Two Types of Cu-Ln Heterometallic Coordination Polymers with 2‑Hydroxyisophthalate: Syntheses, Structures, and Magnetic Properties

Two
types of Cu-Ln heterometallic coordination polymers (CPs),
[Ln4Cu8­(ipO)8(ox)2­(H2O)12] (Ln = Sm (1); Eu
(2); ipO = 2-hydroxyisophthalate; ox = oxalate) (type
I) and [Ln2Cu6­(ipO)6­(H2O)12] [Ln = Gd (3); Tb (4); Dy (5)] (type II), were synthesized under the same
hydrothermal conditions and structurally characterized. The first
type of CPs displays a three-dimensional framework with a rare case
of MoGe2 topology based on {Cu8} and {Ln2} secondary building units (SBUs), while the second type of
CPs exhibits a chain structure built up from {Cu6} SBUs
and Ln ions. Both of the {Cu8} and {Cu6} SBUs
consist of planar [Cu2(ipO)2]2– units linked together by weak Cu–O bonds and π–π
interactions. The structural variation from type I to type II can
be ascribed to different reactions of H3ipO ligands induced
by lanthanide ions. The magnetic investigations revealed that 3 displays a magnetocaloric effect (MCE) with a maximum −ΔSm value of 13.97 J kg–1 K–1 for ΔH = 50 kOe at 4.0 K.
It was also found that 5 displays field induced single
molecular magnet (SMM) behaviors of slow magnetic relaxation and magnetization
hysteresis, with an energy barrier Ueff = 63.68 K and pre-exponential τ0 = 3.77 ×
10–8 s.