THE HETERONUCLEAR CLUSTER CHEMISTRY OF THE GROUP-IB METALS .16. METALEXCHANGE-REACTIONS IN GROUP-IB METAL HETERONUCLEAR CLUSTER COMPOUNDS - SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF THE TRIMETALLIC HEXANUCLEAR CLUSTER COMPOUNDS [MM'RU4(MU-3-H)2(MU-PH2P-(CH2)NPPH2)(CO)12] (M = CU, M' = AG OR AU M = AG, M' = AU N = 1 OR 2) AND X-RAY CRYSTAL-STRUCTURE OF [AUCURU4(MU-3-H)2(MU-PH2P(CH2)2PPH2)(CO)12] (DA, PG 559, 1993)