Reversible ON–OFF switching of single-molecule-magnetism associated with single-crystal-to-single-crystal structural transformation of a decanuclear dysprosium phosphonate

Abstract

{Dy₅(EDDC)₂(μ₃-AcO)₂(μ₅-C₁₅H₁₁PO₃)(μ₄-C₁₅H₁₁PO₃)(μ₂-AcO)₂(AcO)₂(H₂O)(CH₃OH)₂}₂(μ₄-C₂O₄)·xH₂O (I), where H₂EDDC is N′,N′′,E,N′,N′′,E-N′,N′′-(ethane-1,2-diylidene)dipyrazine-2-carbohydrazide and C₁₅H₁₁PO₃H₂ is 9-anthrylmethylphosphonic acid, is found to undergo two consecutive single-crystal-to-single-crystal transformations. The first is under UV irradiation (λ = 365 nm for 3 d in air) to {Dy₅(EDDC)₂(μ₃-AcO)₂(μ₅-C₁₅H₁₁PO₃)₂(μ₂-AcO)₂(AcO)₂(H₂O)₃}₂(μ₄-C₂O₄)·xH₂O (I-UV) where the two CH₃OH are replaced by two H₂O and the second by annealing under N₂ at 100 °C on a diffractometer or under Ar in a glovebox to {Dy₅(EDDC)₂(μ₃-AcO)₂(μ₅-C₁₅H₁₁PO₃)₂(μ₂-AcO)₄(H₂O)}₂(μ₄-C₂O₄) (I-A-N₂ or I-A-Ar) where it has lost two H₂O molecules. The second transformation is reversible by exposure to air at room temperature (I-A-N₂-cool). While the overall structures are the same (retaining the space group P2₁/c), there is a considerable expansion of the unit cell from I (8171 ų) to I-UV (8609 ų) and I-A-N₂ (8610 ų) and the coordinations of the Dy atoms undergo major reconstructions. This is associated with switching the single-molecule-magnetism (SMM) from OFF for I to ON for I-UV and to OFF again for I-A-Ar in air. Such a switching mechanism associated with the retention of crystallinity is unique in the chemistry of dysprosium. The structure of the molecule is formed from two symmetry related pentamers joined by an oxalate. A related compound containing two isolated neutral pentamers {Dy₅(EDDC)₂(μ₃-AcO)₂(μ₅-C₁₅H₁₁PO₃)₂(μ₂-AcO)₃(AcO)₂(H₂O)₂}{Dy₅(EDDC)₂(μ₃-AcO)₂(μ₅-C₁₅H₁₁PO₃)(μ₄-C₁₅H₁₁PO₃)(μ₂-AcO)₃(AcO)₂(CH₃OH)₂}·2CHCl₃ (II) has also been isolated with closely related Dy coordination and it exhibits similar SMM behaviour in zero field.