The novel intennetallic Ca(6)PtCc(11) is orthorhombic, Pnma, Z = 4,.with a = 18.799(2) A, b = 5.986(1) angstrom, c = 15.585(3) angstrom. The heavily condensed network contains three types of Parallel cadmium chains: apically strongly interbon'ded Cd-7 pentagonal bipyramids, linear Cd arrays, and rectangular Cd4/2Pt pyramids. All of the atoms have 11-13 neighbors. Calculations by means of the linear muffin-tin orbitals method in the atomic spheres approximation indicate that some Cd Cd interactions correspond to notably high Hamilton populations (1.07 eV per average bond) whereas the Ca-Ca covalent interactions (integrated crystal orbital Hamiltonian population) are particularly small (0.17 eV/bond). (Pt-Cd single bond metallic diameters,, and unusually uniform (A = 0.14 A). The Cd atoms.make major contributions to the stability of the phase via substantial Ss and Sp bonding, which include back donation of Cd Ss, Sp and Pt 5d into Ca 3d states in the principal bonding modes for Ca Cd and Ca Pt. Bonding Ca Ca, Ca Cd, and Cd Cd states remain above EF, and some relative oxidation of Ca in this structure seems probable. Ca6PtCd11 joins a.small group of other phases in which Cd clustering and Cd Cd bonding are important.