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A Crystalline Hybrid of Paddlewheel Copper(II) Dimers and Molecular Rotors: Singlet‐triplet Dynamics Revealed by Variable‐temperature Proton Spin‐lattice Relaxation
Author(s) -
Bastien Guillaume,
Lemouchi Cyprien,
Wzietek Pawel,
Simonov Sergey,
Zorina Leokadiya,
RodríguezFortea Antonio,
Canadell Enric,
Batail Patrick
Publication year - 2014
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/zaac.201300622
Subject(s) - chemistry , crystallography , dimer , singlet state , coupling constant , spins , relaxation (psychology) , proton , spin–lattice relaxation , molecular physics , condensed matter physics , atomic physics , physics , excited state , quantum mechanics , social psychology , organic chemistry , psychology
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 II ] 2 [1,4‐bis(carboxyphenyl ethynyl)bicyclo[2.2.2]octane] 2 (H 2 O) 2 or [Cu II ] 2 (bbcbco) 2 (H 2 O) 2 . The interconnection of interpenetrated square lattices involves short rotor–rotor H ··· 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 · mol –1 . Variable‐temperature 1 H spin‐lattice relaxation ( T 1 ) 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 II dimers. Remarkably, we reveal how the singlet‐triplet spin dynamics of non‐interacting Cu II dimers is elegantly characterized by solid state NMR spectroscopic experiments yielding an exchange coupling constant, J exp = –365 K = –254 cm –1 , in good agreement with theoretical estimations and experimental data on related Cu II dimer systems.