The shortest metal‐metal bond

The synthesis and isolation of stable bimetallic complexes that contain formally quintuply bonded transition metals is a novel and emerging field of science. Efforts have been undertaken in designing and tuning the ligands to achieve a very short (actually the shortest) metal‐metal bond. The motivation for these efforts arose from the expectation that an increasing bond order may go along with a shortening of the bond length. In consequence, formally quintuply bonded bimetallics could have shorter metal‐metal distances than quadruply bonded ones. A chromium homo‐bimetallic complex with a Cr‐Cr bond length of 1.7293(12) Å has been synthesized, and a formal bond order of five was assigned. This compound holds the record for the shortest metal‐metal bond in a stable molecule to date. At this stage, there is no evidence that additional shortening is impossible. © 2010 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.201000028