A Crystalline Hybrid of Paddlewheel Copper(II) Dimers and Molecular Rotors: Singlet‐triplet Dynamics Revealed by Variable‐temperature Proton Spin‐lattice Relaxation12. Issue 6 (25th March 2014)

• Record Type: Journal Article
• Authors: Bastien, Guillaume; Lemouchi, Cyprien; Wzietek, Pawel; Simonov, Sergey; Zorina, Leokadiya; Rodríguez‐Fortea, Antonio; Canadell, Enric; Batail, Patrick
• Is Part Of: Zeitschrift für anorganische und allgemeine Chemie. Volume 640:Issue 6(2014)
• Page Start: 1127
• Page End: 1133
• Publication Date: 2014-03-25
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry -- Periodicals; 540
• DOI: 10.1002/zaac.201300622
• Languages: English
• ISSNs: 0044-2313

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>We report on the synthesis and application of a 2 nm long, curved ditopic biscarboxylic ligand with a 1, 4‐bis(ethynyl)bicyclo[2.2.2]octane rotator core and an helical twist to the construction of an extended single‐crystalline framework solid with paddlewheel hinges, [Cu<sup>II</sup>]<sub>2</sub>[1, 4‐bis(carboxyphenyl ethynyl)bicyclo[2.2.2]octane]<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub> or [Cu<sup>II</sup>]<sub>2</sub>(bbcbco)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>. The interconnection of interpenetrated square lattices involves short rotor–rotor H<bold>···</bold>H interactions (1.9 to 2.4 Å) such that the moving parts are expected to rub onto each other in the lattice in a Brownian rotational motion with a calculated rotational barrier of 3.7 kcal<bold>·</bold>mol<sup>–1</sup>. Variable‐temperature <sup>1</sup>H spin‐lattice relaxation (<italic>T</italic><sub>1</sub>) experiments carried out on a static crystalline sample did not provide however a value of this rotational barrier because the relaxation proved to be dominated by the coupling of the moving protons to the electronic spins of the Cu<sup>II</sup> dimers. Remarkably, we reveal how the singlet‐triplet spin dynamics of non‐interacting Cu<sup>II</sup> dimers is elegantly characterized by solid state NMR spectroscopic experiments yielding an exchange coupling constant, <italic>J</italic><sub>exp</sub> = –365 K = –254 cm<sup>–1</sup>, in good agreement with theoretical estimations and experimental data on related Cu<sup>II</sup> dimer systems.</p> </abstract>