Electron Paramagnetic Resonance Studies of Nitrosyl and Thionitrosyl and Density Functional Theory Studies of Nitrido, Nitrosyl, Thionitrosyl, and Selenonitrosyl Complexes of Chromium

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• 作者：Johannes R. Dethlefsen ; Anders D&#248 ; ssing ; Erik D. Hedegrd
• 刊名：Inorganic Chemistry
• 出版年：2010
• 出版时间：October 4, 2010
• 年：2010
• 卷：49
• 期：19
• 页码：8769-8778
• 全文大小：954K
• 年卷期：v.49,no.19(October 4, 2010)
• ISSN：1520-510X

文摘

The novel S = 1/2 thionitrosyl complexes Cr(NS)(CN)₅³⁻, Cr(NS)(dmso)₅²⁺, and Cr(NS)(nmf)₅²⁺ (dmso = dimethyl sulfoxide, nmf = N-methylformamide) have been prepared, and their optical and electron paramagnetic resonance (EPR) spectra were studied. The values of the isotropic and anisotropic hyperfine and superhyperfine coupling constants A(⁵³Cr), A(¹⁴N), and A(¹³C) and of g were determined from the EPR spectra at room temperature and at 66 K. The values of A and A_iso in the thionitrosyl complexes were slightly higher than in the analogous nitrosyl complexes. A common feature in the optical absorption spectra of the thionitrosyl complexes in solution at 298 K is an absorption band around 600 nm with a vibronic structure whereas such a band is located around 450 nm in the analogous nitrosyl complexes. Density functional theory (DFT) studies of the series of complexes Cr(N)(H₂O)₅²⁺, Cr(NO)(H₂O)₅²⁺, Cr(NS)(H₂O)₅²⁺, and Cr(NSe)(H₂O)₅²⁺ show that the unpaired electron resides in a metal-based d_xy orbital and that the electronic structure in the equatorial plane is similar in all four complexes and similar to Cr³⁺. The σ donating ability was found in the order N³⁻ NO < NS ≈ NSe and the π accepting ability in the order NO > NS ≈ NSe. Time dependent DFT calculations gave in all four complexes a d_x²−y² ← d_xy transition energy around 17 500 cm⁻¹.