This volume 8 is the fourth in a series dealing with organomolybdenum compounds. An Empirical Formula Index and a Ligand Formula Index provide ready access to the compounds covered. Volume 5 describes mononuclear organomolybdenum compounds with isocyanide, 3 4 carbene, carbyne, alkynyl, alkene, alkyne, L, and L ligands with and without additional CO groups. Volume 6 starts the description of mononuclear organomolybdenum compounds with 5 one L Ligand, a Ligand bonded to molybdenum by five carbon atoms. The compounds contain either zero or one CO group bonded to the molybdenum atom. Volume 7 continues the 5 description of L-molybdenum compounds containing two CO groups, but no additional nl 5 ligands. This volume describes L-molybdenum compounds with two CO groups and additional 1 4 L to L ligands. Following the nomenclature used in this series of organomolybdenum com pounds, nl is an organic Ligand bonded by n C atoms to molybdenum, and mo is an electron 2 donor Ligand with m donor electrons. Thus 0 denotes a Ligand such as PR . 3 Many of the data, particular those in tables, are given in an abbreviated form without units; for explanations see p. X. Additional information, if necessary, is given before the individual table. Frankfurt am Main Manfred Winter November 1992 Wolfgang Petz X Remarks on Abbreviations and Dimensions Many compounds in this volume are presented in tables in which numerous abbreviations are used, the dimensions are omitted for the sake of conciseness. This necessitates the following clarifications.