Transition Metal Nitrosyls: Statistics, Charge Estimates via CDVR, and Studies of Tetradentate Chelate Diamides (pddi)M and (pddi)MNO (M = Cr, Fe, and Co)

Correlations of ν­(NO) with d­(NO), /MNO, and charge from roughly 560 first row transition metal complexes
are graphically depicted. An equation of charge (cNO = {ν­(NO) – 1960}/450 cm–1) was phenomenologically derived within the parameters set by CDVR
(charge distribution via reporters) and used to show that nitrosyl
should realistically not be interpreted as bound “NO+”. The tetradentate chelate [Me2C­{CHN­(1,2-C6H4)­NH­(2,6-iPr2C6H3)2}]n ((pddi)n) was shown to produce (pddi)­M
(2-M; M = Cr, Fe, Co) as precursors to mononitrosyls,
(pddi)­MNO (2-MNO). Significant electronic complexity
was observed in 2-M and 2-MNO (M = Cr and Fe), and 2-Co was unstable, degrading to {[κ3-N,N,N-1,2-ArNC6H4NCHCMe2NO]­Co}2 (3; Ar = 2,6-iPr2C6H3). Structural features of 3 conform
to formally S = 1/2 Co­(II) centers antiferromagnetically
coupled to alkylnitroso radical anions, that is, LS [(LX–) Co2+(↑)RNO(−↓)]­[(LX–)­Co2 + (↓)RNO(−↑)], whose charge elements are consistent with the tenets of CDVR.