Heterometallic Heptanuclear [Cu 5 Ln 2 ] (Ln = Tb, Dy, and Ho) Single-Molecule Magnets Organized in One-Dimensional Coordination Polymeric Network.

The reaction of a multisite coordination ligand, LH3 , with Cu(II) salts and Ln(NO3 )3 ·nH2 O in a 1:2:1 stoichiometric ratio in the presence of triethylamine was found to afford a series of one-dimensional heterometallic [{Cu5 Ln2 (L)2 (μ3 -OH)4 (ClO4 )(NO3 )3 (OH2 )5 }(ClO4 )2 (H2 O)x ]∞ [Ln = Tb(1), Dy(2) and Ho(3), x = 4.25, 5.5, and 5 for 1-3, respectively] coordination polymers. Complexes 1-3 have been characterized by single crystal X-ray crystallography. The detailed study of the magnetic properties has also been performed and compared with the parent [Cu5 Ln2 ] molecular analogues. The ac susceptibility measurements for complexes 1-3 confirm their SMM behavior with the following characteristics: Δeff /kB = 23.4 K, τ0 = 1.1 × 10-6 s and Δeff /kB = 27.9 K, τ0 = 6.6 × 10-7 s under 0 and 1200 Oe dc fields, respectively for 1; Δeff /kB = 8.3 K, τ0 = 3.1 × 10-6 s for 2 under 0 dc field. For 3, the fast QTM below 4 K prevents the estimation of the SMM energy barrier. Remarkably, the magnetic and SMM properties of the previously reported molecular [Cu5 Ln2 ] analogues are preserved after their assembly in these coordination networks.