Variable-temperature 7 7 Se NMR spectroscopic studies of the complexes [CpCr(CO) 2 ] 2 Se (1) and [CpCr(CO) 2 ] 2 Se 2 (2) have been carried out. A singlet 7 7 Se resonance is found for 1 at 213-296 K, but the broadness at the higher temperatures suggests the existence of rotamers exchanging at an intermediate rate on the time scale of Δ δ S e . For 2, the observations point to the existence of two conformers over the range 213-330 K, with relative proportions varying from ca. 1:3.4 at 320 K to ca. 1:6.4 at 213 K. This conclusion is supported by 1 3 C NMR spectra at 213 and 298 K. Also reported are 7 7 Se NMR data for Cp 2 Cr 2 (CO) 5 Se 2 (3), produced in situ by thermolysis of 2 in solution, and solid-state CP-MAS 1 3 C and 7 7 Se NMR data for [CpCrSe] 4 (4).