Two new phases Ca(10)Pt(7)Tt(3) (with Tt = Si, Ge) were obtained by reacting stoichiometric mixtures of the elements at high temperature. Their structures were refined from single crystal X-ray diffraction data. They are isostructural and crystallize in the Ba10Al3Ge7 type structure, space group P6(3)/mcm (No. 193) with a = b = 8.7735(3) angstrom, c = 13.8260(5) angstrom, V = 921.66(6) angstrom 3, Z = 2 for Tt = Si, and a = b 8.7995(6) angstrom, c= 13.9217(14) angstrom, V = 933.56(16) angstrom(3) for Tt = Ge phase. The most interesting structural features in these phases are the propeller shape {Pt(7)Tt(3)} (Tt = Si, Ge) intermetalloid clusters in a D-3h local symmetry. LMTO electronic structure calculations and COHP analyses reveal that both Ca(10)Pt(7)Tt(3) (Tt = Si, Ge) phases are charge optimized, which is not predicted by the classical Zintl concept and the octet or Wade-Mingo's rules, but rather by a more complex bonding model based on the unprecedented electron-rich 4c-6e multicenter bonding. The clusters are best described as three-condensed trigonal planar [TtPt(3)](8-) units, resulting in a central Pt atom also with a trigonal planar coordination of three symmetrical equivalent Si/Ge atoms that are further connected to two terminal Pt atoms each. The "trefoil" electron-rich multicenter bonding is proposed here for the first time, and may be viewed as a unique bonding feature with potential relevance for the catalytic properties of the noble metal platinum.