Partial paramagnetism of the chromium-chromium quadruple bond

Variable-temperature NMR measurements show that Cr 2 (O 2 CR) 4 L 2 compounds (L=MeOH, H 2 O, py, MeCN) and closely related ones possess inherent, temperature-dependent partial paramagnetism. This may be attributed to a Boltzmann distribution between a ground state with S=0 and a low-lying (∼400-1000 cm -1 ) state with S=1