S1 SUPPORTING INFORMATION Reactions of Ar'CrCrAr' with N 2 O or N 3 (1-Ad): Complete Cleavage of the Cr-Cr Quintuple Interaction Chengbao Ni, Bobby D. Ellis, James C. Fettinger, Gary J. Long, and Philip P. Power Department of Chemistry, University of California, Davis, California 95616, and Department of Chemistry, Missouri University of Science and Technology, University of Missouri, Rolla, Missouri 65409-0010 The supporting information contains: 1. Experimental Details 2. Details of the magnetic characterization of 1 and 2. 3. Crystallographic Data. 1. Experimental Details General Procedures. All manipulations were carried out using modified Schlenk techniques under an argon atmosphere or in a Vacuum Atmospheres HE-43 drybox. All of the solvents were first dried by the method of Grubbs, 1 followed by 3 A molecular sieves overnight and degassed three times (freeze-thaw) prior to use. Ar'CrCrAr' was prepared by the literature method. 2 AdN 3 was purchased from Acros Organics and used as received. N 2 O was purchase from Puritan Medical Products Inc. and dried over P 2 O 5 prior to use. Melting points were recorded in glass capillaries sealed under N 2 and are uncorrected. UV-vis data were recorded on a Hitachi-1200 spectrometer. Ar'Cr(µ-O) 2 Cr(O)Ar' (1): About 30 mL of hexanes was added to a flask containing Ar'CrCrAr' (0.270g, 0.3mmol) at room temperature. The flask containing this deep red Supplementary Material (ESI) for Chemical Communications This journal is (c) The Royal Society of Chemistry 2009