STUDIES ON THE FLUXIONAL BEHAVIOR OF THE TETRAHEDRO-TRIOSMIUM PLATINUM CLUSTERS OS3PT(MU-H)2(CO)9(PCY3)(CNCY) AND OS3PT(MU-H)2(MU-CH2)(CO)9(PCY3)(CNCY) USING C-13 EXSY - DIRECT EVIDENCE FOR THE ROTATION OF THE PT(H)(PCY3)(CNCY) UNIT FROM DYNAMIC OS-187-HYDRIDE COUPLING-CONSTANTS