Abstract
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 of a crystal lattice (H2tpda = N2,N6-bis(pyridin-2-yl)pyridine-2,6-diamine). DFT studies both in the gas phase and including CH2Cl2 solvent effects indicate that an unsymmetric structure (C4 point group), with pairs of formally quadruply-bonded metal ions and one terminal metal center, is slightly more stable (2.9 and 3.9 kcal mol-1) than a symmetric structure (D4 point group). Isotopically-labelled samples (2-d8 and 2-d16) have then been prepared to aid in molecular symmetry determination by combined 1H and 2H NMR studies in dichloromethane solution. The spectra are strongly suggestive of a symmetric (D4) framework, indicating fast shuttling between the two unsymmetric forms over the timescale of NMR experiments. Procedures for a high-yield Pd-free synthesis of H2tpda and for site-selective post-synthetic H/D exchange of aromatic H2tpda hydrogens are also reported.
Highlights
Aivaras Dirvanauskas,a,b Rita Galavotti,a Alessandro Lunghi, ‡c Alessio Nicolini,a Fabrizio Roncaglia, a Federico Totti c and Andrea Cornia *a
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 of a crystal lattice (H2tpda = N2,N6-bis( pyridin2-yl)pyridine-2,6-diamine)
In the unsymmetric structure (Fig. 1a) the C2 symmetry element located on Cr3 is lost and an alternation of short (1.85–1.90 Å) and long (2.55–2.61 Å) separations results, which matches the experimental interpretation of X-ray data using a “split-atom” model.[19,20]
Summary
Aivaras Dirvanauskas,a,b Rita Galavotti,a Alessandro Lunghi, ‡c Alessio Nicolini,a Fabrizio Roncaglia, a Federico Totti c and Andrea Cornia *a. Looking for a Pd-free approach to the synthesis of H2tpda, we decided to explore the reactivity of 2-fluoropyridine, which is less toxic than 2-chloropyridine and is a known efficient electrophile in SNAr reactions with anilines or other amines.[60,61,62,63] The order of addition of the reagents was inspired by the best available method, namely the synthesis of Br2H2tpda.[42] Paper the selected base (10 equiv.) was added to solid 2,6-diaminopyridine under Ar and stirred for 10 min at room temperature.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
