Synthesis and structure of cis-dichlorobis(2-phenylazopyridine)chromium(II), an inert chromium(II) compound |
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| Affiliation: | 1. School of Chemistry, Joseph Black Building, University of Glasgow, University Avenue, Glasgow G12 8QQ, UK;2. Department of Pharmaceutical Sciences, Faculty of Science, Utrecht University, P.O. Box 80082, NL-3508 TB Utrecht, The Netherlands;1. Key Laboratory of Novel Materials for Sensor of Zhejiang Province, Institute of Advanced Magnetic Materials, College of Materials & Environmental Engineering, Hangzhou Dianzi University, Hangzhou 310018, PR China;2. The College of Electronics and Information, Hangzhou Dianzi University, Hangzhou 310018, PR China;3. National Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, PR China;1. B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47, Nauky Ave., Kharkiv 61103, Ukraine;2. Department of Chemistry and Biochemistry, University of Arizona, Tucson, AZ 85721, USA |
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| Abstract: | Recent studies have shown 2-phenylazopyridine (Azpy) to be a useful departure from polypyridyl type ligands in coordination chemistry; frequently lower oxidation states are stabilized by this ligand. We have prepared and studied [Cr(Azpy)2Cl2] which is surprisingly inert for a chromium(II) complex. The compound crystallizes in the space group P21/c with a = 7.953(3), b = 21.189(11), c = 12.922(12) Å, β = 114.80(5)° and Z = 4. Based on 6777 reflections the structure has been refined to R = 0.030 and Rw = 0.038. The complex is six-coordinated with cis-chlorides, cis-azo and trans-pyridyl groups. The overall symmetry is close to C2. The azo NN distances are elongated to 1.282 and 1.314 Å, significantly longer than observed in free azo groups.The magnetic moment of 2.8 BM is independent of temperature indicating an orbitally non-degenerate low-spin ground state. In acetonitrile the spectrum shows a band in the red at 1470 nm which is assigned as ligand-metal charge transfer, consistent with earlier interpretations on similar compounds. The compound is stable to air oxidation in acetonitrile or methylene chloride; cyclic voltammetry in these solvents yields potentials of 0.508 and −0.185 V, both appearing to be one electron transfers.The complex is a non-electrolyte in acetonitrile, nearly unchanged over 24 h. However, chloride ions are slowly replaced at 50 °C in this solvent by 2,2′-bipyridyl; this reaction is pseudo-first order in complex with a rate constant of 4.0 ± 0.3 × 10−7 s−1. All data indicate the presence of a strong chromium-Azpy pi-interaction. |
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