Similarly, the NO vibrational frequency extends from 1529 to 1945 cm -1 , corresponding to somewhat under NO -0.5 (1635 cm -1 ) to somewhat over NO 0 (1889 cm -1 ). Overall, the results indicate that the vast majority of the complexes, regardless of their spin state, are best described as metal-NO 0 as opposed to metal-NO -or metal-NO + .