnesium. The Laves phase EuMg forms a hydride EuMgH of black color. Its crystal structure (P222, a = 664.887(4) pm, b = 1136.993(7) pm, c = 1069.887(7) pm) is closely related to the hexagonal Laves phase (MgZn type) of the hydrogen-free parent intermetallic. GdMg and TbMg form hydrides GdMgH with orthorhombic unit cells (a = 1282.7(4) pm, b = 572.5(2) pm, c = 881.7(2) pm) and TbMgH (a = 617.8(3) pm, b = 1045.8(8) pm, c = 997.1(5) pm), presumably also with a distorted MgZn type of structure. CeMgH and NdMgH are paramagnetic with effective magnetic moments of 2.49(1) μ and 3.62(1) μ, respectively, in good agreement with the calculated magnetic moments of the free trivalent rare-earth cations (μ(Ce) = 2.54 μ; μ(Nd) = 3.62 μ).