The new ternary compound Pd 13 In 5.25 Sb 3.75 was found. Its crystal structure was determined using a CCD di4ractometer at room temperature. Evaluations and re5nements 5nally yielded a C-centered monoclinic structure (space group, C2/c; Pearson symbol, mC88, Z โซุโฌ 4) with a โซุโฌ 15.189(2) A s , b โซุโฌ 8.799(1) A s , c โซุโฌ 13.602(2) A s , and โซ.3)1(38.321ุโฌ For the entire data set of 3706 independent re6ections residual values are R โซุโฌ 0.0461 and R w โซุโฌ 0.0789. The structure was found to be isotypic to Pd 13 Pb 9 with In and Sb on the Pb sites. The existence of a further ternary compound, which was already described as Pd 3 In 4 Sb 2 , could be con5rmed. Its composition range was determined by EPMA to be PdIn 1.2+1.3 Sb 0.8+0.7 . It does not melt congruently and we were not able to 5nd suitable single crystals. However, we were able to prepare the pure ternary compound in order to perform X-ray powder di4raction using a Guinier image plate technique. The entire di4raction spectrum was re5ned by full pro5le Rietveld method using the program Fullprof. The -PdSn 2 structure type (space group, I4 1 /acd; Pearson symbol, t148, Z โซุโฌ 16), proposed for this compound, was con5rmed and the lattice parameters are a โซุโฌ 6.4350(1) A s and c โซุโฌ 24.3638(3) A s . The residual values were R p โซุโฌ 5.34 and R wp โซุโฌ 6.70. The tetragonal PdSn 2 structure type is a mixed variant of the CaF 2 type and the CuAl 2 type structure. Also in this ternary compound we assumed a random contribution of In and Sb over the 16e and 16f positions. The electronic structures of both compounds were investigated by extended HuK ckel calculations. Crystal orbital overlap populations show extended bonding interactions between the main group elements. The bonding interactions of the main group elements are almost optimized at the experimentally observed In/Sb ratio of the ternary compound. The In/Sb ratio in Pd 13 In 5.25 Sb 3.75 can thus be rationalized on the basis of the electronic structure. 2002 Elsevier Science (USA)