PdBr2Se6 and PdCl2Se8 are two new compounds with cyclic Se-6 coordinated to PdBr2 molecules and one-dimensional helical Se-X chains coordinated to PdCl2 molecules. PdBr2Se6 is a black solid with a crystal structure similar, but not equal, to PdCl2Se6. It crystallizes in the space group P(1) over bar with the lattice constants a = 4.3946(8) angstrom, b = 7.605(1) angstrom, c = 7.992(2) angstrom, alpha = 66.15(2)degrees, beta = 86.44(2)degrees, gamma = 80.90(2)degrees, and Z = 1 and can be handled in air like the deep red PdCl2Se8 which crystallizes in the orthorhombic space group Pbca with the lattice constants a = 9.609(2) angstrom, b = 8.958(2) angstrom, c = 13.799(3) angstrom, and Z = 4. In PdBr2Se6, two cyclic Se-6 molecules (chair conformation) are directly coordinated to Pd atoms, forming Pd(Se-6)(2)Br-2 groups. These are connected to one-dimensional chains via trans-standing Se atoms. In PdCl2Se8, the selenium substructure consists of helical chains with every fifth Se atom directly coordinated to the Pd atom of a PdCl2 group. Each PdCl2 group on the other hand connects two neighboring Se, helices. The type of Se, helix found for this compound is unique and differs from all other ones reported up to now including elemental alpha-Se. A reproducible twinning observed for PdBr2Se6 crystals in the course of the X-ray single-crystal investigations is checked by transmission electron microscopy in connection with details of the atomic arrangement. The Raman spectra of PdBr2Se6 and PdCl2Se8 are compared to Raman data of elemental Se modifications and give significant support for the Se-6 and helical Se-X to be neutral molecules. A discussion of the results of thermal analyses gives clear evidence that cyclic Se-6 and helical Se-X are considerably stabilized by bonding to the PdX2 molecules because the melting temperatures of the composite materials are significantly higher than the ones of the respective elemental modifications.