This volume completes the extensive Series B of organoiron compounds, exclusively devoted to mononuclear varieties with the exception of ferrocenes. The first and largest part of the present volume continues the description of compounds with one 6L ligand and one 5L ligand, started already in Volume B/18. These complexes are important intermediates for synthesizing substituted cyclohexadienes or benzenes and other organic compounds. The reducing properties of neutral 6LFE5L compounds are used in stoichiometric and catalytic reactions. Compounds with two 6L ligands, mainly bisarene iron(II) salts, form the second part of this volume, and a last short part deals with compounds containing ligands bonded by more than six C atoms. In order to readily access the more than 2000 compounds in this volume, an empirical formula index and a ligand formula index are included. Moreover, a brief overview included at the end of this volume lets one scan the contents of all 38 organoiron Gmelin volumes which have been published since 1974. In all, the organoiron series includes as many as 33 000 compounds and describes in detail their preparation and all their chemical and physicochemical properties.