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.

本研究以图形方式展示了约560个第一过渡系金属配合物中，NO伸缩振动波数ν(NO)与NO键长d(NO)、M-N-O键角∠MNO以及电荷之间的相关性。基于CDVR（Charge Distribution via Reporters，即通过报道基团进行电荷分布分析）设定的参数框架，经验性推导得到电荷参数计算公式：cNO = {ν(NO) – 1960}/450 cm⁻¹，并以此证明亚硝酰基实际上不应被解读为以NO+形式配位。

四齿螯合配体[Me₂C{CH=N(1,2-C₆H₄)NH(2,6-iPr₂C₆H₃)₂}]ₙ（即(pddi)ₙ）被证实可合成(pddi)M（2-M；M=Cr、Fe、Co），作为单亚硝酰基配合物(pddi)MNO（2-MNO）的前驱体。在2-M与2-MNO（M=Cr和Fe）中观察到显著的电子结构复杂性，而2-Co不稳定，会降解为{[κ³-N,N,N-1,2-ArNC₆H₄N=CHCMe₂NO]Co}₂（3；Ar=2,6-iPr₂C₆H₃）。

配合物3的结构特征符合形式上自旋量子数S=1/2的Co(II)中心与烷基亚硝酰自由基阴离子发生反铁磁耦合的模型，即LS [(LX⁻)Co²⁺(↑)RNO(−↓)][(LX⁻)Co²⁺(↓)RNO(−↑)]，其电荷分布规律与CDVR的核心原则一致。