On the verge of short D–D distances in RNiIn deuterides

The paper reports the peculiar structural behavior of RNiIn deuterides. The RNiIn compounds with (R = La, Ce, Pr, Nd) are known as exhibiting unusually short H–H (D–D) interatomic distances of about 1.6 Å (two hydrogen atoms within the R3Ni2 polyhedron). In our paper, the synthesis procedure and structural data for RNiIn deuterides with R = La, Nd, Gd, Tb, Dy, Ho, Er are presented for the first time. The analysis of the collected data revealed that short D–D distances are present only for R = La–Nd. For samples with heavy rare earths, the deuterium content remains nearly the same, although the D atoms occupy different coordination polyhedra. Therefore, an existence of a strict limit for the height of R3Ni2 polyhedron, for which double hydrogen occupation is possible, should be issued. High-temperature X-ray diffraction experiments were performed for chosen deuterides as well.