On the Chemical Bonding in LaPdIn2, LaNiMg2, and LaNiCd2 ‐ Intermetallic Compounds with a Filled Distorted Variant of the CaIn2 Type

The new intermetallic compound LaNiCd2 was prepared by induction melting of the elements in a sealed tantalum tube in a water‐cooled sample chamber. LaNiCd2 was characterized by X‐ray powder and single crystal data: MgCuAl2 type, Cmcm, a = 427.2(2), b = 994.8(4), c = 816.5(4) pm, wR2 = 0.0429, 302 F2 values, 17 parameters. Refinement of the occupancy parameters revealed small nickel defects resulting in the composition LaNi0.958(6)Cd2 for the investigated crystal. The structure may be described as a nickel filled LaCd2 substructure with distorted CaIn2 related arrangement. The cadmium substructure (304‐324 pm Cd‐Cd) resembles the lonsdaleite type. Together the nickel and cadmium atoms build up a three‐dimensional [NiCd2] network (277 and 278 pm Ni‐Cd) in which the lanthanum atoms fill distorted pentagonal channels. The COHP analysis reveals a Cd‐Cd ICOHP bonding energy comparable with cadmium metal. We show by comparison of Cd‐Cd bonds in LaNiCd2 with those in LaCd2 and hypothetical La□Cd2 that Cd‐Cd bonding is significantly weakened by the formation of the strong Ni‐Cd bonds. Higher electron counts, as in LaPdIn2, lead to stronger Pd‐In bonds at the expense of the In‐In bonding.