Integrating Polyoxometalate into Dy(III)-based Single-molecule Magnets with Pentagonal Bipyramidal Symmetry.

Polyoxometalates (POMs) with various coordination fashions are versatile ligands for constructing single-ion magnets (SIMs), but enforcing POM-SIMs with a specific geometry remains a synthetic challenge. Herein, we synthesized a POM-cocrystallized Dy III -SIM [Dy(OPPh 3 ) 4 (H 2 O) 3 ][PW 12 O 40 ]·4EtOH ( 1Dy ) and a POM-ligated Dy III -SIM [{Dy(OPPh 3 ) 3 (H 2 O) 3 }{PW 12 O 40 }]·Ph 3 PO·H 2 O ( 2Dy ) with pentagonal bipyramidal local coordination geometry. Magnetic measurements indicate that 1Dy displays field-induced single-molecule magnet (SMM) behavior and the relaxation is dominated by under-barrier processes. 2Dy exhibits spin-lattice relaxation at a broader temperature region with a reversal barrier over 300 K. Magneto-structural analysis reveals that the enhancement of SMM behavior originated from the equatorial replacement of Ph 3 PO by POM, which strengthens the axial anisotropy in 2Dy . Luminescent experiments indicate that the characteristic Dy III emissions of 1Dy are covered up by the strong π-π* emission of Ph 3 PO at low-temperature regions. As for 2Dy , partial Dy III emission persists thanks to the antenna effect between Dy III and POM.