Solution structure of a pentachromium(II) single molecule magnet from DFT calculations, isotopic labelling and multinuclear NMR spectroscopy

摘要: The structure of pentachromium(II) extended metal atom chain [Cr5(tpda)4Cl2] (2), which behaves as a single molecule magnet at low temperature, was investigated by Density Functional Theory (DFT) calculations and spectroscopic studies without the constraints crystal lattice (H2tpda = N2,N6-bis(pyridin-2-yl)pyridine-2,6-diamine). DFT both in gas phase including CH2Cl2 solvent effects indicate that an unsymmetric (C4 point group), with pairs formally quadruply-bonded ions one terminal center, is slightly more stable (2.9 3.9 kcal mol−1) than symmetric (D4 group). Isotopically-labelled samples (2-d8 2-d16) have then been prepared to aid molecular symmetry determination combined 1H 2H NMR dichloromethane solution. spectra are strongly suggestive (D4) framework, indicating fast shuttling between two forms over timescale experiments. Procedures for high-yield Pd-free synthesis H2tpda site-selective post-synthetic H/D exchange aromatic hydrogens also reported.