Levina Aviva, Turner Peter, Lay Peter A
Centre for Heavy Metals Research, School of Chemistry, University of Sydney, Sydney, NSW 2006, Australia.
Inorg Chem. 2003 Aug 25;42(17):5392-8. doi: 10.1021/ic0340480.
X-ray absorption spectroscopy (XAS) provides a direct means of solving the controversy on Cr oxidation states in nitroso complexes. The first XAS studies of four known Cr-NO complexes, Cr(NO)(OH(2))(5), [Cr(NO)(acac)(2)(OH(2))], Cr(NO)(CN)(5)(-), and Cr(NO)(NCS)(5)(-), have been performed, in comparison with the related Cr(III) complexes, Cr(OH(2))(6), [Cr(acac)(3)], Cr(CN)(6)(-), and Cr(NCS)(6)(-). The X-ray absorption near-edge structure (XANES) spectra of the Cr-NO complexes are distinguished from those of the corresponding Cr(III) complexes by increased intensities of pre-edge absorbancies due to the 1s --> 3d transition, as well as with slight shifts (by 0.2-1.0 eV) of the edge positions to lower energies, with no major changes in the edge shape. These features, together with the available structural data on Cr-NO complexes, show that the effective Cr oxidation states in such complexes are close to Cr(III), due to the pi-back-bonding within the Cr-NO moiety. Multiple-scattering fitting of X-ray absorption fine structure (XAFS) spectra of [Cr(NO)(acac)(2)(OH(2))] supported the assignment of this complex as a trans-isomer (Keller, A.; Jezovska-Trzebiatowska, B. Polyhedron 1985, 4, 1847-1852). The first crystal structure of a Cr nitroso-isothiocyanato complex, (Ph(4)P)(3)[Cr(NO)(NCS)(5)].2.4(CH(3))(2)CO, has been determined.
X射线吸收光谱法（XAS）为解决亚硝基配合物中铬氧化态的争议提供了一种直接方法。已对四种已知的Cr-NO配合物[Cr(NO)(OH₂)(5)]²⁺、[Cr(NO)(acac)₂(OH₂)]、[Cr(NO)(CN)₅]³⁻和[Cr(NO)(NCS)₅]³⁻进行了首次XAS研究，并与相关的Cr(III)配合物[Cr(OH₂)₆]³⁺、[Cr(acac)₃]、[Cr(CN)₆]³⁻和[Cr(NCS)₆]³⁻进行了比较。Cr-NO配合物的X射线吸收近边结构（XANES）光谱与相应的Cr(III)配合物的光谱不同，这是由于1s→3d跃迁导致的预边吸收强度增加，以及边位置向较低能量的轻微移动（0.2 - 1.0 eV），而边形状没有重大变化。这些特征，连同Cr-NO配合物的现有结构数据表明，由于Cr-NO部分内的π-反馈键合，此类配合物中的有效Cr氧化态接近Cr(III)。[Cr(NO)(acac)₂(OH₂)]的X射线吸收精细结构（XAFS）光谱的多重散射拟合支持将该配合物指定为反式异构体（凯勒，A.；耶佐夫斯卡 - 特雷比亚托夫斯卡，B.《多面体》1985年，4，1847 - 1852）。已确定了一种Cr亚硝基异硫氰酸根配合物(Ph₄P)₃[Cr(NO)(NCS)₅]·2.4(CH₃)₂CO的首个晶体结构。
