The Pseudobinary Section La 3 In 5 – La 3 Pb 5 : Synthesis, Structural Chemistry, Phases Widths, and Chemical Bonding

The synthetic, crystallographic, and bond theoretical study of the ternary mixed lanthanum indides/plumbides of the quasibinary section La 3 In 5 – La 3 Pb 5 allows to explore the crystal chemistry of 3:5 polar intermetallic compounds in the electronic region between 24 and 29 valence electrons per formula unit (v.e./f.u.). All compounds of this nearly continuous series exhibiting two different structure types were prepared in pure phase from stoichiometric melts of the elements. The Pu 3 Pd 5 structure type (orthorhombic, space group Cmcm , Z = 4) with slightly distorted nido type square pyramidal (In/Pb) 5 clusters is stable from the known binary compound La 3 In 5 (24 v.e./f.u., electron precise clusters In 5 9– after Wade) up to the composition La 3 In 3.8 Pb 1.2 (25.2 v.e./f.u.) [ a = 1049.99(8), b = 838.76(7), c = 1053.74(6) pm, R 1 = 0.0528]. The stability range of the second structure type, La 3 In 4 Ge (tetragonal, space group I 4/ mcm , Z = 4), starts at slightly higher lead proportions at the composition La 3 In 3.7 Pb 1.3 [ a = 873.4(2), c = 1214.6(4) pm, R 1 = 0.0585]. Several crystals with increasing lead content La 3 In 2.3 Pb 2.7 [ a = 874.32(8), c = 1227.56(8) pm, R 1 = 0.0226], La 3 In 1.3 Pb 3.7 [ a = 876.61(6), c = 1226.69(9) pm, R 1 = 0.0755], La 3 InPb 4 [ a = 878.72(6), c = 1237.44(6) pm, R 1 = 0.0339] up to the border composition La 3 In 0.8 Pb 4.2 [ a = 880.05(7), c = 1238.2(1) pm, R 1 = 0.0553] have also been characterized by single crystal structure analysis. According to the anionic building blocks of this structure type, isolated [Ge/Pb] 4– anions and heavily puckered 4.8 2 nets of three‐bonded In/Pb atoms (i.e. [In 2– (Pb – ) 3 ] after Zintl ), this border composition exactly fits the Zintl electron count. A final compound of this series, the binary phase La 3 Pb 5 is not known. Simple electron counting rules (Zintl concept, together with Wade’s rules) hold only for the border compounds of the two structure types, La 3 In 5 and La 3 InPb 4 . Their validity and the details of the chemical bonding are thus evaluated in an accompanying computational study, where the electronic band structures of the binary compounds La 3 In 5 and La 3 Sn 5 (Pu 3 Pd 5 structure type) and the model system “La 3 Pb 5 ” (calculated using the crystal data of La 3 InPb 4 ) are calculated using FP‐LAPW band structure methods.