Understanding Re−NO Bond Distances: An Analysis of Disorder in [(η5-C5H4SiMe3)Re(CO)2NO]+, [(η5-C5H4Me)Re(CO)2(NO)]+, and Related Compounds

Apparently elongated Re−NO and shortened Re−CO bonds in the new complexes [(η5-C5H4R)Re(CO)2NO]BF4 (R = SiMe3, Me) can be understood in terms of random positional disorder in the unit cell. We report a thorough crystallographic analysis of similar compounds in the literature and find many instances with erroneous Re−NO and Re−CO bond lengths due to unrecognized or unreported disorder. Positional disorder is noted for achiral substituted cyclopentadienyl complexes of rhenium, whereas crystallographic packing disorder is noted for the chiral complexes.